A ~~
Volume 20
A Specialist Periodical Report
Photochemistry Volume 20 A Review of the Literature published between July 1987 and June 1988 Senior Reporters D. Bryce-Smith, Department of Chemistry University of Reading A. Gilbert, Department of Chemistry University of Reading Reporters N. S. Allen, Manchester Polytechnic A. Cox, University of Warwick R. 8. Cundall, MRC Radiobiology Unit, Didcot W. M. Horspool, University of Oundee S. T. Rdd, 7he University of Kent A. C. Weedon, The University of Western Ontario, Canada
SOCIETYOF
ISBN 0-85186-185-7 ISSN 0556-3860 Copyright @ 1989 The Royal Society of Chemistry
All Rights Reserved N o part of this book may be reproduced or transmitted in any form or by any means-graphic, electronic, including photocopying, recording, taping, or information storuge and retrieval systems-without written permission from The Royal Society of Chemistry Published by The Royal Society of Chemistry Thomas Graham House, Cambridge, CB4 4WF
Printed in Great Britain by Whitstable Litho Printers Ltd., Whitstable, Kent
Introduction and Review of the Year D. BRYCE-SMITH A. GILBERT W e may p e r h a p s be p a r d o n e d f o r f e e l i n g some s e n s e o f p e r s o n a l s a t i s f a c t i o n and a c h i e v e m e n t i n r e a c h i n g t h e t w e n t i e t h o f t h e s e a n n u a l r e v i e w s of p h o t o c h e m i s t r y ; t h o u g h i t must a l s o be s a i d t h a t w e have been u n s u c c e s s f u l i n p e r s u a d i n g t h e Royal S o c i e t y of C h e m i s t r y t h a t a c e l e b r a t o r y b a n q u e t f o r t h e hard-working Reporters would be i n o r d e r ,
The c o v e r a g e t h i s y e a r i s much t h e same as i n Volume 1 9 , w i t h o n e major e x c e p t i o n . C i r c u m s t a n c e s beyond o u r c o n t r o l h a v e n e c e s s i t a t e d omission o f P a r t V d e a l i n g with photochemical a s p e c t s o f solar energy conversion. W e hope t h a t i t w i l l p r o v e p o s s i b l e t o r e i n s t a t e t h i s s e c t i o n i n f u t u r e Volumes. Some of t h e R e p o r t e r s have been f e e l i n g t h a t c o n s t r a i n t s on l e n g t h h a v e been p r e v e n t i n g them from d o i n g f u l l j u s t i c e t o t h e work r e v i e w e d . Changes d e s i g n e d t o ameliorate t h i s problem are now u n d e r d i s c u s s i o n , and we hope t o be able t o g i v e d e t a i l s i n Volume 21. W e s t a r t t h i s Review by r e f e r r i n g t o some of t h e more i n t e r e s t i n g developments on t h e t h e o r e t i c a l s i d e o f photochemistry.
Kusba h a s s o l v e d t h e d i f f u s i o n e q u a t i o n f o r l o n g r a n g e e n e r g y t r a n s f e r by d i p o l e - d i p o l e i n t e r a c t i o n accompanied by m a t e r i a l d i f f u s i o n . F r a c t a l models are i n c r e a s i n g l y b e i n g u s e d t o e x p l a i n some e n e r g y t r a n s f e r p r o c e s s e s (von Borczyskowski and K i r s k i ; Tamai e t al.; P i n e s and Huppert; Newhouse and Kopelman). A t t e n t i o n is drawn t o Najbar's i m p o r t a n t t r e a t m e n t of heavy atom effects. V e r y s h o r t t i m e - r e s o l u t i o n t e c h n i q u e s are b e i n g i n c r e a s i n g l y a p p l i e d ' t o t h e s t u d y of v e r y fast processes, f o r example s o l v e n t r e l a x a t i o n and e l e c t r o n - t r a n s f e r t o and from e l e c t r o n i c a l l y e x c i t e d species (Peters i n t e r a l i a ) , Real t i m e femtosecond t e c h n i q u e s now p r o v i d e a probe f o r t h e s t u d y of t r a n s i t i o n s t a t e s ( D a n t o s e t a l . ) . T h i s is a v e r y p r o m i s i n g development. The F i r s t I n t e r n a t i o n a l L a s e r C o n f e r e n c e was h e l d i n 1987 - i n p a r t a V
M
r e f l e c t i o n o f t h e growing u s e of l a s e r t e c h n i q u e s i n p h o t o c h e m i s t r y A v a l u a b l e s u r v e y g i v i n g access t o R u s s i a n and p h o t o p h y s i c s . l a s e r work on p i c o s e c o n d s p e c t r o s c o p y and b i o l o g i c a l p h o t o c h e m i s t r y h a s been p r o v i d e d by Letokhov. Amongst numerous a p p l i c a t i o n s o f f i b r e o p t i c s i n l u m i n e s c e n c e s t u d i e s , UR would p i c k o u t t h e i n g e n i o u s oxygen s e n s o r which u s e s f l u o r e s c e n c e d e c a y t i m e as t h e i n f o r m a t i o n c a r r i e r ( L i p p i t s c h e t a l . ) , and t h e u s e of l i q u i d The informc o r e f i b r e s i n laser f l u o r i m e t r y (Fujiwara e t a l . ) . a t i o n a v a i l a b l e from s t e a d y s t a t e l u m i n e s c e n c e s t u d i e s can be i n c r e a s e d by a computer-based m u l t i d i m e n s i o n a l f l u o r e s c e n c e t e c h Cundall i n n i q u e which h a s been r e v i e w e d by P a t o n a y e t a l . P a r t I of t h i s Volume h a s i d e n t i f i e d c h i r a l i t y c h a n g e s on e l e c t r o n i c e x c i t a t i o n as a f r u i t f u l area for f u r t h e r r e s e a r c h . B r a u c h l e ' s n o v e l phase-modulated h o l o g r a p h i c g r a t i n g t e c h n i q u e h a s been s u c c e s s f u l l y a p p l i e d t o e x c i t e d m o l e c u l e s i n polymer matrices. A p i o n e e r i n g s t u d y by Chatzidimitriou-Dreisman and Brandas h a s been c o n c e r n e d w i t h p h o t o c h e m i c a l e f f e c t s i n m o l e c u l e s s i t u a t e d i n amorphous e n v i r o n m e n t s , i n c l u d i n g l i q u i d s : t h e r m a l motion c a n g e n e r a t e l o c a l c o h e r e n t o r d i s s i p a t i v e s t r u c t u r e s which a f f e c t t h e b e h a v i o u r o f n e i g h b o u r i n g m o l e c u l e s . Bulska h a s proposed 2,2' - b i p y r i d y l - 3 , 3 ' - d i o l a s an a d v a n t a g e o u s new f l u o r e s c e n c e s t a n d a r d , and Wintgens e t a l . have described a f u l g i d e a c t i n o m e f e r p a r t i c u l a r l y u s e f u l f o r imrk on laser e x c i t a t i o n .
Locke and Lim have r e p o r t e d t h e f i r s t example o f a s p e c i e s formed by t h e c o m b i n a t i o n o f tux, e l e c t r o n i c a l l y e x c i t e d m o l e c u l e s : t h e y t e r m t h i s a 'bicemer'. Alkane p h o t o c h e m i s t r y , n o r m a l l y a r a t h e r i n a c c e s s i b l e f i e l d , has been s t u d i e d u s i n g a n i o n i z i n g e x c i t a t i o n s o u r c e (Yoshida and L i p s k y ) . Much s t i l l r e m a i n s t o be u n d e r s t o o d a b o u t t h e p h o t o c h e m i s t r y and p h o t o p h y s i c s o f b e n z e n e , and t h i s hydrocarbon and its d e r i v a t i v e s , including diphenylpolyenes, continue t o provide p e r e n n i a l c h a l l e n g e s . D o u b l e t - d o u b l e t f l u o r e s c e n c e of f r e e b e n z y l r a d i c a l s i n s o l u t i o n h a s been o b s e r v e d by Tokumura e t a l . : nonr a d i a t i v e d e c a y a l s o o c c u r s . Azulene c o n t i n u e s t o a t t r a c t p h o t o c h e m i c a l a d m i r e r s , i n c l u d i n g Hopkins and R e n t z e p i s , i n t e r a l i a . A t t e n t i o n i s drawn t o a two-photon s t u d y o f p y r i d i n e u s i n g a t h e r m a l l e n s i n g t e c h n i q u e ( S a l v i e t a l . ) . The f l u o r e s c e n c e d e c a y k i n e t i c s o f 1 , 2 - d i (1-pyreny1)propane are t h e s u b j e c t o f s t r o n g d i s a g r e e m e n t between t w o g r o u p s ( S i e m i a r e z u k and Ware; Zachariasse and S t r i k e r ) .
Introduction and Review of the Year
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M i a l o c q h a s s t u d i e d t h e f o r m a t i o n o f s o l v a t e d e l e c t r o n s by p h o t o e x c i t a t i o n of i n o r g a n i c a n i o n s and t h e b i p h o t o n i c e x c i t a t i o n of water.
G a r t s t e i n and Zakhidov have proposed t h a t charge-
t r a n s f e r s t a t e s i n mixed s t a c k d o n o r - a c c e p t o r compounds c o u p l e w i t h c r y s t a l l a t t i c e phonons t o form c o m p a r a t i v e l y s t a b l e s o l i t o n s . Examples o f c o m p e t i n g s i n g l e t a n d t r i p l e t p a t h w a y s f o r photochemi c a l t r a n s + cis i s o m e r i z a t i o n o f c e r t a i n s t i l b e n e s h a v i n g i n t r a m o l e c u l a r d o n o r - a c c e p t o r c h a r a c t e r h a v e b e e n d e s c r i b e d by G o r n e r . S e v e r a l o t h e r i n t e r e s t i n g s t u d i e s i n t h e f i e l d have a p p e a r e d t h i s year. V a r i o u s p h o t o p h y s i c a l t e c h n i q u e s c o n t i n u e t o be u s e d i n t h e s t u d y o f p o l y m e r s : some p a r t i c u l a r l y i n t e r e s t i n g work o n e l e c t r i c a l l y - c o n d u c t i n g p o l y m e r s h a s been d e s c r i b e d b y R o t h a n d B l e i e r , i n t e r a l i a . The p h o t o p h y s i c s o f t h i n f i l m s a n d c o l l o i d a l s y s t e m s , i n c l u d i n g micelles, c o n t i n u e s t o be a n i m p o r t a n t a n d a c t i v e f i e l d see e.g. K a l y a n s u n d a r a m ; Debe. C y c l o d e x t r i n s have of research: been found t o i n c r e a s e t h e chemiluminescence y i e l d s from aqueous p e r o x y o x a l a t e s by up t o 3 0 0 - f o l d (Woolf a n d G r a y e s k i ) . Enzymeg e n e r a t e d e x c i t e d s t a t e s o f a c e t o n e h a v e been f o u n d t o i n d u c e q u a s i - p h o t o c h e m i c a l b e h a v i o u r o f r i b o f l a v i n i n t h e d a r k (Rojas a n d S i l v a ) . From s t u d i e s o f t h e l u m i n e s c e n c e o f lo2, Schmidt a n d B r a u e r have c o n c l u d e d t h a t most o f t h e p r e v i o u s l y r e p o r t e d r e d e m i s s i o n d o e s n o t come from t h i s m o l e c u l e . D e l a y e d f l u o r e s c e n c e h a s been o b s e r v e d i n t h e d e a c t i v a t i o n o f h i g h l y e x c i t e d t r i p l e t s t a t e s ( S k v o r t s o v a n d A l f i m o v ; cf. McGimpsey and S c a i a n o ) . The p h o t o l y s i s of a r y l a z i d e s , long used as a source o f a r y l n i t r e n e s , h a s been shown a l s o t o p r o d u c e a t r a n s i e n t d e h y d r o a z e p i n e ( S h i e l d s e t a l . ; Liang and S c h u s t e r ) . I n a r e m a r k a b l e d e v e l o p m e n t , Nguyen e t a l . claim t h a t t h e y have been a b l e t o d e t e c t s i n g l e m o l e c u l e s by a l a s e r - i n d u c e d fluorescence procedure. B i o c h e m i s t s c o n t i n u e t o b e t h e main e x p l o i t e r s o f p h o t o p h y s i c a l t e c h n i q u e s , t h o u g h i t s h o u l d be p o i n t e d o u t t h a t t h e c o v e r age o f t h e s e p a r t i c u l a r a s p e c t s i s s e l e c t i v e r a t h e r t h a n comprehens i v e . Even p r o c e s s e s i n l i v i n g c e l l s are now b e i n g s t u d i e d (Vigo et a l . , i n t e r a l i a ) . Some a s p e c t s o f b i o l o g i c a l p h o t o c h e m i s t r y are u n d o u b t e d l y a n a c q u i r e d t a s t e . F o r e x a m p l e , a t h r e e - d i m e n s i o n a l p r e s e n t a t i o n of t h e t o t a l f l u o r e s c e n c e from u r i n e h a s e n a b l e d L e i n e r et a l . t o i d e n t i f y s e v e r a l f l u o r e s c e n t m e t abo 1i t e s
.
...
Introduction and Review of the Year
Vlll
W e now come t o d e v e l o p m e n t s i n i n o r g a n i c p h o t o c h e m i s t r y . G r g t z e l and co-workers have d e s c r i b e d a p h o t o e l e c t r i c d e v i c e
(1) R
= Me or Et
(3)
(4)R = H or Bun
(5) R’s
Ar
Q
RO
(9) R=Me, Et, or Pr’
(10)
H or Me
Introduction and Review of the Year
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r e s p o n s i v e t o t h e n e a r - i n f r a r e d , a n d w i t h an e f f i c i e n c y o f 37%. Carbon monoxide and hydrogen are produced by c o n c u r r e n t p h o t o r e d u c t i o n o f c a r b o n d i o x i d e and water u s i n g v i s i b l e l i g h t i r r a d i a t i o n o f s o l u t i o n s c o n t a i n i n g [ R ~ ( b p y ) ~ and I ~ +v a r i o u s C o ( I 1 ) species (Ziessel e t a l . ) . P h o t o e x c i t a t i o n o f a s y s t e m c o n t a i n i n g t h e same r u t h e n i u m complex, m e t h y l v i o l o g e n , and q u a d r i c y c l a n e c a n i n i t i a t e a c a t a l y t i c c y c l e f o r t h e valence isomerization of Ishida et a l . quadricyclane t o norbornadiene (Kutal et a l . ) . r e p o r t t h e p h o t o r e d u c t i o n o f C02 c a t a l y z e d by CRu(bpy)2(CO)Z!2+. B i a n c h i n i and Meli have described a n i n t e r e s t i n g new method f o r t h e i n t r o d u c t i o n o f s u l p h i d o , d i s u l p h u r , and d i s e l e n i u m l i g a n d s B e l m o r e et a l . have described t h e f i r s t i n t o complex frameworks. example of t h e p h o t o a c t i v a t i o n o f a m e t a l - c a r b o n d i o x i d e complex i n s o l u t i o n . Dobson e t a l . have d e v i s e d a p r o c e d u r e f o r t h e i d e n t i f i c a t i o n of co-ordinatively unsaturated s u b s t i t u t e d metal c a r b o n y l t r a n s i e n t s which e n a b l e v a l u e s of a l l r a t e c o n s t a n t s f o r l i g a n d d i s p l a c e m e n t r e a c t i o n s t o be o b t a i n e d . P h o t o i n s e r t i o n o f i s o n i t r i l e s i n t o t h e C-H bond of a r e n e s p r o d u c e s a l d i m i n e s , and is c a t a l y z e d by i r o n (Jones e t a l . ) . M e s s e l h h s e r e t a l . have d e s c r i b e d t h e p h o t o c h e m i c a l i n s e r t i o n o f an a l k e n e i n t o an S-S bond i n a c o - o r d i n a t i o n complex. S a k a k u r a and co-workers have d e s c r i b e d t h e r e g i o s e l e c t i v e c a r b o n y l a t i o n of a l i p h a t i c a n d a r o m a t i c h y d r o c a r b o n s i n t h e p r e s e n c e o f a rhodium complex. I n r e l a t e d work, these a u t h o r s have u s e d t h e same complex i n an i n t e r e s t i n g c h a i n - s h o r t e n i n g s y n t h e s i s o f t e r m i n a l a l k e n e s from a l k a n e s , e.g. p e n t a n e + b u t -1-ene. I r r a d i a t i o n o f t h e 0 3 / B r 2 complex l e a d s t o a n e w species w h i c h is b e l i e v e d t o be B r 2 0 ( T u r n e r e t a l . ).
I n t h e f i e l d of o r g a n i c p h o t o c h e m i s t r y , g r e a t l y i n c r e a s e d u s e is b e i n g made o f p h o t o c h e m i c a l p r o c e d u r e s i n t h e s y n t h e s i s o f n a t u r a l p r o d u c t s and other complex m o l e c u l e s . T h e r e i s growing
i n t e r e s t i n t h e e f f e c t s o f n o v e l e n v i r o n m e n t s o n t h e c o u r s e of p h o t o r e a c t i o n s , e.g. z e o l i t e s , membranes, and c y c l o d e x t r i n complexation. The p h o t o i s o m e r i z a t i o n of c y c l o b u t a n o n e s t o t r a n s i e n t c a r b e n e s h a s been u s e d a s p a r t o f an i n t e r e s t i n g s y n t h e s i s o f Intramolecular oxetan formation m u s c a r i n e ( P i r r u n g and D e A m i c i s ) . h a s been u s e d as p a r t o f n o v e l s y n t h e s e s o f medium-ring e t h e r s (1) and t h e t r i c y c l o - o c t a n e ( 2 ) (Carless e t a l . ; G l e i t e r and Kissler). Cossy e t a l . have employed t h e p h o t o r e d u c t i v e c y c l i z a -
X
Introduction and Review of the Year
t i o n of a m i d e s o r u n s a t u r a t e d k e t o n e s i n a new s y n t h e s i s o f hirsutene. P a t t e n d e n and T e a g u e h a v e a c h i e v e d t h e t o t a l s y n t h e s i s of t h e a n g u l a r t r i q u i n a n e ( 3 ) by p r o c e d u r e s which i n c l u d e i n t r a m o l e c u l a r ~ I T + ~ pI hTo t o c y c l o a d d i t i o n o f a n e n o n e . The u s e of c i r c u l a r l y p o l a r i z e d l i g h t f o r i r r a d i a t i o n h a s been l i t t l e e x p l o i t e d i n t h e p a s t , so t h e s y n t h e s i s o f t h e o p t i c a l l y a c t i v e e n o n e s ( 4 ) i n t h i s manner by C a v a z z a a n d Zandomeneghi i s of p a r t i c u l a r i n t e r e s t . Wang a n d P a q u e t t e h a v e d e s c r i b e d t h e The photochemical r o u t e to 1,3-bridged c y c l o - o c t a t e t r a e n e s . a z o m e t h i n e g r o u p i s n o r m a l l y of l o w p h o t o c h e m i c a l r e a c t i v i t y , b u t Kaneko e t a l . h a v e d e s c r i b e d a s y s t e m i n which a CF3 g r o u p a p p e a r s t o h a v e an a c t i v a t i n g e f f e c t , The o x a - d i - r - m e t h a n e p h o t o c h e m i c a l r e a r r a n g e m e n t o f B , y u n s a t u r a t e d systems normally o c c u r s v i a a t r i p l e t pathway; b u t F u c h s and c o - w o r k e r s h a v e d e s c r i b e d a n example i n which d i r e c t i r r a d i a t i o n (presumably s i n g l e t ) g i v e s t h e oxa-di-r-methane product whereas t r i p l e t s e n s i t i z a t i o n f o l l o w s a d i f f e r e n t path. The oxa-di-n-methane r e a r r a n g e m e n t o f b i c y c l o C 2 . 2 . 2 3 o c t e n o n e s h a s been e x p l o i t e d by S c h a f f n e r and Demuth t o p r o d u c e t r i c y c l o C 3 . 3 . 0 . 0 2 ~ 8 1 0 c t - 3 - o n e s , and R a j u and Deota h a v e e x t e n d e d t h i s procedure t o a s y n t h e s i s of l i n e a r t r i q u i n a n e s . Nagamatsu e t a l . h a v e shown t h a t l i q u i d c r y s t a l a n d v a r i o u s o t h e r media c a n g r e a t l y i n f l u e n c e t h e s t e r e o c h e m i s t r y o f u r a c i l p h o t o d i m e r i z a t i o n . P i r r u n g a n d Nunn h a v e shown t h a t i r r a d i a t i o n of a s e r i e s of q u i n o n e m o n o a c e t a l s ( 5 ) i n a c e t i c a c i d p r o v i d e s a f l e x i b l e high-yield r o u t e t o s u b s t i t u t e d cyclopentenones. Tu a n d M a r i a n o h a v e d e s c r i b e d a n i n t e r e s t i n g l - s t e p s y n t h e s i s o f t h e l-azabicycloC3.3.0loctane ( 6 ) by x a n t h o n e - s e n s i t i z e d i r r a d i a t i o n of t h e p y r r o l i n i u m p e r c h l o r a t e (7). Mukai e t a l . have d e s c r i b e d t h e u n e x p e c t e d c o n r o t a t o r y r i n g - o p e n i n g o f a c y c l o b u t e n e t o t h e c o r r e s p o n d i n g d i e n e which o c c u r s v i a c h a r g e - t r a n s f e r T s u j i and e x c i t a t i o n t o g i v e t h e r a d i c a l - c a t i o n of c y c l o b u t e n e . N i s h i d a h a v e r e p o r t e d t h a t i r r a d i a t i o n of t h e s t r a i n e d d i e n e ( 8 ) i n a l c o h o l i c s o l u t i o n g i v e s t h e p r o d u c t ( 9 ) which i s s u g g e s t e d t o r e s u l t from a d d i t i o n o f t h e s o l v e n t t o t h e photoisomer ( l o ) , A t t e n t i o n i s drawn s p e c t r o s c o p i c e v i d e n c e f o r which i s p r o v i d e d . t o t h e e x t r a o r d i n a r y p h o t o i s o m e r i z a t i o n (11) + (12) d e s c r i b e d b y Prinzbach et al.
Introduction and Review of the Year
xi
Cohen a n d co-workers have p r o v i d e d a v a l u a b l e r e v i e w o f c o n f o r m a t i o n e f f e c t s i n s o l i d - s t a t e p h o t o r e a c t i o n s . Mukai e t a l . have r e p o r t e d t h e r e m a r k a b l e d e s e n s i t i z e d p h o t o e l e c t r o n - t r a n s f e r i s o m e r i z a t i o n r e p r e s e n t e d by (13) + (14). T u r r o e t a l . have r e p o r t e d t h a t i r r a d i a t i o n of b e n z o c y c l o b u t e n e g i v e s t h e d i h y d r o p e n t a l e n e s ( 15 ) and (16 ) They p r o p o s e t h e intermediacy of t h e prefulvene-type biradical (17): t h i s t y p e o f i n t e r m e d i a t e was p r o p o s e d e a r l i e r by t h e S e n i o r R e p o r t e r s t o a c c o u n t f o r t h e p h o t o c h e m i c a l f o r m a t i o n o f f u l v e n e and benzv a l e n e from benzene. I t was o n c e t h o u g h t t o be i n v o l v e d i n t h e m e t a - c y c l o a d d i t i o n o f a l k e n e s t o b e n z e n e , b u t a d i f f e r e n t mechani s m is now g e n e r a l l y a c c e p t e d . L a l l e y a n d S p i l l a n e have d e s c r i b e d a n o v e l p h o t o c h e m i c a l r e a r r a n g e m e n t o f t h e sodium s a l t o f m-aminobenzenesulphonic a c i d . Wagner and Nahm h a v e described a n i n t r a m o l e c u l a r p h o t o c h e m i c a l c y c l o a d d i t i o n t o t h e benzene r i n g t h a t i s u n u s u a l i n o c c u r r i n g by a t r i p l e t pathway.
.
C y c l i c osmic esters have l o n g been known t o be i n v o l v e d i n t h e osmium t e t r o x i d e - c a t a l y z e d c i s - d i h y d r o x y l a t i o n o f a l k e n e s , b u t n o t a r e n e s . The i s o l a t i o n o f compound (18) by Wallis a n d Kochi f o l l o w i n g i r r a d i a t i o n o f t h e c h a r g e - t r a n s f e r complex between o s m i u m t e t r o x i d e and benzene i s t h e r e f o r e of p a r t i c u l a r i n t e r e s t , T h i s s u g g e s t s t h a t t h e c o r r e s p o n d i n g u s e of c a t a l y t i c q u a n t i t i e s of osmium t e t r o x i d e i n c o n j u n c t i o n w i t h hydrogen p e r o x i d e c o u l d l e a d t o t h e f o r m a t i o n of p o l y h y d r o x y l a t e d c y c l o h e x e n e s a n d - a n e s . A rare example o f p h o t o c h e m i c a l c y c l o a d d i t i o n t o a CZN g r o u p is p r o v i d e d by t h e f o r m a t i o n o f b e n z o x a z o l e ( 1 9 ) from p e n t a c h l o r o p h e n o l i n a c e t o n i t r i l e . The p h o t o c o n v e r s i o n of 2-methylbenzophenone i n t o t h e a n t h r o n e ( 2 0 ) i n v o l v e s t w o s e q u e n t i a l p h o t o processes *the E-enol ( 2 1 ) which u n d e r t h e i n f l u e n c e o f h i g h i n t e n s i t y laser l i g h t a b s o r b s a s e c o n d p h o t o n t o g i v e t h e c y c l i z e d i n t e r m e d i a t e ( 2 2 ) which u n d e r g o e s a i r - o x i d a t i o n t o ( 2 0 ) (Wilson e t a l . ). N i s h i o e t a l . h a v e described a n i n t e r e s t i n g p r o c e d u r e f o r w i t h pteridin-2,4,7-trione, a s o l i d which c a n be s t o r e d i n d e f i n i t e l y a t room t e m p e r a t u r e b u t which on warming r e v e r t s t o t h e p a r e n t t r i o n e w i t h l i b e r a t i o n o f s i n g l e t oxygen, A d a m and co-workers have d e s c r i b e d a c o n v e n i e n t one-pot s y n t h e s i s o f e p o x y - a l c o h o l s v i a p h o t o - o x y g e n a t i o n o f a l k e n e s i n t h e p r e s e n c e of a T i ( 1 V ) c a t a l y s t .
' s t o r i n g ' s i n g l e t oxygen as a n a d d u c t
Introduction and Review of the Year
xii
CL (19)
Ph
Me H
(22)
N
(24)
(23)
“6
Me3Si -N=Si
Mee i 0H 2 P h
NHBz
=N-SSiMe3
...
Introduction and Review of the Year
XI11
D k r e t a l . h a v e d e s c r i b e d some n o v e l complex c i n n o l i n e d e r i v a t i v e s which show p h o t o c h r o m i c p r o p e r t i e s .
A l b i n i e t a l . have
p r o v i d e d some new e v i d e n c e o n t h e mechanism f o r t h e p h o t o i s o m e r i z a t i o n o f h e t e r o c y c l i c !-oxides. exceptional.
Simple p y r i d i n e N-oxides
Thus i r r a d i a t i o n o f p y r i d i n e x-oxide
a f f o r d s t h e ring-opened product (23).
are
i n aqueous base
Aoyama e t a l . h a v e
d e s c r i b e d t h e u n p r e c e d e n t e d p h o t o c y c l i z a t i o n o f t h e amide ( 2 4 ) t o t h e lactam ( 2 5 ) .
The f i r s t e x a m p l e s o f C2a+21~1p h o t o r e a c t i o n s o f
a three-membered r i n g and an azo-compound h a v e b e e n d e s c r i b e d by Hunig a n d S c h m i t t . N i c o l a o u et a l . h a v e p r e p a r e d t h e f i r s t s t a b l e example o f a 1 , 2 - d i t h i e t h a n e :
t h e procedure involves (21~+2~r)
p h o t o d i m e r i z a t i o n o f C=S g r o u p s . T r a n s i e n t t r i p l e t b i r a d i c a l s h a v e been t r a p p e d by r e a c t i o n w i t h oxygen:
t h e procedure is claimed t o provide an e f f e c t i v e
method f o r e s t i m a t i n g t h e l i f e t i m e s o f t h e s e s p e c i e s (Adam e t a l . ). S t r e i t h e t a l . h a v e d e s c r i b e d t h e f i r s t example o f a p y r i d i n o cyclopropene (26 )
.
The r e m a r k a b l e s i l a n e d i i m i n e (273 h a s been p r e p a r e d by i r r a d i a t i o n o f t h e a z i d e ( 2 8 ) ( K l i n g l e r and P r i n z b a c h ) .
The
u n u s u a l l y s t a b l e t r i a z i r i d i n e ( 2 9 ) h a s b e e n p r e p a r e d by p h o t o l y s i s of t h e corresponding azide. Delduc e t a l . have r e p o r t e d t h a t t h e p h o t o l y s i s of 2 - a l k y l and S - a c y l x a n t h a t e s p r o v i d e s a u s e f u l s o u r c e o f f r e e a l k y l a n d acyl radicals.
P h o t o l y s i s of t h e imide (30) g i v e s tetramethyl-
c y c l o b u t a d i e n e (Kashima e t a l . ).
W e conclude w i t h r e f e r e n c e s t o developments i n polymer p ho t o c h e m i s t r y
.
Polymer f i l m s h a v e been o b t a i n e d by p l a s m a p o l y m e r i z a t i o n o f hexafluorobenzene, N-vinylpyrrolidine,
and c h l o r a c r y l o n i t r i l e
Higuchi e t a l . h a v e shown t h a t i r r a d i a t i o n o f an a z o b e n z e n e -mod i f i e d po 1y ( Y -met h y 1-L -g 1u t a m a t e -CO-L -g 1u t am i c ac i d ) (Munro).
i n b i l a y e r membrane v e s i c l e s o f distearyldimethylammonium c h l o r i d e l e a d s t o t r a n s - c i s i s o m e r i z a t i o n o f t h e polymer:
t h i s leads t o
t r a n s f e r o f t h e p o l y p e p t i d e f r o m t h e h y d r o p h o b i c b i l a y e r membrane inter.ior to the hydrophilic surface. As a r e s u l t , ' t h e r e w a s a d e c r e a s e i n t h e i o n p e r m e a b i l i t y t h r o u g h t h e b i l a y e r membrane a n d t h e f o r m a t i o n of i n t e r v e s i c u l a r a d h e s i o n .
E l s n e r a n d Ritter h a v e
p r e p a r e d p h o t o s e n s i t i v e membranes from a n a r o m a t i c p o l y a m i d e a n d
a c i n n a m a t e t h a t i n c o r p o r a t e s a l i q u i d c r y s t a l l i n e component.
Contents PART I
PHYSICAL ASPECTS OF PHOTOCHEMISTRY Photophysical Processes in Condensed Phases By R.B. Cundall
3
1
General
3
2
Singlet State Processes
9
2.1 2.2 2.3 2.4
2.5 2.6
Electron Transfer Reactions and Exciplexes Dyes and Related Systems Photoisomerization and Related Processes Electronic Excitation Energy Transfer Polymeric Systems Colloidal and Heterogeneous Systems
14 17 19 22
24 25
3
Triplet State Processes
29
4
Other Chemical Systems
34
5
Biological Systems
36
References
40
PART I1
PHOTOCHEMISTRY OF INORGANIC AND ORGANOMETALLIC COMPOUNDS
Chapter 1
The Photochemistry of Transition-metal Complexes By A . Cox
65
1
Introduction
65
2
Titanium
65
3
Vanadium, Niobium, and Tantalum
66
4
Chromium, Molybdenum, and Tungsten
67
5
Manganese and Rhenium
69
6
Iron
70
7 Ruthenium
71
8
Osmium
77
9
Cobalt
77
xv
Contents
xvi 10 Rhodium and Iridium
79
11 Nickel
81
12 Platinum
82
13 Copper and Gold
83
14 Lanthanides
84
15 Uranium
86
16 Actinides
88
17 Miscellaneous
88
References
88
The Photochemistry of Transition-metal Organometallic Compounds By A. Cox
103
1
Introduction
103
2
Titanium
103
3
Niobium
105
Chapter 2
4 Chromium, Molybdenum, and Tungsten
105
5
Manganese and Rhenium
108
6
Iron
111
7
Ruthenium
116
8
Osmium
117
9
Cobalt
117
10 Cobalt and Iridium
118
11 Rhodium and Iridium
118
12 Nickel
122
13 Palladium and Platinum
123
14 Copper and Silver
124
15 Miscellaneous
124
References
124
The Photochemistry of Compounds of the Main Group Elements By A. Cox
135
Introduction
135
Chapter 3
1
Contents
xvii 2
Boron and Indium
135
3
Silicon, Germanium, and Tin
137
4
Nitrogen and Phosphorus
141
5
Oxygen, Sulphur, and Selenium
142
6 Halogens
142
Miscellaneous
143
References
143
PART I11
ORGANIC ASPECTS OF PHOTOCHEMISTRY
151
Chapter 1
Photolysis of Carbonyl Compounds By W. M . Horspool
151
1
Norrish Type I Reactions
151
2
Norrish Type I1 Reactions
156
3
Oxetane Formation
162
4
Miscellaneous Reactions
164
References
170
Enone Cycloadditions and Rearrangements: Photoreactions of Dienones and Quinones By W.M. Horspool
173
Cycloaddition Reactions
173
7
Chapter 2
1
Intramolecular Intermolecular Dimerization 2
Rearrangement Reactions ai,
p-Unsaturated Systems
p, y,-UnsaturatedSystems
173 185 195 197 197 208
3
Photoreactions of Thymines and Related Compounds
211
4
Photochemistry of Dienones
214
I
Cross-Conjugated Dienones Linearly Conjugated Dienones
214 222
5
1,2-,1,3-, an 1,4-Diketones
222
6
Quinones
232
Reference
237
Contents
xviii Chapter 3
Photochemistry of Alkenes, Alkynes, and Related Compounds
245
By W.M. Horspool 1
Reactions of Alkenes Addition Reactions cis-trans Isomerization Hydrogen Abstraction Miscellaneous Reactions
245 245 245 249 251
2
Reactions involving Cyclopropane Rings
253
3
Reactions of Dienes, Trienes, and Higher Polyenes
261
4
[ 2 + 2 ] Intramolecular Additions
267
5
Dimerization and Intermolecular Additions
273
6
Miscellaneous Reactions
273
Reference
280
Photochemistry of Aromatic Compounds By A . C . Weedon
285
Introduction
285
1
Isomerization Reactions
287
2
Addition Reactions
299
3
Substitution Reactions
309
4
Intramolecular Cyclization Reactions
317
5
Dimerization Reactions
327
6
Lateral Nuclear Rearrangements
328
7
Peripheral Photochemistry
333
Reference
338
Photoreduction and -oxidation By A. Cox
344
1
Introduction
344
2
Reduction of the Carbonyl Group
344
3
Reduction of Nitrogen-containing Compounds
347
4
Miscellaneous Reductions
348
5
Singlet Oxygen
348
6
Oxidation of Aliphatic Compounds
3 50
Chapter 4
Chapter 5
Contents
xix
7 Oxidation of Aromatic Compounds
352
8
Oxidation of Nitrogen-containing Compounds
355
9
Miscellaneous Oxidations
356
References
357
Photoreactions of Compounds containing Heteroatoms other than Oxygen By S.T. R e i d
366
Chapter 6
1 Nitrogen-containing Compounds Rearrangements Addition reactions Miscellaneous Reactions
366 366 383 392
2 Sulphur-containing Compounds
392
3
Compounds containing other Heteroatoms
40 1
References
407
Photoelimination By S.T. R e i d
413
1
Elimination of Nitrogen from Azo-compounds
413
2
Elimination of Nitrogen from Diazo-compounds
423
3
Elimination of Nitrogen from Azides
429
4
Photoelimination of Carbon Dioxide
434
5
Fragmentation of Organosulphur Compounds
436
6
Miscellaneous Decomposition and Elimination Reactions
439
References
447
POLYMER PHOTOCHEMISTRY By N . S . Allen
455
1
Introduction
455
2
Photopolymerization
455
2.1 2.2 2.3
456 462 466
Chapter 7
PART IV
Photoinitiated Addition Polymerisation Photocrosslinking Photografting
3
Optical and Luminescence Properties
466
4
Photodegradation and Photooxidation of Polymers
476
Contents
xx
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9
Polyolefins Poly(vinylha1ides) Polystyrenes Polyacrylics Polyamides Poly(Organosi1anes) Rubbers and Polywethanes Natural Polymers Miscellaneous Polymers
476 477 478 478 479 479 479 480 481
5
Photostabilisation Process
483
6
Dyes and Pigments
487
References
490
Part I PHYSICAL ASPECTS OF PHOTOCHEMISTRY By R. B. CUNDALL
Photophysical Processes in Condensed Phases BY R. 6. CUNDALL
It h a s b e c o m e a p p a r e n t o v e r t h e l a s t f e w y e a r s t h a t photophysical research has been largely concerned with the very detailed analysis o f
particular systems.
f w d i n g are reflected
in
The economics of research
t h e s t y l e and e x t e n t t o w h i c h g r o u p s i n
ditferent parts o f t h e world are able to investigate specific problems.
T h e a p p l i c a t i o n o f p h o t o p h y s i c a l p r o c e s s e s in a r e a s s u c h
as molecular electronics
i s s t i l l i n a n e m b r y o n i c s t a t e and m u c h
m o r e w o r k n e e d s t o be d o n e b e f o r e s u b s t a n t i a l p r o g r e s s t o w a r d s u s e f u l d e v i c e s w i l l be a c h i e v e d . T h i s r e v i e w f o l l o w s t h e p a t t e r n o f p r e v i o u s y e a r s and deliberately
s e t s o u t t o p r o v i d e a broad
over a wide area.
survey o f published w o r k
T h i s is c o n s i d e r e d t o be m o r e g e n e r a l l y u s e f u l
than a discussion of a limited number o f special topics. Biochemists remain t h e leading exploiters o f
photophysical
t e c h n i q u e s and it is n e c e s s a r y t o p o i n t o u t t h a t c o v e r a g e o f t h e b i o l o g i c a l and m e d i c a l a r e a s i s not c o m p r e h e n s i v e . Experimentally
t h e past year has seen t h e ingenious
a p p l i c a t i o n o f t h e very
short time resolution spectroscopic
t e c h n i q u e s o f very r a p i d p r o c e s s e s s u c h a s s o l v e n t r e l a x a t i o n and electron transfer following electronic excitation. Subpicosecond o f detecting
t i m e s c a l e r e s o l u t i o n has e v e n r e a c h e d t h e s t a g e
w h a t c a n l o o s e l y be d e s c r i b e d a s t h e “ t r a n s i t i o n
states“ of some o f the most elementary reactions such as unimolecular dissociation.
1
A
General
very l a r g e number o f papers presented
at t h e F i r s t
I n t e r n a t i o n a l L a s e r C o n f e r e n c e i n 1987 g i v e a c o m p l e t e representation lasers’.
o f photochemical research involving t h e use o f
Extensive applications t o l u m i n e s c e n c e and photochemistry
are reported.
A
b o o k e d i t e d by L e t o k h o v 2 o n l a s e r p i c o s e c o n d
s p e c t r o s c o p y and p h o t o c h e m i s t r y
of
3
biomolecules
is largely
Photochemistry
4 concerned w i t h
techniques
and c a t e g o r i e s
o f
compound.
The s u r v e y
i s e s p e c i a l l y v a l u a b l e i n i t s emphasis on Russian work.
The
b i e n n i a l r e v i e w o f luminescence published i n A n a l y t i c a l Chemistrv, i s very
compsehensive and p a r t i c u l a r l y
analysis3
.
special issue of
A
proceedings
o f
i n biomedical. scierice:;.
u s i n g f l u o r e s c e n c e decay
t i m e as
e x c i t e d s t a t e behawiour
wide variety
o f
photoactions.
fl.uosescence
spectrometry
p h o t o c h e m i s t r y and examines t o .solvent
effects
A
technique
t h e power
review o f
available adjunct t o
the multidimensional fluorescence
and u t i l i t y o f
maximising information obtainable from steady
t h i s method f o r s t a t e luminescence7.
T i m e r e s o l v e d l u m i n e s c e n c e i s now t o b e r e g a r d e d a s e x t e n s i v e reviews d e a l w i t h phase r e s o l v e d a n a l y s i s and w i t h l a n t h a n i d e probes. value of of
identification’.
biomolecule tagging strongly fieldg.
The
by
recommmends
former
lanthanide chelates
t h e use o f
t h r e e year
emphasises t h e
selectively as
a means
i n immunoassay e t c .
time resolved
Transmission spectroscopy o f
organized
Two
The l a t t e r d i s c u s : j e s a p p l i c a t i o n o f
systems
review o f the esoteric
luminescence d e a l s w i t h equipment
fluorescence
and
in t h i s
o r i e n t e d molecules by
is a l s o s i g n i f i c a n t i n view o f
p o l a r i z a t i o n modulation spectroscopy the importance o f
routine.
fluorescence i n chemical
incorporating fluorescence l i f e t i m e
i:omponent
i n a
C u m p u t e r s make r n u l t i d i r n e n s i u n a l
a readily
e s t a b l i s h e d methods. illustrates
oxygen
the information carrier5.
has reviewed picosecond o r g a n i c
the relation o f
inany
typic^. 1. o f
i s o n e w h i c h d e s ~ : r j . b e s a f J . b s ~ ?0 p t J . c
~.ntesr?:;tiny p a p e r s
Peters‘
chemical
2nd I n t e r n a t i o n a l Symposium on q u a n t i t a t i v e
luminescence spectrometry
sensor
relevant t o
A n a l y t i c a l C h i m i c a A c t a p ~ ’ u v i . d t , st h e
i n technology
subject o f
and biology.’’.
A
circu1arl.y polarized
and r e s u l t s
largely for
chiral
m e t a l ~ o m p l e x e s ’ ~ .C h a n g e s i n c h i r a l i t y o n e l e c t r o n i c e x c i t a t i o n should prove a A
f r u i t f u l f i e l d
for
further
research.
NATO A S 1 w h o s e p r o c e e d i n g s h a v e b e e n p u b l i s h e d 1 2
i t s e l f with
supramolecular photochemistry.
Amongst
c:oncerned
t h e 30
papers
are contributions which deal w i t h photoinduced charge separation and energy m i g r a t i o n .
excited
The
Journal o f
Luminescence published
a c o l l e c t i o n o f papers on d y n a m i c a l processes i n
during the year
s t a t e s of
solids’3.
c o v e r e d i n some o r g a n i c h o l e b u r n i n g was
one o f
A l l
i n t e r d i s c i p l i n a r y aspects
b u t m a i n l y i n o r g a n i c systems. the techniques described.
u s u a l l y o n l y occurs on t h e picosecond o r because o f t h e circumstances
s h o r t h o l e decay
are
Optical
This
phenomenon
femtosecond t i m e s c a l e
t i m e a l t h o u g h it c a n u n d e r
be found on t h e nanosecond t i m e
scale.
some
R e s u l t s hawe
5
I: Photophysical Processes in Condensed Phases been g i v e n for p - t e r p h e n y l ” .
Brauchlel’
p r e s e n t s a phase
m o d u l a t e d h o l o g r a p h i c g r a t i n g t e c h n i q u e f o r use in o p t i c a l solid State spectroscopy.
It has been applied t o p h o t o a c t i v e m o l e c u l e s
in p o l y m e r i c e n v i r o n m e n t s .
N e w r e a c t i o n paths c a n be i n d u c e d by
two photon laser excitation16.
T h e s e may o c c u r in e x p e r i m e n t a l
systems by e i t h e r a c c i d e n t o r d e s i g n and a r e s h o w n t o o p e r a t e in a w i d e variety o f systems. T h e N o t r e D a m e g r o u p d i s c u s s t h e p r o c e d u r e s used i n t h e a s s e m b l y o f n u m e r i c d a t a b a s e s on t h e k i n e t i c s o f t r a n s i e n t s p e c i e s in SOlUtiOn”.
Recent c o m p i l a t i o n s are d e s c r i b e d and m e t h o d s of
d a t a c o l l e c t i o n and use e x p l a i n e d . An e x t r e m e l y e x c i t i n g a c h i e v e m e n t i s t h e u s e o f r e a l t i m e f e m t o s e c o n d p r o b i n g o f t r a n s i t i o n s t a t e s in c h e m i c a l reactions’?. The m e t h o d , w h i c h shows p r o m i s e f o r t h e s t u d y o f b i m o l e c u l a r and u n i m o l e c u l a r r e a c t i o n s , has a l r e a d y been applied t o t h e d e c o m p o s i t i o n o f ICN. picosecond
R ~ l l i e r e ’ has ~ discussed the application of
s p e c t r o s c o p y t o study a variety o f e l e m e n t a r y
processes. T h e r e a r e f e w t h e o r e t i c a l p a p e r s on p h o t o p h y s i c s i n t h e period u n d e r r e v i e w and no p a r t i c u l a r t h e m e s a r e e v i d e n t . i n t e r e s t i n g t o p i c s h o w e v e r h a v e been c o n s i d e r e d . fractals in luminescence
Some
T h e use o f
s h o w s h o w t h i s s i g n i f i c a n t concept can
be applied t o t h e b e h a v i o u r o f n o n h o m o g e n o u s s y s t e m s z 0 .
A few
i n v e s t i g a t i o n s h a v e a l r e a d y used t h i s a p p r o a c h in t h e study of energy transport.
T h e t h e o r y of b a r r i e r l e s s e l e c t r o n i c r e l a t i o n
in s o l u t i o n t a k i n g i n t o a c c o u n t solvent v i s c o s i t y , c h a n g e o f polarity w i t h t e m p e r a t u r e has been t r e a t e d by Bachi2’.
A combined
e x p e r i m e n t a l and t h e o r e t i c a l study o f h o r i z o n t a l t r a n s i t i o n s in i n t e r n a l m o l e c u l a r t w i s t i n g h a s been m a d e f o r a r o m a t i c m o l e c u l e s including ~ - d i m e t h y l a m i n o b e n z o n i t r i l e 2 2 . Luminescence studies o f i n e r t i a l m o t i o n in l i q u i d s c o n s t i t u t e s an i m p o r t a n t part o f present d a y p h o t o p h y s i c s 2 3 .
Subpicosecond molecular dynamics can
be s t u d i e s by d e g e n e r a t e f o u r - w a v e m i x i n g a s e x e m p l i f i e d by w o r k w i t h CS2 and n i t r o b e n z e n e Z 4 .
A r i g i d polar p r o b e has a l s o b e e n
used t o e x a m i n e t h e r o l e o f s o l v e n t m i c r o s c o p i c r e l a x a t i o n i n highly p o l a r a p r o t i c s o l v e n t ~ 2 ~ .T h e r e i s a good c o r r e l a t i o n b e t w e e n s o l v a t i o n t i m e and t h e m i c r o s c o p i c r e l a x a t i o n t i m e o f individual solvent molecules.
The effect of small clusters in t h e
m o l e c u l a r e n v i r o n m e n t on o s c i l l a t o r s t r e n g t h and s p e c t r a h a v e been examined f o r t e t r a c e n e + Ar and c y a n o a n t h r a c e n e dynamics o f polar solvation has been measured
+
Ar or X e Z 6 .
The
for several probe
6
Photochemistry
molecules by fluorescence upconversion with subpicosecond r e s o l u t i ~ n ~ ~SimonZa . has reviewed the subject for polar media including solvation of e l e c t r o n s , rotational diffusion as evidence of dielectric f r i c t i o n , and time dependent Stokes shifts a s probes o f solvation dynamics.
The influence o f non-Debye relaxation and
molecular s h a p e on the time dependence of the Stokes shift i s examined also by Castner et a 1 J 9 . in polar solvents.
Electron transfer i s possible
A comprehensive analysis of solvent
reorganization in optical and thermal electron transfer p r o c e s s e s , including solvatochromism and intramolecular electron-transfer in spheroidal molecules gives an expression which can be correlated
.
with earlier work3'
Excited state d i p o l e moments and polarization
in centrosymmetric and dimeric mo1ei:ules
have been theoretically
c:alculated for bichromophoric m o l e c u l e s , p o l y e n e s , p o l y y n e s , and cumulenes3'
I
32
.
A q u i t e detailed theory of the effect o f heavy atoms on singlet and triplet states of aromatic molecules has been presented by Najbar33. F r e d r i c k s 0 n 3 ~ has formulated expressions f o r the concentration depolarization o f fluorescence in the presence of molecular rotation.
A
theoretical examination o f diffusion
influenced fluorescence quenching by nearest possible quenching neighbours in liquids has been m a d e 3 = . Smoluchowski
A modified version of
- Collins - Kimball formulation
of
- Volmer
the Stern
equations has been matched w i t h experimental data f o r quenching of anthraquinone derivatives by
N,N-dimethyl-g-toluidine.
Another
paper d i s c u s s e s this work on t h e basis o f t h e kinetics o f partly diffusion controlled reactions36. An interesting state model has been applied t o e x c i t e d - s t a t e proton transfer reactions and used t o analyse data for a number of ~ y s t e m s 3 ~ .End t o end distance distribution of flexible m o l e c u l e s have been estimated from steady state fluorescence energy transfer and the e f f e c t o f quenching induced changes o n the Fbrster exchange distance3'.
For naphthalene ( d o n o r ) and aminonaphthalene
(acceptor) separated by a methylene chain results agree w i t h frequency domain
measurement^^^.
A pioneering study o f some note has been reported which d e a l s w i t h the r o l e o f coherence in disordered matter40.
This paper
examines t h e existence o f coherent ( o r d i s s i p a t i v e ) structures i n amorphous matter l i k e liquids w h i c h a r i s e from thermal motion. Electronic transltiOnS affect the behaviour o f many molecules
I: Photophysical Processes in Condensed Phases
7
around t h e e x c i t e d s p e c i e s and t h i s l e a d s t o c o o p e r a t i v e e f f e c t s w h i c h may be d e t e c t e d by e x p e r i m e n t . As
p h o t o c h e m i s t r y b e c o m e s used i n o t h e r f i e l d s s u b j e c t s w h i c h
m i g h t be c o n s i d e r e d " c l a s s i c a l " c o n t i n u e t o f i g u r e in t h e literature.
F o r e x a m p l e a paper c o n s i d e r s t h e s t a b i l i t y o f l i g h t
s o u r c e s and i m p l i c a t i o n s f o r p h o t o b i o l o g i c a l s t u d i e s h 1 .
A
new
f l u o r e s c e n c e s t a n d a r d , [ 2 , 2 / - b i p y r i d y 1 1 - 3 , 3 - d i o l . has been suggestedh2.
It has t h e a d v a n t a g e o f having a broad g r e e n
f l u o r e s c e n c e band w e l l s e p a r a t e d f r o m t h e a b s o r p t i o n and a q u a n t u m f i e l d o f 0.3 2 0.03 at r o o m t e m p e r a t u r e .
The photoreversible
f u l g i d e , A b e r c h r o m e 5 4 0 . i s a u s e f u l a c t i n o m e t e r f o r s i n g l e or double laser excitation experiments43.
Measurement o f primary
p r o c e s s e s by l a s e r i n d u c e d o p t o c o u s t i c s p e c t r o s c o p y is a p o w e r f u l technique44.
A method
has been r e p o r t e d f o r m e a s u r i n g a b s o l u t e
f l u o r e s c e n c e y i e l d s by m e a s u r e m e n t o f r e l a t i v e f l u o r e s c e n c e e m i s s i o n and n o n r a d i a t i v e
(photoacoustic) datah5.
Low
c o n c e n t r a t i o n s o f a heavy a t o m q u e n c h e r ( C 2 H g I ) very c o n v e n i e n t l y e l i m i n a t e s t h e need f o r a b s o l u t e c a l i b r a t i o n p r o c e d u r e s . Three papers deal with the effect of variation o f temperature on t h e second d e r i v a t i v e o f f l u o r e s c e n c e
Derivative
s p e c t r a g i v e b e t t e r r e s o l u t i o n o f o v e r l a p p i n g bands and d i s c r i m i n a t e very w e l l t h o s e w i t h n a r r o w b a n d w i d t h s . F l u o r e s c e n c e p o l a r i z a t i o n has proved t o g i v e high s e n s i t i v i t y in d e t e r m i n a t i o n o f a v i d i n and b i o t i n by m e a n s o f t h e f l u o r e s c e i n conjugateh7.
S y n c h r o n o u s d e r i v a t i v e s p e c t r o s c o p y c a n a l s o be
u s e f u l as e x e m p l i f i e d by m e a s u r e m e n t o f p e s t i c i d e
composition^^^.
T h e r e has been a c o n s i d e r a b l e d e c l i n e in t h e n u m b e r o f p a p e r s w h i c h d e a l w i t h t h e d e t a i l s of t e c h n i q u e s o f m e a s u r e m e n t o f fluorescence decay.
This is no doubt d u e to the fact that t h e
alternative methods are now essentially w e l l established. Nevertheless a microcomputerized
u l t r a h i g h speed t r a n s i e n t
d i g i t i z e r and l u m i n e s c e n c e l i f e l i n e i n s t r u m e n t has been describedh9.
A
very u s e f u l m u l t i p l e x e d a r r a y f l u o r o m e t e r a l l o w s
s i m u l t a n e o u s f l u o r e s c e n c e d e c a y at d i f f e r e n t e m i s s i o n w a v e l e n g t h u s i n g s i n g l e p h o t o n t i m i n g array d e t e c t i o n s 0 .
Data c o l l e c t i o n
r a t e s could a p p r o a c h t h a t f o r a r e p e t i t i v e l a s e r p u l s e s y s t e m and t h e t e c h n i q u e could be u s e f u l l y applied
t o H P L C or m i c r o s c o p y . T h e
p o w e r of t h i s e q u i p m e n t has been e x e m p l i f i e d by s t u d i e s o n
e-
a m i n o t e t r a p h e n y l p o r p n y r i n s at e m i s s i o n w a v e l e n g t h s u p t o 6 8 0 nm. T h e u s e and p e r f o r m a n c e o f t h e d e l t a f u n c t i o n c o n v o l u t i o n method for t h e e s t i m a t i o n o f f l u o r e s c e n c e d e c a y p a r a m e t e r s has been
Photochemistry
8 c r i t i c a l l y appraised. combining t h e with
from a
that
There
simultaneous
reference samples3.
d i s t r i b u t i o n o f decay r a t e s of
are simplifying
analysis of
for
a f a s t d e c o n v o l u t i o n method
analysis o f
i s a l s o l i k e l y t o be v e r y u s e f u l s 4 .
time
t y p e PM t u b e s
several side-on basis
for
the proper
selection o f
the analysis of
Details
f l u o r e s c e n c e decay t h a n t h e decay
Time r e s p o n s e d a t a
either
of
these tubes
Fluorescence
Time-resolved
i n o r g a n i c powders;
apart
peak h a l f w i d t h ,
and G r a t t o n ”
discuss various
a
i n single
l i f e t i m e s measured by
luminescence
peak maxima,
for
provides
have been used t o m o n i t o r e l u e n t s
l i q u i d chromatographys6.
measurements,
t o a Poisson
(Hamamatsu R 9 2 8 and R 9 5 5 )
photon counting experimentss5. use o f l a s e r e x c i t a t i o n
i n
is considered.
pulse r e p e t i t i o n p e r i o d is l e s s
when t h e e x c i t a t i o n
for
Application
a sample for
advantages
s i n g l e photon t i m i n g data
during
has been used
from l i f e t i m e and i n t e n s i t y d a t a a r e
employeds7. Thompson
t h e phase s h i f t
fluorometric
Rayleigh scattering
shows
w a v e l e n g t h dependence The m e a s u r e m e n t fluorometry
apparentcolour
associated
other
forms
of
anisotropy
10 p s
of
e f f e c t s due t o t h e times by
i n the
frequency
PM t u b e .
- domain
i n details9. A
f l u o r o m e t e r w h i c h uses t h e o p t i c a l K e r r e f f e c t over
for nm d o w n
t h e range 390-900
is u s e f u l f o r t h e s t u d y o f u l t r a f a s t dynamics i n
solution60.
i n g e n i o u s waveguide detecting very
for
0 2 , pH,
capillary
flow c e l l for
passing along the fibre63.
c o o l i n g b e l t designed
keeps t h e sample
at
15K for
fluorometry
for
samples t o e v a p o r a t e q u i c k l y a f t e r
A
l o w temperature
number o f
systems
fluorescence
spectra
An
stage6‘.
intensity i n of
noise i n
has been reduced by u s i n g an OMA66.
f o r making measurements on l i v i n g c e l l s OMA
has been used t o o b t a i n subnanosecond
and a n i ~ o t r o p y ~ ~ T h. i s
study t h e s t i m u l u s induced p l a t e l e t granules.
luminescence
t h e 5 0 pdm3
leaving the cold
f l a s h p h o t o l y ~ e sa~n d~ t h e e f f e c t
have been d e s c r i b e d .
fibres
self-cleaning
Dye f l u o r e s c e n c e h a s b e e n u s e d t o m o n i t o r nitrogen laser
capable o f
l i q u i d core
measurement b u t a l l o w s
s t u d y i n g p h o t o l a b i l e samples
for
a n d e n ~ y m e s ~ ’ , ~ *A. v e r y
l o w l e v e l s i n v o l v e s t h e use o f
with laser l i g h t continuous
f i n d many u s e s i n l u m i n e s c e n c e ,
Optical fibres
example w i t h sensors
A
aspects
equipment have been r e p o r t e d .
o b t a i n i n g t i m e resolved emissions to
technical
f o r determining lifetimes.
electron transit
has been d e s c r i b e d
Various picosecond
of
of
method
secretion o f
A r a p i d scanning
has been used t o
acriflavine-loaded
fluorescence
blood
spectrometer
has
I: Photophysical Processes in Condensed Phases
9
been used w i t h an acoustooptical tunable filter t o monitor pH and Ca2+ concentrations i n living cells68.
A
set up for measuring
fluorescence d e c a y s by means of microscope optics has been used w i t h living cells6'.
An improved apparatus for measurement o f
correlation functions by fluorescence in observed volumes o f about 1 0 pm3
c a n give diffusion data70.
T w o other items are o f particular g e n e r a l interest.
The
observation that picosecond optical phase conjugation can be induced in conjugated organic molecules is of considerable significance for optoelectronics7'. Locke and L i m t 2
have reported the first example o f bicemer,
a d i m e r i c species formed by association o f two electronically excited molecules.
Charge-transfer stabilization occurs by
association of two identical triplet states or intramolecular association in 1 , l - d i - a - n a p h t h y l e t h a n e and I , l - d i - ( 9 - a n t h r y l ) ethane in polar solvents73
2
Sinqlet State Processes
The details o f t h e mechanism of decay o f S 1 retain
their interest.
states in alkanes
The effect of deuterium on fluorescence
lifetimes has been discussed in terms of the theory o f radiationless tran'sition~~'.
Analysis of fluorescence l i n e shapes
and Raman excitation profiles o f t e t r a d e s m e t h y l - @ - c a r o t e n e i n isopentane has been carried out at 1 9 0 and 23QK7'.
Solvation
occurs over a time scale o f about 100 f s whilst vibrational relaxation has a time scale o f about 2 5 0 fs.
The kinetics o f the
interaction o f alcohols with the excited state o f triethylamine shows involvement o f a charge transfer e x c i p l e ~ ~ ~Ionizing . radiation i s a means o f exciting saturated hydrocarbons and t h e complexity of three component systems containing saturated hydrocarbons, aromatic s o l v e n t , and fluorescent solute has been examinedT7. Benzene and its simple derivatives still provides intriguing problems for photophysics.
Tests for scrambling of the ' B z u
state
of benzene have been suggested7B and a theoretical study o f the mechanism of i n t e r n a l conversion of S ,
state m a d e by K a t ~ ~ ~ .
Measurements of two photon cross-sections for liquid benzene and methylbenzene have used two photon induced fluorescence observations for t h e first t i m e a o .
Picosecond transient absorption
measurement o f geminate electron-cation recombination have been
Photochemistry
10
studied by 2 photon ionization of benzene o r azulene in liquid hexane”.
T h e generate pairs have a radius o f about
absorption at 266 nm.
50A
and s h o w
Radiationless decays have been investigated
i n a range o f substituted alkylbenzenes o f the type Ar(CH2 1 . ~ 8 2 . The effects of values.
X
on k f and k i , d o not extend to n = 2 and higher
Two papers describe the photophysical properties o f the
anaesthetic 2-aminobenzoates.
One o f t h e s e deals w i t h solvent
relaxation processesB3 and the other with the photophysical behaviour in defined solvents and phospholipid v e s i c l e s B 4 .
Time
resolved analysis o f data in t h e latter shows t h e multiplicity o f environments w h i c h exist in biological assemblies. doublet
The doublet-
fluorescence o f benzyl radicals in solution shows
nonradiative relaxation occurs in these species8’.
An excimer o f
9-methyladenine which is not formed by diffusion in aqueous solution is observable by ps time resolved spectroscopye6. The excimer i s formed v i a a weakly coupled stacked d i m e r which exists between t w o ground state monomers. The hindrance o f rotational relaxation i n excited states
of
biphenyl and e - t e r p h e n y l by methyl
substituents affects relaxation processes: experimental data are consistent w i t h theoretical calculations”.
T h e photophysical
properties have been measured and photoisomerization mechanisms proposed in case of the 1 , 3 - d i p h e n y l a l l y l c a r b a n i o n 8 8 , 8 9 . Hydrostatic pressure i s useful for obtaining details of photochemical mechanisms.
It has been used t o s h o w that in the
excited s t a t e o f tetramethyl-g-terphenyl hindrance t o conformational relaxation of a twisted ground state is incomplete even in g l y c e r o l s o l v e n t g 0 .
The emission spectrum o f triphenylene
has been reported in detailg’.
Diphenylpolyenes continue t o
provide f r u i t f u l subjects o f research.
Evidence for S2 emission
and for solvent effects o n this has continued t o be a c c u m u l a t e d g 2 . Fluorinated diphenylpolyenes have given information on ground and excited s t a t e geometryg3.
Nonplanarity o f So
indicated and excitation t o the S ,
ground state i s
state changes t h e molecular
geometry significantly. T h e search for useful phototropic molecules continues. For 2-hydroxyazobenzenes light induces changes in pLa and transfer between phases acts as a conveneient detector for changes of ionization statesg4. T h e cis-trans isomerization o f some hydroxyazobenzenes can be used to construct a light powered hydrogen pump by exploiting the difference i n lipophilicity o f t h e geometric i s o m e r s g S .
Other systems involving proton transfer
11
I : Photophysical Processes in Condensed Phases effects o n their photochemistry reported include , N - a l k y l p h t h a l i m i d e s g 7 , and 5 - a m i n o i n d o l e 9 * phenylenediamine~~'
.
A three component self modelling technique has been applied t o a n a l y s i s o f t h e l u m i n e s c e n c e s p e c t r a o f t h e t w o r:onformers
trans-1
, 2 - d i ( 2-naphthyllethene which has a background
d o m i n a t e d by R a m a n e m i s s i o n g 9 .
of
spectrum
Exciplex formation in 1 , 8 -
n a p h t h a l i m i d e s has bee,n e x a m i n e d i n p r o t i c and a p r o t i c solutlon~'~~. Aggregation OCCUI-s in naphthalene carbohydroxamic acids even a t concentrations as l o w a s
dm-3 l o o .
O n e arid t w o
photon processes in the photochemistry o f 1,3-bis(l-naphttiyl)-2propanone s h o w an example o f a " r e l u c t a n t ' Norrish type I reaction o c c u r r i n g f r o m both s i n g l e t and t r i p l e t e x c i t e d states1'*. state properties o f
Excited
n a p h t h y l , phenanthry1,and biphenyl substituted
arylmethyl radicals have been measuredlo3.
T h e corresponding
h a l i d e w a s p h o t o l y s e d a t 3 0 8 n m and t h e r e s u l t i n g r a d i c a l e x c i t e d by 3 3 7 n m .
T h e insecticide carbaryl i s a naphthalene derivative
w h i c h f o r m s 1 - n a p h t h o l a s i t s m e t a b o l i t e . A spectrofluorornetric study has been reportedlo4. Azulene is one o f t h e most interesting molecules from the photophysical point o f view.
A
picosecond measurement o f t h e
vibrational energy decay i n matrix isolated palyatomic molecules shows a t 4 K that molecular modes in a polyatomic matrix d o e s not a f f e c t d e c a y i n t h e S2
v i b r a t i o n a l manifoldlo'.
T h e S2
+
So
fluorescence of pseudoazulenes has been studies in Shpolski matriceslo0.
T h e ionization threshold o f azulene in hydrocarbon
l i q u i d s h a s b e e n d e t e r m i n e d by m u l t i p h o t o n i o n i z a t i o n 1 0 7 .
The
t e m p e r a t u r e d e p e n d e n c e of t h e f l u o r e s c e n c e l i f e t i m e o f 4 , 6 , 8 -
t r i m e t h y l a z u l e n e - 1 - a l d e h y d e s h o w s a s t r o n g t e m p e r a t u r e b e t w e e n 77 and 1 8 0 K d u e t o v i b r a t i o n a l l y a s s i s t e d i n t e r n a l conversionlo'. T i m e resolved synchrotron spectroscopy o f excited fluorescence o f anthracene single crystals has been publishedlo9 a n d t h e t i m e r e s o l v e d and t e m p e r a t u r e d e p e n d e n t f l u o r e s c e n c e s p e c t r a o f a n t h r a c e n e and p y r e n e i n both t h e l i q u i d and c r y s t a l l i n e reported states1I0
Excimer emission i s observed.
T h e spectroscopy o f 9,lO-dihydroanthracenes i n Shpolskii matrices s h o w s that t h e benzene ring fluorescence i s red shifted from t h e excitation origin'11. s p l i t t i n g of t h e 'B2"
This is interpreted as exciton
state w i t h t h e forbidden state having lowest
e n e r g y ; a n a s s i g n m e n t c o n f i r m e d by o n e a n d t w o p h o t o n spectroscopy.
D e t a i l e d a n a l y s i s of t h e p h o t o p h y s i c a l p r o c e s s o f
d i n a p h t h o l C 1 , Z - a : l f , Z f - h 1 a n t h r a c e n e , a s t r o n g l y nonplalnar
Photochemistry
12
overcrowded aromatic molecule has been compared with benzoCc] phenanthrene112. s t ud ied 1n
Intramolecular mixed excimer formation h a s been
a n t h r a :I e n e - p h e n a n t h sene a nd a n t h 1’a ce n e - p y 1-e n e 1 i n k e d
s y s t e m s 1 1 3 . It is noteworthy that the fluorescence decay of 9 , l O dicyanoanthracene in a jet 1:ooled excess e n e r g y 1 1 4 .
alter the decay features. excited
experiment i s insensitive to
Complexation with Ar. X e . and ethanol d o e s not Other relevant papers involve the
state d i p o l e moments of 9 , 9 - b i a n t h r y 1 1
the fluorescence
of 1 , s - d i h y d r o x y - a n t h r o q ~ i n o n r - d ~in n - h e x a n e at 1 0 K 1 l 6 , and
dihydroxyanthraquinone-do
d2
in n-octane at 1 O K 1
and 1 , 8 -
.
The absorption spectrum of the pyrene ~irystal ex~iimrr is similar t o that in s o l u t i o n 1 1 8 , and its formation studied a s an example o f a n oriented bimolecular r e a c t i o n l l g . time i s about 140fs.
The formation
Further studies indicate that relaxation o f
an initially excited delocalized exciton o c c u r s into a selftrapped distorted excimer s t a t e 1 Z 0 .
A
high pressure study on
intramolecular excimer formation of 1 , 3 - d i - l - p y r e n y l p r o p a n e in various solvents shows a strong dependence upon solvent viscosity but not o n polarity12‘.
hindered rotation m o d e l for excimer
A
formation i s based on K r a m e r ’ s theory. Siemiarezuk and W a r e l Z 1 have reinvestigated t h e fluorescence decay kinetics of 1 , 2 - d i ( l - p y r e n y l ) p r o p a n e and concluded in contradiction t o previous r e p o r t s , that there is a distribution o f short lifetimes in addition t o two longer lived fluorescence components.
This proposal has produced a strong dissent by
Zachariasse and Striker
123
w h o on t h e basis o f a global a n a l y s i s ,
maintain that only three d e c a y s are o b s e r v e d , namely two excimer emissions and o n e from the m o n o m e r . Detailed analyses o f
intramolecular structures are possible.
Comparison of NMR and fluorescence data shows meso- and racemic diastereoisomers are found from 2 , 4 - d i ( 2 - p y r e n y l ) p e n t a n e 1 2 4 .
The
polarization o f monomer and excimer o f 4 , 9 , disubstituted pyrenes have been measured i n nematic liquid crystals12’.
Quenching o f
pyrene fluorescence by alcohols in cyclodextrin inclusion complexes has a l s o been studied i n d e t a i l 1 Z 6 .
Solvent effects on the
photophysical properties o f pyrene-3-carboxylic acid has been used t o measure t h e pEa i n different s 0 l v e n t s l 2 ~ . Geminate recombination i n excited state proton transfer reactions has been studied w i t h B - h y d r o x y p y r e n e - l , 3 , 6 - t r i s ~ l p h o n a t e ~ 2 ~A. numerical solution Of
the Debye-Smoluchowski equation w i t h back reaction is formulated for interpretati‘on o f t h e data.
I: Photophysical Processes in Condensed Phases
13
S o l v e n t s h i f t s in van d e r W a a l s c o m p l e x e s o f p e r y l e n e h a v e been studied i n s u p e r s o n i c jet f r e e e x p a n s i o n w i t h r a r e g a s and organic solvent m o l e c u l e s 1 2 9 .
The 1:l
complexes give results
c o n s i s t e n t w i t h solvent s h i f t t h e o r y .
Orientation measurements
have b e e n m a d e w i t h p e r y l e n y l and p e r y l e n o y l p r o b e m o l e c u l e s i n a variety o f s o l v e n t s and l i q u i d c r y ~ t a l s l 3 ~ . Solvent perturbation
o f t h e e x c i t e d s t a t e symmetry o f
r a n d o m l y o r i e n t a t e d m o l e c u l e s of f l u o r e n e has been studied by f l u o r e s c e n c e e x c i t e d by t w o - p h o t o n a b s o r p t i o n 1 3 1 . T h e t e m p e r a t u r e dependence of the rates o f photophysical processes o f fluorenone is a t t r i b u t e d t o energy s h i f t s o f t h e v a r i o u s e x c i t e d states’32. P h o t o p h y s i c s o f a n u m b e r o f o t h e r f l u o r e n e d e r i v a t i v e s have been r e p o r t e d by Dogra and h i s c 0 w o r k e r s ~ 3 3 , ~ ~ E~l,e c~t ~ r o~n i. c s t a t e s o f a c e p h e n a n t h y l e n e have been analysed by a b s o r p t i o n and e m i s s i o n in cyclohexane136.
T i m e r e s o l v e d f l u o r e s c e n c e has been used t o
i n v e s t i g a t e c o n f o r m a t i o n a l c h a n g e p a t h w a y s for 1 , 3 - d i ( U carbazoly1)propane in toluene, another interesting example of i n t r a m o l e c u l a r e x c i m e r f o r m a t i 0 n l 3 ~ . P h o t o c y c l i z a t i o n and f l u o r e s c e n c e s t u d i e s on h y d r o x y s t i l b a z o l e s hydroxyazaphenanthrenes
and
r e p o r t e d in an e x t e n s i v e paper is very
r e l e v a n t t o t h e a p p l i c a t i o n o f t h e s e c o m p o u n d s as f l u o r e s c e n t probe~l3~. T h e f l u o r e s c e n c e s p e c t r o s c o p y o f t h e S2 been examined
state o f coronene has
in t h e solid s t a t e , as i s o l a t e d m o l e c u l e s , and
a l s o in van d e r W a a l s c l u s t e r s 1 3 9 .
The fluorescence o f
f l u o r a n t h r e n e has a l s o been r e p o r t e d at ~ E I K ’ ~ ~ . The dependence o f intramolecular
proton t r a n s f e r on s o l v e n t
f r i c t i o n has been e s t a b l i s h e d f o r 2 - ( 2 ‘ - h y d r o x y - 5 ~ r n e t h y l p h e n y l )
solvent^'^'.
b e n z o t r i a z o l e in a l c o h o l and o t h e r
Excited-state
proton transfer i n 2 - ( 2 / - h y d r o x y p h e n y l ) b e n z o t h i a z o l e has a l s o been s t u d i e d ’ 4 2 .
P h o t o p h y s i c a l p r o p e r t i e s and l a s e r p e r f o r m a n c e o f
w , w ~ - b i s ( o x a z o l - 2 - y l ) - ~ - o l i g o p h e n y l e nin e s d i o x a n e h a v e been m e a s u r e d at r o o m t e m p e r a t u r e 1 4 3 .
9,
increases with the number o f
p h e n y l r i n g s between t e r m i n a l l y p o s i t i o n e d o x a z o y l g r o u p s . Pyridine is another molecule o f enduring interest.
The two
p h o t o n s p e c t r u m o f liquid p y r i d i n e has been o b t a i n e d by t h e r m a l lensing techniques144.
The two lowest
TIIT*
states are of benzene
t y p e and t h e next h i g h e r e x c i t e d s t a t e is n n * .
T h e f l u o r e s c e n c d of
t h e t r a n s - 2 - s t y r y l q u i n o x a l i n e c o n f o r m e r has been found t o c h a n g e markedly with s o l v e n t 1 4 5 .
The photophysics of 6-(2/-hydroxy-4/-
m e t h o x y p h e n y l l - s - t r i a z i n e photostabilizer
has been e x a m i n e d i n
Photochemistry
14
d e t a i l and tautomerization through proton transfer can be important146.
Fast isomerization of the excited en01 form i s
important in the excited state relaxation o f dibenzoylmethane in nonpolar s o l v e n t s 1 4 7 .
Fluorescence spectra and lifetimes o f
chalcone (benzalacetophenone) k e t y l radical anions have also been i n ~ e s t i g a t e d ’ ~ ’ . Various aspects of the photophysics o f 3 hydroxyflavone involving phenyl t o r s i o n ‘ 4 g , intramolecular proton transfer solvent effects and changes in dipole m o m e n t l s 0 , intramolecular proton transfer in isolated molecules i n solid argonlS1 , l 5 2 have reported also during the year. Coumarins are another much investigated g r o u p .
This period
of review has included excited state interactions of coumarin with nucleotide b a s e s 1 5 3 and quenching by chloride i o n s 1 5 4 . Fluorescence lifetimes of angular furocoumarins in several solvents have been measured and correlated with triplet y i e l d s 1 5 5 . Structural and solvent effects on the fluorescence properties o f benzodihydropyranones have been examined a l s o 1 s s .
N-
naphthylsubstituted pyridine cations s h o w unusual S t o k e s ‘ shifts d u e to torsional relaxation of aromatic groups a s shown by the dependence o n solvent
A
two dimensional
fluorescence sensor has been used t o examine solvent effects on 1 ,
5-diphenyl-3-vinyl-A2-pyrazoline1 5 8
.
The laser behaviour o f
variously substituted pyrylium and thiopyrylium salts gives a range
much better than many d y e s 1 5 3 . T h e curious behaviour o f sulphur compounds i s o f great
interest. of the S 2
This i s seen in the effects of deuteration on the decay state o f
anth hi one'^^.
i n the 1 and 8 positions. to S ,
S2
and S 2
Large deuterium effects a r e seen
T h e results are ascribed to competing
t o S o processes; t h e latter results from motions
of the C ( l ) - H and C ( B ) - H atoms towards the thionyl g r o u p .
2.1
Electron Transfer Reactions and Exciolexes
- Photoinduced
electron transfer i s o n e of the most important areas o f research. A
r e v i e w of photoinduced
electron transfer and electron acceptor
complexes usefully surveys the s u b j e ~ t ’ ~ ’ Details . o f the mechanisms can be obtained by very short t i m e resolution spectroscopy.
Dynamic solvent effects on intramolecular electron-
transfer involve solvent fluctuations. Time resolved ps emission spectroscopy has been used t o examine t h e kinetics o f intramolecular c h a r g e transfer in b i s ( 4 - a m i n o p h e n y 1 ) s u l p h o n e i n ethanol a s a function o f temperature i n this respect162.
It has
I: Photophysical Processes in Condensed Phases
15
been shown that electron transfer times are not e q u a l to longitudinal relaxation times in aprotic solvents163.
This shows
that electron transfer and longitudinal relaxation times are not generally t h e same as recent published work i m p l i e d , but micrOSCOplC solvation times are found t o be similar t o electron transfer times i n a broad range o f polar aprotic solvents.
The
influence of dielectric relaxation o n intramolecular electron transfer shows an unusually strong temperature dependence f o r bridged donor acceptor compounds in propylene g l y c 0 1 ” ~ . An extremely interesting study i s that o n charge transfer state formation from ( N , N - d i m e t h y l a m i n o ) b e n z o n i t r i l e in C F 3 H i n the supercritical s t a t e 1 6 5 .
Solvent molecules aggregate around
the Solute and i t 1 s possible t o c o n t r o l the solvation numbers. 1:l
A
solvent exciplex i s not formed and this cannot b e t h e source
of anomalous C T emission.
Dipole moments and the direction o f t h e
transition d i p o l e moment of some intramolecular exciplexes have been determined by the effect of electric field on fluorescence166 . M i a l ~ c q ’has ~ ~ examined t h e formation of the solvated electron by
UV
photolysis of inorganic anions and neutral
molecules l i k e tryptophan in polar solvents and by the biphotonic photolysis o f w a t e r .
Problems o f electron localization and
solvation a r e analysed w i t h reference t o theoretical studies. Specific examples o f electron transfer studies made include a time resolved spectroscopic investigation o f C T complexes o f 2naphthol w i t h triethylamine in polar and non-polar s o l v e n t s 1 6 8 , fluorescence quenching o f carbazole and indole by ethylene thiodicarbonate w h i c h forms ground state c o m p l e x e s ’ 6 9 , and the luminescent charge transfer complex of 4 , b l - b i p y r i d i n i u m ion w i t h tetrakis [ 3 , 5 - b i s ( t r i f l u o r o m e t h y l ~ p h e n y l l b o r a t eanion’’’. Picosecond l a s e r spectroscopy o f 4 - ( 9 - a n t h y r y l ) - N , N dimethylaniline and related compounds in various solvents indicates multiple excited states w i t h different d e g r e e s o f c h a r g e transfer17’. Similar studies o n W - ( l - p y r e n y l ) - P - ~ , ~ dimethylamino-alkalenes in acetonitrile have allowed the intramolecular electron transfer and subsequent recombination deactivation o f t h e charged state t o be s t u d i e d 1 7 2 .
Various forms
of spectroscopy have been a p p l i e d , f o r example t h e mechanism o f donor acceptor electron transfer has been examined by photon gated persistent spectral hole burning in metal-
t e t r a b e n z o p o r p h y r i n / h a l o m e t h a n e systems i n thin films at liquid H e
Photochemistry ternperaturel73.
Study of charge-transfer states o f 4 -
dimethylamino-3,5-dimethylbenzonitrile are two types o f
in a free jet shows there
These arise from a CT state and
also from a twisted higher excited S2 state. T h e soliton concept i s likely t o prove f r u i t f u l in many aspects of photochemistry especially w h e r e organized systems are involved,
It has been proposed that charge transfer excitons in
mixed-stack donor-acceptor compounds exist in a variety of solitortic states'75.
In this effect charge transfer states couple
to lattice phonons in the crystal lattice to f o r m the comparatively stable solitons. The combination o f electrooptical absorption and emission techniques i s valuable.
In the case o f 9 - ( 4 - d i m e t h y l a m i n o p h e n y l ) -
10-cyanoanthracene such experiments s h o w that this molecule fluoresces f r o m two excited states in low and medium polarity solvents'76. solvent.
O n e highly polar excited state only emits i n a polar
In t h e fluorescence quenching
Q-
N-phenyl-l-
naphthylamine by n i t r i l e s , e s t e r s , and amines t h e CT interaction arises through hydrogen bonding for which equilibrium constants have been d e t e r m i n e d 1 7 7 .
Other related systems reported are
fluorescence quenching o f 9-methylanthracene by pipera~ine'~', magnetic field effects of lanthanide ions on pyrene-dimethylaniline exciplex l u m i n e ~ c e n c e ' ~ and ~ , electron transfer from excited states o f anthracene derivatives to methylviologen which results in generation of a cation radical and h y d r o g e n l E O . Fluorescence yields can be chemically mediated by electron transfer in nitroxide/naphthalene adducts and this effect can be used as optical sensors o f radical/redox reactions'''. increases t h e fluorescence yields. 1'4-disubstituted
Chemical reduction
Persistence hole burning of
anthraquinone molecules with electron donating
groups and stearylamino groups show intermolecular hydrogen bonding w i t h t h e matrix i s importantl'2.
Intramolecular excited s t a t e
charge transfer and fluorescence decay o f p-cyano-i,bJdimethylaniline in mixed hydrocarbon/halocarbon solvents shows a viscosity effect d u e t o slowing o f the rate o f TICT stabilizationl'3.
In cerium(1V)-porphyrin sandwich complexes
excited s t a t e deactivation involves neutral exciton or charge transfer excited s t a t e s l e 4 .
T h e neutral exciton state i s
~
l
and ~ l a
substantial CT character is involved in the rapid radiationless decay.
Electron recomination kinetics following laser
photoionization o f t j , N , N ' , ~ ' - t e t r a m e t h y l - ~ - p h e n y l e n e d i a m i n ein
I: Photophysical Processes in Condensed Phases
17
nonpolar solution has been compared w i t h t h e o r y l n 5 . The r o l e of f r e e volume on TICT emission of d i m e t h y l a m i n o b e n z o n i t r i l e and related compounds has been examined i n polymeric m e d i a l a 6 .
The increase in emission w i t h i n c r e a s e in
free volume rules out t h e possibility of specifl~: s o l u t e - s o l v e n t interactions being responsible for TICT emission i n PVA polymer matrices.
Fluorescence quenching o f phenanthrene and chrysene by
K I in m e t h a n o l - e t h a n o l ,solutions shows both electron transfer processes and exciplex formation between aromatic hydrocarbon and perturber are important' e 7 . The influence o f solvent polarity and viscosity on the deactivation of the S l state o f donor-acceptor in substituted t r a n s - s t i l be n e s ha s been d e t e rmi n ed by mea s u r i ng t h e f 1.LA o r e s c. e n c e and adiabatic twisting rate
constant^'^^.
Exciplexes are formed
between amines and t r a n s - 9 - s t y r y l p h e n a n t h r e n e 1 a g . protonation
Effects o f
on t h e photophysical properties of pyrydyl- and
d i m e t h y l a m i n o - d i p h e n y l h e x a t r l e n e d e r i v a t i v e s , wh1.ch can be i~sed a s biochemical p r o b e s , have been reported a l s o l g n .
A
dual
fluorescence observed by picosecond time resolved sprectroscopy in trans-4-dimethylamino-l'-cyanostilbene
is d u e to a TICT state 191.
Another example o f intramolecular CT complex formation is provided by t r a n s - 4 - d i m e t h y l a m i n o - 4 ' - ( l - o x ~ b ~ t y l . ~ ~ t i l b e n e ~ ~ ~ . Solvent effects on t h e spectrum give a value of 220 for the excited state dipole moment. The effect o f electric field on the fluorescence o f 4 - ( 9 - a n t h r y l ) - ~ , N . - 2 , 3 , 5 , 1 i - h e x a m e t h y l - a n i l i n eshows this compound forms an excited state w h o s e dipole moment d o e s not change with solvent'93. between
Chiral discrimination i n exciplex formation
1-dipyrenylarnine and chiral amines is very weak'94.
In the
probe molecule PRODAN ( 6 - p r o p i o n y l ) - 2 - ( d i m e t h y l a m i n o ) - n a p h t h a l e n e the initially formed excited state converts t o a lower CT state as directly evidenced by time-resolved spectra in n - b u t a n o l l g 5 .
Rate
constants f o r intramolecular electron transfer have been measured in both singlet and triplet states o f covalently porphyrin-amideq u i n o n e moleculesl96. Intramolecular excimer formation occurs during the lifetime o f t h e excited state o f bis(naphthalenelhydrazides which a r e used as photochemical deactivators o f metals in polyethylenelg7.
2.2.
Dves and Related Svstems
- T h e s m a l l number
o f citations i n
this section certainly does not represent t h e extent o f interest i n d y e photophysics.
Much work o f technological nature is not
18
Photochemistry
published i n o p e n l i t e r a t u r e .
An i n d i c a t i o n o f a r e s e a r c h o f
c o n s i d e r a b l e t e c h n o l o g i c a l i n t e r e s t i s p r o v i d e d by a p a p e r d e a l i n g with S o - S ,
t w o photon absorption dynamics in d y e
solution^'^^.
A n o t h e r e x a m p l e i s a s t u d y o f l a s i n g potential. o f a d y e , t h e d i h y d r o x y - d e r i v a t i v e o f 2 , 2 ’ - b i p y r i d y 1 1 9 9 .I n t r a m o l e c u l a r d o u b l e p r o t o n t r a n s f e r i s i n v o l v e d and p r o d u c e d by p u l s e i n t h e 4 9 2 - 5 7 2 n m range.
A
r a n g e o f v e r y s o l u b l e and p h o t o s t a b l e p e r y l e n e d y e s h a v e
been r e v i e w e d 2 0 0 .
T h e relation between t h e dipnle moments o f
m e r o c y a n i n e s i n t h e g r o u n d and e x c i t e d s t a t e s h a s b e e n i n v e s t i g a t e d by R u s s i a n w o r k e r s 2 0 1 . P o l y m e t h i n e d y e s h a v e a l s o b e e n i n v e s t i g a t e d by p i c o s e c o n d s p e c t r o s c o p y 2 0 2 .
Picosecond spectroscopy
m e a s u r e m e n t s h a v e b e e n m a d e on t h e s o l v e n t d e p e n d e n c e o f r o t a t i o n a l diffusion b e h a ~ i o u i - ~ F o~r~ c .r e s y l v i o l e t t h e r o t a t i o n a l b e h a v i o u r i s a f f e c t e d by c h a n g e s i n m o l e c u l a r e n v i r o n m e n t a r i s i n g f r o m
It i s an oblate rotator i n
differences in local solvation.
e t h y l e n e g l y c o l and I - d o d e c a n o l a t 3 7 O C b u t a p r o l a t e r o t a t o r i n 1-dodecanol at 26OC. The interpretation requires an assignment of the transition d i p o l e direction. Observation o f photophysical hole b u r n i n g h a s b e e n c a r r i e d o u t w i t h c r y s t a l v i o l e t and e t h y l v i o l e t in v a r i e t y o f s o l v e n t s and t h e d a t a u s e d t o d e t e r m i n e r e l a x a t i o n r a t e c o n s t a n t ~ 2 ~ ~ , T2h~e ~u .l t r a f a s t c o n f o r m a t i o n e q u i l i b r a t i o n i n t r i p h e n y l m e t h a n e d y e s h a s b e e n o b s e r v e d by t i m e r e s o l v e d i n d u c e d p h o t o a b s ~ r p t i o n ~M~a ~ l a.c h i t e g r e e n and c r y s t a l v i o l e t w h e n e x c i t e d by f s p u l s e s s h o w s r e l a x a t i o n c o m p o n e n t s i n t h e s u b p i c o s e c o n d t i m e s c a l e d u e t o t o r s i o n a l m o d e s and s o l v e n t l i m i t e d v i b r a t i o n a l relaxation206. These involve t h e nonrigid nature o f the triphenylmethane moiety. Subpicosecond time-resolved intramolecular electronic energy transfer has been measured i n bichromophoric rhodamine d y e s i n solution207.
A
n e w subpicosecond fluorescence
s p e c t r o s c o p i c s y s t e m h a s b e e n used t o s t u d y t h e t r a n s i e n t s o l v a t i o n o f t h e p o l a r d y e m o l e c u l e s , c o u m a r i n s 102 and 3 1 1 2 0 8 .
R e t t i g and
h i s g r o u p h a v e a l s o m a d e a s e r i e s o f very e l e g a n t
investigation^^^^-^".
For rhodamine dyes with different
l-
s u b s t i t u t i o n p a t t e r n a n e f f i c i e n t d e a c t i v a t i o n p a t h w a y is l i n k e d with rotation o f amino groups towards a state w i t h increased charge localization, a non-emissive TICT state209. Riradicaloid C T states a r e f o r m e d i n x a n t h e n e and r e l a t e d d y e s s h o w i n g t h a t f o r t h e nonradiative process flexible amino groups interact with the x a n t h e n e s k e l e t o n s t o a n e x t e n t w h i c h d e p e n d s on t h e e l e c t r o n a c c e p t o r strengthz”. strongly reduced.
F o r br.idged a m i n o g r o u p s k,,
is zero or
The n o n - e x p o n e n t i a l f l u o r e s c e n c e d e c a y o f
19
I: Photophysical Processes in Condensed Phases crystalline phase222.
T h e s y n t h e s i s and e f f e c t s o f p H o n t h e
spectral characteristics of substituted 2-phenylquionoxalines
have
been reported as part o f a search for luminescent d y e s c a p a b l e o f acting as solar energy collectors223.
T h e bleaching of r o s e
b e n g a l o n i u m s a l t s h a s b e e n i n v e s t i g a t e d and t h e s t a t e s i n v o l v e d identified224.
S i n g l e t and t r i p l e t s t a t e p r o p e r t i e s o f b i s - ( 2 , 5 -
d i - t e r t - b u t y l p h e n y l l i m i d e d e r i v a t i v e h a v e been i n v e s t i g a t e d a s part of an extended
investigation of perylenetetracarbonylic
d i a n h y d r i d e dyes22'.
2.3
Processe s
Photoisomerization a n d Related
- Bagchi226 has
r e v i e w e d p h o t o c h e m i c a l i s o m e r i z a t i o n d y n a m i c s i n s o l u t i o n and considers the diverse behaviour which arises from the nature o f t h e s o l v e n t , v i s c o s i t y , and s h a r p n e s s o f t h e e n e r g y b a r r i e r . a r t i c l e by B a r b a r a and J o r z e b a 2 Z 7
An
considers dynamic solvent
e f f e c t s on p o l a r and n o n p o l a r i s o m e r i z a t i o n s i n c l u d i n g p r o t o n and e l e c t r o n t r a n s f e r , e x c i t e d s t a t e s , and c i s - t r a n s i s o m e r i z a t i o n s particular.
in
An e x t e n d e d f o r m o f t h e K r a m e r s e q u a t i o n , m u c h
employed in interpreting data for photoisomerization proposed22e.
has been
Experimental data for seven different cis-trans
i s o m e r i z a t i o n in t h e l i q u i d s t a t e o v e r r e a s o n a b l y h i g h b a r r i e r s have been fitted t o a simple t h r e e parameter form o f Kramer's equation.
B o t h h i g h and l o w v i s c o s i t y
l i m i t s h a v e been f i t t e d t o
i s o m e r i z a t i o n r a t e c o n s t a n t s f o r t h e s t i l b e n e and D O D C I s y s t e m s
A m e m o r y k e r n e l c a n be f o r m e d i n l i q u i d p h a s e
amongst others.
photochemical cis-trans isomerizations d u e to a time dependent friction effectZz9.
Computer modelling
o f
cis-trans isomerization
reactions where there is transport over l o w barriers indicates t h a t c o r r e l a t i o n o f r a t e s w i t h s o l v e n t v i s c o s i t y i s u n l i k e l y t o be s a t i s fa c t o r y300
.
A q u a n t u m c h e m i c a l study o f t h e mechanism o f t h e cis-trans photochemical isomerization in r e t i n a l l i k e protonated bases uses t h e m o d e l compound l o w e s t e x c i t e d s t a t e is ' 6 :
Schiff
l - i m i n o - 2 , 3 - ~ e n t a d i e n e ~ ~Tlh.e
like state is l i k e but t h e s e c o n d l A 9 The photoisomerization of
particularly labile photochemically.
all trans-retinal has been studied in a variety o f o r g a n i c s o l v e n t s and o r g a n i z e d m e d i a 2 3 2 . involved
in t h e photoisomerization
The structure of the isomers o f r e t i n o i c a c i d and
photoprotective effects i n model physiological determined233.
&-trans
A picosecond
time-resolved
solutions have been
absorption study o f
isomerization of retinylidene acetaldehyde
shows S,
Photochemistry
20
t r i p h e n y l m e t h a n e d y e s i s d u e t o b a r r i e r l e s s r e l a x a t i o n by a n intramolecular rotational relaxation which allows the viscosity e f f e c t s o f s o l v e n t s t o b e examined2l'.
Ground state recovery f r o m
the electronically excited malachite green molecule has been studied v ! transient vibration heating212.
S1
states are produced
by a n u l t r a s h o r t l i g h t p u l s e a t 600 n m and r e l a x a t i o n f o l l o w e d by s p e c t r o s c o p y prohirig b e t w e e n 6 2 5 and 7 2 5 n m . conversion
( T , , ~
heating t o 6 0 0 K . constant o f
-
Rapid i n t e r n a l
3 p s ) t o t h e vibrdtional manifold gives transient T h e second observed relaxation with a time
llps represents the subsequent vibrational energy
dissipation to the solvent.
T h e two-photon l a s e r photochemistry o f
the coumarin l a s e s d y e , 7 - d i m e t h y l a m i n o - 4 - m e t h y l c o u m a r i n , has also been investigated213. The influence o f the counter anion on t h e excited state relaxation time o f cationic polymethine d y e s has a l s o been repoi-ted214
T h e f l u o r e s c e n c e l i f e t i m e is d e p e n d e n t o n t h e a n i o n
in weakly polar media but independent i n polar media.
The
fluorescence behaviour o f highly concentrated rhodamine 6G s o l u t i o n s i n m e t h a n o l and w a t e r c a n b e s e p a r a t e d i n t o m o n o m e r and dimer contributions215.
A b s o r p t i o n e m i s s i o n and e x c i t a t i o n
spectral data support the view that t h e d y e r o s e bengal forms H - t y p e a g g r e g a t e s i n w a t e r and p o l a r p r o t i c ~ o l v e n t s z ~ ~ T h.e s p e c t r o s c o p i c b e h a v i o u r o f r h o d a m i n e 6 G i n p o l a r and n o n p o l a r solvents as w e l l a s i n thin glass and PMMA films shows dimer f o r m a t i o n o c c u r s and t h e i r s t a b i l i t i e s h a v e b e e n c o m p a r e d u n d e r different conditions217.
T h e equilibrium between t h e neutral
z w i t t e r i o n i c and l a c t o n i c ( c o l o u r l e s s ) f o r m s o f r h o d a m i n e 1 0 1 i n p o l a r s o l v e n t s is s t r o n g l y a f f e c t e d by t e m p e r a t u r e 2 l B .
An
excitonic treatment o f the bonding o f aggregates i n rhodamine 6 G i n e t h a n o l w h i c h h a s b e e n used t o r a t i o n a l i z e t h e i n t e r p r e t a t i o n o f d i m e r i z a t i o n and t r i m e r i z a t i o n c o n s t a n t s d e t e r m i n e d a t different temperatures suggests linear structures for aggregates219
T h e polarized spectra o f a serles o f stilbazollum
merocyanines i n polyvinyl alcohol films shows that only exclplexes fluoresce220. Aggregation o f r o s e bengal units i n synthesised dimeric systems has been used as a m o d e l for the medically interesting haematoporphyrin derivative d i m e r 2 2 1 The deactivation o f t h e UV stabilizers o f t h e 2 (hydroxyphenyl1-benzotriazole
class which involve intramolecular
hydrogen bonds has been researched i n m u c h d e t a i l in t h e
I: Photophysical Processes in Condensed Phases
21
lifetimes of about 500ps are longer than for r e t i n a l i ~ o m e r s 2 3 ~ . There is no configurational relaxation of the S ,
states w h i l s t
spectra of the triplet changed w i t h time showing that molecular changes only occur i n t h e triplet manifold.
Solvent effects on
the photoisomerization of bilirubin arise from solvent interference w i t h intramolecular hydrogen bonding235. Cis-trans -
photoisomerization o f diarylethylene i n e t h a n o l
glasses i n the temperature range o f 4 . 2 t o l O O K shows that structural nonequilibrium occurs in such m a t r i c e ~ 2 3 ~ . Theoretical calculations have been made on stilbene which are relevant t o photoisomerization d y n a m i c s .
M N D O calculations o f
stilbene potential energy properties shows no evidence o f a doubly excited "phantom" state but a singly excited ' 8 ,
state w i t h
adiabatic rotation around the c e n t r a l ethylene bond has only a small barrier on this p a t h 2 3 7 .
Calculations o f d i p o l e m o m e n t s ,
optical s p e c t r a , and second order hyperpolarizability coefficients of
some m o n o - and disubstituted stilbene molecules allows t h e
design of useful nonlinear optical molecules238. Solvent reorientation and isomerization of trans-stilbene in alkane solutions has been studied by ps time scale anisotropic absorption and p o l a r i ~ a t i o n ~ ~Coupling ~. of solute and solvent decreases as the size of the solvent molecules increases.
The
applicability of currently favoured models for the activated barrier crossing in the photoisomerization o f stilbene i s discussed.
A
method for measuring quantum yields in the
photoisomerization o f trans-stilbene gives high accuracy w i t h o u t use of a c h e m i c a l a ~ t i n o m e t e r 2 ~ ' .
Evidence has been found for
dynamic solvent effects on the photoisomerization of 4 , 4 ' dimethoxystilbene in w h i c h the effects o f temperature and hydrostatic pressure w e r e made in n - a l k a n e and n-alkyl alcohol24'. A
ps laser time-resolved study fits frequency dependent solvent
shifts but gives results inconsistent w i t h the free volume model. Photophysical and theoretical studies o f trans - 1 - . 2 - ,
and 9 -
styryl anthracenes have studied in different ~ o l v e n t s ~ ~ 2Similar . experimental and theoretical investigations have been m a d e o f the photoisomerism and rotamerism of t r a n s - s t y r y l p h e n a n t h r e n e ~ ~ ~ ~ . This provides a particularly isomers.
comprehensive study of 5 positional
The solvent dependence o f the excited state reactivity
of 1-styrylisoquinoline has been examirted by the direct and photosensitized forms24)4.
isomeritation o f both t h e neutral and protonated
Other related work i s on t h e kinetics o f
Cis-
Photochemistry
22
trans photoisomerization o f 1 , 2 - d i - ( l - n a p h t h y l l e t h y l e n e i n single crystals2"
and regioselective photoisomerization of m - s t y r y l
~ t i l b e n e s ~ ' ~ . T w o groups have studied =-transphotoisomerization
of
1 - ( 9 - a n t h r y l ) - 2 - p h e n y l e t h y l e n e ~ ~ ~ ~A - ~ ~ ~ .
number of 4 - n i t r o - 4 ' - d i a l k y l a m i n o s t i l b e n e s in nonpolar solvents have a mixed singlet and triplet mechanism for the trans
-+
cis
p h o t o i s o m e r i z a t i ~ n ~A~ ~related . study has been made w i t h l-(l-naphthyl)-2-(4-nitro-phenyl)-ethyl)-ethylene
examined for triplet i n v o l v e m e n t 2 5 1 .
which has a l s o been
In 5 . 6 b e n z - Z . Z ' - d i q u i n o l y l
photoisomerization about the carbon-carbon d o u b l e bond in l o w yield
to
i s dependent on the solvent.
T h e electronic
excitation i s localized on the azaphenanthrene m o i e t y z s 2 . Two studies have been reported o n a z o b e n z e n e ~ ~ ' ~ , ~ ' ~ .In the case of the sterically hindered p , Q , g ' , g ' - s u b s t i t u t e d azobenzines the effect of exciting lower '(n,rr*) and higher ' ( r , r r * ) states has been ~ t u d i e d 2 ~ ~In. cyclodextrin inclusion complexes of azobenzene there i s partial blockage of rotational motion about the N = N bondZ5'. A
holographic method has been used t o investigate t h e
cis-
trans isomerization w h i c h occurs in the d y e methyl red dissolved in poly(methy1 m e t h a c r y l a t e ) and polystyrene2s0.
Back isomerization
from the excited state of the laser d y e 3 , 3 ' diethyloxadicarbocyanine
fluorimetric methods2s7
2.4
iodide ( D O D C I ) has been examined by
.
Electronic Excitation Enerav Transfer
-
Studies dealing
exclusively with energy t r a n s f e r , theoretical o r e x p e r i m e n t a l , in homogeneous systems are very f e w in the year under review. Nevertheless some very seminal investigations have been m a d e . The diffusion equation for l o n g - r a n g e energy transfer by the d i p o l e - d i p o l e interaction mechanism which i s accompanied material diffusion has been solved numerically258.
by
T h e theory o f
enhanced energy transfer between molecules embedded in spherical dielectric particles has been developed for application t o dipoledipole energy transfer taking place between molecules embedded in aerosol d r o p l e t ~ 2 5 ~ .T h e experimental systems studied involved the use of the d y e s coumarin as donor and rhodamine 6 G as acceptor. T h e nature o f energy transport and percolation has been examlned in mixed molecular crystals w h i c h are regarded a s fractal structures*60.
Strong guest host interaction produces induced
energy funnels which a r e found to mask the fractal nature o f t h e
I: Photophysical Processes in Condensed Phases
23
percolating triplet guest clusters. The r e l a t i on s h i p between ex c i t a t 11)n t r a n sport a nd f 1 u o r e s c e n I: e depolarization i n two and three d i m e n s i u n d l disordered systems has been discussed by Anfinrud and S t r u v e Z G 1 .
I n t h e usual discuqsion
of excitation transport by dipole-interaction it i s conventional to assume that excitation i s completely depolarized after a single This supposition has been critically examined and a theory
hop.
formulated suitable for application to Langmuir Blodgett films and absorbed species. A
comparison of D O D C I fluorescence depolarization in g l y c e r o l
and ethylene glycol shows the effect of a orientational
orr relation
on excitation t r a n ~ f e r 2 ~ ~T h . e effect of rotational diffusion o n fluorescence depolarization i s separated
from the influence of
excitation transport at higher concentrations.
T h e decay function
analysis o f energy transfer from acriflavin to erythrosin B in ethanol and glycerollwater solution shows hopping at l o w acceptor concentration and a Forster mei:hanism
at higher levels263 .
Energy
transfer from coumarin 4 6 0 to rhodamine 6t is complex and reflects the time dependence of suitable d o n o r - a c c e p t o r pairs264. A
fractal model has been used in interpretation o f singlet
excitation energy migration among different sites which energetically and spatially disordered in Langmuir Blodgett monolayer f i l m s 2 6 5 .
Long-range exchange contributes t o singlet-
singlet energy transfer i n a series o f rigid bichromophoric molecules w h e r e a cyclic ketone acts as acceptor for energy from an excited
1 , 4 - d i m e t h o x y n a p h t h a l e n e moiety266.
Exchange interaction
is found t o be more efficient than dipole-dipole coupling. Energy transfer and chiral asymmetry effects have been examined i n bichromophoric molecules with camphor structures267
.
Bimanes
are other molecules i n which fluorescence and phosphorescence have been used t o observe both singlet-singlet and triplet-triplet
', energy t r a n ~ f e x - ,2z ~6 ~ S e v e r a l other papers introduce concepts derived f r o m solid state physics. For example picosecond spectroscopy is used t o study polaritons in anthracene c r y ~ t a l s 2 ~ ' . Initially formed polaritons are relaxed by phonon interactions w i t h the lattice and these relaxed polaritons act as efficient means o f transporting excitonic energy. T h e behaviour i s complicated by restricting influences referred t o a s "bottlenecks".
Polariton effects i n
anthracene single crystals can be observed in transient grating experiments a t low t e m p e r a t u r e ~ z ~ l .A t high temperature excited
Photochemistry
24
state transfer i s incoherent and excitation i s localised on a given site in the lattice and then randomly hops.
At l o w temperatures
phonon interactions are reduced and coherent states become important. These states are no longer localised and energy transfer occurs by propagation o f excitation wavepackets.
At very l o w
temperatures the polariton structure involves an interaction of the whole m a t e r i a l with the illuminating electromagnetic field.
In
s o l i d phases o f octasubstituted phthalocyanine derivatives e x c i t o n
diffusion lengths o f 1 0 0 - 2 0 0 A occur in molecular superlattices formed by columnar mesophases arising from segregation aromatic cores and flexible side c h a i n s 2 7 2
of
rigid
. The nonlinear spectra
of J aggregates o f pseudoisocyanine in solution shows evidence o f singlet-singlet annihilation of exciton d o m a i n s * 7 3 . i n
Harri~nanZ~~
reviewing energy transfer in synthetic porphyrin arrays show:;
that exciton coupling i s important i n some
o f
these systems.
Exciton migration processes occur in phycocyanin 6 6 5 and allophycocyanin27 2.5
.
Polymeric Systems
-
M 0 r a w e t z 2 ~ ~has recently reviewed the
study o f synthetic polymers by nonradiative energy transfer. Excimer dynamics in poly-(N-vinyl carbazole) films have been revealed by t i m e correlated single photon counting in the picosecond region277.
An emission f r o m an overlap excimer i s
observed immediately whereas the alternative sandwich codformation emission shows delayed formation. T h e s a m e g r o u p have investigated a l s o the fluorescence of the monomer and t h e role o f tacticity o n
the behaviour o f the solvent in tetrahydrofuran278.
Tacticity
influences t h e t i m e resolved spectra and affects t h e rise and decay of t h e fluorescence spectra. Non-exponential picosecond trapping of singlet excitation in poly-(&-vinyl
carbazole) has been modelled by
making allowance for excimer dissociation and the t i m e dependence for trapping o n monomer and excimer fluorescence decays2”.
Another
example of picosecond timescale dynamics is a study made o f ionized and excited states in polystyrene films following
2
photon laser
p h o t o l y s i ~ 2 ~ ~The . dynamics and mechanism o f generation of excited states by recombinatiori fol lowing ionization and excimer formulation have been elucidated.
T h e photophysics o f alternating
copolymers o f both acenaphthylene and methacrylic acid w i t h maleic acid has also been i n v e ~ t i g a t e d ~ ~ ’ . T h e u s e o f fluorescence probes t o determine polymeric structures is of w i d e application.
Excimer formation i n pyrene
I: Photophysical Processes in Condensed Phases
25
labelled hydroxypropyl Cellulose i n water has been investigated by picosecond fluorescenceza2.
Two different structureless bands d u e
t o different excimers are found.
The quenching o f fluorescence of
probes covalently bound t o polyelectrolytes by m e t h y l v i o l o g e n , sulphonated propylmethyl v i o l o g e n , and a neutral zwitterionic viologen has also be studied by time resolved t e c h n i q u e ~ 2 ~ 3 . Aggregation numbers in polymeric micelles can be determined by luminescence quenching.
Intramolecular micelles formed by a
copolymer of maleic anhydride and hexyl vinyl either have been studied by the quenching of tris ( 2 , 2 ’ - b i p y r i d i y l ) r u t h e n i u m ( 1 1 ) by 9 - m e t h y l a n t h r a c e n e 2 B 4 . T h e influence o f alkoxysilanes on pyrene excimer production can be used to indicate the speed of g e l formation2e5. T i m e dependent absorption and emission of the excimer can both be used and i t w a s shown that in methoxysilane g e l production w a s faster than w i t h t h e ethoxy homologues. T h e developing interest in the possible use o f organic materials i n electronics i s opening up n e w areas o f photophysics. Polyacetylene i s the prototype conducting polymer and its properties a r e being examined by photophysical techniquesza6. Nonlinear optical properties o f polymeric media a r e important since l a r g e second order nonlinear optical enhancement can occur d u e t o cooperative interaction between dipoles in polymer c h a i n s Z e 7 . Polydiacetylene is another interesting system w h o s e absorption and fluorescence spectroscopy has been researched in Picosecond time resolved and frequency domain coherent Raman scattering has been related t o nonlinear optical processes i n a soluble p ~ l y d i a c e t y l e n e ~ Relaxation ~~. measurements i n polydiacetylene polymers shows singlet exciton lifetimes o f about psZgo.
1
Deactivation occurs to a conformatianally relaxed ( k i n k e d )
singlet state.
Rice and P h i l p 0 t 2 ~ ’ have examined t h e r o l e o f
polarons and bipolarons in m o d e l tetrahedrally bonded homopolymers such as p o l y - ( o s g a n o ~ i l y l e n e ) 2 ~ ’ .T h e s e states are available in the polymer for either the addition or the excitation of electrons Or holes. T h e width of these polarons are a f e w bond lengths and interchain photoexcitation is possible. Picosecond orientations of transition dipoles i n polysilanes has been studied by fluorescence a n i s o t r 0 p y 2 ~ 2 . Excitation energy transfer in these polymers i s ultrafast in accord w i t h the Rice and Philpot polaron m o d e l . 2.6
Colloidal and Heteroqeneous Systems
-
Photophysics in
colloidal systems remains a very significant area o f research in
Photochemistry
26
spite o f the sparse practical returns from work related to solar energy. The recently published book by K a l y a n s ~ n d a r a m provides ~~~ an extensive survey o f the whole subject.
A review paper considers
fluorescence a s a means of studying microemulsions and reversed micelles and applications in analysis294.
Colloidal media offer
interesting possibilities f o r selective photochemical reactions. L a t t e ~shows ~ ~ ~that i s o m e r i s a t i o n , d i m e r i z a t i o n , and photoaddition can be achieved and he correlates structure-chemical and photochemical reactivity relationships in microemulsions.
Another
review considers the significance of static fluorescence quenching in the study o f micellar systems296.
Static quenching i s shown to
be the dominant effect in luminescence quenching in interpolyelectrolyte c o m p l e x e s 2 9 7 . Fluorescence probes can be used to investigate anionic polymer interactions2”.
- cationic surfactant
Perylene has been employed as a probe o f the
rigidity of sodium taurocholate r n i c e l l e ~ and ~ ~ ~its effects o f metal cations on the fluorescence intensity of polycyclic aromatic hydrocarbons g i v e further information on the same systems300. Analysis of fluorescence decay curves can be used t o determine the mean aggregation number o f aqueous micelles.
T h e use o f 1 -
methylpyrene quenching by the immobile quencher ltetradecylpyridinium chloride in S D S micelles gives an aggregation number of 6 9 in excellent agreement w i t h literature values3”. Excimer formation o f a water soluble fluorescence probe in anionic micelles and nonionic polymer a g g r e g a t e s , such as a pyrene d e r i v a t i v e , is an indicator of cluster s t r u c t u r e 3 0 2 .
Fractal
modelling has been used for luminescence quenching in m i c r o emulsions w h e n quencher exchange between different droplets i s allowed303 Ru(bpy)32+ fluorescence in t h e presence o f Fe(CNIG3in water and o i l emulsions has been analysed in this w a y . Malliaris304
has used fluorescence t o follow changes induced
i n S D S micelles w h e n a l k a n e s , a l c o h o l s , and ketones are solubilised.
By means of steady s t a t e methods information on
micellar s i z e , m i c r o p o l a r i t y , interfacial charge d e n s i t y , etc. can be obtained.
P y r e n e and two oppositely charged derivatives have
been investigated in NaF ion30S.
Anthracene and 9-methylanthracene
have also be’en entensively studied in detergent m i ~ e l l e s ~ and ~ 6 Iions are shown by anthroyloxy probes t o interact w i t h cetyltrimethylammonium bromide m i c e l l e ~ ~ ’ ~ Internal . mobility o f Triton X - 1 0 0
micelles has been investigated by fluorescence
anisotropy and excimer p r 0 b i n g 3 ~ ~ .
I: Photophysical Processes in Condensed Phases
27
A number o f colloidal systems containing d y e s have been investigated.
T h e fluorescence lifetime of acridine o r a n g e has in the S D S premicellar region3”.
been measured
A short l i f e t i m e
of less than 3 n s is found for the monomer but the emission lifetime increases w i t h dimer formation and S D S concentration. Quenching o f 7-ethoxycoumarins by inorganic ions in S D S 3 l 0 ,
d y e solubilizates in
micelle l i k e complexes o f surfactants w i t h p o l y e l e ~ t r o l y t e s ~ ‘ ~ , time resolved fluorescence depolarisation o f rhodamine d y e s in Triton X - 1 0 0 micelles and Aerpsol OT reversed m i c e l l e s 3 l 2 , and Static and time resolved fluorescence in an amphiphilic flavin in Aersol OT reversed m i c e l l e ~are ~ ~ ~ other photophysical systems reported.
A picosecond timescale resonant energy transfer from
rhodamine 6G t o malachite green has been used t o study micellar size and s h a p e 3 1 4 .
In this very detailed work it i s found that
d y e s a r e solubilised at the surface o f the S D S micelles. CT
complexes are formed and electron transfer occurs from
excited molecules of anthracene derivatives t o methylviologen in aqueous micellar m e d i a 3 1 5 .
Methylene blue quenches pyrene
fluorescence by electron transfer in S D S micelles316
.
Electron
transfer between anthraquinone sulphonate radicals and duroquinone i n S D S micellar solution occurs in t h e aqueous phase; there i s n o evidence of intramicellar transfer3I7.
Photoionisation o f
).I,N,N’, N ’ - t e t r a m e t h y l b e n z i d i n e in anionic-cationic mixed micelles has been studied in d e t a i l by ESR318.
The photochemistry
o f the
semi-oxidised forms o f eosin Y and rose bengal have been investigated
in colloidal solutions319.
Relevant to t h e
fluorescence o f proteins i s a study of fluorescence quenching o f
indolic compounds by amino-acids in S D S . C T A B , and CTAC m i ~ e l l e s ~ * ~ Rate constants for proton transfer o f several hydroxyaromatic compounds have been measured solutions321. of
in a variety of surfactant
Photoprotolytic dissociation does not require exit
the reactant molecules from the micelles.
Micellar solutions
can b e used to improve t h e fluorescence determination of 2 - n a p h t h o l by inhibiting proton transfer or proton inducing reactions322.
The
decay of t h e radical pair composed of diphenylphosphonyl and 2 , 4 , 6 trimethyl benzoyl radicals in S D S is affected by magnetic f ields32 3
.
A useful r e v i e w o f optical probes in the study of thin organic films has been written by Debe3z4.
Apart f r o m conventional
luminesence the discussion of internal reflective fluorescence excited by t h e evanescent w a v e i s especially interesting.
Pressure
28
Photochemistry
area i s o t h e r m s and f l u o r e s c e n c e b e h a v i o u r o f 1 2 - ( l - p y r e n y i ) d o d e c a n o i c acid at a n air-aqueoius i n t e r f a c e s h o w s e x c i m e r f o r m a t i o n d o m i n a t e s t h r o u g h a g g r e g a t i o n d r i v e n by h y d r o g e n bonding o f c a r b o x y l i c acid g r o u p s 3 2 5 .
D a n s y l f l u o r e s c e n c e has a l s o been used
a s a p r o b e f o r polarity a t t h e a i r - w a t e r i n t e r f a c e 3 2 6 .
The
interaction of carboxylic porphyrins with dioleoylp h o s p h a t i d y l c h o l i n e i n spread m o n o l a y e r s and t h e e f f e c t s o f l o d i d e ion quenching i s another system studied327.
T h e f1uoresc:ence
lifetime of 5 - ( 4 - c a r b o x y p h e n y l ) - 1 0 , 1 5 , 2 0 - t r 1 t 0 1 y 1 p o r p h y r i t i
ln mixed
L B f i l m s w i t h d i o l e o y l - p h o s p h a t i d y l c h o l i n e has b e e n proposed
standard328.
as a
Fluorescence drainage profiles of thin liquid films
has been o b s e r v e d w i t h r h o d a m i n e c o n t a i n i n g
surf act ant^^^'.
F l u o r e s c e n c e and e n e r g y t r a n s f e r o f n e g a t i v e l y charged c y a n r n e d y e s bound t o m o n o l a y e r s i s a n o t h e r study r e p o r t e d 3 3 0 .
A
t l m e resolved
s t u d y o f t h e e f f e c t s o f m o l e c u l a r o r g a n i s a t i o n i n pyrene l a b e l l e d p h o s p h a t i d y l c h o l i n e is compared w i t h d a t a f r o m ~ y c l o h e x a n e .~ ~ Order p a r a m e t e r s a r e used t o i n t e r p r e t d a t a on ~ r d e rand f l u i d i t y o f a n u m b e r o f probes i n l i p i d m e m b r a n e s o b t a i n e d by m e a s u r e m e n t s of fluorescence anisotropy decay332.
Ambiqultles in the
interpretation of time resolved fluorescence anisotropy m e a s u r e m e n t s i n l i p i d v e s i c l e s y s t e m s w i t h D P H o r T M A - O P H probes a r e attributed to t h e u n s a t i s f a c t o r y m o d e l s being used t o i n t e r p r e t the data333.
T h e s o l u b i l i s a t i o n o f d i p h e n y l p o l y e n e s i n lipid
bilayers has been c r i t i c a l l y e x a m i n e d 3 3 4 .
I t i s c o n c l u d e d that
such p r o b e s a r e s a t i s f a c t o r y i f used a t low c o n c e n t r a t i o n s . F l u o r e s c e n c e t e c h n i q u e s c a n a l s o b e used t o study s o l i d surfaces. 6G
A f r a c t a l a p p r o a c h has been used t o i n t e r p r e t r h o d a m i n e
probed m o r p h o l o g y o f p o r o u s s i l i c a s u r f a c e ~ 3 ~ ~ M i.g r a t i o n o f
excitation agrees with a one step energy transfer mechanism. Excimer f l u o r e s c e n c e d e t e r m i n a t i o n o f s o l i d - l i q u i d i n t e r f a c i a l pyrene l a b e l l e d p o l y - ( a c r y l i c acid 1 i n d i c a t e s strand coiling336 . P i c o s e c o n d pump p r o b e s p e c t r o s c o p y has been a p p l i e d t o e l e c t r o n i c relaxation in aggregates o f pseudoisocyanine molecules on c o l l o i d a l s i l i c 0 n 3 3 ~ . Energy t r a n s f e r a t i n t e r f a c e s c a n a l s o b e s t u d i e d by d i f f u s e r e f l e c t a n c e l a s e r p h o t o l y s i ~ ~ E ~ l~e . ctron t r a n s f e r t o m e t h y l v i o l o g e n f r o m c o l l o i d a l C d S and T i 0 2 has been s t u d i e d by e x a m i n a t i o n o f t h e k i n e t i c s f o l l o w i n g l a s e r p u l s e ~ 3 3 ~ , 3 F~l~u o . r e s c e n c e , photochemistry. and s i z e q u a n t i s a t i o n e f f e c t s o f c o l l o i d a l s e m i c o n d u c t o r ( c d J s , Z n S , and T i O Z ) p a r t i c l e s h a v e b e e n surveyed by Henglein3('.
Very s m a l l p a r t i c l e s u n d e r g o a
transition from semiconductor t o molecular properties.
Emission
29
I: Photophysical Processes in Condensed Phases spectroscopic evidence i s obtained for Rr$nsted calcined Vycor g l a s s 3 4 2 .
acid sites i n
Other solid surface studies include
pyrene on T i 0 2 3 4 3 , evaporated merocyanine d y e l a ~ e r s . 3 ~ ~ ~ fluorescent probes o n clay p a r t i c l e s 3 4 5 , and diphenyl polymers on alurnina346.
3
Triolet State Processes
The longer lifetime and enhanced biradical character of the triplet State produce a difference in the style of research and the influence of time resolved spectroscopic techniques on the subject i s less marked than for excited singlet states. Selective enhancement of room temperatures phosphorescence i s achieved by cyclodextrin treated cellulose s u b s t r a t e s 3 4 7 . surface active a g e n t ~ 3 ~and ~ , for heterocyclic compounds by absorption on silica gel coated plates submerged in (~hlorofoi-m-containing solvents349. Delayed fluorescence can occur during deactivation o f highly excited triplet states3”.
Energy is transferred to the m e d i u m ,
which may be an electron acceptor andlor d o n o r .
Extended and
localised triplet states in disordered media can be examined by optical and ESR t e c h n i q u e ~ 3 ~. ’ Fashioning of electron spin echo spectra has been used in studying the triplet states of azaromatic m o l e c u l e ~ 3 ~ ~Diffusion . limited phosphorescence quenching in polymer solutions involving small molecule interactions has been interpreted by f r e e volume theory3’3.
Disordering enhances diffusivity o f triplet excit,ons
in condensed aromatic s y s t e m s 3 5 4 .
Fractal like triplet-triplet
annihilation kinetics operate in naphthalene doped poly-(methyl methacrylate) as shown by a delayed fluorescence decay t i m e w h i c h i s less than
that for phosphorescence, suggesting a geometric
fractal dimension o f 1 . 0 t o 1 . 6 3 5 5 .
Long distance intra-molecular
triplet energy transfer rates have been compared w i t h those for electron t r a n ~ f e r 3 ~ ~T.h e former process requires l i t t l e solvent reorganisation but the l a t t e r , because o f a need for t h i s , i s strongly temperature dependent.
Polystyrene i s a good m e d i u m for
the study of long distance electron transfer reactions involving triplet states and i n o n e c a s e t h e r a t e is temperature invariant between 7 7 and 1 C 3 K 3 5 7 .
T h e nature o f the energy g a p dependence
for electron transfer rates in triplet exciplexes has been examined358 and a l s o t h e geminate r a d i c a l pairs formed b y quenching o f phosphorescent states i n polar s o l v e n t ~ 3 ~ ~T h . e r o l e o f spin
30
Photochemistry
orbit
coupling effects
on t h e
geminate recombination o f Magnetic yields
field
for
kinetics
t r i p l e t
has been examined
radical pairs
show a dependence o f
effects
photogenerated b i r a d i c a l s o f
t h e modulated t r i p l e t
the type
upon t h e m e t h y l e n e c h a i n l e n g t h 3 6 1 . T h e r e i s the y i e l d micellized The e f f e c t
of
oxygen on c y c l i c
1,3-diradicals
the t r i p l e t
state
r e s o l v e d r e s o n a n c e Raman s p e c t r o s c o p y triplet
states
theoretical triplet
been used t o The d e c a y
symmetric
triplet
state
relaxation
of
explain experimental data triplet-triplet
biradical
(two sub-levels)
and 7 7 K i n S h p o l s k i m a t r i c e s 3 6 7 . carbene
isomers
and n o n - s y m m e t r i c
kinetics of
mesitylene
shows
lifetime363.
A
fluorescence
for
phosphorescence
of
the excited
has
substituted b e n ~ e n e s 3 ~ ~ .
fluorescence
i n the
h a v e b e e n m e a s u r e d b e t w e e n 10 state o f dimesityl
of
absorption spectra
spectra
of
4,5of
the
from
dimethylphenols
states determined37'.
a t
77K
A
a n d C N D O s t u d y h a s b e e n made o n t h e p y r i d i n e - B C L ,
complex372 and l a s e r p h o t o l y s i s bipyridine
the
k e t o n e ~ 3 ~ A ~ .
i s o m e r s h a v e been m e a s u r e d 3 7 0 and
and p h o s p h o r e s c e n c e
of
aromatic molecules
The t r i p l e t
b e n z o c y c l ~ h e p t a t r i e n y l i d e n e ~ ~T~- . T
the p s values
that
of
h a s a l s o b e e n c h a s a c t e r i ~ e d ~ a~n'd a l s o t h a t
three trichlorobenzene
on
Time
has a l s o been r e p o r t e d on t h e a - c l e a v a g e
states o f
mechanism f o r
1 n-* D-
has been used t o examine
produced from d i f f e r e n t
study
A + - ( CH2
a l s o an e f f e c t
radical p a i ~ s 3 ~ . 2
triplet
c o n f o r m a t i o n can a f f e c t
i n the
i n m i c e l l e ~ ~ ~ ~ .
triplet
has
characterised
i o n i n ~ y c l o h e x a n e 3 ~ 3 .Other
made o n t h e t r i p l e t
states
of
the 2 , 2 ' studies
have been
1,2,6-trimethyl-3,5-diphenyl-l-
p ~ r i d o n e 3 ? ~p ,h t h a l a ~ i n e 3 ~a n ~ d. t e t r a m e t h y l a n d t e t r a e t h y l - p phenylenediamine3' ODMR
stilbene;
.
has been a p p l i e d t o t h e i t
i s found
rigorously planar
that
i n single
cyanobenzene complexes on t h e
of
crystals378.
the t r i p l e t
spectra
of
trans-
i s not
i s almost
spectrum of
stilbene completely
1,4-
are most
Spectroscopic
significant studies
i n triplet
state
i n c l u d e t i m e r e s o l v e d ESR
enols of o-hydroxybenzaldehyde3a2, energy t r a n s f e r
states
of
state
I n crystals o f
excitation
acetophenones t o 9,10-dibromoanthracene
substituted
sub-levels
has also been p u b l i s h e d 3 " .
Carbonyl groups photochemistry.
triplet
of
~ t i l b e n e ~ ' ~T .h e p h o s p h o r e s c e n c e
diazatriphenylene
studies
study
t h e phosphorescent
of
(S,)
which involves
from
higher
t h e donor383, two photon e x c i t a t i o n o f
triplets
of
a ~ e t o p h e n o n e 3 ~t ~ r a, n s i e n t
r e s o n a n c e Raman
d e u t e r a t e d b e n z o p h e n ~ n e s ~a n ~ d~ ,d i f f u s e r e f l e c t a n c e o f
I: Photophysical Processes in Condensed Phases
31
t r i p l e t s i n b e n z o p h e n o n e r n i c r o c r y s t a l ~ 3 ~ ~T.w o p h o t o n e x c i t a t i o n of benzophenone triplets results in rapid energy transfer t o benzene solvent3a7 and quenching o f benzophenone triplets by electron donors does not give satisfactory correlation with ionization potentials388.
Details o f t h e mechanism o f
d e h y d r o g e n a t i o n o f e t h a n o l by a s e r i e s o f w a t e r s o l u b l e b e n z o p h e n o n e s h a v e a l s o b e e n r e p o r t e d 3'9
Rotational relaxation
s t u d i e s o f t r i p l e t s t a t e s o f t r i i s o p r o p y l b e n z o p h e n o n e ~ ~n~ ~T*, a n d TIT*
S t a t e s o f 4 - h y d r o x y b e n z o p h e n o n e i n ethanol3',
ketone in
, and Michler's
are other systems which have been studied
spectroscopically.
Conformers have been established i n triplet
b e n ~ i l s ~p o~l y~s ,t y r e n e q u e n c h e s t h e p h o s p h o r e s c e n c e o f b e n ~ i 1 3 ~ ~ , a n d t h e t r i p l e t a n d q u i n t e t s t a t e s f o r m e d by t r i p l e t - t r i p l e t r a d i c a l pairs o f benzoylphenylmethylene are produced by photolysis o f c r y s t a l l i n e a z i b e n z i l p o w d e r at 7 7 K 3 9 5 . The dynamics of excitons in isotopically mixed naphthalene c r y s t a l s h a s b e e n r e ~ i e w e d 3a~n d~ t h e e f f e c t s o f o r i e n t a t i o n o f m e t a l ion perturbers i n naphthalene-crown ether metal ion complexes on the external heavy atom examined397. The triplet excimer phosphorescence from liquid solutions o f naphthalene and di-2-naphthylalkenes in isooctane previously reported has not been confirmed and t h e emission probably arose from impurities like biacet~l3~'.
Exciton trapping has been
studied in doped 1,4-dibromonaphthalene3gg, ENDOR applied t o t h e s t u d y o f t r i p l e t t r a p s o f p h e n a n t h r e n e - T C N B i n naphthalene-TCNB'OO, and triplet 1 -
and 2 - n a p h t h y l p h e n y l c a r b e n e s produced by photolysis
of diazo compounds401.
Conformers o f triplet states o f 2-
n a p h t h a l d e h y d e at 300Kk02
,
T,
a n d T2
states from dual
p h o s p h o r e s c e n c e o f 1 , 4 - n a p h t h o q ~ i n o n e ~a n~ d~ ,T - T a b s o r p t i o n o f 5 , 8 - d i h y d r o x y - l , 4 - n a p h t h o q u i n o n e by f l a s h p h o t o l y s i s a r e a m o n g s t other interesting papers404.
Q u i n o l i n e , isoquinoline, and t h e i r
protonated cations in phosphorescent triplet states have been measured in C H 3 0 H / H 2 0 and stretched PVA fibres at 7 7 U 4 0 5 .
Heavy
atom effects on the room temperature phosphorescence of dibenzo [ f , h ] quinoxaline absorbed on filter paper have been examined in some detai1406.
Characterisation o f sub-levels o f the non-
p h o s p h o r e s c e n t t r i p l e t s t a t e o f c i n n o l i n e h a s b e e n m a d e by t i m e resolved ESRko7. Assignments of the I R spectrum o f matrix isolated anthracene t r i p l e t s 4 0 0 , i n v e r s e i n t e r s y s t e m c r o s s i n g , T~
-+
S n , studies o f
stepwise t w o photon excitation o f anthracenes409 triplet exciton
Photochemistry
32
f u s i o n at e d g e d i s l o c a t i o n s i n a n t h r a c e n e c r y s t a l s 4 1 0 , and t i m e r e s o l v e d ESR o f a n t h r a c e n e t r i p l e t i n a s e r i e s o f a l k y l t r i m e t h y l a m m o n i u m h a l i d e m i c e l l e s a f f e c t e d by h e a v y a t o m s a r e a n o t h e r group o f related studies.
T r i p l e t - t r i p l e t a b s o r p t i o n and
cis-
trans-isomerization have been correlated 2 - e t h e n y l - a r 1 t h r a c e n e ~ ~ 2 and 2 - s t y r y l - a n t h r a c e n e and r e l a t e d
compound^"^.
T h e photophysics
and p h o t o c h e m i s t r y o f s u l p h o n a t e d d e r i v a t i v e s o f 9 , l O - a n t h r a q u i n o n e shows that lowest
TTI*
t r i p l e t s a r e w e a k photosens.it.izers w h i l s t , i n
c o n t r a s t , nT* t r i p l e t s a r e s t r o n g s e n s i t i ~ e r s ~ ’ ~T.h e e f f e c t o f substitution o n triplet yields o f aminoanthraquinones shows internal hydrogen bonding i s effective i n causing i n t e r n a l c o n v e r s i o n 4 ’5
.
T r i p l e t s t a t e s o f x a n t h o n e d e p e n d u p o n t h e c o m p o s i t i o n of t h e solvent; t h e presence o f w a t e r enhances t h e yield o f 3
~
s~t a t*e 4 1 6
D u a l phosphorescence f r o m 2 - ( 2 ’ -hydroxyphenyl) benzoxazole
is d u e
t o k e t o - e n 0 1 t a u t o m e r i ~ m ~and ’ ~ the kinetics multi-exponential decay i s d u e t o differences o f environment418.
Triplet state
p r o p e r t i e s and t r i p l e t s t a t e - o x y g e n i n t e r a c t i o n s o f t h e b i o l o g i c a l l y i n t e r e s t i n g l i n e a r and a n g u l a r f u r o c o u m a r i n s a r e useful in view o f possible clinical application4Ig. Oxygen quenching o f phenanthrene phosphorescence involves a n exchange mechanism420 which also operates for triplet state energy transfer involving phenanthrene in biphenyl421.
Radiationless
p r o c e s s e s o f e x c i t e d s t a t e s o f 5 , E i - d i a z a p h e n a n t h r e n e i n h e x a n e and h e x a f l u o r o i s o p r o p a n o l h a v e b e e n s t u d i e d by both t r i p l e t and s i n g l e t luminescenceC22.
An e x t r e m e l y f a s t r a d i a t i o n l e s s t r a n s i t i o n i n t h e
t r i p l e t s t a t e o f 9 , l Q - d i a z a p h e n a n t h i - e n ei n b i p h e n y l and f l u o r e n e hosts at 3 K i s d u e t o softness o f t h e twisting m o d e o f t h e nitrogen-nitrogen d o u b l e bond423.
P h o s p h o r e s c e n c e e m i s s i o n and
p o l a r i s a t i o n o f h a r m a n e i n m e t h y l c y c l o h e x a n e and EPA g l a s s e s a t 77K
is from a
3 7 1 ~ *
s t a t e 4 Z 4 . V i b r o n i c c o u p l i n g and p r o x i m i t y e f f e c t s
are analysed. Phosphorescent states o f aromatic thioketones with l a r g e z e r o f i e l d s p l i t t i n g h a v e b e e n i n v e s t i g a t e d by ODMR42’. Excitation wavelength dependence o f phosphoresence o f thioxanthone and 2 , 4 - d i - i s o - p e n t y l - t h i o x a n t h o n e shows that red shifting o f the luminescence is d u e t o hydrogen bonding particularly with w a t e r C 2 6 . T I - T 2 inversion in aromatic thiones produces dramatic changes in t h e p h o s p h o r e s c e n c e s p e c t r a by i n t e r c h a n g i n g 3 n a * a n d 3 n ~ * s t a t e s 4 Z 7 . T h e d e c a y is n o t b i e x p o n e n t i a l .
T h e concentration
dependence o f t h e photochemistry o f 4 H - 1 - b e n z o p y r a n - 4 - t h i o n e i n v o l v e s g r o u n d s t a t e q u e n c h i n g of t h e t r i p l e t s t a t e , p o s s i b l y by
I: Photophysical Processes in Condensed Phases triplet excimer formation420.
33
Interesting photochemical studies
have been made o n the triplet states of monothioanthraquinone and pivalothiophen~ne~~'.
T h e acidity of the triplet state o f 2 -
nltrothiophen has been measured:
p%*
= -0.95
0 . 2 0 ~ 3 ' .
Triplet states are very important photosensitizers
and this
fact has prompted many investigations, for e x a m p l e , the triplet yields of a series of cyanines and photosensitization through singlet oxygen have been related t o substituent effects and quenching rate d a t a 4 3 2 .
The photophysical properties of the
porphyrin, c h l o r i n , a potent sensitizer for photochemotherapy
shows
that the high absorption of both the singlet and triplet states make this compound suitable for sequential biphotonic excitation4j3.
Intersystem crossing in p o r p h y c e n e ~ ~ 3 ~ .
phosphorescence quenching of z i n c tetraphenyl porphin on solid supports by molecular oxygen shows marked differences on silica g e l and sodium chloride c r y s t a l ~ ~ 3t i ~ m,e resolved spontaneous and coherent Raman scattering of nickel octaethylporphyrin in the triplet state436 a r e other related researches.
Triplet-triplet
energy transfer i n the Cu( I 1 1 poi-phyrin free base porphyrin ,.
and z i n c tetraphenylporphyrin and 2-piperidoanthraquinone in aligned nematic and isotopic phases o f liquid crystals exhibiting no enhancement of intersystem crossing in the nematic phase are other interesting porphyrin studies438.
A method
o f oxygen
detection using phosphorescent, Langmuir-Blodgett films of the m e t a l l o p o r p h y r i n , tetraphenylporphine palladium
( 1 1 ) has been
proposed439. Photochemical l i k e behaviour o f riboflavin i n the dark is promoted by energy transfer from e n z y m e generated excited triplet states of acetone440.
Energy conversion by energy transfer from
triplet lumiflavin t o ferricyanide ions occurs without electron transfer whereas w i t h ferrocyanide electron transfer gives semireduced lumiflaven and f e r r i ~ y a n i d e ~ ~ ' .Phosphorescence f r o m 2 - ( ~ - t o l u i d i n y l ) n a p h t h a l e n e - 6 - s u l p h o n a t e and l-anilinonaphthalene-
6 - s u l p h o n a t e bovine serum albumin has l i f e times o f milliseconds442 It is interesting to note that in these experiments oxygen w a s removed f r o m t h e system by glucose together with the enzymes g l u c o s e oxidase and catalase.
Electron transfer from triplet
states o f xanthene d y e s gives r i s e t o t h e methylviologen r a d i c a l 4 4 3 . Unreactive ion pair complexes form between the d y e eosin and M V 2 + and addition o f alcohol increases the efficiency o f energy transfer.
Photochemistry
34
Triplet states o f t h e a m i o d a r o n e , a n antiarrhythmic d r u g w h i c h shows cutaneous t o x i c i t y , are involved in its p h o t 0 1 y s i . s ~ ~ ~ The . lowest triplet states of the drugs codeine and morphine and their molecular s u b units veratrole and guaiacol are
Other Chemical Systems
4.
Ferradini and Bensa~son''~
have reviewed flash photolysis and
pulse radiolysis as tools for studying the kinetic and thermodynamic properties o f
+
02
,
. OH,
lo2.
and
The problems involved in detecting luminescence from singlet oxygen in biological systems have been assessed447 and examination of the red luminescence from ram seminal vesicle microsomes shows pitfalls in the use of spectrally resolved luminescence440.
Direct
measurement o f 1268nm emission shows most of t h e previously reported red emission is not from
lo2.
spectrometer has been used t o determine decay
( l A g , u = O -+
A
very sensitive
lo2
3 1 - g , u = O ) at 127Onm449.
lifetime by direct Using weaker excitation
intensities much longer lifetimes are found i n perhalogenated solvents, C S 2
and C D C 1 3 .
In this c a s e deactivation involves
coupling of highest fundamental vibrational mode o f the acceptor with a ( ' A g , u = O
---*
3 E = 9 , u = m ) transition.
Perturbations of this
transition on the luminescence yield o f ' 0 2
in organic solvents and
water has been examined experimentally4s0.
The yield in benzene i s
higher than expected when compared with results for a number of different
sensitizer^^^'.
Interaction o f O2
('Ag) with
disubstituted olefins gives evidence for physical quenching induced by the hydrocarbon chain452.
T h e interaction i s not w i t h d o u b l e
bonds but may be with CH3 and C H 2 groups o f the side chain substituents.
A
photochemical amplifier for liquid chromatography
based o n singlet oxygen sensitization involves '02 reacting w i t h a substituted f u r a n 4 5 3 . Singlet oxygen generating efficiency of aterthienyl and some o f its synthetic analogues s h o w these m a t e r i a l s , used as mosquito l a r v i c i d e s , f u n g i c i d e s , and n e m a t o d i c i d e s , are excellent ' 0 2 deactivation o f
s e n s i t i z e r s h s 4 . Generation and
l o 2 by helianthrene and its
derivative^^^^,^^^
hypercin4S7 have also been reported. T h e photosensitized
and
production
o f ' 0 2 P M M A glasses w i t h acridine sensitizers has been measured by time resolved spectroscopy4s8.
In these conditions sensitizers are
found t o quench the generated l o 2 . Deactivation of singlet oxygen by thiols and related compounds have been examined a s possible protectors against skin p h o t o s e n ~ i t i v i t y ~ ~Variation ~. of acidity
35
I: Photophysical Processes in Condensed Phases shows t h a t
'
O2
theoretical
reacts exclusively
study of
with thiolate
reactions o f
examined p o s s i b l e i n t e r m e d i a t e s . effects
Singlet
oxygen y i e l d s
properties
and
lo2
yields4G1.
energy
:I
pairs.
I
Types
photooxidation o f
crf
of
Typical rose
and
I 1 processes
tryptophan
and
and d r a w s
attention to
l i f e t i m e i n t h e membrane.
The
components.
concepts
emphasis
the
fact
sensitizing
h a e m a t o p o r p h y r i n d e r i v a t i v e components depends cellular
are involved
t y r o s i n e by
current
b i o l o g i c a l membranes w i t h
o x y g e n mechanisms
with different
dyes
r e q u i r e s t h e r e t o be a l o o s e
p h t h a l ~ c y a n i n e s ~ ~ V' . a l e n ~ e n oh~ a s~ d ~i s c u s s e d the photomodification
longer
st a te
to
from t r i p l e t dye t o t h e
i n detail463.
production.
b i n d i n g between i o n
singlet
t r ip l et
with
azodyes d u e
by u s i n g m e t a l complexed
transfer
have been i n v e s t i g a t e d
bengal behaviour,
sensitized
o r I' e l a t e d
fading of
I and Type I 1 s e n s i t i z e r s based o n r o s e b e n g a l
m e t a l i o n s 4 6 2 . Type onium s a l t s
The
c a n be i n h i b i t e d
photogenerated lo2
w h i c h quench by undergbing
has a
and r a d i c a l .
i n the photosensitized photooxidation o f ester o f
po l y u ns at u s a t e d f a t t y a c i d s h a v e been
i n the
a11i.ons~~~ A .
O2 w i t h o r g a n i c s u l p h i d e s has
on
on
that
lo2
efficiency
on i n t e r a c t i o n
Hydrophobic e f f e c t s
p o r p h y r i n a g g r e g a t i o n and f l u o r e s c e n c e
influence
Polyethylene
g l y c o l m o d i f i e d h a e m a t o p o r p h y r i n has t h e p o s s i b l e advantage as a photosensitizer i n that organic
Cherniluminescence of
i t i s
soluble
i n b o t h aqueous
e x c i t e d ketones
has
formed
and
been used t o measure t h e r e l a t i v e y i e l d s from s e l f
alkylperoxyl radical pairs46E. azides a dehydroazepine spectroscopy and t r i p l e t
nitrenes of
and nanosecond l a s e r
reaction of
i s detected
a t
and
media produces a t r i p l e t
state
have a l s o been d e t e c t e d . i n a ~ i d e s ~ ~ ' . Picosecond
t h e nn*
reaction
o f d i m e t h y l s i l y l e n e produced by
triplet471.
o f dodecamethylcycloherasilane review o f
techniques which
acetate
t h e p--nitrobenzylanion
a f t e r cleavage o f kinetics
Absorption,
i s another
i n aqueous and C 0 2
emission,
and
f l a s h photolyses
interesting
f l a s h p h o t o l y s i s s p i n resonance describes CIDEP can be used t o i d e n t i f y
free radicals473.
r e s o l v e d E S R a n d ENOOR h a s b e e n u s e d d u r i n g t h e p h o t o l y s e s
dimethoxy-W-phenylacetophenone, initiator474
red Singlet
o f f?-nitrophenyl of
aryl
room
4-nitrophenyl
photolysis
and
by t i m e r e s o l v e d i n f r a
and dehydroazepenes
3-
alkoxyl
I n the photochemistry o f
and f l a s h p h o t o l y s i s
t h e photochemistry
A
solution
solvents467.
an e f f i c i e n t
Time o f W,W-
UV c u r i n g
.
Some s t u d i e s o f
chemiluminescence can be c i t e d as b e i n g o f
36
Photochemistry
physicochemical interest.
It i s c o n s i s t e n t w i t h p r e s e n t d a y t r e n d s
t o w a r d s n o n - h o m o g e n e o u s k i n e t i c s t o find r e p o r t s o f o s c i l l a t i n g chemiluminescence w i t h luminol in a continuous f l o w stirred tank reactorh7'.
T h e first study o f peroxyoxalate chemiluminescence i n
microemulsions has a l s o appeared476.
Cyclodextrins increase the
y i e l d s o f c h e m i l u m i n e s c e n c e f r o m a q u e o u s p e r o x y o x a l a t e s by f a c t o r s u p to 3 Q 0 4 7 7 .
Many f a c t o r s a r e i n v o l v e d b u t irrcLusion o f b o t h t h e
r e a c t i o n i n t e r m e d i a t e and f l u o r o p h o r e i n t h e c y c l o d e x t r i n c a v i t i e s i s proposed. The study o f photochromic materials i s a n active area o f research.
P i c o s e c o n d t i m e r e s o l v e d s p e c t r o s c o p y h a s b e e n used t o
investigate primary processes i n ring opening i n the photochromism o f s p i r o x a ~ i n e s ~ ~C A~R.S h a s a l s o b e e n used t o i n v e s t i g a t e s o l v e n t e f f e c t s on i s o m e r i c d i s t r i b u t i o n s i n t h e s a m e s y s t e m s 4 7 9 . Resonance Raman studies o f the photochromism o f 1 ' , 3 ' , 3 ' - t r i m e t h y l spiro
- [ 2 H - I - b e n z o p y r a n - 2 , 2 ' - i n d o l i n e 1 show at least four
t r a n s i e n t s h a v i n g m e r o c y a n i n e s t r u c t u r e s a r e involved4".
A
two
step two colour l a s e r study o f piperdinospiropyran and a nitrochromene shows that photolysis a t 355nm followed excitation of t h e t r a n s i e n t s by a s e c o n d 5 3 0 n m p u l s e p r o b a b l y p r o c e e d s by a s i n g l e t mechanism"'. Photochromic behaviour o f salicylidene anilines incorporated in a L a n g m u i r - 8 l o d g e t t m u l t i l a y e r shows that thermal decoloration is s u p p r e s s e d by t h e h i g h l y o r d e r e d d e n s e l y packed e n v i r o n m e n t 4 8 2 .
.
B i s t a b i l i t y h a s b e e n o b s e r v e d w ~ t ht h e t r i p h e n y l i m i d a z o l y l r a d i c a l dimer when irradiated at
A
transition between t w o states
i s i n d u c e d by c h a n g i n g e i t h e r t h e f l o w r a t e or i n c o m i n g l i g h t f l u x . This is believed t o b e t h e first example o f chemical instability induced in a n i s o t h e r m a l p h o t o c h e m i c a l s y s t e m .
5 .
Biolocrical S v s t e m s
A p p l i c a t i o n s o f p h o t o p h y s i c s i n b i o l o g y and m e d i c i n e a r e very e x t e n s i v e and o n l y a f e w t o p i c s c a n b e m e n t i o n e d i n t h i s r e v i e w .
A
survey o f t h e u s e o f lanthanide ions a s luminescent probes o f b i o m o l e c u l a r s t r u c t u r e 4 1 4 and a g e n e r a l a c c o u n t o f l o n g d i s t a n c e e l e c t r o n t r a n s f e r i n p r o t e i n s and m o d e l s y s t e m s 4 8 5 a r e very helpful.
T h e m e t h o d s a p p l i c a b l e t o t h e s y n t h e s i s and a c t i v a t i o n o f
a n u m b e r o f p h o t o a c t i v a b l e f l u o r o p r o b e s h a v e b e e n d e s c r i b e d and photoactivation yields measured486. T h e e f f i c i e n c y and m e c h a n i s m o f f l u o r e s c e n c e q u e n c h i n g by a c r y l a m i d e and s u c c i n i m i d e f o r s i m p l e a r o m a t i c f l u o r o p h o r e s h a s
I: Photophysical Processes in Condensed Phases
37
been e x a m i n e d w i t h regard t o t h e i r e x t e n s i v e use as b i o c h e m i c a l probes in a q u e o u s s o l u t i o n 4 8 7 .
UV
resonance Raman excitation
p r o f i l e s o f t y r o s i n e s h o w that t h e t e c h n i q u e is a p p l i c a b l e for e x a m i n i n g e x c i t e d s t a t e interrnediates4O8.
Picosecond resolution of
i n d o l e a n i s o t r o p y d e c a y s and r e l a x a t i o n can be followed by 2 G H z f r e q u e n c y d o m a i n s p e c t r o ~ c o p y ~ ~ ’ .R o t a t i o n c o r r e l a t i o n t i m e s as s h o r t as 8 p s can be m e a s u r e d .
P r o t o n induced q u e n c h i n g of
t r y p t a m i n e and r e l a t e d indoles4”
as w e l l a s tryptophan4”
have
been e x a m i n e d i n s o m e d e t a i l and e n v i r o n m e n t a l i n f l u e n c e s s t u d i e d , for example 18-crown-6 ether structure effects. lifetime distributions
Fluorescence
in h o m o t r y p t o p h a n d e r i v a t i v e h a v e been
m e a s u r e d a s a f u n c t i o n of t e m p e r a t u r e and v i s c o s i t y c 9 2 .
Decay
processes a r e affected by m o t i o n s of t h e t e t h e r e d s i d e c h a i n q u e n c h i n g g r o u p . P i c o s e c o n d f l u o r e s c e n c e has been used t o study s i n g l e t r y p t o p h a n r e s i d u e s i n a s e r i e s of p o l y p e p t i d e h o r m o n e ~ ~ ~ 3 . T h e effect o f u n f o l d i n g o f t h e p r o t e i n on t h e t r y p t o p h a n y l f l u o r e s c e n c e l i f e t i m e in a p ~ m y o g l o b i n ~ ’and ~ molecular dynamics s i m u l a t i o n s o f f l u o r e s c e n c e p o l a r i z a t i o n s of t r y p t o p h a n s i n myogl~bin~a ’ r~e o t h e r i n t e r e s t i n g p h o t o p h y s i c a l i n v e s t i g a t i o n s . high r e s o l u t i o n f l u o r e s c e n c e d e c a y and d e p o l a r i z a t i o n
A
study o f
a p o l i p o p r o t e i n s s h o w s t h a t t r y p t o p h y l f l u o r e s c e n c e s h o w s d o u b l e and tri-exponential decays496.
T h e s e a r e assigned t o i n t e r n a l m o t i o n s
of t h e p r o t e i n . A g e n e r a l a r t i c l e d e t a i l s t h e m e t h o d s o f f l u o r e s c e n c e q u e n c h i n g r e s o l v e d s p e c t r o s c o p y of p r o t e i n s 4 9 7 . T r y p t o p h a n r e s i d u e p h o s p h o r e s c e n c e in r e v e r s e d m i c e l l e s has been used in protein d y n a m i c s of l i v e r a l c o h o l d e h y d r o g e n a ~ e ~ ’and ~ a l k a l i n e p h o ~ p h a t a s e ~ ~ ’ .R o t a t i o n a l m o t i o n s of m y o s i n heads i n m y o f i b r i l s has been studied by using p h o s p h o r e s c e n c e a n i s o t r o p y d e c a y at 2 0 0 ~ 5 0 0 . 5 - E O S i n y l m a l e i m i d e i s a u s e f u l r o o m t e m p e r a t u r e t r i p l e t probe.
T h e d i s t a n c e b e t w e e n f l u o r e s c e n t probes a t t a c h e d t o
f o u r e s s e n t i a l l y s y l r e s i d u e s in p h o s p h o e n o l p y r u v a t e c a r b o x y l a s e has been m e a s u r e d by r e s o n a n c e e n e r g y t r a n s f e r s a ’ .
The topography
o f a c e t y l c h o l i n e r e c e p t o r has a l s o been r e v e a l e d by f l u o r e s c e n c e energy t r a n s f e r s o 2 .
T h e e f f i c i e n c y o f long r a n g e n o n r a d i a t i v e
e n e r g y t r a n s f e r among t r y p t o p h a n r e s i d u e s in b a c t e r i o p h a g e T4 l y s o z y m e has been studied using singlet e n e r g y t r a n s f e r , l o w t e m p e r a t u r e p h o s p h o r e s c e n c e and ODMR s p e c t r o s c o p y S o 3 . f a c t o r s a r e assigned
from crystallographic data.
Orientation
F l u o r e s c e n c e has
b e e n used t o m e a s u r e s u r f a c e d y n a m i c s o f l y s o z y m e s absorbed on hydrophobic silicaso4.
This is the first direct kinetic method
m e a s u r i n g c h a n g e s o f s t a t e o f a protein on a b s o r p t i o n .
Other
Of
38
Photochemistry
detailed studies have been made on b a c t e r i o r h o d o p ~ i n ~ ~ ~The - ~ ~ ~ . non-exponential
fluorescence decay functions of a single tryptophan
residue in erabutoxin b shows considerable freedom o f internal rotation around a covalent band in the s u b ns t o ns t i m e s c a l e s o 9 . Picosecond and nanosecond germinate recombination o f myoglobin w i t h C 0 , 0 2 , N 0 ,and isocyanides have been examined in details1’. The method o f triplet state detection i n d y e labelled proteins by fluorescence recovery spectroscopy has been described in a paper presenting this new m e t h 0 d 5 l 1 . A very
spectacular achievement i s the claim to b e a b l e t o detect
single molecules by fluorescence microscopy.
Single molecules of
phycoerythrin labelled w i t h 2 5 rhodamine 6 G chromophores are evidently detected in hydrodynamically focussed flows by laser induced f l u o r e ~ c e n c e ~. ’ ~ Acrylamide and O2
fluorescence quenching has been used as a
probe of solvent accessibility of aromatic fluorophores complexed with D N A 5 l 3 .
Binding o f c o r o n e n e , proflavin. and Hoechst 3 3 2 5 8
have been studied and a l l found insensitive t o quenching by acrylamide. Effects of excimer laser light in inducing strand breaks i n single strand514 and plasmid
DNA5”
have been
investigated in s o m e d e t a i l and two photon excitation demonstrated laser flash photolysis of DNA intercalated ethidium bromide i n the presence of methylviologen shows quenching by electron transfer516.
The hydrophobicity
o f DNA interior has been estimated
using 5 - and 8-methoxypsoralen as probesS17.
The environment
appears t o be very similar in polarity to methanol.
Fluorescence
energy transfer from tyrosine has been used as a probe for interactions of proteins w i t h D N A 5 1 e . Photochemical hole burning has been used for daunomycin i n solution and intercalated w i t h DNA519.
Experiments with d(ATIS and d ( C G I S
from environment.
s h o w differences arise
CIDNF has been used to study the reactivity o f
the furocoumarin photosensitizing
drugss2’.
Fluorescence lifetime distribution o f D P H r e v e a l the effects o f
cholesterol o n the microheterogeneity o f erythrocyte
membraness2 . All aspects of photodynamic t h e r a p y , including relevant photophysics, Angeles522.
are covered in a report o f a conference held in Los T h e r e is much information provided o n the nature of
haernatoporphyrin derivative structure.
A ,representative t y p e o f
study is the determination o f pK values f o r haematoporphyrin -a I X by absorption and fluorescence spectroscopy523. Fluorescence.
I: Photophysical Processes in Condensed Phases
39
quenching of a cationic porphyrin by cationic and anionic aromatics involves formation of ground state c o m p l e x e s 5 2 4 .
Axial-ligand
control o f the photophysical behaviour of Ru(I1) tetraphenyl and octaethylporphyrin produces contrasting properties of TI*)
excited states52’.
and ( r
(IT,IT*
The fluorescence and triplet properties of
water soluble tetra s o d i u m - m e s o - t e t r a ( 4 - s u l p h o n a t o p h e n y l ) porphine ( 1 2 - h y d r a t e ) in erythrocyte c e l l ghosts have been measured with the efficiency of
lo2
efficiency s 2 6 .
together
Multifrequency phase
and modulation fluorometry has been used for resolution o f porphyrin photoproduct mixtures527
.
Photophysics o f cof acial
porphyrin quinone cage molecules and electron transfer studies have been reportedsz8. Transient Raman spectroscopy has been used to observe the photodynamics of metal p o r p h y r i n ~ ~ 2 ~ . Picosecond fluorescence spectroscopy shows that incorporation of
haeinatoporphyrin derivative into malignant tumour cells occurs
iri vitro530.
The aggregate component i n H P D increases in cells
with incubation t i m e .
A
fluorescence imaging device for endoscopic
detection o f early stage cancer uses a fluorescent porphyrin mixture o f dihaematoporphyrin ether and e s t e r S 3 l .
Autofluorescence
is eliminated and the image intensified by a d i g i t a l image processing
system.
MerocyanineS4’
is
p r o b e w h o s e photophysical properties
another useful fluorescent have been investigated532.
It
is useful for identifying leukaemic c e l l s , analysis of plasma m e m b r a n e s , inactivation of v i r u s e s , etc. Theoretical calcul’ations have been made for photosynthetic pigrnents’33.
An extensive review of models o f energy and electron
transfer events of synthetic molecules for photosynthesis has been prepared by W a s i e l e w ~ k i ~ 3 ~Other . studies have made on tetraphenylporphyrin-polypeptide
pigmentss3’, photosensitization of
triplet ~ a r o t e n o i d s ’ ~ ~ fluorescence , yields and lifetimes for bacteriochlorophyll c 5 3 ? , triplet yields and ESR of chlorophyll a 5 3 8 , and quenching processes o f pheophytin
s39.
Other biologically relevant studies are on t h e fluorescence and phosphorescence of harmal and harmald at 7 7 K S c 0
and on also the
photophysics o f the antiflammatory drugs n a p r o x e n , benoxaprofen, and indornethacins4’.
It is perhaps an extreme case o f biological
relevance t o report a paper on t h e total fluorescence of human urine542.
A three dimensional presentation o f luminescence data
allows several fluorescent metabolites t o be detected and identified.
Photochemistry
40 References
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Part II PHOTOCHEMISTRY OF INORGANIC AND ORGANOMETALLIC COMPOUNDS
1 The Photochemistry of Transition-metal Comdexes ~ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ _ _ _ _ _
BY A. COX
1, 1ntt d u c t ion
Reviews have appeared of the structure and reactivity of metal-centred
Ru( I I )
transitlon metal
complexes
photocatalysis campounds,
having
induced
excited
aromatic
states,
Jumineacent
heterocyclic
J igands,
light-sensitive
by
coordination
photochemical reactions between t x a n a it ion metal
complexes and gases at high pressuree ,4 inorganic photochemistry at
high
pressure,5
cobalt( I I [)-mine
and
the and
complexes6
p- peroxocobalt ( I I I )
photochemistry
complexes.
of
8-8
some
w-superoxo-
and
The
appl ication
of
metal-catalysed photor eact ions to sugar molecules has al.so bean reviewed - 8 2. A
Titanium
charge-transfer type complex formed by
[Pe(CN),J4photoresponse
by
Ti02
onset
is
particles over
700
nm
reported with
a
daorption o f to
have
its
photon-to-current
converaAon efficiency a8 high as 37%.9 Ti02/NI0 la an actlve catalyst. fur the photodecompoeition of water, lo a correlatlnn w j t.h pH-dependent surface structures has been astab.1 I shed P or the
photacat.alytlc activity of T i 0 2 suspended In aqueous AgN03,’’
and
the photocatalytic activity and melect-fvity of V/TIOz fn the
oxidation of lsobutene I R dependent an the c r p t a l modlf ication
of the Tio2.I2 Titania loaded with tungetosilicate ISiW,,0,,J4-
Is active in the photoproduction of hydrogen under band gap
65
Photochemistry
66
i l l ~ m i n a t i o n .Platiniaed ~~ titania has been used to catal.yse the photareduction of sodium carbonate to C and HCHO,"
and a new suspended in
method for the N-alkylation of ammonia by T i O Z / P t
alcohols has been published.l5 Semicanductor-semi ti zed radi cal Pormation is the initial step in the photacat.a.lyt.icreaction of dienea on irradiated Ti02 p0wders.l' sensitization of
Ti02
Reports have appeared of the
in the visible
light region usi.ng a
water-soluble anionic zinc porphyrin17 and of khe use o f t.ik3ny.l moncwners and dimera as
and vanadyl meso-tetraphenyJporphyrin
catalysts for the photooxidation of alkenerr.'O Photareduction of Ti( JV) in alcohol8 gives the act.ahec3ra.l complexes
[TiClz(ROH)qJ+, [TiC13(ROH)3J , and
the tetrahedral
complexes [TiQHC13J and [TiORC13J .l9 The same authors a l s o report the Pormation of hydrogen, and correlate its yie1.d to the a-CH bond energies in the alcohol. 3. Vanadium, Niobium, and Tant-a.Zum Hydrogen
chemiaorption
causes
large
increases
in
the
photoionisation threshold of isolated txana it inn metal. cl.nat-srs such as Vx, Nbx, and Fe,
( x =
induced shifts for
H
both
3-25).21
and
NH3
as
The dJrection of the
absorbatea haa
been
ratianalieed using a frontier molecular orbital model, Redox and photochemical propertiea of V(I1) polypyridine complexes have been
combined
to
achieve
the
first
example
of
photoredox
initiated 2-electron oxidation at a single transition metal centre.22 Studies have appeared of t h e photooxidation of V( 1 1 ) in acidic solution23 and
the
redox
chemistry of
water-soluble
vanadyl porphyr ins,24 and the mechanism of methane photooxidat ion
on
a
vanadium/silica
catalyat
has
been
shown
to
invol.ve
interaction of CHI with surface oxygen anions bonded to vanadium
1111: The Photochemistry of Transition-metal Complexes
67
ions25 The
photoredox
reaction8
of
the
cluster
compounds
'' have been deaclr
2+r [ NbgBr 123 2 t , and [ TafiC11~ ) [NbfiC11Z]
ihctd. 26
4. Chromium, Molvbdenum. and Tunaaten A
Cr(I),
study of the photoredox reactions of [M(C!N)5NOIn- (M Mn(I),
Mn(I1))
=
has shown that in the case of C r ( J ) and
Mn(1) the process is intermolecuJar h u t that. for Mn(J1) it. is intramolecular 27 Purther
temperature dependence
studies
of
the
doubl.et
lifetimes of coordination complexes of Cr ( I l I ) have tlhown that the RISC (reverse interaystem crosaing) is the lifetime Limiting process in compounds with a sma.ll energy separation.28 A small reduction
of
the
lifetimes
of
excited
[Cr(NH3)6I3+
and
[Cr(cyclam)(NH3)2J+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) with increased solvent mobility has been observed but which is absent in the deuterated analogues29. This has been interpret,ed to indicate that enhances
increased anharmonicity jn accepting modes
nonradiative
rates.
The
in
acidic
&-[ CK ( CYClam) (NH3)21 3+
--
ICr (cyclam)( H2O) (NH3 ) ) 3 t .
New
photoaquation
evidence
media shows
of g ivea
that
the
reaction proceeds yia a chemically reactive intermediate that is formed in concert with the decay of the loweat electronical.Ly excited doublet state. 30 An examination of the C.F photocherniatry
-
of [ ~ Y ~ - C Y ( N H ~ ) ~ ( C( X) X ] H20, ~ ~ NCS-, soiution suggests a c o m o n precuraor (%Z/4B2)
and )'P
in acidic
for all oP their
phuLorusctions implying that doublet deact lvatf on occurm mainly
rFrr
back lntersyetem crossing to the lowest excit-ed quartet
atate. 31
Mechanistic
implications
of
pKeSFJUKe-dependctnt
photochemical and photophya ical parameters of Cr ( I I I ) compl.exes
Photochemistry
68
have been considered.32 In particular, i.t i s suggested that a stxongly associative pathway for (4T2g) [Cr(NH3)613+ aguatjon i s followed-
study of the photoinduced water exchange of the
A
eight. possible amineaguachromIum( I I I ) ions uefng J80J abel l ing a
has allowed aemimpirical Cr(II1)
rationalisation of
current
empirical
and
tho photostereochemistry of
complexes.33 Ligand field irradiation oP [d~-Cr(en),F2]+
acid
in
critical evaluation of
solution
leads
successively
to
cia-[Cr (en)(en-H)F2 (H20)1 2+,
-.-cis- [ Cr (en)2F (H2D) ]
'+
[Cr(er~)(en-H)P(H,o)~]~+ and [Cr(en-H)2F2(Hp3)2J2t- 34 Lifetimes of the doublet excited states of some tr is( polypyr i w l ) complexes of Cr(II1) measured as a function of pH and [ C l - 1 ,
reflect. the
environment in the vicinity oP the met.a.1 centre and suggest. the existence of HZO, HO- or C1- within the intraligand pockets o f miss ion
2T,/2E; 35
properties
1,4,7-triazacyclononane, X
=
Cr (tacn) X 3
of
P, Rr,
CN,
(tam
=
NCS) have also bean
measured. 36 Electrogenerated chemiluminescence has been reported
for [Cr(m)6]3- and [Cr(bpy)3J3+ in pKOtiC
S O l V d S . 3 7
Various
aliphatic and aromatic hydrocarbons have been photooxidiaed using Cr03/AcOH
or Cr2072-/H$30q/H20/Bu4NBr38
and ZnO ha8 been s h m to
be an efficient catalyst for the photoreduction of Cr(V1) even in 8unlight.39 Studies of the kinetics of the photoaquatfon of [Mo(CN)8J4i n alkaline media,40 the 1 Ight-Induced redox reaction8 of [MS4 1"(
M
=.
Mo(VI), W(VI) , V ( V ) , Re(V1 I)) ,41 and of molecular hydrogen
formation on
photoreduction
of
Mo(V1)
in
aquenus-ethanolic
have been published. A kinetic invest tgation of the mechanism of photodissociation of WCl6 and W C l 4 in the ga8 phaae containhg H2 has been
A
study of the effect of
IIII: The Photochemistry of Transition-metal Complexes
69
counter-ions on the photooxidat ion of secondary alcohols Y3[PW12040] ( Y
-
H,
and y~'[W10032] (Y'
TBA)
tetrabutylanmnoniwa) has appeared; 44
UCIing
TBA) (TBA
K,
-
strong precomplexation is
required and the reaction occurs by a rapid two-electron transfer process.45
Hydrogen
eolutions
under
can
be
generated
photocatalysis
by
from
aqueous organic
polytungstatea 46
The
involvement of hydrogen-bonding protone in delocalisation of the paramagnetic
in
electron
a
aingle
crystal
photoreduced
of
decatungstate ha8 been reported47 and the same authors have also discusaed the photodjmerisation of o l d h a via abstraction of an a l l y l hydrogen using decatungstate.48
5. Manaanese and Rh enium Mn (TPP)CIOQ (TPP
-
5,10,15,20-tetta~enyl~orphyr inato) can
be photoconverted to Mn(TPP)Cl with concomitant oxidation of organic substrates, including alkane hydroxylation and alkene expoxidation.49 A n lnftial photoinduced oxygen a t o m
tlcansf el:
to
generate an active metal-oxo intermediate appears to be Involved. Fhotoreduct ion
of
tetrakis(4-methylpyridyl)porphyr inato-
manganese(II1) in the presence of a proton donor occurs by a reversible 1-electron process to give the corresponding I&I( I I) porphyrtn.
Photoirradiation
meso-tetraphenylporphinato)
In
of
Mn( I I I ) (TPP)N3 a
-
range
of
temperatures reveale a competition between oxidation of
the
2-MeTHF
over
(TPC
central manganese atom of the complex to yield Mn(V)(TPP)N, and
.
reduction to give Mn( I I ) (TPP) 51 Photodecompositlon products of aqueous Mn04- are reported to include a long-lived peroxo m(V) complex intermediate. 52 Discussions have appeared of! the photochemistry of some rhenium phosphite complexes such as t r w , m-ReC13py21P(OEt3) 1,
Photochemistry
70
cis,mer-ReC13(PEt3)[P(OEt)g]~, -
ReCI3 C P ( OEt)3 1 3,
and
ReC14[P(OEt)3]2, 53 and of the emission from [Re2Clg12-, which Beems to originate from the
l88*
excited state of the eclipsed
ion. 54 Iron
6.
Light-induced excited spin state trapping (LIESST) has been isothlocyanato)bis(l, 10-phan) iron( 1 I) J and
observed in --[bis(
[hexakis(1-propyl-1H-tetrazole)iron( I I ) 1 Solvent
of
tuning
the
ketrafJ u o r ~ b o r a t e , ~ ~
excited-state
propertjes
of
(BuqN)2[Fe(bpy) (CN)4] has been reported .56 Iaaer photolysis of [ FeL2 J 2+
( H3L
[Fe(H3L2)J3+
=
1,4,7-tr iazacyclononane) at pH 8-10 produces
and
[ Pe(H3L) (H2L)12+
hydrated
a
electron:
at
>
pH
7.0,
and a hydrated electron are formed at the same
rate. 57 The quantum yields of photodissociative axial ligand substitution reactions o f
low-spin FeN4XY
compl.exes,
(N4
=
bis(dimethylg1yoximate) or bis(naphthoquin0ne dioximate); X or Y =
CO,
PBug, P(OBu)3,
PhCHzNC, or methylimidazole) have been
observed to decrease with decreases in the u-acceptor strength of the axial 1 i ~ ~ d . 5Ratios 8 of quantum yields f o r loss of Y
x
yersua
in both ground and excited states were found to be similar The
kinetics
[Pe(CN)s(H20) J2' reported. 59
of
the
photochemical
.
decomposition
of
have been measured and activation parameters
Individual quantum yields of Pe( I I I) ( H C O Z - ) ~( n
1-4)60 and of [F~(III)(OX)~~-H,,,+] (Ox2'
= C2042-
n
=
1-3, m
=
0,1)61 have been determined in aqueous acidic solutions, and
photocatalytic effects of the pentan-2,4-dionates of Pe( I I C ) and Cr ( I I I )
on the decompos it ion of
1,2,3,4-tetrahydro-l-naphthyl
hydroperoxide have been measured,62 I n the presence oP excesa phenanthroline at pH
N
1.5, [Fe(phen)3l3+ can be photoreduced.
llll: The Photochemistry of Transition-metal Complexes
71
The process is wavelength dependent and the reaction is inhibited by some inorganic l i g a n d ~ s . ~ ~
7. Ruthenium Report8 have appeared of a timedependent shift of the emission spectrum of the M&CT excited state of [R~(bpy)3]~+at low temperature64 and of the properties of the lowest excited states
of
containing
8 ingle-crystal
[ Ru( bpy) ] ( PP6)
[O~(bpy)~]~+
redistribution
in
the
A
excited
host
mater ial
atudy
of
Ru(1L)
polypy~idyl
stater, o f
energy
complexes concludes that the excited atate energy is localised on the ligands in the lowest MLCT statea and is funnelled into the energetically favoured ligand after InitiaJ excitation.66 The recent assertion67 ascribing the polar ization anomaly observed in the
photoselection
heterogeneity,
has
of
spectrum now
been
[Ru (bpy)
12+
challenged.68
solvent
to The
MCPL
of
[Ru(bpy)3I2+ in PVA and 4:1 EtOH/MeOH 801fd solutions is reported
to
be
wavelength dependent
preferential distortion
excitation in
the
of
this
ions
with
ground
state
-
I n teract 4 ons 69
s o l vent/coun t.erIon measurements
of
and
is
interpreted
various d u e . to
~1r cuI. ar
electrochemilumineacence
the
degrees
species7'
and
[ (NH3)s R U ( I 1) ( m N )12+, [ (bpy)2Ru( II)Cl(DMABN)
1'
the
polar i sat J on
Prom
observed
of the
photoluminescence
properties
r (w3)
B I 3+, N I
(DMABN
-
II
r
~
~
of
asymaetric
(+)-I Ru( phen)3 J2+ show that the ECL arises from emission Ru( I t )
as
of
and
(dimethylamino)benzonitri~e),
complexes which exhiblt twisted internal charge transfer states,
of d - R u ( b ~ ) ~ ( N ~ ) ~at - H245 ~o have been d l s c ~ a s e d .Excitation ~~
nm and in an alcohol glass at 77 K leads to a st-rong luminescence; in MeCN-H2O photosubetltution occur8 to g i v e
Photochemistry
72
.
[ Ru (bpy) (N3)( CHsCN)3 + 7 2 The same author has also investigated
[ R U ( ~ W ) ~ ( C H ~ C N(PP6)2.73 )~]
Biphotonic
luminescence of
3 2+
[ Ru (bpy)2 ( AA)
effects
in
the
2,2 ' -biquinoline , or
( AA
6,7-d ihydto-5,8 -d imethyId ibenzo [6.1 ] [ 1 , l O ] phenanthro 1ine) associated with polytungstate anions such as [ C O ( H ~ O ) S ~ W ~ ~ O ~ ~ ] and
[Mn(OH)PWl103,]6-
proper t ies of
the new
(L
[ Ru (bpy)2L]2+
=
have been measured ability
on
have
complexes
CT
[Ru(bpy)~(bpz)12+
The
emission
[W u (bpy)Lz ] 2+
[ RuL3 ] 2t,
and
pyr id inopyrazoles and pyr idinopyrazolines) and the effect
properties
luminescence
reported .74
been
of
the
transfer
of
the
complex
i n ~ e s t i g a t e d ; ~the ~
of
spectra
ligand n-acceptor
[Ru(bpz) ] 2+
and
have also been measured .76 The photophysical
properties of Ru( biq)2 (CN)2, Ru( DMCH) ( C N )2 and Ru( i-biq) (CN)2 (biq
2,2'-biquinoline, DMCH
=
6,7-dihydro-5,8-dimethyldibenzo
[ 3,2-b.2 ' , 3 ' -/] [ 1,lO]phenanthroline,
i-biq
-
2,2 ' -bi-
=
isoquinoline) have been studied with particular reference to acidity
and
temperature
tuning observed
of in
the the
luminescence 77
Solvatochromism has
been
excited
state of
cis-[Ru(phen)2(CN)2]
and attributed to electron donor-acceptor
interactions involving the cyanide ligands.78 The visible spectra of C R ~ ( ~ P Y ) ~ ( P P ~ )and ~ I + C ( b p y ) ~ R u ( p p ~ ) R u ( b p y ) ~ I 4(ppz + planar
ligand,
localised on the different ligands, and the assigned to a ppz(r*) calculated
to
be
+
lr*
the
are
4',7'-phenanthrolino-5',6':5,6-pyrazihe)
composed of MLCT transitions which terminate in the
=
orbitals
luminescence is
Ru(II)t2 t ~ a n s i t i o n .These ~~ states are
weak
reductants
but
powerful
oxidants.
Picosecond absorption spectroscopy has been used to measure the spectra of
the primary MLCT e x c l t e d
pentaamineruthenium(I I ]
complexes and
states of
a series of
they are
Pound
to be
73
IIII: The Photochemistry of Transition-metal Complexes consistent with those expected from a model of these states as
Ru( I [I)L--
Excited state lifetimes are interpreted in
terms of the lowest excited state tuning model.
The effect8 of
the a-donating and n-accepting abilities of the axial ligands on the photophysical behaviour of Ru(I1) metalloporphyrinB have been In particular, two classes of comp.1 exes, RuP( cfQ)I. and
examined. RuPL2
(P =
tetraphenylporphyrin
or
octaethylporphyrin;
J.
=
piperidine, pyridine, W O , EtOH) have been investigated and the results compared with those for complexes in which t h e porphyrin macrocycle P is TPP or O E P . ~ ~ Measurements of quenching rate conatants of excited RuJ.s2+
(L = 4,4'-dialkyl-2,2'-bipyridine)
by aromatic amines and of the
activation parameters suggeat that in highly ewergic regions the process
is
adiabatic.82
liganda
cause
a
However, bulky
decrease
in
substituents on
transmission
coePficient
the with
increasing free energy of activation. The kinetics and mechanism of the [ Ru( bpy) 33 2+ sen8it ized chain react ion between formate and peroxydfaulphate have been reported,83
and comparison of t-he
rates of both reductive and oxidative quenching of [ R ~ ( b p y ) ~ ] ~ +
and cia-[Ru(phen)2(CN)2]
by aromatic amines and nltroaromatfcs
has shown that electrostatic interaction within product ion pairs determined the quenching mechanism, and hence the temperature dependence of the quenching.84 The
formation of
radicals by the photochemical ox idat ion of
semiqu inone
hydroquinones or
reduction of quinones using [Ru(bpy)3]2+ as sensitizer ha8 been examined in the range pH ~
8 Pair.
agreement ~ ~ was achieved
between the observed rate constants and those calculated using
Marcus theory. pyrldinium
--a I somerisatfon of N-methyl-4-pstyryl-
eensitized
by
[Ru(bpy)3I2+
proceeds
by
a
Photochemistry
74
one-electron transfer reaction, but it is reported that in the presence of colloidal s ilica an efficient electron-relay chai.n reaction on the colloidal surface supervenes .86 Photocatalyaia o f the Pachorr reaction by [ R ~ ( b p y J2+ ) ~ in t.he fluorenone, fluorene and dibenzofuran series has been reported and
is thought t.o
involve an electron tranafer mechanism.87 Measurements of the luminescence decaya of [Ru (bpy)3 3 2+ and [Ru(bpy)3 ] 2+ absorbed on metal oxide powders, 9 , S i 0 2 , SrTiOg, Ti02, have enabled t.he electron transfer rates from the excited Ru(1I) complexes to the semiconductors to be evaluated.88 The
dif€usion-controlled
constant f o r
rate
the
dynamic
~ +[Ru(bpy)z(4,4'-Cl2bpy)I2+ quenching of excited [ R ~ ( b p y ) ~ ]or the
heteropolytungstate
[ Co(H20)SiWll039 J6- shows
be Pitted by
phenanthrollne) by Ag'
=
in this
may
be
[ RhC1( dpm) J 3- (dpm
and
an ionic strength dependence which can 1,umineacence
bpy or 4,7-dirnethyl-l,10-
is no longer thought to occur by oxidative
electronlc transfer , but
exciplex
[Mn(OH)PWl,039]6-
the nebye-Smoluchowki equation.89
quenching of [RuL3J2+ (1,
exc iplexes.
anions
by
rather by
process
involved.
-
format ion of
luminescent
a termolecular metal
compI.ex
The
complex
Wilkineon
type
3-Ph2PCgH4S03-) ha8 been used successfully
as a homogeneous catalyst in conjunct-ion with [ R ~ ( b p y ) ~ ] ~and + ascorbic acid for the reduction of
Ascorbic acid has
also been photooxidieed to dehydroaecorbic acid with hydrogen evolution
using
Pt
loaded Ti02
in
an
aqueous solution of
[Ru(bpy)3 J2+.92 Carbon monoxide and hydrogen can be produced by the simultaneous photochemical reduction of C02 and H 2 0 by the visible
light
irradiation
of
organic
[Ru(bpy)3J2+ and a variety of Co(1i)
solutions
containing
species aa homogeneous
I I I l : The Photochemistry of Transition-metal Complexes
75
catalysts. 93
* [Ru (bpy)31 2+
Rate constants for the oxidative quenching of
by W2+ have been studied as a function of the concentration of
added electrolyte.94 The results have been used to evaluate critically the various literature expressiona for the dependence
of diffusional parameters on ionic strength. Rate constants for the quenching of [ R u ( b ~ ) ~ ]by ~ +various viologens with charges ranging from 0 to +4 have also been measured and variations interpreted in t e r m of Coulombic fnteractions of the reagents,95 and the effect of lipid and viologen structure on crosm membrane electron transfer [Ru(bpy),J2+
as
in donor
a
vesicular photosystem and
viologen
as
consisting of
oxidant
has
been
investigated. 96 Photoactivation of the three-component system [Ru(bpy)g J2+/KV2+/quadricyclene is
reported
to
initiate
a
catalytic cycle for the valence isomerisation of quadricyclene to norbornadiene.97 The primary photochemical step is oxidative quenching of the emissive ldLCT state of [ R ~ ( b p y ) ~ ] by ~+ W2+, followed by oxidation of quadricyclene by [Ru(bpy)3I3+ to give
the utructurally labile Q?.
A
photoinduced tranaacetalization
between 2-phenowytetrahydropyzans and octan-1-01, and involving the
Ru(bpy) 3 J 2+-methylviologen consens it izing system has been
described.98 It appears to proceed by initial electron transfer
from the excited ruthenium complex to the viologen, followed by electron
abstraction
from
the
acetal
by
[Ru(bpy)3I3+
Photohydrogenation of phenylacetylene and nethylphenylacetylene has been observed in a H2O-cyclohexane system using [ R u ( b ~ y ) ~ J ~ + as
photosensitizer, N,N'-dialkyl-4,4'-bipyridinium
as
charge
relay, FZDTA a8 sacrificial electron donor, and a Pt or Pd colloid stabilised in the organic phase as a hydrogenation
Photochemistry
76
Photoreduction o f CO;! t o HCO;!H
has been st.udi.t?d i.n t h e syst-em
TROW I Rii (bpy) 3 1'+/bi.s (viol.oqsn)/formake
dehydroqenase,
as
well. as i . t s photoreduct ion t o methane a.nd hi.gher hyrlroCAtrhonR us inq
co 1.1.0i d s - '-'I.
1: uthen ium
r Ru ( bpy ')3. ( CO)
The comp l.ex
3
'+ i.s
also an rtffic.ient- catalyst for khe photoradnct.ion of
The
e f f i c i e n c y of apat.ia.l charge separat.ion jn khe vets.icn.lar s y s k e r n
r Rl1( bpy)
12+
( internal.
(menJnrane)-oxidant.
(external
Sirnu1t-aneoua genaraki on of achieved
been
s o l l i t ion) ao.lut.inn)
heen
has
measursd
hydrogen and oxygen from water haft v.iaih.le
under
/octadecyl.v i.ol.oqen
1 ight
cho.1.ine
dipa.lmi toy.1 -D,T.-a-phoaphatidy.l
irradiat-ion
of
uo i nq
veo ic.1cta
rRn(bpy)3j2+ iinrler various condi.t*i.ons,1.04and t.he same qroup has
a
invest iqated [ R u (hpy) 3. ( 4 , 4
system
' -d ihept.adecy.l-7.,2' -hi pyr i d i n e ) 1
bil.ayer l i p i d mmbrane, K$3208 solution,
c0ntai.ni.nq
and
a
Co(II[)
surface.
The
trimetallic
compJex
12' ,3'-h]quinoxa.l h e ,
a
the
membrane
the new non7.i.nsar
1.i.feti.me o f
hexacheJat.ing
i nto
i.n t h e ext-arnal.
on
fixed
dipyrazino[2,3-f 1-
[[R~(bpy)~]~I.1~ (I.+ = a
htr .i 1 t.
as el.ect,ron donor
catalyst
luminescence
'+
.l .iganr11.06 and
of
the
photophysical pr0pert.j es of the din11c.lear and tetranuclear Ru( I I )
clusters
I (drnb);!Ru*JJt~(dmb)~]~+and
4 , 4 ' -dimethyl-:!,
[r ( d ~ n b ) ~ R ~ ~ r . J ~(dmb R u ) ~=+
2 ' -bipyr i d i n e ; L = I., Q - b i s / 2- ( 4 'methyl-
2,2 '-bipyridyl-4-y3 ) e t h y l I h e n ~ e n e ' lhave - ~ ~ appeared.
Measurement8
of
t-he
fluorescence
and
s p e c t r a of [ R ~ ( b p y J)3+ ~ i n aqueous s&i.um that
the
m i c e l l e . Io8
ruthenium
complex
Chemiluminescent
is
bonded
reactions
chemf J uminemence
dodecyl.sul.phate show
to of
the
surfactant
[Ru(bpy)3]+
and
[Ru(hpy)g13+ with solvent* a c e t - o n l t r i l e and also of [Mo6CIl41- and
under t-he same c o n d i t i o n s have heen report-ed.
'''
77
I I I l : The Photochemistry of Transition-metal Complexes 8.
Osmium
The metal-ox0
photoxidanta
trans-[Os(tmc) (0)212+
(bc
1r4,8,11-tetranrethyl-1,4,8,il-tetraazacyclotetradecane)
=
and
.
trans- ( 0 s ( C N ) (0) 2 J 2- have been reported 'lo
9 - Cobalt Photochemical
react ion
of
Co ( I I ) ( d q B P 2 ) 2
in
methanol
containing an excess of PBu3 gives H+[Co(I)(amsBpz)2PBu3]-, probably
involves
MeOH
as
reducing
agent..
'"
and
Cobalt ( I I )
tetraaulphophthalocyanine chemically bound to the surface of Ti02 is an efficient electron relay for the photocatalytic formation and depletion of hydrogen peroxide in aqueous suspensions.'I3. Free radicals do not appear to be involved. The same author8 have also propoaed a kinetic model for the oxidation of S(1V) to S ( V 1 ) using
In
this
a
mixture
compriaing
proflavine
monochlorohydrate a8 aeneitizer, [Co( 1 1 ) (bpy)3]Cl.z as t-relay, (HOCH2CH2)3N as donor and KqPtClg as CataJyst, the photoinduced electron transfer from sensitizer to the Co(l1) complex is more efficient in SDS anionic micellar solution than In water.l14 Oxidation of (Co(edta)'21
by S2Oa2-
is greatly accelerated by
irradiation in aqueous solutions containing [Ru(bpy)3 ]2+.115 A chain reaction is involved which is initiated by quenching of photoexcited [Ru(bpy)3 12+ by S2Oa2-.
An
external mechanical load
applied to crystals of Co(NH3)5NO2C12 is reported to decelerate the rate of nitro-nitr ito photoisomer isation. The energy level transitions and the bond energiea in the ground and excited state of CoX5Ln ( X C l ' ,
NOZ-,
=
NH3, C";L
-
H20, NH3,
CN-) have been calculated by the INDO-CI mathod.'17
The results may have
implications €or
the photosubst itut ion
chemistry of Co(I11) complexes. A model has been advanced in an
Photochemistry
78
I
2+
1
2*
n
$)N '
2CIOi
i < )
2 c 1Oi
Ph
Ph
(4)a R = H ; R ' = N ~ b R =CMt3 ; R' = NEtz c
R=R'=H;
R =R'=OMc
IIII: The Photochemistry of Transition-metal Complexes
79
a t t e m p t t o u n i f y a p p a r e n t l y d i f f e r e n t patterns o f photmchemi.str:y
of some d6 system. of
pattern
tt iplettl,
T h i s is based upon a wavel.engt~h-i.ndspendent
ar k i n g
reacti.on8 and
from vi.htat.i.onal.1.y eqiii.l.i.hr:akad
a wavelength-dependent
reactimn
s i n g l e t st-ate. '.I8 . P h o t o s u b a t i t t i t ion react,i.ons o f anl
- O , N ) b i a ( et-hylenediamine) cobal.t( I I t )
wi.t,h
ar i.8 i.ng i.n t h e (bi.dent-at.o-O,O at*hyl.enttiii.ami.ne
have been atndi.ed i n a weakly al.kal.ine aqueons sol.uti.on i n the [ Ru (bpy) J
presence of
'+
118 i.rq
c ixcnl.ar l y polar: i.sed l.i.ght,.
E x c i t a t i o n o f t-he a x i a l . l.igand CT t r a n s f e r : [C0TXz]Is1.04 and CoIJ,Cl.Y](Cl.Oq),
(I,
R b m r p t i o n hand
in
Y = NCO-,
NCS-,
t h o presence of oxygen,
of
5,5,7,1.2, 1.2,'I.l-hexsmet.hyl.-
3 , 4 , 8 , J ~ - t e t r a a z a c y ~ ~ o t ~ ~ ~ r a d e c a - 4 , 1 1 - dX~ e = n e :Cl,
N O - , NCS-;
'.'"
Rr,
N3-,
(n-2)) i n methanol. and
N3 ( n = l . ) , H20
.leads to f o r m a t i o n of C ! O ( J ~ ) . ' ~ ~ " The
same aut.hors have also jnvestigated t.he photochami ca.1 propart-ies of
the
Co(1JJ)
related
hcsxamet.hyI-.l.4,8,
wit.h
complex
maao-S,'7,7,13.,1J,.14-
~ J - t e t . r a a ~ a c y c ~ o t ~ t . r a d s c a n ~ :Reports l2~
have
appeared of tho phot~odecarhoxy.lat.ion of ( I ) and f . C o ( e n ) T , ) C . l ~ ( H T .=
y-aminobatyr.ic acid)
to g i v e
(2)
and
[~~(csn)~(~XCH~CH 1 (C.104)2 3 . N H ~ ) rePlpect~vely,1.22,1.23 and cryst21 structure
of
of t h e
IC o ( bm)2( CH2NH) 1 ( Cl.04) 2 , the phot.ol.ye i.e
of product of [Co(bpy)2gl-y1( C 1 . 0 4 ) 3 . - H ~ 0 , ' . L 4 @-a phot.oi.somc3t:i.aat.i.on
cohaloximes .in the 80.1 Jd atat.e,'25 [Ru(CN),I4-
electron
to a I.iganrl t i . e l d exci.t-ed skate
g l y c i n e ) have been r e p o r t e d ;
is
and
r (CN) 5Ru ( I J ) (p-C!N)Ru ( J I J ) (CN) 1.0.
mod i.um and
transfer
by
o f C l ~ ( g l . y )( ~ ~ 9 l . y=
the product. i.n this l.att.er c a n e
16-
-
tr i.di.nm
Ext-erna.1 magneki c f iel d ef f ects on t h e e.wc.it.ed s t a t e pr0pert.i ec1
of R h ( I ) and J r ( J ) complexes have hean d i a c t ~ s s e c l : ~ ~ - ~ A
3cwr-temperat.urs phosphorescence
and WMR study o f
t.he
80
Photochemistry [ Rh(bpy)3 J
excited state of properties
have
been
Cm(trpy) ( ~ P Y(PY) ) i3+,
has appeared.128 Photophys ical
reported
and
2,2':6',2"-terpyridine)
'
for
[Rh(tr~y)~]~+,
C R ~ ( ~ ~(P~YP)Y ) c ~ I ~(trpy +
=
and photolysis of [Fth(trpy)(bpy)C1I2+ in
aqueous solution induces photolabilisation of the chlorine as seen with other Rh( I I I ) chloro m i n e complexes.I2'
A
discussion
of the photoinduced cis-trans isomerisation of cis-[Rh(bp~)~XZ)"+ (X,Z
=
C1, OH, n-1; X
respectively; X
=
= Z =
H20, Z
=
H20, n-3; X = C1, 2
-
OH, H20, n=l,2,
OH, n-2) showa that some sterically
congested isomers not available by other routes, can be prepared photochemically.130
Long
wavelength
excitation
solutions of the ion pairs [Rh(bpy)3]3t[M(CrJ),]4-
of
aqueous
(M = Pe(JI),
Ru(II), Os(I1)) promotes charge transfer from the metal of the cyan0 complex to the bipyridine ligand of the rhodium complex and leads
subsequently
to
photoaquation
and
formation
of
[ Rh( bpy)2 (H2O)2 J 3 + . 131 Photogeneration of hydrogen from water has
been reported using a platinum catalyst fixed on a bilayer lipid membrane in the system [Rh(bipy)3J3'-[Ru(bipy)3J2+-EDTA,
and rate
constants for the various steps determined. Differences have been discussed of the effect of deuteration of m i n e
and aqua llgands in
a-and
trans-[Rh(NH,)4(H2O)*I3+
and in cia- and trdnS-[Rh(NH3)4(H20)Cl]2+,
on the cis to trans,
and trans to cfs photoisomerisation processes - 133 Ligand P ield
(X excitation of cia- and tran~-[Rh(en)~X~]+
=
C1, Br) in acidic
aqueous solution gives [Rh(en)2(H20)XI2+ and excited-state halide dissociation and nonradiative deactivation rate constants have been described.134 The same group has also determined the triplet excited
state
NH3
and
C1
dissociative
rate
nonrad iat ive deactivation rate constants for
constants
and
IIIl: The Photochemistry of Transition-metal Complexes Direct I R evidence has appeared for the
[Rh(en)z(NH3)C1]2t photoejection
of
81
vinyl
chloride
from
Rh(acac)L2
(L
=
CH2:CHC1) .136 Irradiation of [ (trlphos)Rh(S2CO)IBPh4 (triphos
-
MeC( CH2PPh2)3 ) in CH2C12 promotes chelotropic elimination of both CO and COS to give [ (tripho~)Rh(~-S)~Rh(triphoa) 1 (BPh4)2.CH2C12
This ~~ and [(triph~s)Rh(p-S~)~Rh(triphos)J (BPh4)2, ( C H ~ C 1 2 ) 1 . 7 5 . ~ process, which can be extended to include diselenocarbonates, provides a new method of diselenium Uganda
introducing sulphido, disulphur and
-
into complex frameworks
Laser photolys is
studies of C1Rh( I I1)TPP (TPP = tetraphenylporphyrin) in ethanol have revealed both electron-transfer and axial ligand ejection processes,138 and a highly regtospecif ic 1,4-photoreduction of NAD(P)+ models using a R h ( I I 1 )
parphyrin axially substituted by
acetyl has appeared.13'
11. Nicke l The 1: 1 adduct of bis( 1,2-diphenyl-l,2-ethylenedithio1ato)nickel(0) (3) and quadr icyclane undergoes photodissociation to (3)
and
norbornadiene.140
[NiS4C4RR' It(
is
formed
on
photolysis of the dithiine complex (4) in poly(N-vinylcarbazole) and poly(acrylonitrile-styrene) matrices containing CHI3
The
process is believed to involve charge tranafer complex formation between the matrix and photooxidation of
(4).
CHI3 which then participates in the Resonance Raman spectra obtained from istence of
transient nickel porphyrin species demonstrate the
c
photoinduced
proto-
ligation
changes
in
nickel
3
and
~~ octaethylporphyrin species on a subnanosecond t i ~ n e s c a l e land carbon dioxide has been photoreduced to carbon monoxide in water
using
1,4,8,11-tetraazacyclotetradecanenickel(II)
catalyst .I43
chloride
as
Photochemistry
82
12. An
&-bis[
Plat inom
investigation of the photochemistry of orthometalated 2-(2-thienyl)pyridfneJplatinum(I I )
has
concluded
its reactions in CH2C12 involve Pt(thyp~)~Cland
CH2Cl
that
radicals
generated via a CTTS excited state, which itself is populated from the intraligand and MLCT states.144 The photophyaics and photochemistry
of
[ Pt2 (P205H2)4 ] 4-
Photoreduction
of
nitric
acid
have to
been
revi w e d . 14’
nitrite
inn
by
the
electronically excited platinum complex [Pt2( P ~ O S H ~ ) ~occurs ]~-
v i a the intermediates [Pt211,1J (P205H2)4]3- and HN03-.146
The
da*po triplet excited state o f this same complex is reported to
abstract a H atom from R3EH (E g ive [ Pt2 ( P2O5H2)4H2 J
Photochemical
-
Sn, Ge, Si; R
alkyl, Ph) to
=
147 ‘L48and PtzH2 as ultimate product. 14’
[Pt2(p-P205H2)4C12 J 4-
of
conversions
[Pt2(fi-P20sH2)4I2I4-
=
with
added
halide
ions
have
and been
describedlSO and the same authors have also shown that alkenes and alkynes will quench the triplet state of this complex by energy
transfer,
mechanisms.15‘ [Pt(CN),J2-
hydrogen
T12Pt( CN)4, containing
prepared. 152 The
abstraction,
and
a non-columnar luminescent form of platinum-thallium
bonds,
luminescent character istice of
dihalotetraamine
and
diradical
dihalod iethylenedlamine
has
been
a series of complexes
of
Pt(1V) have been reported, and constitute suitable models for studying the structure and properties o€ the unstable Pt(I1I) complexes having the same ligand environment.153 [Pt(CN)4X2J2- (X process, with complexes
=
C1, Rr) promotes photoaquation as the sole
formation of
display
Irradiakion of
different
[Pt(CN)4X0Hl2-; kinetics .154
however,
the two
Photosubstitution
processes a€ [PtC16J2- in MeCN involve homolysis of a Pt-C1 bond,
83
I I I l : The Photochemistry of Transition-metal Complexes and solvent effects appear to be determined by the efficiency of the photoinduced electron transfer from Ligand to metal, or medium to metal to give [PtC15]2--155,156 The same workers have also
investigated the mechanism of
[PtBKgJ2-
the photosubstitution of
in CH3CN. 157 Photochemically induced oxidation of
hexane with [ptC16I2- leads to the formation of B u C H - C H ~ P ~ , a compound also formed Prom hex-.2-ene and NaZPtClg in acetone-158 13.
C o m e r and Go1d
Picosecond flash photolysis studies of [Cu(dmp),]'
2,9-dirnethyl-l,lO-phenanthroline)
[ Cu (bcp)2 1'
and
2,9-dimethyl-4,7-diphenyl-l,lO-phenanthroline) excited
state absorption
spectra
respective ligand radical anions
to
(drnp
=
shown
the
those of
the
have
resemble
(bcp
=
Quenching kinetics have been
measured and interpreted in terms of a mectiwiisrn irivolving an intermediate *Cu....Q.
The
same
authors
also
report
that
photobleaching of [Cu(dmp);! ]+ in CHZC12 is a biphotonic procesa in which the second photon is absorbed by a relatively long-lived CTML
excited state. 160 Outer-sphere electron transfer between
CH2C12 and a high-lying excited state of the complex gives The temperature profile of t h e
[Cu(dmp)2J2' and C1- as products.
emission intensity is shown to depend strongly on the nature of the
phenanthroline
ePf iciency of
[Cu(dmp)P2]+
phenanthroline; P MV2'
ligand
-
as
well
(dmp
=
as
the
solvent.161
The
2,9-dimethyl-l,10-
tertiary phosphine) in the photoreduction of
has been improved by substituting PPh3 with PCyPh2 or
P ( E - C ~ H ~ O M ~ )and ~ ' ~advantage ~ has been taken of the special topography of [C~(dap)~]+[dap
=
2,9-bis(p-anieyl)-l,lO-
phenanthroline] in order to use it as an efficient photocatalyst for the reductive coupling of E - O ~ N C ~ H ~ C-163 H~B~
Photochemistry
84
The role played by the ground- and excited-state potential surfaces in the temperature dependence of the electronic spectrum of the planar [CuC14J2- ion has been investigated.164 A
study of the photoredox reactions of some gold pOKphyKins
has shown that chlorogold meso-tetrakis(4-N-methylpyridyl)porphine
tetrachloride
Is
durable
a
catalyst
for
eJectron
transfer processes involving water -1'5 14. Lan thana d -
The luminescence of divalent europium crown complexes in var ious solvents has been studied at various temperatures and the results
correlated
with
structural
differences
of
the
complexes. 166 A
number
of
papers describing
luminescence studies of
lanthanide complexes in the solid state have appeared. include emission from Ln(biq02)(N03)3'nH20 Sm; biqO2
=
(Ln -- I d , Ce, Pr, Nd,
2,2'-biquinoline N,N'-dioxide) which arises from the
transition *biqO2 + biq02,167 from Ce(II1) in LnOX (Ln
Y;
X
=
These
C1,
BK,
I),168
or
and
from the
Eu { p-XC6H4COCHCOBu t,
europi um ( I I I )
pipH[EU{E-XC6H,COCHCoBUt)ql
piper idine)
The
(X *
=
La, Cd or
p-diketonates of
and
CH3, CH30, H, F, C1, N02; pip
fluorescent
properties
of
=
PVC-Ce( [ I I),
P M - C e ( I I I ) and polystyrene-Ce( I I I) f ilma have been reported as well as those of analogous films containing 1 0 - c r 0 w n - 6 . ~ ~The ~ examination of
the excited state properties of
the lamellar
solids Ln0.33U02P04 (Ln = La, Ce, Pr, Nd, Tb, D y , and Yb) derived from
uranyl
phosphate
and
lanthanide
ions
shows
photoluminescence decay curves are exponential.
that
the
Lifetimes,
radiative quantum yields, unlmolecular radiative and nonradiative rate
constants
are
all
reported.
Luminescence
spectra
of
IIII: The Photochemistry of Transition-metal Complexes Tb(RLSA)3 and
in
(TMSA =
various
85
bi8(tKimethylsilyl)aIIIido) in the solid state
solvents,
have
been
used
to
analyse
the
coordinative behaviour OF the s01vent.s'~~ and the hydration of [Tb(PPP) 2 J
(PPP = bistr iphosphate) has been determined from
measurements of the luminescence lifetimes in H20 and D ~ 0 . l ~ ~ Studiea of
the luminescent properties of single crystals of
EU(NO~)~-~ down H ~ Oto liquid He temperatures suggest that water molecules are responsible of the emission.174
between Eu ( No3)
€OK
a considerable amount of quenching
The metal
ion sites of the 3:2
and the A- isomer
excitation and emission spectra.17' a88 ignment
dicyclohexyl-18-cro-6
of
(DC18C6), [Eu(N03)2(DC18C6)]2[Eu(N03)5]
complex
have been probed using
This ha8 made possible the
of different conformations of the complex cation.
Fluorescence measurements of Ln( I [I)
( ~ n EU, Gd, Tb, ~ y )
ions complexed with aminopolyacet ic ac ids have been obtained. These have enabled a simple theoretical model to be proposed from which certain generalisations concerning the fluorescence of the lanthanides have
der ived. 176 ,
been
luminescence of Eu(tI1)
and T b ( I I 1 )
Sene it izat ion
of
the
ions by orotic acids is
reported to involve excitation energy transfer Prom the acid. 178 The luminescence of Eu(N03)3*6H2O in n-propanol solution show8 a double exponential decay at temperatures below 240 K; the long wavelength
component
corresponds
to
emission
from
Eu( I I I)
containing one additional NOg- ligand in its first coordination sphere
compared
to
the
short
wavelength
component.17'
The
seneitized photoluminescence of Eu(II1) in acidified aolutions of sodium molybdate and anvnonium paramolybdate has been ascribed to energy
transfer
to
heteropolycomplex.180
Eu( I I I )
inside
Crystalline
the
europium-molybdate
europium
polymolybdate
Photochemistry
86
from
obtained
thia
has
~iol.at-i.on
( N H ~ ) ~ ~ R U ~ M O ~ ~ )and ~ Q shows O - ~ H a~ ~br iqht
Fluorescence
character i s t i c s
and
energy
the
cornpa i t. i.on
red
l.iimi.ne8cence.
t-canafer
wi.t-hin
a
Ce ( J J I ) -2,2 ’-bi pyr id i ne compl e x have heen descr i bed Tmninescence s t u d i e s of 7.,7.*-h.ipyridine-haaed crypt.at.es of Eli( J I J )
and Th( I I 3 ) show t.hat compared w.i th t.he corresponding
aqua comp.1a x , t h e w a v e . 1 angkh of khe l timinascence i~l una.ffect.ed by
tho cryptsate or watmr
.l.igands, b a t
the
that
. l . i f e t . i m e of
t.he
exc.i t . 4 skate and the .laminascence q n a n t u m yield a.re strong.ly aItered.l*’
The same workers have measured the ra.t.ea o f el.sct.ron
and energy t r a n s f e r r aact.i.ona bat-ween some cyani.de comp1.exe.s and
*
E u C 2.2.1 J
’+,
*Ruaq3+,
* 1TbC 2.3.- 1.3 3 t
Rnerqy
*Thaq3+.
and
t r a n s f e r quenching occurs much f a s t e r for t h e free i.ons khan for the cryptates,
while t h e r a t e const-ants for sl.ect.r-on t-canafar
qiienching are practi.cal.ly t h e
8-8
for c r y p t a t e and aqiio iona.
Some a,a’ -bipyridine and l., 1.0-phenanthrol.ina-cont.aining cryptate8 and Tb( I J I ) are repo.rtx4 t.o display energy transfer
of Eli( J J J )
luminescence of examinat.ion
of
viaihle t.he
.1 ight. iipon
IN
photophysical
. i r r a d . i a t . . i ~ n .and ’ ~ ~ an of
prope.rt..iea
the
hexaaz(UMcrcmyc.1ic complex [ R U ( C ~ ~ H (CH3COO) ~ ~ N ~ )1 (CH3croO)C.l ‘2H20
shown t.hat. , l u m i n e s c e n c e .in ef.Picient .for f-f
excitation and th at
energy transf t w from l .igand to mata.1 atom i a nsg.1i g.i bl e
Ce(1V)
and
Tb(JV)
p,recipit.at.ea
are
formed
-
’*’
in
th e
photaassist.ed oxidation of tho systems C a ( C . l 0 4 ) 3 - N a 4 P 2 0 7 -
(NH41~ S Z O ~ - H C3 04 !
and
Th(C.104) 3-NaqP3.07- (NH4) 2S208-HC.104
resprtcti.vs~y.18~’.’87 These procefjaes may fi.nd some a.ppl.i.cati.on i n t h e separation o f the c a r e earth el.ement.8. 1.5. A
Uranium
system c o n s i a t i n g of
aqueous sol.utiontl o f
riranirim and
I I I l : The Photochemistry of Transition-metal Complexes
87
copper salts with an organic electron donor such as propan-2-01
or cyclohexanol has been shown to be capable of the photolytic product ion of hydrogen. 188 Luminescence spectra and lifetimes have been descr ibed for U02(N03)2-XH20 (x
=
6,3,2)lg8 and earlier work of Marcantonatos
reporting emission from excited states of U022+ above that giving the
usual
green
investigation of
emission,
has
been
challenged.lgl An
the photophysical behaviour
of
some mixed
transition metal-uranyl complexes with polyketonate ligands has shown the uranyl chromophore to be vibronically isolated. lg2 Tertiary aromatic phosphines and arsines will photoreduce U022+ in a process whose primary step is electron trans€erlq3 and the the U(V)-U(V1)
kinetics of
self-exchange reactjons have been
investigated.lg4 U(IV) is formed on irradiation of a mixture of
and N2H4 at ~
UOz2+, HNO3,
o and ~ the mechanism c ~ of the ~ rapid ~
photostimulated exchange of 0 between U022+ and H20 has been
- ~ aH ~poly(viny1 o Irradiation of H ~ u o ~ ( I o ~ ) ~ in
discusaed.l96
alcohol) matrix leads to interactions of the excftd 2)022tand H+ ions
with
of
formation
l2
and
the
13-,lg7
steady-state
luminescence spectrum of solutions of U022+ containing F- has and U02F+,
been separated into contribution8 from [U022+],q
and IR multiphoton decomposition of solid etate U02(HCOO)2-H20 gives u308 v i a U02(0H) (HCOO) 'H2O as intermediate.199 The colour of the emission of U ( V 1 ) luminescence in oxides is
reported
to
shift
gradually
from
green
to
red
if
the
coordination of the uranium changes from 6 to 4,200 a Liebig ti tration involving the interlamellar ?ig+ ions of A ~ U O ~ P O Q - ~ H ~ O and
based
on
HU02PI4-4H20
photoluminescence has and
HUOflsO4-4H20
been form
descr ibed,201 solid
and
solutions
Photochemistry
88
representing
HU02( PO4) 1 - x ( A ~ 0 4 ) x ,
Emily
a
of
luminescent solids that can serve a8 hosts for chemistry.202
The
spectral distribution of
lamellar
intercalation
photodissociation
yield has been measured following [IF6 excitation in the B band and the dissociation found not to be uniform.203
16.
Actinides
2-Thenoyltr ifluoroacetone Pu(II1)
on
will
exposure to normal
Pu ( IV)
photoreduce
light204 and
jn nitric
to acid
solution, irradiation of compounds of Pu(III), Fe(III), and N2H5+ leads to their complete and rapid oxidation.2Q5 17. Miscellaneous An
ESR and ENDOR study of the photoinduced electron transfer
ins from magnesium and zinc tetrakis (4-sulphonatopheny1)porphy~ to K3Fe(CN)6 molecular
in
a
H20-Me2S0
glass
ha8
electron
transport
chain
composed
tetrakis(N-methyl-4-pyridyl)porphyr in
appeared.206
and
of
EDTA,
new
A
z Fnc
methylviologen
spatially organised by 1F-diameter zeolite 1, particles207 has been descr ibed and the mixed semiconductor catalyst (ZnS-CdS) supported on alumina has been used to photogenerate H from H20-208 Hg ( ) I I ) ions have been photocatalyt ically eliminated from aqueous solutions with ZnO a8 catalyst209 and the same authors have also photoreduced Hg( I I ) ions using aqueous suapensions of
Ti02 and WO3 .210
1.
J. F. Endicott, T. Ramasami, R. Tamilarasan, R. B. Lessard, C. K. Ryu, and G. R. Brubaker, Coord, Chern. R e v . , 1987, 1.
2,
R. A. Krause, Struct. Bonding (Berlin).
1987, 67, 1.
77,
Illl: The Photochemistry of Transition-metal Complexes 3.
H.
89
Hennig, R. Billing, and D- Rehorek, J. Inf.
1987,
Rec.
Meter.,
15, 423.
m, 139.
4.
M. J. M i r b a c h , ACS Symp. S e r . , 1987,
5,
R. V a n E l d i c k , NATO AS1
6.
P. N a t a r a j a n and P. Ramamurthy, Proc. lndlan Narl. Scl. Acad., Part A. 1986,
7.
N.
197, 357.
52, 865.
Shinohara,
Keiretsu. 1987,
8.
S e r . , Ser. C , 1987,
YOkOh8m8-shkltSU
Diageku
Ronso,
Shloen
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IIII: The Photochemistry of Transition-metal Complexes
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LIZ,
2
The Photochemistry of Transition-metal Oreanometallic Compounds
-
BY A. COX
Reviews have appeared of the photophysics of molybdenum complexes,
primary and secondary processes in organometallic
f laah phOtOly8i8 of Pe(C0)S and Cr(CO)gr3 dinuclear che~nistty,~ manganese
carbonyl
complexes
isolated
low
in
diene
complexes,6 p coordinatively
i c idium,
compounds,
redox
-
compounds lo Synthetic
photochemistry of
temperature
complexes,
unaaturated
and
the
species
metal
cluster
phatoproduction containjng
chemiluminescence and
matrices,
metal
organic
of
rhodium
of or
organometaL1i.c
photochemistry
in
industry has also been reviewed.l1 2. Ti t a n i urn Carbon dioxide has been photochemically inserted into the Ti-Me bond of (q5-C5H5)TiMeZ under photocleavage conditions to give (q5-CSH5)2Ti(OAc)Me,l”
and use has been made of the new
titanium complex [(C5Me4H)2TiMe~] €or the initiation of some ole€ in isomer isations. l3 Irradiation of the tltanacyclobutane (1)
brings
about
a
clean reductive elimination process to form
cyclopropanes and t itanocene.
Stereochemical studies suggest
that the pr imary photochemical step involves metal-carbon bond
homolya is
to
produce
a
metal-centred
1,4-biradical
intermediate.14 The primary process in the photolysis of the titanocene dichloride conrplexes (RCsH4)2TiC12 ( R pentyl)
iS
-
Me,
Et, Pr,
h o ~ l y a i sto give RC6H4’ and (Rc6Hg)TiCl~;~’ atlalC#gOUS
103
104
Photochemistry
4i
I ; R' = Me$ R = R'= Me
(1) R = H
Me\
Me2CH
(21
lIl2: The Photochemistry of Transition-metal Organometallic Compounds
105
reactions occur with zirconocene and haf nocene. l6 3.
Niobium
Nb clusters will photoreact with benzene, and at low laser intensi t b 8
the
probability
dehydrogenation
Of
NbXC6H6
Of
clusters has maxima for x = 5, 6, and ll.17 4. Chromium, Molybdenum. and Tunasten An ESR study of the radicals produced in the photoinduced
reactions of M(CO)6 (M of
-
CK, Mo, W) in CCl4 has shown the presence
together
eCl3
with
dlalkyl-
diphenyl-
and
acrylphenyl-nitroxides. l8 The average number of CO molecules produced
from
M(CO)6
using
infrared
SP~-sensltlzation is reported to be Cr(C0)6,
MO(Co)gr
and
3.0,
radiation
and
and
€or
3.0,
w(c0)6
1.5
PhotolySis
Of
Cr(C0)6 in ethene-saturated pentane solutions leads to sequential formation of (q2-ethene)Cr(CO)s at -2OOC and trang(q2-ethene)2Cr (CO)4
at -5OOC. 2o Analogous processes occur with
Mo(CO)6 and w(c0)6.
Irradiation of a solution of [b¶(CO)6] (M
-
CK, Mo, or W) in the presence of a pyridtne 2-carbaldehyde imine ligand 2-CsHqNCHNR
(L; R
-
transient complex [M(C0)5L]
Thermal ring
Ph, tert-Bu, n-Bu,
Pr) gives the
in which L is monocoordinated.21
closure to give
[M(CO)qL]
has been
monitored
kinetically. The same group has also reported the photoproperties and redox behaviour of a series of homonuclear and heteronuclear ligand-bridged (OC)~M-L-M'(CO)S complexea, (M and M' = Cr, Mo, or W;
L
=
pyrazine,
4,4'-bipyridlne,
I,2-bis(4-pyridyl)ethylene,
and
w-
1,2-bia(4-pyridyl)ethanne) .22
TKeahent of (2) with L i A l H 4 and UV light la reported to give (3),23
[ 4+6J -photocycloaddition
RCH:CR'CR':CHR2
(R, R2 = H, Me; R'
of conjugated dienes such as
-
H) to hexacatbonyl-
Photochemistry
106
6-1,1' -bi(cyclohepta-2,4,6-tr ien-1-yl)dichromium(O)
p-q6*
descr ibed ,24
been
photocycloadd it ion
and
1,1,2,2-tetrafluoro-t,2-disllacyclobutene R'
H,
=
Me; R
transition
=
metal
H, R'
=
pathway
migrations.25
M(CO)5L
and
involving and
between
and CH2:CRCR':CHz
(R,-
Me) can be mediated by Group VIR
carbonyls
I,l-addition
react ions
has
a
proceed
hydride
both
M(C0),L2
(M
Cr,
=
an
unusual
and
fluoride
CIO,
W;
L
=
l-phenyl-3,4-dimethylphosphole, 1-phenyl-3-methylphosphole and
1-phenylphosphole) have been synthesised photochemically from
M( CO)
and the
appropr iate phoaphole, and the photochemical
react.ions of these compounds wit.h alkenea have appeared.26 Ab i n i t i o
SCP
calculation8 have been used to generate state
correlation diagrams f o r
the photosubstitution reactions of
M(C0)sL (M = Mo, L = NH3, PMe3, CHOMe, C p 4 ; M
=
Tc, L.
=
Cl),27 and
mechanisms have been reported for the formation of ionic products on photolyaia OF MI(CO)~X (X = C1, Br, I), C1,
I),
and
(Q~-C~H~)F'~(CO) in~ I the
($-C~HS)MO(CO)~X ( X presence
of
=
various
liganda.28 Photolysie of (q5-C5Hs)2MoH2 in the presence of C02 produce8 (qs-C5H5)plo( q2-C02) which on continued irradiation
it3
converted to ($-CsH5)$40(qz-C03) .29 Thjs is the f i r s t solution phase example of the photochemical activation of a metal-carbon
dioxide complex.
Propene is produced by reaction of C2H4 w i t h
Mo(IV) in photoreduced Mo(VI)/Si02 catalysts, and a mechanism for Mo
carbene
formation
by
isomerisation
of
olef in-Mo( IV)
n
complexes proposed. 30 ESR data have appeared for the photolysie products o€ (q5-C5H5)Mo(CO)3Me,31 and it is also reported that (14-C5H5)(q5-C5Hg)m(OAc) (CO) and (n4-C5H5) (q5- C 5H 5 )MoMe(C0) are
formed when the substrate is
irradiated in the presence of
c y ~ l o p e n t a d l e n e . ~Photolysis ~ of
[ (q5-CsH5)Mo(dmp)H31
(dmp
=
107
III2: The Photochemistry of Transition-metal Organometallic Compounds Me2PC%%PMe2)
i n C&
containing M e 2 0 ,
AcOMe, PhMe and other
compounds causes H-D exchange between C6D6 and t h e H atoms of t h e starting
material.33
[ (q5-C5H5)Mo(CO)3COJ2CP2
undergoes
photoinduced l o s s of CO t o g i v e [ (q5-C5H5)Mo(CO)3COCP2Mo(CO)3(q5C S H ~ ) ]and ~ ~ i n r i g i d methylcyclohexane a t 93 K, i r r a d i a t i o n of give8 a mixture of t h e mote s t a b l e isomer
(q5-C5H,)Mo(CO)3Mn(CO)5
( Q ~ - C ~ H ~ ) M ~ ( C O ) ~ ( ~ - C O ) M ~ and. ( C O ) ~t h e
stable
less
isomer
possessing ~ - q ',q2-C0, wl t h l o s s of CO as t h e
(q5-C5H5)NoMn( C O ) only pho t o r eac t ion. A
of
k i n e t i c s method has been described for t h e i d e n t i f i c a t i o n
coordinat i v e l y
unsaturated
substituted
metal
carbonyl
t r a n s i e n t s and s u c c e s s f u l l y applied t o cie-[Ph3PW(C0)4] .36 The procedure a l s o enables v a l u e s of a l l r a t e constants for ligand displacement
reactions
t o be obtained.
Rates and a c t i v a t i o n
parameters have been measured for t h e ring-closure, coordination,
in
Cis-[(q'-pd~p)W(CO)~J
(pdpp
-
y&
coordinatively
olefin
unsaturated
CH2:CH(CH2)PPhZ),
produced
pulsed laser f l a s h photolysis of --(pip)(q'-pdpp)W(co)q p i p e r i d i n e ) . 3 7 A study of t h e carbonyl-loss
via
(pip
=
r e a c t i o n s of t h e
tungsten t h i o l a t e ( q5-C5Hs)W(CO) 3SR (R = Ph, _p-tolyl) show8 t h a t
i n t h e absence of o t h e r l i g a n d s ,
t h e y i e l d s of t h e products
[ (qS-C5Hs)W(CO)2SR]2 and [ (q5-C5H5)W(CO)SR]2 a r e dependent upon R
and t h e conditions. 38 D i m e r isat ion is suppressed i n t h e presence of a ligand such as Ph3P. the
photolysis
of
The same authors have a l s o discussed (q5-C5H~)W(CO)3S02R-3g
Photoinduced
carbonylation of t h e carbyne ligand in (q5-C5H5) (CO)2W!(JTol (To1 =
-p - t o l y l )
gives
(4);
recorded. 40 Bidentate
some
related
transformations
are
also
(alkenylcarbene) tungsten complexes r e a c t
photochemically with olef ins to g i v e o l e f in-carbene complexes i n
Photochemistry
108
or
which the g2-olefin and carbene liganda are trans.41
example
irradiation of (5) in the presence of C2H4 gives (6). A wide range
of
tungsten
and
molybdenum
2-oxaalkyl
(q'-enolate)
complexes are reported to undergo CO loss on irradiation leading to q3-enolates. 42
5. Mana anese and Rhenium A CAS-SCF
contracted-Ci investigation of the lowest excited
states of HMJI(CO)~and Pe(C05) has appeared.43 Laser photolysis and
electron
impact
ionisation W3
studies have
shown that
excitation of the a* state of Mn2(CO)1~ induces both metal-metal bond homolysis and ligand l o e 1 3 . ~However, ~ excitation of the n* state leads to ligand loss only.
Ionic cluster fragments derived
from Mn2(C0)1~ and carbonyls of Fe and Co have been studied by laser ion beam photodissociation, and relative photodissociation cross-sections for each ion and upper limits to bond dissociation energies for M-M and M-CO
Thiolate metal carhonyl
complexes have been prepared by irradiating M2(C0)10 (M = Mn, Re)
or R ~ ~ ( c o ) ~ ( P with R ~ ) ~RSSR (R
=
Me, Ph) or MeSSiMe3.46 Laser
flash photolysis kinetics studies reveal the electronic and steric effects of L ligands in the Re(CO)&
radical and the
steric effect of the R group in RSSR on the group transfer rate constantgives
a
Photoreaction of Mn2(C0)10 mixture
of
three
with 1,l-dimethylallene
mononuclear
and
two
dinuclear
complexesQ7 and the same authors have shown that low-temperature photol~ais of Rez(CO)lo
in the presence of C2H4, styrene or
isoprene give8 Re2(CO)8H(p-q2:'-R)
(R = CZHQ, C4H7, E- and
Z-CHICHPh, CsH7) and Re3(C0)13(p-q2:l-R) .48 eq-Re2(CO)g(N2) ha8 been obtained from photolysis of Re2(CO)10 in liquid Xe doped with N2 and also from narrow band photolyeis at 313 of Re2(CO)10
IIi2: The Photochemistry of Transition-metal Organometallic Compounds
(71
I
Mn(C013
(91
(10)
109
110
Photochemistry
isolated in a N2 matrix at 20 K.49 9,lO-phenanthraquinone to
Photochemical addition of
Re2(CO)Z0
gives
Re2(C0)7L2
(HL
=
9,lO-phenanthrasemiquinone) in which Re(C0)4L and Re(C0)3L units are linked by a bridge formed by one semiquinone 0 of the chelated ligand
of
the Re(C0)4L
coordination
site
of
unit; this 0 bridges the
Re(C0)3L
unit.50
to the vacant Photolysis
of
cymantrene, Ph2PC5H4Mn(C0)3, in the presence or absence of Ph3P gives Ph2PC5H$dn(CO)2(PPh3) and a mixture of (7) and (8),51 and in the presence of n-donor ligands, photolysia of the fulvalene bridged metal complex (9) gives (10) (L
ethylene, cyclooctene,
=
.
but-2-yne) 52 HOWBVBK, u-donor ligands yield the disubstituted complexes (11) (L = THF, PPh3,. Ph2PCH2PPh2, py). ( q5 -CsHs)H
e ( CO)3
Irradiation of
and Me2C=CCLS iMeg g ives the v inylidene complex
(q5-C5Hs)MnMe(CO)2( :C:CMe2)
as the major product together with
the butat 1: iene complex ( q5 -C5H5) W
e ( CO ) ( q2-Me2C :C :C :CMe2 ) .
Room temperature ligand field luminescence has been observed from IReCl(C0)4L]
(L
pip, PPh3), I(q5-C5H5)Re(CO)2(NH3) J and
=
[ (~~-C,H,)Re(Co)~(pip)1 , 54
studies of ReBr (C0)3L [L
=
and
Ph,
H,
Me)]}
[ fE-Re( bpy) (CO)3Br 3
and
electrochemical
2-acetylpyridine, 2-pyr idylcarbonyl-
methylides [C~HQNC(O)CHZ, 2 CN,
emission
-
PPh3, AaPhg, SMe2, NC5H4R-4 (R =
have and
appeared.55
tr iethylamine
in
Irradiation
DMP
leade
of to
photobleaching of the complex to give the 5-ethyl-2,2'-bipyridine complex;56
the
same
photosens it ize the
group
has
also
isomer ieat ion of
used the
this
complex
to
tetrahydrodimera of
1-benzylnicotinamide. 57 ereparat ion of ( q5-C5Me5)ReO12 has been in the presence of achieved by photolysis of (Q'-C~M~~)R~(CO)~ iodosobenzene,58 photolysis of the rhenium( I ) 'enolate complex ~ A G - ( C O ) ~ ( P M ~ ~ ) ~ R ~ ( O C in M ~CHZC12 C ~ H ~ )solution leads to cleavage
IIl2: The Photochemistry of Transition-metal Organometallic Compounds
111 and in
of the Re-0 bond and formation of fac-(C0)3(PMe3)2ReC1,59 the
presence
of
propene,
(PPh3)2(q-CH2:CHMeCH:CHNe)ReH3
of
photolysis give8
the
or
(PPh3)2ReH7 bisallyl
hydride
(PPh3)2(q-C3H5)2ReH-60 (q4-C5H5)Re(PPhg)2H3 has been prepared by photolysis of R ~ ( P P ~ s ) in ~ Hthe ~ presence of cyclopentadiene.61 At
long
irradiation
times
(q5-C5H5)Re(PPh3)H4
is
formed.
Photolysia of Re02(CH2SiMe3)3 in hydrocarbon solvents gives the d'-d'
dimer
Re204(CH2SiMe3)462 forms
Re2(p-u:q3-CHCHCMe2) (CO)9
and
the
of
irradiation
p-butadienyl
complex
J. 63
[ Re2 (1-H) ( p-u: q2-CH-CHC( Me)=CH2 (CO)
a An ASED-MO study has shown that the oxidative addition of CH
bonds of methane and ethylene to ground state 3d64s2 F e atoms is hindered by a closed shell repulsion between the CH u bond pair and the 48 electrons of the Fe atoms.64 However, excitation of the Pe atom to the 3d64s14p1 configuration greatly reduces this barrier.
Laser-generated
La'
reacts
with
Pe(CO)5
to
LaFe(CO)3+ which after colliaional activation gives We',
give and
which itself reacts with a wide variety of linear, branched and cyclic alkanes in proceasea which differ from those of either La' or Pe+.65 An iron catalysed insertion of isonitrile into the C-H bond of arenes to produce aldimines has been described.66 Thus irradiation of Fe(PMe3)2(CNR)3
(R = Me, me3, CH2CMe3, Ph, or
2,6-xylyl) in benzene solution gives the corresponding aldimlne PhCH:NR.
~ gradual The related complex P R ( C N M ~ ) ~ ( C N )undergoes
ligand-solvent photosubstitution on irradiation in MeCN to give f iret
Fe(Me)3(NCMe) (CN)2
Pe(CNMe)2(NCMe)2(CN)2.67 matrix
isolated Pe(CO)4
and
subsequently
The IR laser-induced photochemistry of
ha8
been
discussed
in
terms
of
a
Photochemistry
112
distorted octahedron and an analogy drawn between the reactions of Pe(C0)4 and Hb,'* species
Pe(CO),
and Mkissbauer parameters of the unstable
-
(n
2-4),
generated
by
photolysie
of
matrix-isolated Fe(C0) 5, have been measured.69 Investigations of the photochemistry of Pe(C0)s deposited on to single crystals of A1203, Si(lOO), and Ag(ll0) s ~ r f a c e s , ~ and ~ ,a~Si(ll1)-(7 ~ x 7) surface72
have
been
descr ibed,
and
irradiation of
Pe(CO)
physisorbed on to porous Vycor glass 3s reported to lead to efficient formation of Fe(C0)4, a species which rapidly reacts with
the
surface
to
form
H-Fe(C0)4-OSi
and
H-Pe(M)g-OH.73
Continued photolysis promotes further decarbonylation and may lead to atomic iron or elemental iron aggregates. [M(CO),_l(~-C3H5)1+BPqformed when M(CO),
is
(M
=
Pe, n = 5 ; M = MO, W, n
irradiated with ally1 alcohol
= 6)
is
in the
presence of HBF4-OEt2; other similar reactions are reported.74 Irradiation of a mixture of ethylene and hydrogen containing a catalytic amount of Pe(C0)S is an efficient system for ethylene hyd~ogenation.~' A reservoir of Pe(CO),(C2H4)2
appears to be
formed which thermally dissociates to yield the active catalyst Fe(C0)3(C2H4).
Photolysis of trans, trans, cia-cycldodeca-1,5,9
-triene with Fe(CO)S
in benzene gives complex (12)76 and the
cycloaddition reactions of 1,1,2,2-tetrafluoro-l,P-disilacyclobutene with buta-1,3-diene have been studied in the presence of Fe(CO)5, and the effects of substituents i n ~ e s t i g a t e d . ~The ~,~~ same authors have also examined the metal carbonyl mediated isomerisation of 1,4-diailacyclohexa-2,5-dienes.79 Pe(CO)2(q2-S2CNMe2)2
and Fe(q2-S2CNMe2)2 have been prepared by
visible light photolysis of solutions containing Pe2 (CO)9 or Fe3(C0)12
and [ (v5-CgH5)(CO)3W(q1-SCSNMe2) J .80 Photolysis of a
113
lIi2: The Photochemistry of Transition-metal Organometallic Compounds
auapenston of PeZ.(CO)g and ( ~ J ~ - C ~ M ~ ~ ) ~ MinO ~ toluene ( C O ) gives ~ (q5-C5Mes)2Mo2Fe2(CO)9 (p2-C0)(qz, p 4 - C 0 ) ,
a
new
62-electron
butterfly Mo-Fe cluster .81
Low
temperature photolysis
(+-Ole€ in)Pe(C0)4
var ious
of
complexes of @-unsaturated
that loss of CO ia the predominant
matr ix
isolated
esters ha8 shown Three products are
observed, none of which is the expected (q2-olePin)Pe(CO)3, and haptotropic rearrangements involving these three occur under Dissociative loas of CO is the primary
selective irradiation. photochemical
event
following
species.83
(q4-cyclopentadiene)Fe(C0)3
transfer
of
5-&o
the
q5-cyclopentadienyl the
complexes of phosphite; L
=
group
complexes. type
This
or
(H
CO or MeCN)84
of
is
(P
various
followed
Me)
Photochemical
[(q5-CgHs)PeP2L]+
=
to
by form
studies
of
phosphine
or
and of the acyl-iron complexes
(R = H,
CF3) to
[ q5-C5H5 (CO)Fe[p-C( CF3) :C(R) (SMe))2Fe( CO)-$-C5Hs]
have
(cyclic P e - S
[q5-C5H5(CO)PeC(0)C(CP3)C(R)SMe]
give
excitation
appeared.8 5 The same authors also descr ibe the photochemistry of (qS-indenyl)2Pe2(CO)4 in the presence of 2e-donor ligands such as CO, PPh3, and PPh2H and report the reversible formation of the Photolyats of PpSiMepiMeR2 [ P p =
radical8 ( indenyl)Fe(C0)2L.86 ( q5-C5H5)Pe ( C O ) ;
R
=
Me, Et 3 g ives the monos ilyl-Pp der ivat ives ,
F pS iMe2Et ,
FpS iMeEt2,
P pS iMe3,
(~~-CgH5)2Pe,
and
( ~ J ~ - C ~ H ~ ) ~ P B ~The ( C products O ) ~ . ~ ~are explained by postulating the formation of silyl iron complexes as transient intermediates. Irradiation of a mixture of [(C0)3FeS]2 and ethylene leads to insertion of the alkene into the S-S bond; [(CO)3Pe]p2CO analogously reactions
produced of
if
ketenimines
CO
is
with
used -88
iron
Some
is
photochemical
carbonyls
have
been
Photochemistry
114
co
(13) R = C H M q
H2C=
CH/J
(15) R =TS-C5H5
@
Me I-
Fe
I181
(14) R =y5-C5H5
1112: The Photochemistry of Transition-metal Organometallic Compounds
qPh Me
C-t
Me
cKTcH2R
115
116
Photochemistry
descr ibed8’ and a mechanism
€OK
the photosubstitution reactions is assumed
of (13) has been proposed in which PhCH:CHCH:NRFe(C0)3 to be the initial primary photoproduct in The
alkylcarbene
photolysis of (15)-
complex
(14)
has
been
produced
by
The reactive intermediate Pe(DMPE)2 (DMPE
=
Me2PCH2CH2PMe2) generated by photolysis of FeH2(DMPE)2 has been shown to be sufficiently reactive to add intermolecularly to the
H bonds in pentane at -9OOC to form a-(l-pentyl)FeH(DHPE)2g2 A t -3OOC
the
analogous
reaction
Z-&-(pent-l-enyl)FeH(DMPE)2.
to
leads
E-
and
The ring-expanded complexes (16)
are formed on photolysis of the (aminocyclobutyl)iron complexes (17) (R
=
Me, CHMe2).93
The quantum yield of formation of the T1 state of ferrocene has been determined by the sensitized isomeriaation of D-glucose phenylosazone,94
and
2,2,2-tr ichloroethanol,
the
same
ferrocene
authors is
report
photoxidised
that
to
in the
€err icenium cation. 95 The heterocyclic derivatives of f errocene (18) and (19) undergo photolysia to (20) and (21).96
7. Ruthenium
Complexes of the type M(CO)4(~2-CF3CsCCp,)
(M
-
Ru, 0s)
have been prepared by photosubst itut ion of M( CO) 5 with the al-e and react with M(C0)s to give dimetallacyclobutenes, which in solution have P luxional atructurss .” M3(C0)12 (M
The photocherniatry of
Fe, Ru) in low temperature fluid solution and in
rigid organic solvents has been studied, revealing a wavelength, medium,
and
temperature
dependent
compet it Ion
between
The thermal and dissociative loss of CO and Pragrnentati~n.~~ photochemical behaviour of [Ru,(CO),z(PhC2R)] [ R U ~ ( C O ) ~ ~ ( P ~ CJ ~ Mhas ~ ) Zbeen describedg9 and
(R = Me, H) and irradiation of
IIf2: The Photochemistry of Transition-metal Organometallic Compounds ( q5 - C 5 m 5 )
H/D
P ( C H b 2 ) 3,PPhq ) in CgDg found to induce
RUH3 ( PR3 ) (R
exchange among solvent, hydr ide ligands and
phoraphine.lOO Re(C0)S; S i n
The =
117
complexes
m i n
[U
-
coordinated
(q5-C5HS)Ru(C0),,
MegSi, MegSi2, Me7Si3, CH2SiMe3, CH2SizMe~l have
been reported, and in contraet to the related (q5-C,H,)Fe(CO),, are
photolabile with
not
respect
to
deoligomerisation to
monosilane metal d e r i ~ a t i v e 8 . l ~ ~
LAalim Mult isubst itut ion of 0s (CO)5 by ethylene has been achieved
and has allowed isolation and full characterisation of moat members of the aeries O S ( C ~ ) ~ - ~ ( C (~xH =~ )1-4) ~ .lo2 Photolysis
of the carbene-containing cluster complex O S ~ ( C O ) ~ [ C H N M ~ ~ ] (p-me) (p-H)
give8
083(CO)~(p-Ct~Ne2) (p-SMe)(p-H)2,
a
compound
possessing a bridging (dimethy1amino)carbyne ligand-lo3
Halobenzoic acids and halobenzenes are photocarbonylated to benzenedicarboxylic acids and benzoic acids in the presence of some cobalt salts.lo4 This new procedure avoids the use of cobalt
carbonyl
and
complexes
Ph2C=C=CRC02Re ( R
-
reducing
Me, R'
=
agenta,
Irradiation
of
Et) in the presence of C02(CO)g is
reported to give PhaC=CH-CH-CPhZ together with
(22).lo5 !Fwo
ieomers of the coordinatively unaaturated species CH3Co(C0)3 have been produced photochemically and their reactions with the matrix and dihydrogen studied.lo6 Some related work on HCo(C0)q has also been
carried
out.
Photolysis
of
the
hydrido
complex
CoH[PPh(OEt)2]4 in the presence of allyl benzoate or allyl phenyl ether induces allyl-0 bond cleavage, and for s o m e allylic amides double
bond
migration
stereoisomers of
OCCUKS
to
give
kinetically controlled
an
E,Z
mixture
of
composition.lo7 The
Photochemistry
118
of
mechanism
the
photoisomer isat ion
1-phenylpropene in the presence of
of
3-phenylpropene
CoH[ PPh(OEt) J
to
ha8 been
studied and shown to be a photoinduced catalytic reaction rather than a photoassisted reaction.lo8 Photolysis of the aralkylcobaloxime (23) (X
=
CH2, (CH2)2,
(CH2)3, OCHZ) in CHCIQ has been discussed109 and the same authors have investigated the photolysis of 2- [ (alkylthio)carbonyl]-2[ (arylethy1)propylJ cobaloxime.'lo
Organocobalt
complexes
[(H20)L.CoRJ2+ ( R = Me, E t , Pr, CH2C1, CH2Br, CH20Me, CHzPh, L 1,4,8,1l-tetraazacyclotetradecane) photolysis
of
the
corresponding
have
been
prepared
alkylcobaloxlmes.'11
=
by
These
complexes are themselves photosensitive, readily decomposing to Co(I1) and carbon-centred radicals in visible light.
10. Cobalt and Iridium
Photoinduced homolysis of ( 2 4 ) (R
=
Co(sa1ophen)py) in the
presence of radical trapping agents such as 0, NO, S02, Ph$32, PhzSe2, MeSO2C1, BrCC13 and iodine gives adducts (24) (R
=
OH,
NHz, SPh, SePh, C1, Br, I , SOZH) after reductive workup.'12 11. Rhodium and Iridium
In the presence of PPh3, photolys is of [ Eth(NO) (CO)(PPh3)2 J leads to 108s of NO and formation of trana-[Rh(CO)Cl(PPh,)2]. similarly
[Ir(CO)Cl(PPh3)3]BP4
[ Lr(N0) (CO)C1(PPh3)2]BF4.'13
terminal
methyl
group
is
f ormed
and
from
Regioselective carbonylation of the of
n-pentane
has
been
achieved
by
irradiation of n-pentane under an atmosphere of CO and in the presence of EthCl( CO) ( PMe3)2 ; be R h C 1 ( W e 3 ) 2.
the active species is thought to
Both benzene and cyclohexane have been s imi,larly
carbonylated.115,116 The 8ame complex ha8 also been used f o r the regioselective synthesis of terminal olef ins from alkanes. lL7 For
lil2: The Photochemistry of Transition-metal Organometallic Compounds
119
example, pentane and decane have been converted into but-l-ene and
non-l-ene
respectively
acetaldehyde-
In
propan-2-01
is
the
with
liquid
simultaneous phase,
photocatalysed
by
format ion
of
dehydrogenation
of
the
related
complex
trans-[RhCl(CO) (PPh3)2J, and [RhC1(PPh3J2 has been suggested as the
active
species.'18
Evidence has
photolysis of (q5-C5H5)Rh(C2H,)2
appeared
to
show
that
in N2-doped liquid Xe at 173 K
leads to the formation of (q5-C5Hs)Rh(C2H4)N2; in the presence of CO,
brief
photolysis
(q5-C5H5)Rh(C2H4)C0.119
of
the
dini trogen
complex
gives
The same authors have also studied the
C-H and Si-H bond activation reactions of (q5-C5Hs)Fth(C2H4)C0 in low temperature matrices.l20,121 relay
A
system,
incorporating
[(s5-C5Me5)Rh(ppy)Ll2+ (ppy
the
novel
oligopyridine ligand, n
-
complex 1,2; L
=
H20, OH, C1, I), and capable of using weakly reducing electrons of a Ti02 colloid for hydrogen evolution has been described,122
The
photocatalytic
cis-[Rh2C12 (C0)2L2 J
system
(L
=
composed
of
acetone
and is
bis(dipheny1phosphino)methane)
effective in producing hydrogen from Me2CHOH123 and an ESR study of the mechanism of formation of hydrogen during photolysis of
alkyl(disalicylideneethylenediaminato)rhodium(lII)
shows
that
.
alkyl, hydroxyalkyl radicals, and atomic hydrogen are formed 124 Sunlight
irradiation
of
solutions
of
alkenes
and
(q5-C5H5)2Rh2(CO) (CP3C2CP3) induces transfer of H from the alkene to one of the "C(CP3) carbons to give the bis-alkenyl complexes ( q5-C5H5)2Rh2(alkene-H)[C ( CP3 )-C
(CF3)H] - 125
Photolysis of [ Ira ( CO)2212- in CH2Cl2, a complex consisting
of two t r 4 tetrahedral clusters linked by a single Lr-tr bond and unsupported by bridging ligands, gives [ 1r4(Cl) (CO)ll]-.126 This
120
Photochemistry
R
R'
127) R = 1 R'= I Me
, , CH2I
(28) R = Ph,
R'=
CF3
Bu
,
SiMcg
, OMc
Ill2: The Photochemistry of Transition-metal Organometallic Compounds
121
is thought to arise via hornolysis of the inter-cluster bond. Selective catalytic dehydrogenation of alkanes to alkenes has been achieved using the neutral catalyst [ IrH2(q2-O2CCP3) (PR3)2] (R
=
4-PCgH4, cyclohexyl)
Carbon-hydrogen bonds in THP, Me2C0
(I. = P(CH2CH2PPh2)3) a
and benzene can be .activated by [LIr]'
species which can,be generated by photolytic dehydrogenation of cis-[LIrH2)(S03CP3) .128
Similarly,
photolysis
of
(25)
and
(a5-C5Me5)Ir(C0) (q2-NCC6H4C1) in hydrocarbon solvents results in activation of
the solvent C-H
bonds,129
and a study of
the
photoactivation of methane matrices by complexes of the type [ M ( Q ~ - C ~ R ~ ) ( C O(M ) ~=~ Ir or Rh, R = H of Me) has been reported.130 Photoinduced charge separation and recombination kinetics have been measured for the dimeric [ I~(p-pz')(CO)(PPh2{0(CH2)2R))) -e
l 2 [pz'
pyridine (py), 4-phenylpyridine]
these
complexes
are
well
=
Ir( I)
complexes
3,5-dimethylpyrazolyl; R The results suggest that
adapted
to
detailed
studies
of
intramolecular electron-transfer reactions. Photolyeie of matrices
of
C2H4
(v5-C5H5)Ir (q1-CH2CH2)2 or
CO
(q5-C5H5)Ir(L) (&CHCH2)
gives
the
in low temperature
vinyl
(L = H2CCH2, CO)
hydride
complexes
Photooxidative
addition of (26) with 12, MeI, and CH212 produces the dinuclear dffridium(I1) complexes (27) (R [ Ir2AuCl2(CO) (p-dpma)2 1' [ IK2AUCl,(CO)2(r-dpma)2]+
=
has (d-
iodo, R' been
-
9
fodo, Me, C H Z I ) , ~ ~ ~ photoox id ised
ABPh(CH2PPh2)2)
to and
luminescence has been observed from [Ir~T1(Co)~Cl~(p-dpa)2JN03 and [IrzPb(Co)2~12(p-dpma)Z] (N03)2.135 Photolysis of LIrMe (L = octaethylporphyr in) in C& d imer .136
gives an Ir ( I I ) octaethylporphyrin
Photochemistry
122
12. Nickel Methane is reported to react with photoexcited nickel a t o m in AK matrices to give MeNiH. 13' the reactions of
A
PTIR matrix isolation study of
atomic and diatomic nickel
in solid argon
indicates that at very low concentrations of the metal, the nickel atom forms a n-complex with the triple bond
the
of
acetylene.13* Photorearrangement of this complex gives nickel vinylidene, NiCCH2. A
theoretical study of the photolytic reaction of Ni(CO)4
using LCGTO-X,
has appeared, and the observed luminescence is
assigned to emission from the charge-transfer excited fragment Ni( C0)3.
Multiple
luminescence
has
been
observed
from
continuous wave laser irradiation of gas-phase Ni(CO)4 at room temperature.140 oscillating
Two
of
the
reaction and
emissions
all three
molecular photofragments of Ni(CO)4
are
probably
coupled
in
an
originate from
rather than from Ni(CO)4
itself Mono- or zerovalent nickel can be produced by single or successive one-electron transfer steps during the photoreduction of silica-supported nickel catalysts in a hydrogen atmosphere. 14' The fundamental step is the formation of (Ni+-O-)* excitons from
ions and oxygen bound to
pairs of tricoordinated isolated N i 2 +
the surface of the Si. trans-[Ni[CCl:CCl(CgH~Y-4)}Cl(Pne3)21 trans-[Ni[C(C6H4Y-4) :CC12]C1(PMe3)2]
(Y
=
Me,
C1)
arise
and on
~ ) ( P M ~by ~)~] photolysis of ~ ~ ~ ~ s - [ N ~ ( C C ~ : C C L ~ ) ( C ~ H ~ Y -possibly
reductive
elimination
followed
by
oxidative
addition.142
Quenching of singlet oxygen by nickelocene is reported to be an efficient
process
and
to
involve both
reversible charge transfer interactions
energy
transfer and
lIl2: The Photochemistry of Transition-metal Organometallic Compounds 13.
123
Palladium and Platinum
Evidence derived from measurements of the lifetimes and electronic spectra of the tetrahedral complexes M(dppp)z (M = Pd, Pt; dppp in
-
bis(dipheny1phosphino)propane) in the solid state and
fluid
( It2(n*pu*)
solution
indicate
that
1 [t2(do*)ll). 144
the
emissive
Quantum
state
yields
of
(4-PAP-N02
photoisomerisation of trans-[Pd(PPrn3)(4-PAP-W2)C12]
pyridine-4-aldehyde-4-nitrophenylhydrazone)
-a
is
following
intraligand excitation have been determined
of
Photoisomerisation
[Pt(PPh3)2(RCICX)]
acetylido complex [Pt(PPh3)2R(CiCX)] (R = X = Ph, CH20H
or CMe20H and R = H, and
the
Me02C), but if R
= X
CH20H, C02H or CH2NH2, no
Details have appeared of the
analogous transformation occurs mechanism of
X =
=
gives
hydrogen production from photolyais of
aqueous
solutions of [PtH(PEt3)3]+ 147 and of a catalyst suitable for the hydros ilylat ion
of
ole€ ins. 148
[ PtClzYL]
(Y
=
subst ituted
pyridine, L = O-donor ligand) has been prepared by irradiation of [PtC12Y(CH2:CH2) 1 in solution.14g Thermally Induced loss of the O-donor ligand gives [ (PtC12Y)2J as a pair of cis/trana isomers whose
proportions
can
be
varied
photochemically.
a-bLs(2-phenylpyr ldlne)platinum( I I) and s;ia-bis[2'-thienyl)pyridinelplatinum(I1) undergo a oxidative
addition
with
stereoselective photochemical
various
organic
halides
to
yield
complexes of Pt(IV) with the halide and a u-bonded C-atom in the m - p o s it ion. 150
The
wavelength-dependence
of
the
photoelimination reactions of the diphenylplatinum(I1) complex (28)151 and of gj&-[Pt(PBu3)2(C6H4R-4)2J
(R
=
CP3, Me, CMe3, OMe)
have been atudied,lS2 In the latter case, the substituent is stable a t 2 5 3 . 5 run whereas at longer wavelengths it undergoes a
124
Photochemistry
regiospecif ic per icyclic reaction at platinum. 34.
CODDeK a d Silver
examination
An
of
the
wavelength
dependence
of
the
photorearrangements of CuCl complexes of cyclododeca-1,5,9trienes has revealed no reason to assume that the t w o types of reaction, cis-trans-photoisomer iaat ion and rearrangement, occur on
separate
(Ph3P)3CunX,
energy
surfaces .153 154
(n -- 1,2; X
C1, Br , I ; biL
=
The
photolysis
of
C1, Br, I, CN) and (PhgP)(biL)CuX (X
=
2,2 '-bipyr idyl, 1,lO-phenanthroline) has been
=
examined by ESR,15'
and Ph. and Ph2i) identified as spin adducts
with phenyl-tert-butylnitrone. photocatalyt ic
A
activity
[Cu212(PPh3)2(dpk) 1 ,
and
study has been made of the Of
[CuqIq(dpk)3]
[Cu(PPh3)2(dPk)lN03, (dpk
=
di-2-pyridyl
ketone) in the solar energy storage reaction, norbornadiene/ quadr icyclane. lS6 The effect of Ag( I)
on alkene E/Z phOtOiSOmt3Kif~atiOn has
been described together with further observations on the Ag( I) photoinduced 1,3-hydrogen shift .157 15. Miscellaneous
Luminescence spectra of a series of Ce(1") halide,
alkyl,
hydrocarbon
aryl,
ligands
ether,
have
been
conditions158 and a matrix synthesis
of
nitrile,
and
recorded
isolation W
( c ~ H 4 ) ~ E uusing
compounds containing cyclic
under
a
aromatic range
of
study of the direct
europium
atoms
ha8
been
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The Photochemistry of Compounds of the Main GrouP Elements BY A. COX 1.
Introduction
Reviews
have
appeared
of
laser
induced
photochemical
reactions of diborane and its mixtures with other compounds,'
the
~ of interaction of O('D) atoms with O3 during W p h ~ t o l y s i s ,and polysilane high polymers .3 2. Boron and Indium
Excitation of pentaborane(9) at 193 nm in the gas phase causes primary dissociation to BH3 and B4H6, followed by the ground state transformations shown below,
1 Reduction of the esters RC02R' (R and 4-MeC6H4, photoexc ited
2- and
mono-
=
4-C1C6H4, and
cyclohexyl ; R'
Me) has been
Their
Ph, 2-, 3-,
achieved
di-p-naphthoxyborane
tr i-B-naphthoxyborohydride.
=
react ivit Fee
and
lithium
have
rationalised in terms of the increased acidity of the excited state.
using
been (T,T*)
Tr imes itylbor irene ( 1) has been prepared us ing a
d i-n-methane-liFe photorearrangement of dimes ityl(mes itylethyny1)borane and its properties that
irradiation
of
NaBPh4
in
An earlier claim7 MeCN
or
THF
gives
the
diphenylborene anion has been challenged .8 4,4'-Bipyridinium ions
form ion-pair CT complexes with tetrakis[3,5-bis(trifluoro-
135
.
Photochemistry
136
M Ph ,e, Ph
Ph
(1) R = mesityl
1IN: The Photochemistry of Compounds of the Main Group Elements
methy1)phenyllborate
anion
and
show
for
the
a
broad
137 structureless
lumineacence at 553 nm. 9 The
quantum
EtIn(II1)TPP
(TPP
yield =
photodecomposition
tetraphenylporphyrin)
of
is increased in the
presence of pyridine and this has been interpreted in terms of the facile dissociation of the C-In bond in 3EtIn( I I I )TPP(Py) * assisted by the axial pyridine.l0
The same workers have alao
investigated the electron transfer reactions of EtIn(I1I)TPP
to
tetracyanoquinodimethane.I1 3.
Silicon, Germanium. and Tin
Si('D2) has been detected following photoexcitation of S i H Z into high bending vibrational levels of the A1B1 electron-transfer
photochemistry
state."
Some
a-silylamine-cyclohexenone
of
s y s t e m together with medium effects on the reaction pathways followed
have
been
describedl3
and
ethers
using
of
a
induced desilylation of trimethylsilyl enol
an
1-cyanonaphthalene polyailylated
isolation
two groups of ~ o r k e r s - ~ ~ t ~
silanimine has been reported by Electron transfer
matrix
excited haa
also
diazomethanea
(Me3Si)3SiC(N2)SiMe3
state been such
photosensitizer reported. l6
such
Photolysis
as Me3SiSiMe2C(N2)SiMe3
as of and
leads to the formation of sbonded silenea
by migration of a trimethylsilyl group to a carbane centre.17 That it is this group excluaively which migrates, may reflect vertical charge stabiliaation by the donating effect of the Si-Si u-electrons to the vacant p-orbitals of the silylcarbenes. A
ailylated
cyclobutene
has
been
prepared
by
the
photocyc loadd it ion of male ic anhydr ide with RC !CS i M e 3 ( R-H, Me, MegSi)18 and photolysis of H2C:CHSibfe2SiMe2CH:CH2
of butadiene gives a mixture of
a and
in the presence
trans vinylailacyclo-
138
Photochemistry
butanes
and
s i 1.acyc1.ohexans
Me2Si :CHCH2SiMe2CH:CH2.'I
v ia
the
The ene reacti.on o f al.l.yl.ai.l.anea wi.t.h
s i.ngl.et oxygen, 2o photoadd i t ion o f R9eH and
R!3eCH2CH2Si( Q M e ) 323
a i.l a n e
i.nt,ermedi.atx
t.0
s o h i t ion
hydros1.l y J a t i o n of ai J y.l acety.l enea"
H3.C :C H S i.( OMs)3 t-o 9 i.ve
phase
photochemi.ca1.
have been d e s c r ibed.
AbwoJute r a t e c o n a t a n t s have been measured for si.ly.lene r e a c t i o n s with hydrocarbons at. 3.98 K and t h e s e ahow that- si.ly.lsne
reacts r a p j d l y but unsel ect,ive.ly with iinsatiixat,ed hydrocarbons; hwever ,
a j .lyJ ene
j
a
unreacki ve
kowards
a.1kanea z 3
DimethyIailyIene has been produced hy y-irrad.iation saJutjons
of
dodecamsthy.lcyc.lohaxaaj .lane. 24
of
benzene
Rs.lat.jve
rake
c o n s t a n t s f o r the r e a c t i ons of methyl phenyl s i .1 y.l ene qenexated by p h o t o l y s i a of t h e Si-bridged 2,3-dimethylbu ta-I, 3-di ene,
arene have
( 3 . ) w.it,h EkOH,
been
Et3S.iH, and
pob.1ished. 3.5
R e 1ated
r e a c t i o n s have been urred t o prepare 2,2,6,6,8,8-hexamethy.l-~'r7-
4-thia-8-sj~ahicyc.loCS.3. O J o c t e n e ,
s t r u c t u r e shows ( 3 ) ,3.7 and
descr i b d .
j
compound
a
whose
X-ray
t to be pseudoaromat.ic,26 t h e a.i.lacyc.1opentenes
react ions o f di.methy1.ai 1.yl.ene w i.t-h p i.nenes have been
'*
The
photochemical
g e n e r a t ion
a
of
cyclopropeny-lsily-lene haa heen reported2'
and on photo.1ya.i a of
this
major
compound
in
a
Et2CHMe
glass,
the
product
a
ja
silacyclobutadi.ene. 3Q I r r a d i a t i o n o f 3.-cycl.op,:opyl.-j!-phenyl.hexamethyltr is ilane
i.n
2,3-dimethylbuta-I., 3-di.ene
preasnca
the
gi.ves a mi.xt.nre
of
of
product-a
whi.ch
arises from t h e intermediacy of cyc.loprapy.lpheny.ls.i.ly.lene-3'Follmwing n , n * e x c i t a t i o n of: arp-iinRaturat-ed si.1.yl. ketonea such
as
followed
(41,
the
by
y-H
main
phot.opxocea8ee
ahat-raction;
are
E/X-iaomexlmtlon
photo.iaomerjastlon
by
a b s t r a c t ion i.s also observed. 33. Photolys i.s of (Me3Si.)$3 i.COR
8-H
[IN: The Photochemistry of Compounds of the Main Group Elements
Me
Me
(6) R = mesityl
(7) R = mesityl
139
Photochemistry
140 (R
-
Et,
CHMe2,
CH2Ph)
gives
a
mixture and
Me3SiOCHR(Si(SiMe3)212C(OSiMe3):CHPh)
of
(w.
linear
cyclic
head-to-head
dimers ( 5) of the intermediate silenes, the proportion of cyclic dimers increasing with the bulk of R.33 The same authors have also examined the photoreactions of stable ailenes with dienes and alkenes;
[2+4],
[2+2],
and
ene
reactions
have a.11 been
observed. 34 A
study
of
the
phenylethynyldisilanea s i x-member ed
r inga
photophysical has
have
appeared. 35 been
formed
of
behavionr
some
Various by
novel
photolya i a
of
hexa-tert-butylcyclotrisilane in the presence of ni tr iles such as
MeCN and PhCN.36 Persilylcyclotrisilane,
[ (Et3Si)2SiJ3 has been
photolysed to produce (Et3Si)2Si:Si(SiEt3)2,37 and the same group reports that irradiation of hexaneopentyltrisilaoxetane leads to extrusion
of
dineopentylsilanediyl
and
of
formation
tetraneopentyldis ilaoxirane. 38 Some cyclotetras ilanes have been trradiation of the cyclopolysilanes (RR’Si), or 4; R = R ’ = Me3CCH2, MezCH, MeCHEt; R
alcoholic
medium
using
= Me3C,
9,lO-dicyanoanthracene
R’ as
(n
=
3
Me) in an
=
sensitizer
induces ring opening and formation of EtO(SiRR’)nH.40 An electron transfer reaction appears to be involved in which the polysilane functions as donor.
Photoreaction of tetrakis[bis(trimethyl-
silyl)methyl]disilene in methanol generates [(Me3Sl)2CH]2Si(OMe)H41
and photolysis of oxaailirane (6) in an inert matrix at
77 K gives the silacarbonyl ylid ( 7 ) . 4 2 Aryltriethylgermanes, diaryldiethylgermanes, benzyltriethylgermanee,
and
dlbenzyldiethylgermanes,
are
readily
photolysed to germyl radicals, which In the case of the radicals arlalng Prom the latter two compounds, add to C-C bonds.43r44
I I N : The Photochemistry of Compounds of the Main Group Elements
141
PhOtOlySiS of benzoyltriethylgerme, EtgCeCOPh has been shown to lead to the initial triplet radical pair Et36e and Phh0.45 The photochemistry OF dialkyl and diarylgermanium(1V) porphyrins ia consistent with
a mechanism
involving
bond. 46 Some organogermylenes R2Ge: (R been prepared by photolysis
=
cleavage
-
the Ge-C
Me, Et, Ph, mesityl) have
in a matrix and their electronic
spectra reported.47 The germylenes R2ge, R * & R , C1, OMe; R m
of
and Rm2ge ( R = F,
Et, Ph, mesityl) generated photolytically, undergo
a regioselective cycloaddition with 3,5-di-tert-butyl-~-quinone The first synthesis of a stable t o give 2-germa-1,3-dioxolane~-~* germathiirane has appeared4’ and a CIDNP study of the photolyais 0
(n = 1-3) to give Ph#e3-nGe
of Ph#eg,,GeLi
a contribution from
d
triplet mechanism.
’*
at 77 K has revealed Homolytic substitution
in trialkylstannyl iodides by photochemically generated iodine atoms has been descr ibed. 51
(Trialkylstannyl)acetylenes of the
form MegSnCiCPh photoreact with RI
(R
=
CF3, n-C3F7) to give
RCICPh.52 A proton CIDNP study of some benzyltin compounds,53
E-2
photoisomer isation
of
2-stannyl-l-borylalk-l-enes, 54
and
selective photoalkylation of the 10-methylacridinium ion using tetraalkylstannanes or d iethylmercury under vi s i ble i rrad i at ion5’ have all been reported.
Photoinduced allylation of aromatic
carbonyl compounds56 and of furyl- and th i e n y l d i c y a n o e t h e n e ~ ~ ~ have also been described. and
probably 4. An
involves
The latter process is regioselective an
electron
transfer
process.
Nitrocren and Phosohoxus
aqueous suspension of coprecipitated hydrous oxides OF
Fe(II1) and Ti(1V) is reported to photocatalyse the reduction of N2
to NH3
using
visible
light.58
Observations
of
the dual
Photochemistry
142 1.a.ser e x c i.tati.on
wavelength
diir i.ng
NO
of
phot-oexci.tat-i.on o f
S P ~ - N O mixtures59 and of t h e azi.da radi.ca1. u s i n g laser-i.ndnced f l u o r e s c e n c e 6o have been made. The f 1-uorescence of
form
Ph2P(0)R
=
PhCH2CHPh)
PhCH2CHMe,
1-,
(R
2-naphthyl.,
Me, i.8
dfphosphene
d e s c r ihed6'
Et,
p-RrC6H4,
PhCH:CMe,
PhCH:CPh,
weak wher ?as t h a t from Ph2P(O) R ' (R' =
9-phenant-hrenyl
r e p o r t e d t o be s t r o n g e r . the
t - e r t i a r y aryl.phosphi.ne oxidea o f t h e
'.'
9-MeOC6H4,
=
bi.phenyl.yl.)
i.8
phot-oi.somer i.nati.on o f
The c i . s - t r a n s
(R
RP=CR
,
has
2,4,6-(MegC)2C6H2)
and al.kenes have been phot.oepoxi.d i.sed
11s i.ng
been
1.i.ght- i.n
a r edox sya tern i nvo.1v.i ng t-etrapheny.1 porphyr i nant .imony(V) .6 3
5. Oxycren, Su'l p h w and Se.1end um comp1.s~ l.eadn t-o a n e w s p e c t e a
Photo1.ysis of t h e O g / R r 2
.
w h i ch may he RrORr 64
In
the
qaa
phase,
(R
H2C:CH(CH2),S.iMeR2_,(OAc)m
.
HS ( CH2)n+7.Si.MeR(OAc) 6 5
photoreact-i.on =
Me, Et,; n
=
H2S
and
= 1,2)
gives
of
0,l; M
e m i . s a i.on
Fluorescence
fol.l.owi.nrJ
excjtatjon of SO3 at. 3 4 7 and 357 nm oriqinakea f r o m S 0 2 6 6
and
infrared f luoreacence has been reprt.Ftd Prom khe laser-induced
senai t f z e d reactfon in t,he SF6-IIF6-H3.
syskem. 67 SP5C!l
has been
photoadded to carbon-carbon doiihJe honda .in a procesa in which &P5
i n i t i a t e s t h e a t t a c k . 68 Analngous addi.ti.ons o f TeF5C1., but.
not SeP5Cl, have a1.m been observed. ehotoly8i.s of t h e ster ical.1.y protected I., 2,3-sel.enadi.axol.e
(8)
in
the
preaence
of
a
siiitab7.e
o1.efi.n
r e g i o s e l e c t i v e cycloadducts (9) ( R = C02Me,
l.eads
CN) v i a an
tm
the
n it. i.al.1.y
formed z w i t ter f on f c jnt.ermed i a ts .69 6.
Haloaea
Absolute r a t e constantxi have been o b t a i n e d for t h e Cl.z/ H R r
1113: The Photochemistry of Compounds of the Main Group Elements
143
chain r e a c t ion using t h e l a s e r - i n i t i a t e d chemical. chai.n xeacti.on technique. 70 The photochemistry
of
methyl bromide absorbed
on
plat inum( 111.) ,71- t h e photofragmentat ion dynamica of i.odoethane, l , l , l - t r i€luor0-2-iodoethane,~~
1-iodopropane
2 - i o d o p ~ o p a n e have ~~ been i n v e s t i g a t e d ,
and
and emission f r o m tF(R)
has been observed following t h e p h o t o l y s i s o f a mixture o f C P 3 t ,
P2 and Ha using a pulsed 248 nm KrP.excimar .laaer.74 The origin of fragment r o t a t i o n in cyanogen i o d i d e phot-odiaaociation has been discussed75 and t r a n s i e n t i n t e r m e d i a t e s have been r e p o r t e d i n t h e
photolysis of iodonium cations.76
Mi scel l a n e o u
7.
Aqueous persul-phate using
p l a t inised
p-CuCNS
i.8
photodecomposed
coated
with
i n v i s i.bl.e l i g h t
Rhorlamine
R
to
give
oxygen - 77
3. 2.
A. M.
M. R a r r i d a , A c t a Cisnt. Venez, 1986, 37, 607. P. Popovich and Yu. V. Pil.ippov, Vestm.
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H e , H. HOU, Q . Qin, Zhonuuuo, Jiuuanq, 1987, l4, 279. Grelbig,
Kruegerke,
T.
2. Anora. A . l J u . C h e m . , 3987,
69
-
A.
Wataru,
544,
K.
and
Sappelt.,
74.
Y. Kurnamoto, and N. T o k i t o , T e t r a h e d r o n I , e t t . ,
3986, 2 7 , 6107.
70
-
D. A .
R.
Dolson and S.
Leone,
J.
Phva.
Chem.,
1.987,
a.,
3543. 72.
S. A .
Coste11.0,
J. Phvs. Chem., 73..
C. P a t e r s o n ,
B.
Roop, Z .
M.
r,iu,
J.
M.
Whi.te,
Corry, M o l .
Phvs.,
and
1988, 92, 1.02.9.
F. G.
Codwin,
and P. A .
1987, 60, 729. 73.
Y. Huang, J. R. Cao, Y e Wen, X . Zhong, J . Zhang, W . Fang, X.
74.
13.
Wu, and Q. Zhu, Wu1.i Huaxue Xuebao, 1987, Raybone,
T.
Chem. Phvs. I.ett..,
M.
Watkinflon,
and
J.
3, 337. Whitehead,
C.
3 9 8 7 , L33, 442.
75.
C. H. Dugan and D. Anthony, J. Phvs. Chem., 1987,
76.
R.
J. nevoe,
M. R. V. Sahyuin, N. S e r p n e ,
Sharma, Can. J . Chem.,
77.
K.
Tennakone,
1987,
fi,
and
n.
K.
3.343..
S. Wicktamanayake,
J. Chem. SOC., Caradav Trans.
a,3929.
and
I , 1987,
M.
U.
83, 2 5 5 3 .
Gunasekara,
Part 111 ORGANIC ASPECTS OF PHOTOCHEMISTRY
1 Photolysis of Carbonyl Compounds
I
BY W. M. HORSPOOL Pfoertner has scale
up
reviewed
of
problems
photochemical
discussed
chirality
processes.e
Gilberta
which
can arise during
A
experiments.*
transfer
in
the
review
some
has
photochemical
has published a review dealing with the
use of the carbonyl group in the synthesis of steroid systems. The second edition of a textbook o n organic photochemistry by Coxon and Halton.
Norrish Type I Reactions
1 High
has been published.
intensity
irradiation
hexane/isopropanol
mixtures
carried
of
out
dibenzyl and
dibenzyl
ketone
1,2-diphenyl
in
ethane
and
A study of the photochemical
toluene as the sole products.' behaviour
of
yields
ketone
adsorbed
the results found
on
to be
zeolites has dependent
been
upon the
Si/A1 composition of the z e o l i t e e m A leser flash examination of
the behaviour
demonstrated
of dibenzyl
that
a
ketone in Nafion membranes has
modest
yield
of
benzyl
cations
is
f ~ r m e d .A ~ study of the physical photochemistry of the ketone ( 1 ) has shown that
the excited state is a carbonyl localized
singlet state. This ultimately decays to afford localized from
the singlet
radicals study of
state
to afford
radical
has
photochemical
been
behaviour
of
the photochemical ( 4)
ketones
reported.s of
derived
from
report also that
the
the 1-
from the triplet state. A
is formed
the modification
a-alkyldibenzyl
cyclodextrin
products
(3). The authors.
(2) and
naphthyl methyl the
a naphthalene
triplet state. Norrish Type I cleavage does occur
the
A
by
behaviour
complexation
similar
study
of
of in the
(5)
in
conversion
to
alkyldeoxybenzoins
cyclodextrin has also been made.lo Irradiation
of
( 6 ) at
300nm
brings
about
dehydrohumulinic acid (7) by epimerization at C-4 and (8)
151
152
Ph otochernistry
qR
s Ph+Ph
Ph
0
A
A
Ph
x
0
0 /
(81
/
(9) a; R’ = H, R2 = CN dr C02Mc b;R’=F, R 2 = C N orC02Me
(11) n = 2; 6 5 2 n = 3 ;47% n = 4 ; 7%
(12) n = 2 ; trace n = 3 ; 4% n = 4 ;10%
I I I I l : Photolysis of Carbonyl Compounds
153
Norrish Type I fission of the side chain carbonyl group again Laser flash irradiation has been used as a method
at C - 4 . I 1 for
the production of n-butylketene
chemistry
of
this
cyclohexanones processes
ketene
(9a)
on
was
undergo
irradiation.
from cyclohexanone. The
studied
both The
in
Norrish
detail.%=
I
Type
fluorinated
The
I1
and
compounds
(Sb)
showed a preference for Norrish Type I 1 behaviour. Within the Norrish Type
I 1 biradical
fluorine substitution leads
to a
preference for cyclization rather than cleavage. The Norrish Type I biradical afforded a ketene rather than a n alkenal.lm A study of the photochemical reactivity of the diones (10) has
shown that both Norrish Type I and Type I1 reactivity can take place. The Type 1:Type I1 product ratio is dependent upon ring size. Thus dione (lOa) affords the Type I 1 products ( 1 1 ) and (12) while
dione
( 1 0 ~ )yields
the Norrish
I products
type
(13c-15c) and low yields of the Norrish Type I1 products ( 1 1 ) and (12). Compound (lob) is intermediate between these results affording a Type I: Type I1 ratio of 0.3. A mechanistic study of the reactions was carried 0ut.l.
Irradiation (254 n m ) of the keto lactono brings about
a Norrish Type
(17). Elimination of ketene product
(18)
in
good
(16a) in t-butanol
I fission to yield a biradical from
yield.
this affords the isolated
Similar
irradiation
lactones (16b) yields only polymeric products.*'
the
of
Irradiation
of the keto epoxides (19) in methanol results in Norrish Type
I fission to afford a mixture of products the major components of which are the esters (20) and the aldehydo alkenes (21).
Minor products were detected in the ceses of (1%) and (19b) but these were not identified. A minor product from the irradiation of (19c) was identified as (22). formed by rinq opening of the epoxide following the Norrish Type J fission. Irradiation of the epoxide the ring
opening
of
identified.
Epoxyketone
Scheme
on
1
(19a) in ether gave evidence for
the epoxide although no products
(19b)
irradhtion
gave under
the the
products same
were
shorn
in
conditions.
Epoxyketones (19c) and (19d) were also photoreactive in ether but
affarded
complex mixtures
from
which
no
pure
material
could be isolated. The ketone (23) pave the alkenes (24) and
(25) on irradiation in ether and ( 2 6 ) and ( 2 7 ) in
Photochemistry
154
(13) n = 3 ; c + f = 8% n = 4 ; c + t = 24%
(16) a; R = But b; R = Et or Bui
(14) n = 3 ; 4%
n = 4 ; 19%
(15) n = 3 ; 3% n = 4 ; 8%
(17)
(181
,
(19) a; R1 = Me, R2 = C8H17, Sa 6a b; R1 = Me, R2 = C8H17, Sp 6p c;R1 = H , R 2 = O H , 5a,6a
,
d; R’ = H,
Scheme 1
R2=OH,
SB 9 6g
IIIII: Photolysis of Carbonyl Compounds
123)
155
(24)
c@
OHC H
' H
(26)
(27)
(28) a; R = H b;R = D
(29) a; R = H b;R = D
1301 a; R = H b; R = D
(31) a; R H b;R=D
(32) R ' = R 2 = C N R' = CN, R2=C%Et
( 33)
(34)
Photochemistry
156 Stiver of
and
Yatesi7
have
some hydroxy-keto
isomeric
compounds
obtained,
(30)
(28a.
and
configuration of
of
( 2 8 , 29).
29a)
(31)
the
attached. The use
studied the photochemical
steroids
showed
that
respectively,
carbon
to
which
reactions
Irradiation
had
the
the
retained
hydroxy
deuteriated derivatives
of
the
products
group
the is
(28b. 29b) has
identified the hydrogen abstraction processes involved in the conversion of these ketones into the lactones ( 3 0 b ) and (31b) respectively. The authorsi7
propose that there are two major
factors which control the stereospecificity of the reactions. These
are
the
shape
of
the
hydroxy-bearing
hydrogen transfer within the biradical
C-atom
and
the
formed o n Norrish Type
I fission. The stability of the biredical intermediate clearly plays
an
important
part
in
determining
the
outcome
of
the
reactions.
The
photophysics
of
the
a-cleavage
reactions
of
cyclobutanethiones such as ( 3 3 ) have been studied.ig ( 3 3 ) undergoes conversion at 20K
Matrix-isolated
heptan-3-one
to the carbene
( 3 4 ) . The identification of
achieved by
this
species was
trapping experiments and by i.r. spectroscopy.=)
Irradiation of
the ketone (35) in methanol
expansion to the acetal
brings about ring
(36) by way of the standard carbene
path. Chemical conversion of this afforded a synthetic path to moscarine ( 37 )
Norrish Type I 1 Reactions
2 The
.* *
amide
( 3 8 a ) is
photochemically
inert
on
irradiation
in
ether. The related compound (38b) is, however, photochemically reactive and undergoes fission by a Norrish Type I 1 process to yield a mixture of products.g1
The results of a study of the
enantioselective photodeconjugation reactions of the lactones ( 3 9 ) have been published.PP The behaviour of the ketones (40) and
(41)
in
the
isotropic
and
the
two
solid
phases , o f
heneicosane ( C P I H ~) ~has been evaluated. The influence of the various
phases
on
the
ratio
of
elimination
products of the ketones was discussed.es the photoreactivity of ketones
(42)
to
cyclization
The modification of
in cyclodextrin has been
11111: Photolysis of Carbonyl Compounds
(38) a; X = NMe
Me NyPh
PhyxK
0
b; X =CHR, R = alkyl
0
0
157
(39)
M (401 n
*
LnH
= 13,15,19,21
(41) n = 7 . 8,10,11 or 12
or 23
~1
( 4 2 ) R1=H,Me,Bu,pentyl ,decyl, R2=R3=H,X = CH2 R’ = R2= H ;R1= H R2= =R2 = Me ;X = 0,R3 = H
,
R3=p-Mc, R’=H,R2=butyl or pentyl, X = CH2 R3=m-Me,R1=H,R2=butyl or nonyl, X=CH2 R3=o -Me, R’ =H, R2=butyl or nonyl, X = CH2
R3
(441
&Jy HO ( 46)
-
k3
(44) (47) a; R1 =H b; R’ =Me
(45)
Photochemistry
158
Bu‘
(50)
Ph
/
Scheme 2
C02 H
Me
(531
OH
159
11111: Photolysis of Carbonyl Compounds studied
in
detail.
This
work
shows
the
consequences
of
restricted rotation on the Norrish Type I1 biradicals.e4 Two studies have
dealt
with
corresponding these
the
(43)
methylbenzophenone
photoenol
publications
laser-jet
where was
the
photochemistry
the
formation
observed.e6
In
the
the
second
of
was
successfully trapped by an electron transfer technique.='
The
(44) are photochemically reactive and on
quinone derivati'ves in
of
the
ketone
irradiation
photoenol
2-
of
of
/
benzene
t-butanol
undergo
conventional
Norrish Type I 1 hydrogen abstraction to afford good yields of the
cyclobutane
accompanied
by
(45).
derivatives the
rearrangement
These
compounds
products
(46)
and
were (47).
Subsequent experimentation shows that these are formed in good yield
from
secondary
irradiation
of
the
cyclobutane
derivatives (45).=? Irradiation of the ketone (48) affords the indanol (49) as the sole
product.
This
compound
is
produced
by
1.6-hydrogen
a process akin to a Norrish Type I 1 reaction by
transfer
the carbonyl oxygen from the proximate methyl group of the t butyl group
followed by
1,5-biradical. The
bond
formation within the
(50) behaves
ketone
somewhat
resultant
differently
( 5 2 ) as the major reaction produot
yielding the redox product
and a small amount of the indanol (51). The triplet lifetimes of the two ketones (48) and
(50) in toluene were found to be
1.7 ns and 25 ns respectively. The authorsPo suggest that the difference
in
difference
in the angle of
and
the
the
behaviour
di-t-butyl
formation
of
the
of
substituted
redox
the
twist
ketones
benzene
product
is
due
to
a
between the carbonyl group ring. The
method
( 5 2 ) is still unsure
but
of a
possible path could involve the route shown in Scheme 2. Some
benzophenone
quaternized behaviour
carboxylic
with has
benzophenone converted mice1 les . a o
to
been
amino
acids
alcohols
studied.='
carboxylic tertiary
acid
as
and
their
Amphiphilic and
alcohols
myristic by
(53) have
such
their
been
aggregation
derivatives acid
have
of
been
irradiation
in
Photochemistry
160
( 57)
(56)
R
(61)
(60) R = Me or Et
a;ratio 1:l
( 6 5 ) a ; R =Me, n 5 2 b ; R =Et, n = 2 c ; R =Me, n = 4
b; ratio 1:1.2
w
55YO
15%
Scheme 3
IIIII: Photolysis of Carbonyl Compounds
161
Q cb Me
' 0
0
(661 n = 4 or 5
Me
(671
(68) a ; n = 1 b;n=2
(70) (71)
he
( 7 2 ) a;R2=CN b;R2 =COzMe
(73) a;R' = H b;R' = Me
d;R= 0
f Si
e ; ~ =
*x' Y
R' (761
(97)R'=Me, R2=CN R' =Me, R2=CO~Me R' =H, ~ 2 CN =
(78) R1=H or Me
162
Photochemistry Oxetane Formation
3
The photoaddition of benzophenone to the vinyl sulphides ( 5 4 ) affords a mixture of the oxetanes ( 5 5 ) in yields ranging from 12 -
79%
dependent
on
the
alkene
used.as
Photoaddition of
aldehydes to 2,3-dihydrofurans has been studied. The addition affords oxetanes of the type shown by benzaldehyde derivative addition
affords ( 5 7 ) was
of
two
isomers.
also
aldehydes
studied.
afforded
(56) where addition of
Addition In
to
this
two
the
furan
instance
types
of
the
oxetane
illustrated by (58) and ( 5 9 ) . = = Intramolecular
cycloaddition
within
the
ketoalkenes
(60)
affords the oxetanes ( 6 1 ) as the principal products ( > 85%). These oxetanes can be ring-opened in methanol a
trace of
trifluoroacetic
acid) to afford
(acidified with the medium
ring
( 6 3 , 6%) was also obtained from the
ethers ( 6 2 ) . The product
irradiation of ( 6 0 , R = M e ) as a component of a mixture of minor products. The oxetane (64) was a minor product obtained from the irradiation of ( 6 0 , R=Et). The shorter chain keto-alkenes (65) are also photoreactive and afford the products shown in Scheme
3.
These
additions are
less
regioselective than the
previous examples.3a The intramolecular
photoaddition of the
keto-alkenes ( 6 6 ) to afford the oxetanes ( 6 7 ) has been used as a step in the synthesis of the tricyclo-octane tricyclononane ketones oxetanes
(68b).=*
( 6 9 a-d) ( 7 0 a-d)
Irradiation of
using
>
wavelengths
in good
yield. The
(68a) and the
the
endo-norbornenyl
300
nm
affords
thienyl ketone
the
(69e),
however, only affords the corresponding oxetanes (708) under sensitized
conditions.
irradiation
with
the
The
ketones
use
of
( 6 9 ) was
shorter also
wavelength
studied. Ketone
(69b) was shown to afford a complex mixture of products under such treatment while the ketone (69c) was converted into the oxetane (70c) and the aziridine derivative (71).==
Photochemical
addition of electron deficient
the pyridine
thione
(74). This reaction arises by spiro-thietane products.
In
( 7 5 ) which the
alkenes (72) to
(73a) affords the substituted
case of
the formation of an
pyridines unstable
fragments to produce
the isolated
the N-methylpyridine
thione
(73b)
111l1: Photolysis of Carbonyl Compounds
163
(81)
(83)
(82)
Photochemistry
164 addition
of
This
also
is
( 7 6 ) as
methylacrylonitrile yields formed
from
an
unstable
the product.
thietane
but
by
an
alternative fragmentation path resulting in the elimination of thioformaldehyde. The isolation of thietanes (77) was achieved by the irradiation of the thione ( 7 8 ) in the presence of the same
electron
Ramamurthyg7 deficient
deficient
report
alkenes
that
add
alkenes.s' both
to
Devanathan
electron
the
rich
and
(79) to
thione
and
electron
afford
the
(80) Scheme 4. The addition occurs from the lowest
oxetanes
triplet state of the enone and a biradical and an exciplex are presumed
to
be
involved
in
the
study of the photochemical
formation of
reaction of
products.07
A
(81) with
the thione
electron rich alkenes has reported that the formation of the (82)
adduct
and
the
(83) arise
oxetane
from
the
triplet
excited state. The formation of the products occurs from both S z
and S x
excitation.sg The photoaddition of the same enone
to electron deficient alkenes has also been investigated. The irradiation
in
this
system
affords
oxetanes
from
the
S n
singlet state.**
4 The
Miscellaneous Reactions
4.5-corane
(84)
decarbonylation
is
obtained
the
of
in
60%
yield
pentacsclic
on
photo-
(85).*O
ketone
Photochemical decomposition of the carbonate ( 8 6 ) , by the loss of carbon dioxide, affords a mixture oxirane. Triplet benzyl
styrene sensitized
radicals.4a
254 n m ) of phenyl
oxide,
the
bibenzyl
irradiation An
earlier
carbonate
carbene.
and
products
of
and
yields
products
study of
the
( 8 7 ) reported
carbon
containing
phenylacetaldehyde.
dioxide
solely
from
irradiation (at
that
were
benzaldehyde, produced.ee
A
reinvestigation of the irradiation of this compound (at 254 nm in
acetonitrile)
trans-stilbene
deoxgbenzoin and bibenzyl.
has
oxides
When
provided
evidence
(88) and
(89) are
that
the
formed
cis-
as
and
well
as
smaller amounts of diphenylacetaldehyde and methanol
is
used
as
the
solvent
the
same
products are produced accompanied by benzylmethyl ether. 1 . 2 diphenylethanol.
and
2.2-diphenylethanol.
These
authors*=
suggest that the oxiranes ( 8 8 ) and (89) are formed by ray of
I I I l l : Photolysis of Carbonyl Compounds
(91)
165
( 92)
CHflCOR
(9114%) a; R = H b; R =OAc
qH20Me
I
RCOOH
(96) R = Me,p-MeCgH4 benzyl or 1 naphthylmet hyl
-
( 97)
(99) n = 1 or 2
(98)
166
Photochemistry
the
1,3-diradical
( 9 0 ) produced
by
decarboxylation
of
the
carbonate. A study has examined
the influence of a g-nitro group on the acetate .*.
photochemical hydrolysis of phenyl
The enol ester
(91a) undergoes homolytic bond fission to afford the radical pair (92) as the key intermediate to the products formed. The authors."
propose
benzylic (93a)
radical
or
combines
Irradiation products product
that
of
a
which
1,2-hydrogen
either
with
the
enol
ester
the
migration
abstracts acyl
yields
hydrogen
radical
yielding
(91b) affords
a
affording
the
(94a).
analogous
(93b) and (94b) and in addition produces the cyclic (95). This is presumed to be formed by cyclization of
the radical (92a) with the 9-acetyl group followed by a series of
steps before
the
final product
is formed.."
Irradiation
(96) affords the acid ( 9 7 )
(340 n m ) of methanol solutions of and the ether (98).'= Irradiation
of
the
iodoketones
(99)
has
shown
that
the
products obtained are formed by competing radical and cationic A
processes . 4 7
previous
account
of
the
photochemical
solvolysis of the chloroketone (100) reported the formation of two photoproducts reinvestigation photoproduct
from
second product
(101) and the solvolysis product
of
this the
reaction
reaction
has
is
shown
the
(102).*.
that
alcohol
the
A
only
(101). The
(102) is formed by an acid catalysed thermal
process.
A
study
of
the
photoreduction
has
acetonitrile/triethylamine (103 a , b ) afford
the alcohols
the amides (103 c , d ) and
of
the
shown
oxoamides that
the
(103)
in
oxoamides
(104) in high yield. However,
(105) are also reactive and afford
the cyclized compounds (106
-
108) respectively. The failure
of the oxoamides (103 a,b) to undergo cyclization is presumed to be due to intramolecular hydrogen bonding."O which
this
reductive
cyclization
occurs
The ease with
with
amides
or
unsaturated ketones has been exploited in a new synthesis of hirsutene (109). Thus irradiation (254 n m ) of the ketone (110) in acetonitrile/triethylamine affords the alcohol (111, 20%) and
the
material
desired
is
cyclic
readily
compound
converted
to
(112,
58%).
hirsutene .=*
This
letter
The
ketone
IIIi1: Photolysis of Carbonyl Compounds
167
Rqy N‘R2
M Me e)(%
0
,
(103) a; R’ = allyl, $= H R3=Me b; R1 =CH$’=CH,R2=H,R3=Me c; R’ =R2=allyl,R3= H or Me d ;R’ = propargyl R2=R3 =Me
NH
0
1104) R =ally1 or propargyl
,
eN, Q
X$$J 0
0
0
A (109)
(107)
(1081
I4 (110)
(111)
A
A (112)
(113) Me
CHzOH
Me Me
Me Me
(114)
(115)
1J
Photochemistry
168
M . q c o M e
(1 18)
(117)
(116)
+ 0
R' &R2
R2 = Ph (120) R' = H R' =CN, R2=Me or H R' = C l , R 2 = P h R' = Me, R2 = p - M e C & ,
(119)
L & OH
Me3Sn
R'
(121) R = H or
Me
(122)
ph> R
(123) a; R =Me
b j R =Ph
M Ph>Aco2H t
trace
22Oh
11111: Photolysis of Carbonyl Compounds
169
(113) reacts photochemically with methanol in the presence of titanium
tetrachloride to yield
the stereoisomeric products
(114). In the absence of the metal chloride only the methanol adduct (115) is formed by a hydrogen abstraction path.== Wavelength
dependence
bicyclobutane
of
(116) has
the
been
photolytic studied
in
behaviour inert
of
solvents.
the
At
254 nm and 300 nm the irradiation affords the three products (117), (118). and (119) but the ratio of products is different at the different wavelengths. The authorsmm believe that the state. Irradiation at 300 nm in
reactions arise from the z-x* diisopropyl
ether
or
in
toluene
yields
only
the
methylene
cyclobutane (117).'= Takuwa
and
his
irradiation of presence
of
coworkersse
have
demonstrated
the aromatic carbonyl compounds
the
stannanes
(121)
affords
that
the
(120) in the
the
unsaturated
alcohols (122) as the principal products. An electron transfer mechanism the
is proposed. Electron transfer is also involved in
reaction
of
amines
with
alkenes
such
as
the
phenylethylenes (123). The electron transfer in this instance affords an alkenyl been
demonstrated
radical by
reaction
has
been
example,
the
alkene
a
anion the presence
variety
uncovered
in
(123a) with
of the
of which has
techniques.
A
photoreaction
N,N-diethylaniline
further of,
for
in
the
presence of carbon dioxide. This treatment affords the three carboxylated derivatives (124). (125). and
(126) by trapping
of the radical anion by carbon dioxide. Similar carboxylation
was demonstrated for (123b) and biphenylene. The influence of the amine on the yield of product was studied.='
170
Photochemistry 5
References
1.
K. H. Pfoertner. S p e c . P u b l . - R . SOC. C h e m . , 1986, 57
2.
3.
A . G . Griesbeck, EPA Nersl.. 1986. 28, 13. A. Gilbert, S p e c . P u b l . - R . S O C . C h e m . , 1986, 57
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J. M . Coxon and B. Halton, O r g e n i c P h o t o c h e m i s t r y , 2 n d
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L. V. Romashov, Yu. I. Kiryukhin. and Kh. S. Bagdasar'yan, Dokl. A k e d . Nauk S S S R , 1987, 295, 427 ( C h e m . A b s t r . , 1988,
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L. J . Johnston and J. C. Scaiano, J .
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B. N. Rao, M. S. Syamala,
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I I I I I : Photolysis of Carbonyl Compounds
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2 1 . H. G. Henning and C. Hentschel. 2. C h e m . .
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( C h e m . A b s t r . , 1 9 8 8 , 108, 1 3 0 8 0 1 ) . 22.
J . P . Pete, F. Henin, R. Mortezaei, J . Muzart, and 0. Piva, Pure A p p l . C h e m . . 1 9 8 6 , 5 8 , 1 2 5 7 .
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R. G. Weiss, J . A m . C h e m .
S O C . , 1987,
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6215. 24. G.
D. Reddy, B. Jayasree, and V . Ramamurthy, J . Org.
C h e m . , 1987, 5 2 , 3107.
25. R. Y. Wilson, K. Hannemann, K. Peters, and E.-M. Peters, J . Am. C h e m . S O C . , 1987. 109, 4741. 26.
R. M. Wilson, K. Hannerann, W. R. Heineman, and J . R. Kirchhoff, J . A m . C h e m . S O C . , 1 9 8 7 , 1 0 9 , 4 7 4 3 .
2 7 . P.
J . Wagner, B. P. Giri, R. Pabon. and S. B. Singh, J .
Am. C h e m . S O C . , 1987, 1 0 9 , 8104. 2 8 . A . Osuka,
H. Shimizu, H. Suzuki, and K. Maruyama, C h e m .
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H. J . Schaefer. L i e b i g s Ann. C h e m . ,
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30. A . Gogol and H. J. Schaefer, L i e b i g s Ann. C h e m . , 1 9 8 7 , 597. 31.
T. H. Morris, E. H. Smith, and R . Welsh. J . C h e m .
SOC.,
C h e m . C o m m u n . , 1987, 964.
32. H. Itokawa, H. Matsumoto, T. Oshima. and S. Mihashi, Y e k u g a k u Z a s s h i , 1987. 107, 767 ( C h e m . A b s t r . , 1988, 108, 186609). 33.
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34. R. Gleiter and B. Kissler, T e t r a h e d r o n L e t t . , 1 9 8 7 , 2 8 , 6151.
35. R. R. Sauers. A . A . Hagedorn, tert., S. D. Van Arnum, R. P. Gomez, and R. V . Moquin, J. Org. C h e m . , 1 9 8 7 , 5 2 , 5 5 0 1 . 3 6 . T. Nishio. J . C h e m . S O C . , P e r k i n T r a n s . I , 1 9 8 7 , 1 2 2 5 . 3 7 . S . Devanathan and V . Ramamurthy, J . O r g . C h e m . , 1988, 53, 741.
40.
P. Rao and V . Ramamurthy, J. O r g . C h e m . , 1 9 8 8 , 5 3 , 3 2 7 . V. Rasarurths, J. O r g . C h e m . . 1 9 8 8 , 53, 3 3 2 . L. Fitjer and U. Quabeck, Anpen. C h e m . Int. E d . E n g l . ,
41.
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38. V.
3 9 . V . P. Rao and
1987, 26,
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C. White and
S. Ma. J . Heterocycl. C h e m . . , 1 9 8 7 . 2 4 ,
1203 (Chem. A b s t r . .
1988,
108, 1 3 1 6 3 7 ) .
Photochemistry
172 4 2 . G.
W. Griffin, R. L. Smith, and A. Manmade, J . Or#. Chem..
1976, 4 1 , 338.
T. R i x , J. Org. Chem., 1 9 8 7 , 5 2 , 2 3 0 9 . P. Kuzmic, L. Pavlickova, and Y . Soucek, Collect. Czech.
4 3 . R . C. White and 44.
Chem. Commun., 1 9 8 6 . 5 1 . 1 2 9 3 ( C h e m . Abstr., 1 9 8 7 , 106, 195627). 4 5 . M. Alvaro, V. Baldovi.
H. Garcia, M . A. Yiranda, and J .
Primo, Tetrahedron Lett., 1 9 8 7 , 2 8 , 3 6 1 3 . 4 6 . M.
Inamura. K. Tokuda, N. Koga, and H. Iwamura, Chem.
Lett., 1 9 8 7 . 1 7 2 9 . 47
f
B. Sket and M . Zupan, Bull. Chem. SOC. Jpn.,
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50.
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5 4 . A. Takuna.
H. Tagana, H. Iwamoto, 0. Soga, and It.
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2 Enone Cycloadditions and Rearrangements: Photoreactions of Dienones and Quinones BY W. M. HORSPOOL Intramolecular.- The apide ( 1 ) is converted on irradiation in benzene/ethanol
into a complex mixture of products
The
of
first
two
these
established
were
as
(2)-(5).
the
primary
photoproducts. The cyclopropyl aldehydes arise from secondary photolysis
of
photoproduct
(2)
while
the
ester
(4)
is
a
secondary
of irradiation of the aldehydes (3). Oxidation
also arises during the secondary photolysis of ( 2 ) and affords the aromatised product ( 5 ) . % The intramolecular photocycloaddition of the vinyl ketenes (6) has
been
reported.
(2+2)-adducts
This
shown
in
yields the syn-adduct one
case
only.
encountered
also
1.*
in
migration
the
the
cycloaddition
( 8 ) is formed in
reactions
formation of
photocyclizes
yields of
Primarily
(7). The anti-adduct
Hydrogen
resulting
(9)
Ketene
system affords good Scheme
are
isomers of
affording
the
also (7).
tricyclic
compounds (10) and (11) Scheme 2. A
previous
report
gave
an
account
of
the
intramolecular
photocyclization of the enone (12) to afford t h e head-to-head adduct
(13).* The adduct
(13) obtained in this ray has been
used as a starting material for ester (14).* While the above
pentalenolactone G methyl reaction only yields a
head-to-head adduct this is not the case with the enone (15a) which
undergoes
photocyclization
1 , 5 - ~ y c l o a d d i t i o nproduct biradical product.
(17)
followed
by
yield
the
bonding
yield
observed the the
( 1 5 ~ )which
(18) is
the
not
(15b) and
biradical
to
formed in this instance and the cyclization affording five-membered ring is predominant. This is not so with enones
alternative
to
This is formed by way of the presumably
arising
The
(16).
yield products
(19) and
(20)
from both modes of cyclization. The 1.6-cyclization
Photochemistry
174
Q R
N
M
NMc
e
0
+?
45)
C0,Et
R'
d2
0 NMe
0
2
1
( 3 ) R = CHO, R = H R 2 = CHO
R'= ti,
e$
w
0
R2
R' 2
( 6 ) a : R'= Me. R = ti
( 7 1 a: 43%
b: R ' = R 2 = ti c : R ' = H . R 2 = Me
H
(yo+ ti
( 8 ) a:
-
b: 10% C:
R a t i o 1: 1 . 5 Scheme 1
R'
b: 58% c : t o t a l yield 39%
+
11112 Enone Cycloadditions and Rearrangements
175
e05&
0
+
(9)
Scheme 2
boyc= 0 \I\
0
‘c*
-C* (12 1
O
H
(141
(151 a: R’
= Me, R 2 = H
b: R’ = R 2 = H c: R’
=
H , R 2 = Me
R’
Photochemistry
176
&
q:
R2
R2
(19 1
(18)
R'
= = R =
(21)a: R b: R c:
=1 H;n= 2
H: n
Me: n = l
(221 a : ratio 50 b : ratio 50 c : ratio 1
1 (231
1 50
Scheme 3
H
(24)
(251
177
11112 Enone Cycloadditions and Rearrangements
&
b
OR
=
(26) R
0
CH2CH=CH,, CH,C H W e 2 . CH,CMc =CMcH (cis and t r a n s )
=
(27)
Ph
0
-
( 2 8 ) A r = Ph, 1 naphthyl, 2 - naphthyl or 9 phcnanthrenyl
-
0 (29)
& 0
0
(30)
( 3 11
y C 0 2 M c
(32)
R2
( 3 3 ) R ' = H, R 2 = CO,& R'
=
C02Mc. R,=
H
Photochemistry
178
H
Me
Me
.'e 0 x 0
R2 (37) n
R2
= 2 or 3; R'= R ~ H = 1
2
n = 3 o r L ; R = R = C02Me n = f,; R'= H , R 2 = OSiMe2CMe3
Me
(39)
(38)
Me
(LO) X
=
H , Br o r OMc
11112 Enone Cycloadditions and Rearrangements
179
path does not go to completion and instead the biradical ring-opens
affording the enones
(20).5 Matlin
(18)
aL.=
9t
have
examined the influence of the position of the attachment
of
the side chain as well as enone ring size o n the cyclization of the enones (21). Closure to the head-to-tail products (221, following the r u l e of f i v e . is the preferred route as shown in Scheme 3. The notable
exception to this is seen with
enone
is preferred affording (23) as the
(21c) where the 1.6-closure principal product.
A
70%
yield
of
the
adduct
(24)
is
obtained
on
brief
irradiation through Pyrex of a hexane solution of the enone (25).7
Intramolecular
( 2 6 ) has been
cyclization. of
A
reported.
the
enone
typical product
derivatives
formed from
this
reaction is shown in (27) and involves a head-to-head addition of the alkenyl side chain to the enone double bond.'
A study
of
carried
the
out.s
photoreactions The
benzyl
intramolecular
of
the
( 2 8 ) has
(28, Ar=Ph) was
derivative
cycloaddition.
(28) did undergo
enones The
1-naphthyl
cycloaddition to yield
been
unreactive
to
derivative
of
the unstable adduct
( 2 9 ) which thermally or photochemically reverted
to starting
material. Both of the other enones also undergo cycloaddition affording
the
adducts
adducts photochemically
(30)
(31)
and
revert
respectively.
to starting material
These
and
the
authors'
propose that this is brought about by the excitation
of
dihydronaphthalene
the
moiety
either
or
by
(32)
in
directly
intramolecular energy transfer from the carbonyl group. The
intramolecular
photoaddition
chlorobenzene using wavelengths ( 3 3 ) in a ratio of mixture
of
achieve
a
products total
>
of
the
enone
350 nm affords the adducts
1 . 5 : l and in a total yield of 87%. can be
synthesis
carried of
the
forward
This
successfully
to
laurenene.*O
A
diterpene
total synthesis of (A)-pentalenene ( 3 4 ) has been carried out using the intramolecular photocycloaddition of the enone ( 3 5 ) affording the tricyclic ketone ( 3 6 ) as a key step.** An efficient route to the synthesis of the cscloalkanones (37) involving the intramolecular photochemical cyclization of the enones
( 3 8 ) has
been
described.
This
yields
the
tricyclic
180
Photochemistry
0
LO& (46) a :
R
3
CO,R
Me,
Me
( 4 8 ) a: n = 1 b : n = 3 c : n = 2
H
( 4 9 ) a: n
=
1
b:n= 2
181
111f2 Enone Cycloadditions and Rearrangements
& (CH 1
0 H
( 5 0 ) a: n b:n
0
= 3 = 2
(511
or 2
(53)
0 (52) n
= 1
0
182
Photochemistry
intermediates (39) which o n ring opening affords the desired products.
A study of the photochemical reactions of the naphthalenones (40) has
sought
to
establish
the
mechanism
by
which
the
products are formed. Irradiation affords the two adducts (41) and
(42). The results obtained
from this present
study have
shown that both products are formed via the intermediacy of a complex ( 4 5 ) giving a biradical
( 4 4 ) which bonds in two ways
(Scheme 4 ) to yield (41). as a primary product, and (45). This latter
compound
migration
to
possibility
is not
yield
of
a
isolated
(42).ia
and
This
3,5-migration
a photo-1,3-
undergoes
evidence
which
had
rules been
out
the
postulated
originally by Brooke et al.=+ The scope of the reaction was investigated
with
regards
to
the
substitution o n
the enone
ring and also on the chain length of the alkenyl group.iB Irradiation (Pyrex filter ( 4 6 , R = M e ) affords
the
in benzene
study was also extended
solution) of
the ester
(47) in high yield. The
cycloadduct
to cyclization of
the &-isomer
of
( 4 6 , R = M e ) and a comparison of the quantum yields of product formation quantum
was
made.
yield
reaction
is
is
The
authors*=
measured
reversible.
induction was
considered
for The
and
the
suggest,
cyclizations,
possibility
studied
since of
a
low
that
the
asymmetric
in the cyclizations of
the esters ( 4 6 , b and c). The incorporation of nitrogen into the enone system does not radically affect
the cycloaddition reactions as seen in the
(2+2)-addition reactions encountered with the enamides In
this
study
intramolecular
the
influence
cyclization
of
of
the
chain
length
enones
(48)
evaluated. Thus with a four atom chain the
crossed
chain
(48b)
addition the
(48).
on has
the been
(48a) the product
compound
(49a). With
head-to-head
adduct
a
six
(50a)
atom is
is
side
formed
exclusively while with a five atom chain ( 4 8 c ) a mixture of (49b) and
(50b) is
are obtained
produced.*.
The
(2+2)-cycloadducts
(51)
in good yield on irradiation of the enone (52).
The reaction is dependent o n the nature of the substituent o n
C-3 and when this is H or C1 no cycloaddition reaction takes place o n irradiation.i7
11112 Enone Cycloadditions and Rearrangements
183
I
(58)
.
Pr' (59)
Me
CO,Me
(60)
(611
(63) R = H or Me
Photochemistry
184
OAc
H
( 6 6 ) a: R ' = H
( 6 7 ) R2= H or Bu
b: R 1 = M e 0
hM:
RR1
Me
Me Me
R2
Me 1
(68)
(691 R
= pentyl, R 2 = H
or vice versa
COMc
(721
185
11112 Enone Cycloadditions and Rearrangements Pirrung
and
Webstersg
photocyclization
of
have
the
reported on
enones
their
(53-55).
study of
This
arises from earlier work where intramolecular were
also
studied.
In
the present
work
the
investigation cycloadditions
enones
of
the
type
shown in (53, 54) were found to be unreactive and did not show evidence in flash photolysis experiments for the generation of a
transient
which
might
have
been
the
--isomer
of
the
enone. The carbon analogue (54) did show evidence for a short lived
intermediate
products
arising
and
also
from
cycloaddition products
is
was
photoreactive
yielding
deconjugation.
The
indicative
relaxation around
that
absence
of
the enone double bond is preferred to (2+2)-cycloaddition. The diene
( 5 5 ) was
reactive and
cycloadducts (56), ( 5 7 ) , and the
solvent
was
irradiation afforded
the
three
( 5 8 ) in a ratio of 22:31:29 when
cyclohexane.
Some
for
evidence
dependency was detected. Intramolecular
solvent
cyclization has been
reported following the irradiation of the enone (59). This o n irradiation
in pentane
under
an inert atmosphere yields the
(2+2)-cycloadduct (60).19
Intermolecular.photochemical the
Reviews
have
described
some
of
the
(2+2)-cycloaddition reactions of enones used in
synthesis of natural
p r o d u c t s . e o * e % Other
reports have
also focussed on such additions as key steps in the design of natural
products.
Thus
the
photoadducts
obtained
by
the
cycloaddition of the enone ( 6 1 ) to the alkene ( 6 2 ) have been used a s the starting materials for the synthesis of terpenoid intermediates.Pe The
cycloaddition
of
the
allenes
(63)
to
cyclopentenone
results in the formation of the two adducts ( 6 4 ) and (65) in a ratio of the
4:l. The addition reaction occurs primarily
less
substituted
double
bond
Cycloaddition of acetylene and but-1-yne can be
brought
about
using
of
the
across
allene.='
to the enones
left-circularly
polarised
(66)
light.
The resultant cyclobutane derivatives are readily converted to the optically active enones (67).er The photoaddition of hex1-yne
to
the
lactone
(68) affords the two isomeric
adducts
(69) resulting from both modes of addition. The isolation of
(70) from the reaction mixture suggests that the cycloaddition
186
Photoch ernistry
C02Et
4fo H
K
O
H
(761
OH
(771
(78)
OH
OH ( 7 9 ) R = H or Me
b... (81 1
OH
(801 R = H or Me
Me0
(82)
b., (831
11112 Enone Cycloadditions and Rearrangements
187
OR2 OMe
( 8 5 ) R2 = ( - ) - 3 - m e n t h y l
6
H
C0,R'
Ph 1
(86) R
= ( - 1 -3-menthyl
(87)
R' = ( +) -3 -ment hyl
H
Me
H
Me
(90) n
=
Ph
Ph
(88)
(89)
5,7,8 or 9
(91)
Me
188
Photochemistry
occurs by a from
the
two-step mechanism. This affords biradical
head-to-tail
,
undergoing compound
a hydrogen
addition
mode
abstraction
to
is
capable
afford
the
open
(70).es Pentyne, also, adds photochemically
steroidal
enone
( 7 2 ) to give
the
isomeric
study of
A
(74) in a ratio of 10:l.em
(71)
which
adducts
of
chain to the
( 7 3 ) and
the photoaddition of
alkenes to the dione ( 7 5 ) has been r e p o r t e d e e 7 Saligenin
(76)
is
in
basic
irradiated
photochemically
reactive
(MeOH/HeO).
media
The
(254 n m )
when
reaction affords
phenol/formaldehyde type resins in reasonable yield. The route to
the
enone
condensation
process
involves
( 7 7 ) by photochemically
the
formation of
the
induced expulsion of hydroxide
from the phenolic anion generated from (76). This enone then reacts with another
anion ultimately
to build
up oligomers.
Evidence for this process comes from the minor products formed during
the
produced enone
by
reaction. the
These
are
addition of
the
methanol
ether
( 7 8 ) which
(the solvent)
to
is the
(77). Furthermore the diphenslmethane derivatives (79)
and (80) are also formed by the condensation of two substrate molecules
either
with
or
without
the
addition
solvent.
of
Products of this type are considered as good evidence f o r the condensation reaction proposed.em
(2+2)-Photocycloaddition of ethoxyethene to the enone (81) at 254 nm
in methanol affords the adduct
(82). Addition of
the
a cyclobutane
same alkene to the enone ( 8 3 ) also proceeds
intermediate but this is unstable and ring opens to afford the cyclo-octane
derivative
(84)."
the optically active alkene
A
study of the
( 8 5 ) to the enone
four cyclobutane adducts two from
head-to-head
addition of (86) affords addition and
two f r o m head-to-tail addition. These cycloadditions lead to a double
induction
giving
diastereoselectivity.ao ethylene
to the enone
either
The
increased
intermolecular
( 8 7 ) yields
or
decreased
cycloaddition
the two adducts
of
( 8 8 ) and
(89). The photoadducts are apparently susceptible to secondary irradiation and the maximum yields of the adducts was obtained at 50% consumption of the starting material conditions
(88)
respectively. The steps
to
afford
and
(89)
isomer
were
obtained
(88) was
ultimately
taken o n
racemic
(87). Under these
in
71
through
sterpuric
and
23%
several acid
a
11112 Enone Cycloadditions and Rearrangements
189
Me OTMS
OTMS
a qMe OT MS
(92)
(93)
(941
0
I (95 1
(961
(97)
(98) a: R = Ac
OH
b: R
= Me
0
OAc (991
%
OMe CH,
(100)
190
Photoch emisrry
(102 1
(101)
(1031 R
= H
o r Me
OR
R'
A
0
(105 1
(104)
R4= H
R ' = R3= R'= H , R
R2
(1061
R' = M e , R2= OCH2CH,0, R3 = R4= H R' = R 2 = H, R3 = OCH2CH20 , R4 = Me R'-
Q
2
z
OH
R ' = R2= R4= H, R3= OH
191
11112 Enone Cycloadditions and Rearrangements sesquiterpenoid
A
fungal metabolite.aa
route to 1.3-bridged
cyclooctatetraenes has been developed using the photochemical addition of process
trans-1,2-dichloroethene to the enones (90). This
affords
transformed
the
to
the
(91)
adducts desired
which
products.mg
are
The
chemically
generality
cycloaddition of cyclohexenones ( e . g . 92) to the alkene has been
360 nm
studied. This photocycloaddition, brought light,
Thermolysis
pentane
in
of
these
the
affords
yields
the
adducts (95)
diketones
of
(93)
about
by
94).
(e.g.
which
are
useful compounds for the synthesis of the perhydroazulenes This
specific
product
example
( 9 5 ) was
daucene ( 9 6 ). m a
converted
Otherss4
photocycloaddition of the enone
have
into
also
the
.
natural
described
the
(92) to the cyclobutene ( 9 3 )
to afford the (2+2)-adduct ( 9 4 ) in 2 4 X yield. The adduct was transformed triplet
into
state
the
of
natural
conjugated
product enones
balanitol
can
be
(97).
The
photochemically
reduced by sodium borohydride.== High regioselectivity
is found in the photochemical addition
of allene to the enones (98). With enone (98a) cycloaddition affords
(99)
compound
was
while used
(98b)
for
yields
subsequent
the
adduct
reactions
(100).
This
in syntheses of
taxane-like molecules.ms Cycloaddition of the enol and
2-naphthol
or
the
form of acetylacetone (101) to 1corresponding
methyl
ethers
gives
products dependent on the naphthol used. Thus addition to the 2-naphthol system affords the diketone (102) presumably v i a a non-isolated cyclobutane adduct
(103). Such addition and ring
opening is well established as the de Mayo reaction. Addition to the 1-naphthol
system yields two products (104) and (105).
The first of these arises by addition of the enol to the 1,2bond
of the naphthalene skeleton in the same fashion as for
the formation of (102). The second arises by (2+2)-addition to the 3,4-bond of the naphthalene again followed by cyclobutane ring opening to yield the diketone
(105)
In this instance
aromatization does not occur. An earlier report dealt with the synthesis of hirsutene utilising the de Yayo cyclization. This approach involved the cycloaddition of the alkene (106) to the dione (107). The resultant cycloadduct (108) readily undergoes ring
opening
to
afford
the
new
diketone
(109). This
was
Photochemistry
I92
Cl Cl
do
OMe
d-l,
H
H
(110 )
CJ:xo
(111)
R'
(112) X = NMe or NEt, R' = Me X = NMe, R
1
(113)
= H,Bu,penti or Ph
X = NEt, R 1 = Ph
X = NPh, R ' = Me X
= 0, R 1 = Me, Bu,penti or Ph
(115 1
(115) R ' = H, Me, CO,Me, O,CCH=CH,, CO,CH=CH2. R 2 = H or Me. X = 0 or NH
(116) X
=
N H , NMt or
0
(117)
193
11112 Enone Cycloadditions and Rearrangements
0
o*Rf / OMe 11181
(119)
R
= deoxy-p- 0-ribofuranosyl
Me
OMe (12 0 1
(121 1
&1
0
PXo1
H *’
0’
(122 1
Ar
(123)
CN
&OMe
CO, Et
H
(121)
C0,Et
Ar
(125)
(126)
Photochemistry
194
0
YI .
.
# I
II
H
H
q
Me02C Ph
0
H
Ph C02Me
(129)
(128)
(127 1
Me
A
+
Ph
+
Me
(O-LM1
(0.02M1
52h
1
hV
Me02C Me
B,: I
Me02C H
B-1:
+
1
1 :I mixture
hA
bh h e
Scheme
5
R0 S
II
- P ( 0 E t l2
Me
.Cl
0 (1301
(131 1
195
11112 Enone Cycloadditions and Rearrangements subsequently
transformed
in
a
few
steps
to
the
desired
product.ao Full details of this have been published.as Photocycloaddition (110) affords
of
1.1-dichloroethene
the adduct (lll).40
to
the
The triplet
quinolone
excited
state
of the enones (112) are photoreactive and undergo addition to alkenes
to
afford
(113).41 Both
reasonable
elect,ron
photochemically
add
rich
to
yields
and
the
enone
the
azetidines
(114)
to
alkenes
afford
the
the C = N is unreactive
cyclobutane adducts (115). Normally (2+2)-cycloadditions but
of
electron deficient
the authors4=
believe
that
to
in this
case the C=N system is activated by the trifluoromethyl group. The
azetidine-2-ones
(116)
can
be
readily
prepared
by
irradiation of the enones (114) in the presence of ketene.*m A study of the photochemical addition of 2,3-dimethylbut-2-ene
to
the
furocoumarin
establish
an
alkenes to
order
of
derivatives
(117-119)
reactivity
for
the enone double bond.4*
the
The
has
sought
cycloaddition
(2t2) adduct
to of
(120)
exhibits temperature dependent fluorescence.4s
Photochemical
addition
affords
two
the
of
furan
to Pummerer’s ketone
(4+2)-cycloadducts
(122)
and
(121)
(123).
The
structures of both of these products has been established by
X-ray
crystallography.
Spectroscopic
studies
on
the
enone
(121) suggest that the triplet state is highly twisted and the authors4*
suggest that
formation
of
two
the addition to furan results in the
biradicals
products. No evidence for
which
lead
the involvement
to of
the a
observed
trans-ground
state enone was ~ b t a i n e d . ~ ’
Direrization.- A reinvesti6ation of the dimerization of
(124)
in the solid phase has identified (125) as the product.47 The irradiation of microcrystalline methyl cinnamate ( 1 2 6 ) affords a
complex mixture
of
products. However,
the
preparation
of
crystalline complexes of this ester with boron trifluoride or stannic chloride followed by of
the a-truxillate dimer
complexes
with
crystalline
the
same
complexes
irradiation affords high yields
(127). Ethyl reagents
affords
a
but
cinnamate also forms irradiation
mixture
of
of
dirners
these
in
lor
Ph orochemistry
196
%
0O
W
0
o0
0
O-r
O H H O (133)
(132 1
@ I )
0
0
OH (134)
OH (1351
Me
Yp
(1381 R'
t
CECH OCH2Ph
R
(136 1
(137) R
H , Me or Et
(139)
R'=
RL
= Me, Me0 o r C l
(140) H or Me H, MePh,SMc,OMe
Pri o r p - Cl C,H, R3 = Me, Pri, PhCH,
197
11112 Enone Cycloadditions and Rearrangements
yields.
Dimerization
solution
phase
in
of
methyl
the
presence
cinnamate
also
of
acids
Lewis
occurs
in
affording
truxinete and truxillate dimers as well as E-2 isomerization. Crossed additions of methyl cinnamate and alkenes can also be brought
about
presence
of
in
dichloromethane
Lewis
Photodimerization
acids
of
as
by
irradiation
illustrated
cyclopentenone
is
in
also
in
the 6:.
Soheme
influenced
by
Lewis acids. In the presence of such species the dimerization affords head-to-head
(128)
dimer
predominates while in their
absence the head-to-tail dimer ( 1 2 9 ) is the major product.ag The
enone
(1301,
the
pesticide
regioselective dimerization 313
nm. The
Irradiation methanol
product of
Coumaphos,
irradiation at
identified
was
the
on
furocourarin,
as
the
undergoes
wavelen6ths dimer
(132),
Imperatorin
affords a low yield of the (2+2)-direr
>
(131).m0
(133).
in This
product is accompanied by the dealkylated compound ( 1 3 4 ) and the rearrangement product ( 1 3 5 ) . This last compound is formed by a photo-Claisen rearrangement. The influence of solvent was studied and the dimer was obtained only in methanol. The other two products were formed in a variety of polar and non polar solvents. In any solvent
the dealkylated compound
(135)
was
the main
2
Rearrangement Beautions
a,@-Unsaturated
A
Systems.-
review
has
surveyed
the
photorearrangements of enones and dienones.ER A study of tbe photodeconjugation reaction of the ester ( 1 3 6 )
in the prmsence of a variety of optically active amines such as
(1R,2S)-l-phenyl-2-isopropylamino
the product about
70
alcohols
Irradiation
yields
of
(methanol. ethanol
derivatives path..*
propanol has shorn that
can be obtained with an enantiomeric excess of
(138)
Excitation
by of
a
free the
the cyclized products
were verified by X-ray
the
or
alkynylketones
propanol) affords radical
hydrogen
cyclohexenone (140)
(137)
the
in
furan
abstraction
derivatives
(139)
the structures of which
crystallography. The formation of the
amide products is reminiscent of a Norrish Type I 1 process.
198
Photochemistry
(142 1
(141)
OMc
H
CHMe 0 (144 1
(143)
eCNWC &CN
(1461
(145)
PCN &cN
(148)
(147)
CN
199
11112 Enone Cycloadditions and Rearrangements
CN
CN
(151 1
O
(153 1
C
N
(154)
(156)
y
CN CN
+':o -
0 (159)
(158)
(157)
0:
R
= H
b: R = 4',6'-diMeO
Rqp 0
0
(161 1
(160)
.wPh WPh OMe
\
0 (162)
R
0 (163 1
Photochemistry
200
R3 R4h
N
JH f
(164)
-
2
+
R3&R2
R4
3&R2
H
R'
R3
R4
R2
H
H
H
COOCH(CH,
H
R4
l2
H
Me
Me
COOCH( C H 3 12
Me
H
H
CO,E t
Me
Me
Me
CN
Me
H
H
CN
Me
Me
Me
CN
Scheme 6
R2
R3&
R4 (166 1
(165)
H
dR 0
(167)
0
(168) R
= 0 or
Me
201
IIll2 Enone Cycloadditions and Rearrangements The hydrogen abstraction, in this instance, presumably occurs at
the P-carbon of
ring
closes
excited enone
to
triplet
state
(141) into
involves
the enone
afford is
the
hydrogen
cyclization
the
(139). The resultant biradical observed
involved
spiroketone
abstraction
within
the
products.6s
in
(142). The
by
The
IC--L*
the conversion of
the
6-carbon
biradical.==
the
reaction again followed
by
Photocyclization
of
enamides such as (143) has led to a new synthetic approach to the
yohimbine
an4
photocyclization
reserpine
the enone
of
type
alkaloids . s 7
The
( 1 4 4 ) provides a route for the
synthesis of 3,10-dimethoxyprotoberberines.so Previous work by
Jeger
and his
coworkerssg
has studied
the
photoreactivity of 8,6-epoxy enones. More recent work by Ishii et
has
al.=O
examined
related nitriles
(145) 'brings about
via
formed
by
the
a
irradiation
by
ring
nitrile
intermediate.
epoxide
reactivity
the major
cyclopropenyl (145)
isomerization. The direct
(147) as
carbene
of
photochemical
(146). The direct
isomerization
cyclopropane to afford accompanied
the
(145) and
only
the
opening
of
the
product. This
is
(148) presumably
Triplet
sensitized
about
trans-cis
brings
(149) is
of
irradiation of
also
photoreactive
irradiation affords the products (150)
-
and
(156) either
by the intermediacy of an ylide ( 1 5 7 ) or a carbene (158).=* Irradiation of the chalcone (159) at wavelengths
>
365 nm in
methanol yields only the cyclized product (160). However, when irradiation of either nm
(159a) or (159b) is carried out at 405
in methanol with an electron acceptor the three products
(160),
that
(161), and
all
of
(162) are produced. The authorsma suggest
these
are
formed
from
the
common
intermediete
(163). Celas-Mialhe ~t el.== report the efficient cyclization of the enones (164) to afford the derivatives shown in Scheme 6 . The authorsmP
suggest that product
formation arises by a
conrotatory cyclization followed by a 1.4 suprafacial hydrogen transfer
within
the
ylide
(165). A
detailed
study
of
intramolecular photochemical cyclizations of the enones
the
(166-
168) has been reported.ma The results obtained indicate that the enones (166) and (167) produce radical intermediates which revert
to
measurement
can
of
starting material the
change
in
a
fact
alkene
established by
geometry
in
the
recovered
202
Photochemistry
-A hv
0-0
(170)
R'
+
@o
c (172 1
(173 1
+ +
R
(175)
R ' = H, vice versa
C02H
(176 1
Scheme 7 Me
Me
0
Me R
Me0 (177) R = OEt or NHEt R'
CHO
(138) R ' = R 2 = H
R'= H ,
R2= Me
R'= Me, R
2
= H
go (174 1
R*= CHO o r
Me
CHO
203
11112 Enone Cycloadditions and Rearrangements
H 11821
(180 1
vo II
PhC 0 (185)a:R
(183)
1
= H, R 2 = Ph
b: R1= Me, R 2 = Me o r Ph
Ph
Y
Ph
Ph
phYph
OCOPh
(187)
(186)
0 (188 1
m = n = l m = 2 . n =I
m : n
= 3
R = Me, Ph, p - McOC6H4, m
- MeO%H4, p - CF3C6H4. a-naphthyl
Or
p-ClC6Hb
Photochemistry
204
starting material. This is not the case for the enones (168) which apparently cyclize to product without any decay back to starting material. The
enone
epoxide
irradiation shown
in
in
(169) is photochemically
benzene
Scheme
solution
7. The
afforded
formation of
reactive the
six
products
and
on
products
involves
the
formation of two intermediates ( 1 7 0 ) and (171).
photochemical
These thermally intermediate
rearrange to the observed (172 -
(169) yielding furan
(176).04
products
175) while The
with the
intermediate
(171) affords
the
reaction paths
is to be contrasted with the simpler reaction
complexity
of
these
path described earlier by Mukai et a l . = = A
study
aromatic
the
of
sensitized
retinoids
photochemical
(177)
has
shown
( 4 + 2 ) - ~ y c l o d i m e r i s a t i o n s . ~ The ~
behaviour that
photo
they
of
the
undergo
reactions
of
the
pentaenals (178) has been reported.m7 Wagner and NahmeD have observed the photoaddition of a remote double bond
to the benzene ring of
affording ( 1 7 9 ) and
acetophenone derivatives
(180) from the irradiation of
(182)
In
another
publication
(181) and they
have
reported further on the process and have demonstrated that the from the reaction is a secondary photoproduct.
final product Thus
the
irradiation
(181)
of
has
been
shorn
spectroscopy to afford an initial photoproduct
by
n.m.r.
(183). This is
thermally labile a n d , i s converted into the triene (184) which undergoes
a
photochemical
cyclization
to
yield
the
stable
product (179):The enol esters
(185) show photochemical
be
in terms
rationalised
N.C-3
bond
in
the
undergoes typical
diene.
of
the
Thus
a methyl
molecule
is
now
conjugated. The photochemistry dominated (187)."O
by
1.3-acyl
behaviour which can
the degree of the
flat
tranq-&-isomerization
(186). However, with part
of
twisted
migrations
these to
around ester
the
(185)
to afford the diene
substituent of
twist enol
on C-3
and
is
the diene no
longer
compounds (185b) is
afford
the
diketones
A detailed report of the photochemical conversion of
the enamides
(188) into
the spiro
compounds
(189) has been
11112 Enone Cycloadditions and Rearrangements
205
0
C02Me
CO R'
c0,Me
(1901
(1911
(192) R'= Me 2
R
=
MeOor
vice versa
&
6
CO R2
COR'
1
= OH, R 2= OMe b: R' = R2 = OMe
(193 1 a: R
(194)a: R' = OH, R2= OMe or vice versa b: R'= R2= OMe
C0,Me 1
Me eM-
C02Me
Me (195)
(1961
4
H
(1971
(198)
0
Photochemistry
206
RS (199 1 a: R'= R2= R3= H
(2001
b: R'- R2= (CH212, R3= H c: R1= R2= H,
F?= (CH=CH),
Ph
(201 1
Ar
Ar
(2021
R
t
Ph
12031
Ph, p - MeC6H4 or p - McOGH,
Scheme 8
H
A
(2041
r
*
11112 Enone Cycloadditions and Rearrangements
H
R
0
PhtH,
Ph
207
Ph
R
( 209
(2101
1
0
0 R Php
s
O
Ph QoMe Me
Me
(211 1
(212)
d
0
Me
OR
Ph
(21 11
Me (215) R
(213)
Me
GR
Me
H
= CF,, Me. H
(216 1
0
Photochemistry
208 published.7i
This
supplements
material
published
in
note
form.7=
fi,&-Unsaturated dienone well
Systems.-
(190) affords
as
triplet
the
products
sensitized
methane product same is
true
The
direct
irradiation
the oxa-di-x-methane of
ring
opening
irradiation
does
(192).
not
of
product
the
(191) as
Interestingly
give
the
oxa-di-x-
(191) but only affords the trienes (192). The
for
the enones
(193) which
yield
the
trienes
(194) as the sole products of sensitized irradiation. Similar ring opening is also observed for the diene (195) which yields
A series of sensitized oxa-
(196) as the all di-x-methane
rearrangements
based
on
the
isomerization
of
(197) into (198) has been described as useful methods for the synthesis of
some naturally occurring compounds.7*
D e ~ t a ' ~have
described
the
synthesis of
Raju and
the adducts
(199).
These compounds are photochemically reactive and undergo the oxa-di-%-methane on
rearrangement
irradiation in
sensitizer. (203) are
to
(200).7m The - enones
derivatives
benzene
Under formed
these by
afford
using
acetone
conditions
the
the
polyquinane
(201) undergo rearrangement the
migration
of
or
acetophenone as
products
(202) and
or
a n aryl
a
phenyl
group. The variation in migratory aptitude of the groups was studied
and
shown that 2-chlorophenyl, _p-cyanophenyl and
2-
tolylphenyl were superior to the others. O n the basis of this it is proposed that the intermediate (204). related to an oxadi-%-methane ionic
process,
character.
photoreactive The direct the
and
and
(205) afford mixture the
formed on
undergo
sensitized of
enone
the
(202)
&-stilbene reaction
products.
products is
excitation has
products
different
decarbonylation yields
The
paths
(206) which
on
in
considerable are
(203)
type
Direct
shown
primary
and
also
cyclization.7g the
of
furanones
irradiation affords Scheme
photochemical secondary
8
whereby
event.
This
irrsdiation
is
transformed into products (207) and (208). Direct irradiation of
the
ketone
benzyl
derivative
(205. R=CHePh)
only
affords
the
(207, R=CHoPh). Sensitization, affording the triplet
state. brings about C-C bond fission to yield the radical pair (209). This either yields the dimer lactone (211).77
(210) or the rearranged
209
111/2 Enone Cycfoadditions and Rearrangements
CHCOMe 2: *
0 (220 1
(219)
R'
=
H , R * = H or C O , E ~
R ' t Me, R 2 = C0,Et
P
0
MeR
\
Me
(221 1 a: 51%
(222) a: 10V0
b: 69%
b: 10%
+ 0
HO
d,
Me (224)
0:
R
b: R
= H = Me 0
Me (2271
-3
1223) (36%)
0
I'
Me
1225)
(2261
Photochemistry
210
v
v
0
0
(230 1
( 2 2 9 ) R = H or Me
I
Me (232)
(231 1
NMe
Meo 1
Me 0
(231)
(233)
Me0 L
O
Me OXMe 0
( 2 3 5 ) R'
=
Ph, R 2 = Me or Ph
( 2 3 6 ) a: R b: R
=
I
=
aryl
11112 Enone Cycloadditions and Rearrangements The
cyclohexenone
(212)
is
21 1
photochemically
reactive
in
methanol and affords the bicyclic derivative ( 2 1 3 ) by a 1.2phenyl
migration
in
a
di-=-methane
rearrangement.
is
This
accompanied by and the cyclohexenone (214) presumably formed by
a
reduction-elimination
benzene
afforded
only
pathway.
bicyclic
Change
compound
enones
( 2 1 5 ) undergo photo-rearrangement
(216)
and
(217).
The
independent
in
obtained
benzene,
in
that
reaction
the
same
of
or
to
three
to the two products
appears
to
rearrangement
t-butanol,
solvent
(213).70 The be
solvent
products
acetonitrile. The
are first
compound ( 2 1 5 . R=CF*) does behave differently in t-butanol and acetonitrile in that the rearrangement
is accompanied by the
cycloalkanone (218).7) The triplet excited photoconversion of (220).0°
state is proposed the
epoxyenone
to be involved in the
(219) into
the
indanones
The lactones (221). (2221, and (223) are obtained o n
irradiation of the acids (224) and
(225) respectively in the
presence of 1-cyanonaphthalene. Other examples of the process were also reported. The authorsos of
the
lactones
arises
by
an
suggest that the formation
electron
transfer
mechanism
involving cyclization within the radical cation (224).
3
Photoreactions of Thymines, etc.
Photoaddition of alkenes to the azathymine (227) affords the adducts (228) the structures of which were determined by x-ray crystallography.eP azauracil
Acetone-sensitized
derivative
(229) yields
the
irradiation cyclobutane
of
the
(230)..*
Irradiation of the uracil (231) in isotropic solvents is known to yield all four (2+2)-dimers in low yield especially at low concentrations. A study has shown that dimerization in smectic media
affords
a
high
yield
(94%)
of
the
trans-anti
dimer
(232). In frozen solutions the specificity is reversed and the
&-u dimer
(233) is formed. The influence of a variety of
media on this process was studied in detail . O * treatment
of
the
photochemical
addition
psoralens such as (234) has been published.gm
of
A theoretical alkenes
to
Photochemistry
212
BU'
h,
ON m B u t
R
R'
(237 1
(238)
R = Me o r CH,Ph
0 NKNR'
A&
R2
R
( 2 3 9 ) R ' = Me, R 2 = Ph
= R' = R' = R'
=
(240) X
Me, R2= p - MeC6H,
I CHOCH2Me I Me
P r , R2= Ph Ph, R2= Me
(241)
(242)
a: R' b: R'
= =
H,
R 2 = Ph or Me, R3= H
Me, R Z = Ph,
R3= H
c: R ' = R 3 = M e . R 2 = Ph
11112 Enone Cycloadditions and Rearrangements
213
(244)
(243)
(245) R=Mc, E t , CH,CH=CH, CH2CH,0Ac or CH,CH,CH,Cl
0
0
Me0
M e 0 &O2Me
C02Me
Me
(246)
OH
OH
t+
C02Mc
R
R
C02Me
(218)
(2191 R
*o
t
CH,CH,CH,Cl
I
A
H
(2501
1251 1
214
Photochemistry
The photoreactions of the pyrimidinethiones (235) with alkenes has
been
studied..=
affording
Arylation
of
the
(236b) can be brought about by
presence
of
the
appropriate
iodouridine
(236a)
irradiation
in the
aromatic
compound
and
triethylamine.m7 The pyridones (237) afford the valence isomers (238) in good yield on irradiation.mm A and
photochemical
2( 1-H)-pyrimidones
has
review dealing with the synthesis
of
reactivity been
N-substi tuted
published.Og
An
example
of
hydrogen abstraction by a n imine nitrogen has been reported. This follows from a study of .the photochemical
behaviour of
the pyrimidones
(239) in the presence of hydrogen donors such
as
sulphides.
ethers
and
The
products
from
this
adducts ( 2 4 0 ) which are formed in variable yields.-"
are
the
A study
of the photodecomposition of 5,5-diethylthiobarbituric acid in aqueous and non-aqueous media has been reported.-% Irradiation of
the pyrimidines
( 2 4 1 a , b ) using
triphenylene-
sensitization in tetrahydrofuran results in their conversion to the spirotriketones (242). The path by which involves fission of bond which
this occurs
in (241) affording a biradical
'a'
cyclizes to the observed products
(242). The evidence
for a biradical intermediate is supported by the formation of (243) from the irradiation of. pyrimidine ( 2 4 1 ~ ) .This product arises by hydrogen abstraction within the biradical formed by the fission of The
source
peroxide
of
of
'a' followed by a free radical hydroxylation. the
hydroxyl
radical
tetrahydrofuran
is
produced
thought in
the
to
be
the
reaction
,. mixture =
4
Photochemistry of Dienones
Cross-conjugated Dienones.- The photochemical rearrangement of a series of cyclohexadienones (244
-
Schultz
and
reactions
typical
of
bicyclic
his such
species,
coworkers. compounds
The and
247) has been studied by
involve
encountered
rearrangement
are
to
a
In the first example, the irradiation of
(244). the bicyclic species could not be isolated or detected since rapid ring opening was presumed to take place affording
11112 Enone Cycloadditions and Rearrangements
215
COzMc
c0
o
~
O
d
(252 1
5
(253 1 a: R
=
0-0
b: R = H
R H
J
@
0
Me0
0: (254)
= H X = Me
( 2 5 5 ) a: X b:
Me0 0
0
(256)
(25 7 1
(258)
0-
0
Me0 OMt
Me
@OMe
‘&Ph
Me Me
CCl,
1259)
Ph
Me
Mc
(260 1
(261)
Photochemistry
216
0-
0
Q
R
Ph
Q+
OMe
(263)
(262 1
(2641 R
R
OMe
=
Me, Et, P r i or But
gN
0 Me
. 0 $
OMe
( 265 1
(2671
(2661
(263 1 f?'
Ro Ac 0
(270)
Me
Me
R'
=
H, R 2 = OMe
L,
Me, R 2 = H
R7 R'
OAc
(271)
217
11112 Enone Cycloadddions and Rearrangements the isomeric phenols (248) and (249). Dienones (245) did yield the
bicyclic
compounds
surprisingly and
even
(250) and
(251) on
these compounds were
resistant
after
prolonged
irradiation only
irradiation trace amounts
phenols could be detected. The study w a s extended the irradiation of
the outcome of
and
to ring opening of
to examine
the enantiomerically pure
species (246) and (247). The data obtained shows that there is a clear pathway
to
its
ground
for reversion of excited state dienane state and
to
the
(246)
(247). This pathway
isomer
could involve the fission of. a 4,5-bond of the dienone..'
A
study
of
the
cyclohexedienones
photochemical
of
behaviour
(252) in non-protonatinq
solvents
the
Ouch
as
toluene or dioxan has been carried out. The Type A reaction path is not followed by these compounds. Instead the compounds follow a deprotonation
path
to afford
the azulenoqe olefins
(253). The mechanism for the deprotonation step is thsught to involve
an
intramolecular
(254)
zwitterion
hydroazulenone products
intramolecular
are
in
the
with
by
the
is proposed anhydrous
abstraction ring
example
produced.
attack
zwitterion and i t present
In
skeleton.
(255)
hydrogen
concomitant
within
expansion
(252b) two
These
carbomethoxy
the the
additional
also
are
to
formed
group
on
by the
that the small traces of water
solvents
could
be
responsible.
Evidence for this comes from an experiment with added methanol where the ortho ester (256) is formed.-* Further work by Schuster and his coworkers has shown that the dienone
(257) yields, as well
reported
in earlier
formation
of
(259).9m
The
compound
this
as
publications, species
the many the
arises
cyclohexadienone
(260)
new
from
products enone the
sffords
already
(258).
The
intermediate the
bicyclic
(261) on irradiation in methanol. This is formed by
the trapping of a zwitterion by methanol. Seaondary photolysie affords the cyclohexenone (262) by ring opening of the adduct (261).-The dienones (263) are photochemically reactive on irradiation in
methanol
involve
a
solution. zwitterionic
The
reaction
intermediate
opening is trapped by solvent the
acetals
(265).97
A
is
again
presumed
(264) which
on
to ring
to afford reasonable yields of preliminary
study
of
the
Photochemistry
218
hV
R J'R f4
glacial CH3COOH
R3
R2
U (272) a: R'
Me, R2 =
t
0
R3 = R4 = H
a: 79%
3
b: R ' = R 2 = Me, R = R 4 = H 1
c: R
= R2 =
d: R ' = R2 =
b: 89 '10
R 3 = R4= Me
c : 85 O h
R3: R4=
d: 8 2 %
H
Scheme 9
pf
0
Q Ph
OMe
0
Me
(275)
(275)
(273)
0
0
ButQBut Me0 But li
( 2 7 6 ) R'
=
Me, R 2 = Ph
or vice versa
(277)
11112 Enone Cycloadditions and Rearrangements
219
b-f (2781
(279)
0
‘0
Me0 OMe OMe c (280) R
=
H o r Me
0-
0
R
(2811
‘OMc (282 1
Me0 e:Q R Me0 OMc
(2831
0
220
Photochemistry
intramolecular
trapping
photochemical
of
zwitterions
rearrangement
of
the
generated
by
cyclohexadienones
the (266)
afforded the adducts (267) and (268).-. A more detailed study of this process has sought to establish
the scope of the process. Thus Schultz and his coworkers have reported affords
that the
irradiation
adduct
of
the
(270). This
cyclohexadienone
process
can be
(269)
quantitative
using extended photolysis times but if the reaction is stopped after 14 h a 1:l mixture of (270) and (271) is obtained. Other examples of the process are reported.)-
The irradiation of a
series
in
of
quinone a
provided
monoacetals
flexible
high
(272)
yield
acetic
route
to
acid
has
substituted
cyclopentenones. Such a rearrangement path is typical of the processes cross
encountered
conjugated
in
the photochemical
cyclohexadienones.
Some
rearrangement examples
of
of
the
utility of this system are shown in Scheme 9 . l o 0 Earlier
work
difference
by
Matsuura
in
the
al.
et
reported
photochemical
there was
reactions were
of
a
santonin
dependent
on whether
liquid or
solid phase.'oa
More recent work has demonstrated
that
dienones
and
the
the
that
behaviour
(273)
(274)
carried out
do
not
in
exhibit
the this
difference in behaviour. Irradiation of these compounds yields the
same products
(275) and
(276) respectively
whether
the
reactions a r e in solution or in the crystal. The authorssoR suggest
that
this
similarity
in behaviour
is due
to
loose
crystal lattice structures. The solid state irradiation of the dienone (277) results in the formation of the normal products for
such
systems,
namely
the
corresponding
photoketone.
photophenol, and lumiketone. The ratio of these three products was
sensitive
dependence
was
irradiated
in
to
temperature.
detected. the
In
solution
Interestingly
solid
with
when
wavelengths
no
temperature
the
dienone
>
400
is
nr
a
quantitative yield of the lumiketone is obtained.som The cyclohexadienone
(278) is photoaheaically reactive and on
irradiation both Z-E-isomerism and
(2+2)-cycloaddition
Interestingly
no
path was reported.
evidence
of the aryl substituted double
affording for
the
(279) usual
takes
place.*o'
photorearranserent
11112 Enone Cycloadditions and Rearrangements
(287 1
221
(289)
(288)
Ph
UR
(291 1 a: R = Ph b: R
(290)
= OEt
0 Ph EL02C*
\ /
CO,E t
COPh
COPh
( 293)
(292)
phw 0
PhCO
PhCO
Ph
(294)
COPh
(295)
0
COPh
(296 1
Photochemistry
222 Both the dienones (280) are photochemically be
converted
into
the
enones
reactive and can
(281).
These
are
also
photoreactive and subsequent irradiation. or over irradiation of
the initial
formation
of
solution yields the norbornenones
the
enones
(281) is
zwitterionic
intermediate
rearrangement
of
the
thought
(283)
cross
(282). T h e the
v to arise &
analogously
conjugated
with
the
cyclohexadienones
reported above. The norbornenones (282) are formed by a 1 , 3 migration within the enone (281).Lo6
Linearly
Conjugated
complexes
of
Dienones.-
Irradiation
of
the optically active diynediol
studied. Under
dienones
(284) has
these conditions the complex of
as
been
the trienone
(285) affords the optically active bicyclic ketone (286) in 28 % yield. The complex of the dienone (287) and the
optically
irradiation
of
active
dimer
uncomplexed
(288)
dienone
55%
in
(284) gives yield
while
(287) yields the racemic
dimer (288) in low y i e l d . L o m
5
The
adduct
1.2-, 1.3-, and 1.4-Diketones (289) is
diphenylpropene
and
benzophenone and carried (290)
out
from The
the
irradiation
adduct
is
of
1,l-
by
accompanied
1,l-diphenylacetone when the irradiation is
in the
is reported
methanol
obtained benzil.
presence to be
of
formed
oxygen.L07
The phenanthrene
on irradiation of
benzil
in
. * O m
Phototautomerism
of
the
1.3-dicarbonyl
compounds
(291) and
(292) has been studied.*OVarious
reports
on
the
photochemical
behaviour
of
the
tetraketone (293) have been reported over the years.lxo In a reinvestigation irradiation
Rubin
in methanol
and
SanderLix
solution affords
have
shown
(294) as
that
t h e . only
product. Indeed low temperature irradiation and irradiation in hydrocarbon glasses failed to yield anything other than (294). However, irradiation of (293) as a solid at 10K brings about a 1,5-phenyl migration yielding the ketene (295) identified by
223
11112 Enone Cycloadditions and Rearrangements
COPh
Ph ( 2 9 7 1 a: R b: R C:
R
d: R
=
%OPh
( 2 9 8 1 a: 64 -82.10
CH,OH
- 68%
= CH2CH3
b: 62
= =
CH2Ph
c : 63 o/'
C,H,
d: 18
- 23%
+
( 2 9 9 1 a:
-
b : 13
- I8V0
c : 19O/O
d:
-
Scheme 10
R
COPh
%p 0
%ph
(300)
( 3 0 11
(3021
Photochemistry
224
(3031
(304)
R4
0 ( 3 0 5 ) a: R’
=
Me. R2 = Ph, R 3 = R4 = H
(3061
b: R ’ = R 3 = R 4 = Me, R 2 = Ph c: R ’ = Me, R
2
=
Ph, R3= R 4 = CMe3
0
php@;3
Mi R4 ( 307 1
(308)
Me
0 Me
(309 1
0 (310)
IIii2 Enone Cycloadditions and Rearrangements
225
4
Me 0 Me
(3111 X
CN
= 0 or
NH
(312)
(3131 R’
= R2 =
H o r Me
(3141
Me0
(316 1 n
= 1 or 2
(317 1
&Na+
Me0
0 (3181
(319 1
226
Photochemistry
its i.r. spectrum. This ketene is the precursor to the final product (294). The conversion of the tetraketone to the ketene was
shown to be
incomplete
and
the authorsliX
this is due to the conversion of the conformer
suggest
thet
( 2 9 3 ) into the
ketene (295) while conformer (296) is unreactive. A detailed
study of the photochemical
substituted
dibenzbarrelenes
(297)
transformations of the has
been
carried
out.
Triplet excited states are involved in the transformation of the derivatives (297) into the products ( 2 9 8 ) and (299) shown in
Scheme
opening
of
Additional
10. The the
second
product
non-isolated
products
were
(299) arises
isomeric
from
semibullvalene
ring (300).
also reported. A discussion of
the
observed regioselectivity was reported.lLP The cage compound (301) is formed efficiently on irradiation of
the adduct
(302).**=
Irradiation of
affords the cage compound (304) by a The Diels-Alder
adducts
Irradiation of
(305) are
the ene dione
(303)
(6+2)-~ycloaddition.~~~
photochemically
reactive.
(305) affords either the cage compounds (306)
by a (2t2)-cycloaddition reaction. a process favoured by the adducts (305 a , b ) , or the oxetanes (307). The structures (306, 307)
were
verified
by
X-ray
diffraction
studies.*"
The
quinone adduct (308) also undergoes photochemical cyclization to afford the cage diketone (309). This material was subjected to
flash
vacuum
pyrolysis
to
yield
the
diketone
(310)
important in the synthesis of perhydroindecenes.*=. Olefinic
dienophiles such as meleic
add
4.6-dimethyl-2-pyrone
to
adducts.
These
on
photo-decarboxylation, dienophile
to
to
anhydride and maleimide afford
irradiation a
afford
diene the
which
mono
Diels-Alder
afford, can
products
be
a
by
trapped
(311).aL7
by
a
Acetone-
sensitized photoaddition of the oxazolones (312) to maleic and dimethyl maleic anhydride yields the adducts (313).*=. The
photoreactivity
investigated. Norrish
Type
of
Irradiation
I1
compounds (315)
related
the
succinimides
brings process
about
to
(314)
has
cyclization
afford
the
been by
Q
tricyclic
11112 Enone Cycloadditions and Rearrangements
@
227
m
NH
o
N
M
e
0
0 (323)
(32 5 )
(y$
Ph
0
1327 1
(3261
Me
I
Me
I
OYNYO
Me
I
63 \
(328 1
Ph (329)
.'
Ph Me Me
(330)
Photochemistry
228
S
ph*
Ph
(3311
(332)
(333)
0 (3351
(336)
Ph
m-l($:e H' \
S ( 3 3 41
n (337 1
(338)
0 (339 1
0
11112 Enone Cycloadditions and Rearrangements
229
Interest in the photochemistry of the phthalimide systems has continued.
The
phthalimide
derivatives
(316)
are
photochemically reactive and o n irradiation in acetone yields the cyclized products
(317). The
abstraction to yield
reaction involves hydrogen
the biradical
(318) which subsequently
A recent study has
bonds to afford the observed products.*'" examined
the behaviour
of
the anion
reduce electron transfer processes.
( 3 1 9 ) in a n attempt In t-butanol
affords the solvent addition product product
presumably
by
a
free
to
irradiation
(320) as the principal
radical
path.
Minor
products
(321) and ( 3 2 2 ) are also formed but are probably artefacts of the work-up procedure.
Irradiation of
(319) in methanol with
added cyclohexene follows a different reaction path. In this system the reaction with methanol is minor while the dominant reaction is addition of the alkene to afford the adduct (323) in
20
X
yield.les
photochemically
The
benzene
Dewar
unstable
and
derivative
( 3 2 4 ) is
irradiation
affords
tetrarnethylcyclobutadiene.*==
In an earlier report Mazzocchi and his coworkers reported that the
photo-reaction
phenylcyclopropane
of
(325)
N-methylnaphthalimide
involved
the
of
production
a
with
radical
cation/radical anion pair. The product from the reaction was the cyclic ether
( 3 2 6 ) . L p m A study of the mechanism of this
reaction using suitably deuteriated compounds has demonstrated that
the reaction is not
biradical studied.
In
the
naphthalimide Thus,
concerted
and
takes place
via
the
( 3 2 7 ) . * = * Other systems related to these have been
with
present
(328) with
paper
the
alkenes
1-methylstyrene
photoreactivity
in methanol
cycloaddition
was
occurs
of
the
examined. to
the
naphthalene moiety to afford the adducts (329) and (330). The mechanism
proposed
for
the
addition
involves
an
electron
transfer process whereby the radical cation of the styrene is trapped by radical
methanol
anion
as
(332)
the radical ultimately
(331). This adds to the to
afford
the
observed
products. Several examples of the reaction were described.*'' The
dihydro
dithiosuccinimides
reactive and yield
(333)
the cyclized adducts
are
photochemically
(334) by a Norrish
Type I 1 process. A variety of ring sizes can be synthesized by this
approach.*=.
The
irradiation
of
the
thiophthalimide
Photochemistry
230
&+q
Q& \
0
-0 (311 1
(3421
(344)
Scheme 11
o+But But (348)
(345)
R (32910: R
=
H
b: R - R s ( C H = C H ) ,
(350 1
11112 Enone Cycloadditions and Rearrangements
23 1
W0JH
OH
0
R2
R3 (351 1 a: R'
= R 2 = R3 = I
b: R ' = R 3 = H ,
(352 1 a: 17%
R2= Me
b: 34'/0
c : R ' = R 2 = Me. R 3 = H
C:
36%
d: R' = R 2 = H, R 3 = a l l y l
d:
90%
c: R' = H, R 2 = Me, R 3 = a l l y l
t:
83%
f: R'
f:
80%
g:
= R 2 = Me, R 3 = a l l y l R' = R2 = H , R3 = p r o p y l
9:
92.10
0
0
cl@cl CI
Cl
Br 'QBr
0
Br
0 (3531
(354)
(35s 1
go I I
Br
Br
0
0 (356)
(357) OH
0 (358)
Photochemistry
23 2 derivative adducts
(335) in the presence of thietane affords the two
(336) and
subjected presence
to of
the regio
to be
This
isomers
formed by
thia-anhydride
>
(wavelengths
c&-but-2-ene.
identified as presumed
The
(337). s p 7
irradiation
320
afforded
(339) and
the addition of
(338) was
nm) two
in
the
products
(340). These
are
the alkene to the
anhydride in two modes affording the intermediates (341) and (342). Collapse of publication
these
cites
yields
results
the observed
obtained
from
products.
the
The
addition
of
several alkenes . * * I Irradiation of the dione (343) affords the two products ( 3 4 4 , 50%)
(345. 15%).
and
follow
the
The formation of these is presumed
path
monodecarbonylation
outlined affords
in
the
to
Scheme
11
where
diene
(346)
which
keto
undergoes a n intramolecular Diels-Alder addition affording the (344). A second decarbonyletion of (346) yields
minor product the
tetraene
(347)
which
photocyclizes
by
(4t4)-
a
cycloaddition yielding the polycyclic compound ( 3 4 5 ) . s u s
6
Quinones
A review has highlighted the kinetic studies of electron and hydrogen transfer processes in quinone photochemical
reactions
of
the
The
quinones
(348 -
350)
with
amines has been studied using time resolved techniques. This approach has allowed the assignment of which triplet state is involved
in
such
systems.*ss
The
laser
irradiation
of
the
quinones, 3,5- and 3,6-di-t-butylbenzo-1,2-quinone, has shown that the triplet state is produced. These states are rapidly quenched
by
the
semiquinones
The
photochemically Pyrex
pyrocatechols
p-quinone
to
yield (351)
derivatives
the are
reactive and on irradiation in benzene using
filtered
methylenedioxy
corresponding
light
they
are
converted
into
the
derivatives (352). The route preferred by the
authorssmm involves a Norrish Type I 1 process affordinE the biradical
( 3 5 3 ) which
observed products.
subsequently
cyclizes
to
yield
the
11112 Enone Cycloadditions and Rearrangements
233
:R+O
(360)
( 3 6 11
aR2 0
R'
R3
0
(362)
(363 1
f y 4 R 4
f y 4 4 R 4 R5
R5
0 (364 1
OAc
R 1 = OMc or H R2=
H, R3= Br or c[
R 3 = H , R2= Br or C[ R 4 = h, R5=
R6co
R 5 = H, R4= R'CO
WNH' 0 (366)
(365 1
Photochemistry
234
Q
0 (368)
@co2H \ 0
(369)
R2 R@ '
0
R'
t
R2= H 2
R ' = Me, R = H R ' = R 2 = Me
RR21*
R ' = OMe, R 2 = H
0 (371 1
R'-R2
=
C6H4
11112 Enone Cycloadditions and Rearrangements
OPh 0
(375)
235
0
OPh
(376)
Photochemistry
236 A
detailed
study
benzoquinone
of
(354)
the
photochemical
with
arenes
has
behaviour been
of
the
reported.%**
Photoreaction of the quinone ( 3 5 5 ) with morpholine affords the amine substituted occur
with
quinone
several
(356). This reaction was found to
amines . * I s
Sunlight
irradiation
of
an
ethereal solution of the diquinone (357) is reported to afford the light stable intramolecular cyclized product (358).amm at
Tsuji
a1.a*7
have
previously
reported
the photochemical
behaviour of the quinones (359a) and (360a). In an extension of the work they have examined
the behaviour of the quinone
derivatives (359b and c ) and (360b and c ) . These derivatives behave in the same manner and afford
the products
(361) and
(362) on irradiation in THF-methanol.*sm The
halo
afford
quinones
the acyl
(363) undergo
(364) and
photochemical
the quinol
acylation
derivatives
to
(365).*=*
The sunlight irradiation of acetic anhydride solutions of the quinone
(366)
Irradiation
affords
of
(366) in
the
triquinone
acetone
product
also affords
(367).
(367) but
in
addition the diquinone (368) is formed by a free radical path initiated by the abstraction of hydrogen from the amino group by excited state acetone.lao The quinone (369) photochemically adds to a variety of alkenes by a (2+2)-addition to afford the adducts (370).1** A kinetic study of the photohydroxylation of the quinone (371)
in potassium hydroxide and perchloric acid solution. hes been reported.'*=
The
phototautomerism
.of the quinone
(372) has
been studied and the effect of pH and acidity evaluated.**g The
quinones
( 3 7 3 ) are
photochemically
reactive
and
are
converted into the quadricyclane derivatives (374) by use of light of wavelength
>
( > 63
quantum
X )
and
the
410 nm. The yields are generally high efficiency
reaction appears to be unaffected subs t i tut ion,
by
is
about
the methoxy
0.21.
The
and methyl
4
A triplet excited
state has been shown to be involved in the
isomerization of (375) into (376).%*5
237
11112 Enone Cycloadditions and Rearrangements 7
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S . Tateuchi, M . Yachida, Y. Nishibata, K. Y. Seto, and Y. Kanaoka, Chem. Pharm. B u l l . , 1 9 8 6 ,
3 4 , 3142 (Chem. A b s t r . , 1 9 8 7 . 1 2 0 . S . V . Kessar, T. Singh, and
107, 58986).
R . Vohra, T e t r a h e d r o n L e t t . ,
1987, 28, 5323. 121.
R . Suau Suarez and R . Garcia Segura, T e t r a h e d r o n L e t t . , 1988. 29, 1071.
122.
I . G . Pitt, R. A. Russell, and R. N. Warrener, S y n t h . Commun., 1 9 8 6 , 1 6 , 1 6 2 7 (Chem. A b s t r . , 1 9 8 8 . 1 0 8 , 131498).
P. H. Mazzocchi, C. Somich, M . Edwards, T. Morgan, and H. L. Ammon. J. A m . Chem. S O C . , 1 9 8 6 , 1 0 8 , 6 8 2 8 . 1 2 4 . P. H. Yazzocchi and C. Somich. T e t r a h e d r o n L e t t . , 1 9 8 8 , 123.
29, 513. 1 2 5 . C. Somich.
P.
H . Yazzocchi. and
H. L. Ammon, J . O r g .
Chem., 1 9 8 7 , 5 2 , 3 6 1 4 . 1 2 6 . K. Oda, Y. Yachida, and
Y. Kanaoka. Chem. Pharm. B o l l . ,
1 9 8 6 , 3 4 , 4406 (Chem. A b s t r . , 1 9 8 7 , 107, 2 3 2 1 0 ) . 127.
M. Yachida, K. Oda. Y. Yoshida, and Y. Kanaoka, H e t e r o c y c l e s . 1 9 8 7 , 2 6 , 147 (Chem. A b s t r . , 1 9 8 7 , 1 0 7 , 198198).
Photochemistry
244 128.
Y. Kubo, K. Okusako, and T. Araki. Chem. L e t t . ,
1987,
811. 1 2 9 . A. Srikrishna and
G. Sunderbabu, J. O r g . C h e m . , 1 9 8 7 , 5 2 ,
5037. 130.
P. P. Levin and V. A . Kuz'min. U s p . K h i m . ,
1 9 8 7 , 5 6 , 527
( C h e m . A b s t r . . 1 9 8 7 , 107, 2 3 5 6 4 7 ) . 1 3 1 . H. Shimoshi. K. Ariyama,
S. Tero-Kubota. and Y.
Ikegami, Chem. L e t t . , 1 9 8 8 , 2 5 1 . 132.
P. P. Levin, A . B. Belyaev, and V .
A . Kuz'min.
I z v . Akad.
Nauk S S S R , S e r . K h i m . , 1 9 8 7 , 4 4 8 ( C h e m . A b s t r . . 1 9 8 7 , 1 0 7 , 235976). 1 3 3 . A. Takuna, 0 . Soga, M .
Itoh, and K. Maruyama, Chem.
L e t t . , 1907, 727. 1 3 4 . G . Jones. 11,
W . A . Haney. and X . T. Phan. J . A m . Chem.
S O C . , 1 9 8 8 , 110, 1 9 2 2 . 135.
H. J . Kallmeyer and W . Fritzen, A r c h . Pharm. (Weinheim C e r . ) , 1987, 320, 769 (Chem. A b s t r . , 1988, 108, 37330).
1 3 6 . M . Natake and
K. Abe. Jpn. K o k a i T o k k y o Koho J P 6 2 8 4 , 0 7 5
(Chem. A b s t r . , 1987. 107, 217475). 137.
T. Tsuji. Y. Hienuki, M . Miyake. and S. Nishida, J .
Chem.
S o c . , Chem. Commun. , 1 9 8 5 , 4 7 1 .
1 3 8 . M . Miyake,
T. Tsuji, A. Furusaki, and S. Nishida, Chem.
L e t t . , 1988, 47. 139.
N . Tachikara. Chem. E x p r e s s .
1 9 8 6 , 1, 5 8 7 ( C h e m . Abstr.,
1 9 8 7 , 107, 7 7 4 0 4 ) . 140.
F. J . C. Martins, A. M . Viljoen, S. J . Strydom, L. Fourie, and P. L. Wessels, T e t r a h e d r o n . 1 9 8 8 , 44, 5 9 1 .
141.
T. S . Fang. H. T. Chang, and S. J . Shih-Chen, J. C h i n . Chem. S O C . , 1 9 8 5 . 3 2 . 4 5 7 ( C h e m . A b s t r . , 1 9 8 7 , 106, 193342 1 .
1 4 2 . N. A . Vysotskaya and N.
A . Ogurtsov. U k r . K h i m . Z h .
( R u s s . E d . ) , 1 9 8 6 , 5 2 . 1 1 4 1 ( C h e m . A b s t r . , 1 9 8 7 , 107, 153723). 143.
F . Salinas, A . Wunoz do la Pena, and J . A. Yurillo,
144.
T. Suzuki, Y. Yamashita, T. Yukai, and T. Yiyaohi,
T a l a n t a , 1986, 33, 923 (Chem. A b s t r . . 1 9 8 7 . 107, 9 6 2 1 1 ) . T e t r a h e d r o n L e t t . , 1 9 8 8 . 29, 1406.
P. Strokach, V . A. Barachevskii. N. T. Sokolyuk. and Yu. E. Gerasimenko, Khim. F i z . , 1 9 8 7 . 6 . 3 2 0 ( C h e r . A b s t r . . 1 9 8 7 , 107, 2 3 5 7 9 6 ) .
1 4 5 . Yu.
3 Photochemistry of Alkenes, Alkynes and Related Comnounds BY W. M. HORSPOOL
1 Addition styrenes medium
Reactions of Alkenes
Eeactions.and
.*
phenyl
The
photohydration
acetylenes
(1)
Diyne
reactive(irradiati0n at
has
is
been a1 so
of
substituted
studied
in
acid
photochemically
300 nm) with methanol affordins the
Z and E isomers. The ( 2 ) are photochemically labile and are interconverted on prolonged irradiation affording a photostationary mixture.e (2)
addition product isomeric
as a mixture of
products
Interest in CdS mediated surface photochemistry has continued. The irradiation (wavelength
>
aerated
results
420 nm) of the alkene ( 3 ) in an in the formation of the products shown in Scheme 1. Under deaerated conditions all the products shown apart from the ketone ( 4 ) are formed. The results obtained are interpreted as involving electron suspension of
CdS
transfer from the alkene to the CdS affording a radical cation (5).
Subsequent
cyclization
and
back
electron
transfer
or
disproportionation yields (6) and (7). Deprotonation followed by back electron transfer or disproportionation yields (8) and (9).r
The
reactions
described
were
all
quenched
when
irradiation w a s carried out in the presence of the electron donor, 1.2.4,5-tetramethoxybenzene. CdS samples was carried out.
A
comparison
of
various
Ysriano and his coworkers have continued their study of the photoreactions of iminiui salts. Thus the xanthone-sensitized irradiation of the pyrrolinium perchlorates (10) brings about cyclization yielding the products (111..
&-trans
1aorerization.- &-trrnq-Isomerization of alkenee has been discussed in a review lecture. Laboratory experiments 245
Photochemistry
Ar Ar
A Ar
Ar
hV
CdS, h >420nrn
Ar
( 3 ) Ar = p
- MeOC6H,
( 41
(91
(8)
+ Ar
Ar
+ Me0
Ar Ar
(6)
Scheme 1
ArnAr Ar
Ar
(5)
(72) R
=
H or Me
Me0
@ Ar
(7)
Ar
I I I N : Photochemistry of Alkenes, Alkynes and Related Compounds
0
**
247
\
\
(13) R
= H. Me or Pr'
'Xk
R'O
Me0
R
R
(161 a: R' = Me, R = 9 - a n t h r y l b:R = H
(171
(18)
248
Photochemistry Ph
R2 ph+R1 Ph ( 2 1 1 a: R ' = R 2 = Me b: R' = Me, R 2 = Et
Ph (231
(22)
c: R' = Me, R2= Pr'
Scheme 2
x\ 'CHMc
(281
H2s '%"Me
(29)
x2cHM"' H
(301
(311
Illl3: Photochemistry of Alkenes, Alkynes and Related Compounds illustrating
d . = have
isomerization also
photochemical
were
described
also
249
mentioned.=
laboratory
--&-isomerization
Levine
experiment of
stilbenes
for
the
and
the
of
the
of
the
chromatographic separation of the products. Physical
details
stilbenes
(12)
relating have
photophysical properties'of high
the
isomerization
A
from
study
the styrylstilbenes ( 1 3 ) has shown
trans-&
that quantum yields for singlet but
to
been
isomerism are low from the
the triplet
stat0.O The photochemical
isomerization of the alkene ( 1 4 ) in an ethanol glass affords the --isomer
with high
temperatures.)
1,2-di-l-naphthylethylene crystalline
of
The
( 1 4 ) has
A
phase
isomeriz&ion reported.
efficiency
even at
liquid helium
Photochemical &-trans-isomerization
a
study
series of
mechanism
also been of
styryl
of
the
the
a-
of
studied
in
the
photochemical
phenanthrenes has reaction
been
involved
was
discussed.%% An
investigation
dianthryl
of
the
(15,
ethylenes
photochemical 16)
has
behaviour
been
the
of
carried
out.%P
Irradiation of the 2-isomer ( 1 5 ) brings about the formation of the (4+4)-addition product ( 1 7 ) with a quantum yield of 0.16. Irradiation
of
the
E-isomer
cycloaddition product tren~-&-isomerization much
lower.
different
The
also
affords
this
quantum yield, 0.002, is
the overall
irradiation
route and
(16a)
( 1 7 ) but because of the need for prior
yields
of
the
enol
(16b) follows
( 1 8 ) following an
a
intramolecular
hydrogen transfer process. Hydrogen Abstraction.-
Xanthone-sensitized irradiation of the
(19) affords
dihydroisoquinoline
a
6%
yield
of
the
spiro
The reaction is akin to a Norrish Type I 1
derivative (20).'O
process but in this instance hydrogen abstraction by the irine nitrogen
is
involved.
The
resultant
biradical
cyclizes
to
yield the observed product (20). A
study
alkenes
of
the photochemical behaviour
(21-24)
in
the
presence
sensitizers 1.4-dicyanobenzene in
deconjugation
to
of
of
the
the
1.1-diphenyl
electron-accepting
and 1-cyanonaphthalene results
afford products
isomeric with
starting
250
Photochemistry
(33 1
(32)
SPh
JY
phXF
SO2Ph
Ph
R
(341
136) R
Ph
Cl
=
Me, E t , a l l y 1 o r benzyl
F
X
L
Ar
A
Ph
H
Ph
(37)
(39)
(381
Ar
t
(40) Ph o r p-ClC,H,
R'
GR2 Me
(411a: n = 1 b:n= 2
( 4 2 1 a: R' = Me, R 2 = H 1 b: R = H, R 2 = Me
[:AN CN
(431
CN
r
11113: Photochemistry of Alkenes, Alkynes and Related Compounds material. Typically isomers
(25-27)
the alkene
251
(21b) is converted
into
the
shown in Scheme 2. The reaction involves a n
electron
transfer
acceptor
and
process
from
rearrangement
the
alkene
within
the
the
electron
resultant
to
radical
cat ion.% a Sensitized irradiation of the allene (28) in xylene-methanol afforded
the photochemically
(29)
stable reduced compound
as
the only monomeric product. In this instance excitation of the alkene moiety
results.
The
allene
(30) reacted
differently
under the s a m e conditions affording the isomeric trienes (31). The
formation
excitation
of
of
these
products
is
presumed
the allene. This gives
rise
to
arise
by
to the biradical
(32) which cyclizes to yield (33) in a process analogous to a Cope reaction.%" Collapse of the biradical ( 3 3 ) yields (31). Miscellaneous reported
in
A
Reactions.the
photochemical
conversion of
the
1.3-migration
thiophenyl
is
sulphone
(34)
into the isomer (35).*= Irradiation of the fluoroalkene
(36)
results in the formation of the reduced-dechlorinated (37)
and
the
migration.a7
product The
(381,
compounds
the
result
produced
of
in
a
this
product
1.2-phenyl
reaction
are
influenced by solvent and by the nature of the second halogen. Radical and cationic intermediates are thought to be involved. Irradiation of
the
tetracyanoethylene
the
cyclobutene
affords
propose
that
irradiation of
cation
of
the
the
( 3 9 ) as
diene
(40).
the complex
cyclobutene
and
a
complex with
The
yields
that
this
authorsag
the
radical
undergoes
stereospecific electrocycloreversion to the diene. Irradiation of the alkene (41a) at 185 nrn in isooctane affords cyclohexa1.3-diene. cyclopentene and acetylene. The larger ring alkene (41b) is also photochemically reactive at 185 nm yielding
cis-cycloocta-1,3-diene,
&-
cis-trans-cycloocta-1.3-diene,
cyclohexene, acetylene, and the bicyclic alkene (43). The ring opening
of
the
alkene
(41)
is
not
stereospecific.
Non-
stereospecific ring-opening is also shorn by the cyclobutenes ( 4 2 ) on irradiation. This suggests that both disrotatory and conrotatory ring opening is involved in the reactions.am
Photochemistry
252
CN
HRN
Me
:C
CN
/
\
Ph
CN
‘R
( 4 8 ) a: R = OCOMC
(47 1
(46)
Ph
b:R
Ph
ph%, Ph
= OH
C ZN
Ph
N- OAC
(491
(50)
Me Me
Ph
Ph
ph&CHO Ph
‘Ar ‘Ar
(52 1
(51) Ar
(53)
= P h . 4 - MtOC6H4, 4-CIC6H4, 3
- MeOC6H4,
L
- CNC&
An
IIll3: Photochemistry of Alkenes, Alkynes and Related Compounds The alkene ( 4 4 ) is photochemically
253
reactive on irradiation in
a matrix at low temperature. An analysis of the i.r. spectrum of
the
photolysate
showed
acetaldehyde are formed.*O media
failed
to
perpendicular thermal
give
alkene
of
had
of
ketene
the
been
the
( 4 4 ) in argon the
(45)
singlet
led
formation
predicted
and
carbene
of
a
following
state.
Extended
to the formation of a new
identified as the oxirane
compound which was addition
the
for
evidence which
equilibration
irradiation of
that
Other experiments in a variety of
(47),
( 4 6 ) formed by
produced
by
secondary
irradiation of (45). to acetaldehyde.
2 Armesto
Reactions involving Cyclopropane Rings
et
have
a1
isomerization
of
irradiation
the
using
is
the
acetate
acetophenone
(49). This
derivative
reported
enol
affords
thermally
photochemical
(48a).
Sensitized-
the
cyclopropyl
unstable
and
during
isolation undergoes loss of acetic acid to afford the nitrile
(50). The reaction is a further example of the acyclic aza-diz-methane process and results by photochemical the
1.1-diphenyl
feature
in
this
irradiation under
alkene work
is
moiety that
in
the
excitation of
(48a). The oxime
interesting
(48b) is
the same conditions. I t
inert
is suggested
on
that
the presence of the acetoxy group minimises the influence of an
electron
transfer
process
which
prevents
the
aza-di-x-
methane rearrangement. In another study theyPP have reported on the photochemical reactivity of
B.
-unsaturated imines. In
this work Armesto, Horspool and coworkerszP
have studied the
influence of
substituents on the aryl group attached to the
nitrogen
compounds
in
(51).
Irradiation using
acetophenone
sensitization converts all of the compounds studied into the corresponding cyclopropylimine ( 5 2 ) which were then hydrolysed and
isolated
yields
showed
as
the
that
aldehyde the
most
(53). Measurement
of
quantum
efficient -cyclization in
the
series arose with a p-cyano substituent. The results obtained suggest that the aza-di-x-methane process is more efficient in these examples when the lone pair on the nitrogen is tied up by
overlap
with
the aryl
substituted function. This, also,
suggests that the lone pair o n the nitrogen must
in some w a y
254
Photochemistry
An
+Y
An
+ An
An
(58)
(57)
An &An An
(60)
(59 1 An = p
- MeOC6H, Cl
&
R a t i o 33: 67
(61)
OMe Scheme 3
&N
+
Ratio
25~75
R a t& io
6 0 : 10
7
-
+
cL*
a: X = C I
X
R a t i o 8 3 : 17
(62)
x
h
h
cL&)
/
Scheme 4
N
IIIN: Photochemistry of Alkenes, Alkynes and Related Compounds
255
Ql+ 4ridget-t;::
(63)a: R' = RR22= MeR' b: R' = R 2 = S i M q c: R' d: R'
=
Me,
= Me,
R 2 = Br R2=CN
&R2
R'
( 6 6 ) a: CN b: Me c: M e 0 d: C02Me e: C l f: C N 9: C02Mc
(65) V i n y l ic control
R'
R2 H H
H H H CN C02Mc
(681 a: 100 b: 70 c: 100 d: 100
R2
R'
(67) a: CN b: Me C:
d:
c: f:
g: h: i:
CF3 Me CN OMc CL CN C02Me
'control
( 6 9 ) a: b: c: d:
30
-
R'
~1
R2 H H
H Me Me H H CN C02Me
(701 a: 100 b: 73
86 d : 50 c: 100 C:
( 7 1 ) a:
b: c: d: e:
0 27 14 50 0
R2
PhoI ochemistry
256
adversely affect the efficiency of the cyclization. The actual nature
of
this
is unknown
at
this have
sensitized
dianisyl
about
irradiation
irradiation
direct
the
These
and
other
of
the
( 5 4 ) brings
formation
of
the
rearrangement. Direct
hand
compounds
all-carbon
the acetone-
alkene
the
afforded
are
also
the cyclopropane ( 5 5 ) and i t
irradiation
the
shown that
di-z-methane
(54) on
of
(56-59).
irradiation of the
the
( 5 5 ) via a
cyclopropane products
of
isomerization
trans-cis
In
time.
systems Zimmerman and Kamathes
alkene
the
four
produced
on
is presumed that
( 5 4 ) proceeds
to
the
cyclopropane followed by secondary irradiation. Thus the four products arise from the biradical cyclopropyl affords
ring
bond.
product
( 6 0 ) formed on fission of a
Hydrogen
( 5 9 ) while
the
abstraction other
within
three,
this
(56-58).
are
formed by a 1.2-migration of the methoxy cumyl radical. Some evidence was obtained
to indicate that
these
three products
can arise by a disproportionation-recombination path.
The
triplet
state
methanoquinoline
di-z-methane
(61, 6 2 )
systems
reactivity have
been
of
the
studied.
The
results of the irradiations are shown in Schemes 3 and 4 where
it
can
be
seen
that
each
compound
usually
affords
two
products. The results indicate that the pyridine nitrogen does not
manifestly
alter
the
photochemical
behaviour
of
the
compounds. A detailed analysis of the reasons for the observed regioselectivity theory
.=.
is made
The
benzonorbornadienes Paquette
and
on
the basis
di-z-methane
of
molecular
reactivity
orbital
of
the
( 6 3 ) still excites considerable interest.
Burkegs
have
studied
the
triplet
state
reactivity of the derivatives ( 6 3 ) in an attempt to establish the influence of bridgehead substitution. Thus the irradiation of
(63a) results
in the formation of both
isomers
(64a) and
(65a) in 4 2 and 58 X
respectively. Similar yields are shown
for
of
the
irradiation
(63b)
when
the
two
products
are
obtained in similar yields to the above. However, irradiation of the derivative (63c) results in the formation of only the cyclized
product
(64c)
while
the
derivative
with
the
bridgehead cyano (63d) yields both (64d) and (65d) but in 10 and 90 X yields respectively. The authorsLm present arguments to explain the observed
specificities leading to products of
either bridgehead control or vinylic control of the biradical
257
11113: Photochemistry of Alkenes, Alkynes and Related Compounds
CO2BuS
R2 R'
R3
c
H
A
Ar2
C02Me
Ar' (75)
CO, Me
CO, Me I
C0,Me Ph
Ph phJ%: C02Me
(76)
Ph
C02Me
(77 1
Ph
(78)
R' = CO2Mc, R 2 = R' =
H
H, R 2 = C 0 , M
R
Meofrph \
(79)
Ph
(80) R' t CN, C0,Me R 2 = Ph or 2-pyridyl
(81) R X
= =
C N or C 0 2 M e CH or N
Photochemistry
258 intermediates
involved in the rearrangements. Other workerse'
have also studied the influence of substitution and ring size on the photochemical and
(67).
Both
reactivity of the bicyclic compounds ( 6 6 )
acetone-
or
acetophenone-sensitization
and
direct irradiation were used to effect the conversions and the triplet process w a s established
a s being more efficient. T h e
(68. 6 9 ) and ( 7 0 ,
regiospecificity of the reactions affording
7 1 ) were
studied
appropriate bicyclic
and the yields obtained are shown under the
structures. T h e authorsP6
compounds
( 6 6 e-g)
and
rearrange o r the rearrangement results were discussed
The
irradiation of
also observed that the
( 6 7 f-i)
either
was extremely
the optically active dibenzbarrelene isomeric products
ratio
(73)(atb):(73)(c+d)
products
to
in some detail.
in solution affords the four of
failed
inefficient. T h e
formed
(72)
( 7 3 a-d).
The
55:45.
is
Irradiation of a single crystal affords the same four products but
<
in
25 % .
a
ratio
The
of
results
9O:lO
when
obtained
the
show
conversion that
was
kept
is n o
there
to
chiral
selectivity in the solution phase conversion but that there is a preference for the formation of one of the regio isomers (73 a . b ) . T h e solid a f f o r d s the
state reaction is considerably different
regio
isomer
( 7 3 a ) in high optical
purity
and
(80 %
enantiomeric e x c e s s ) . e 7
A
review has discussed
the photochemical
reactivity of small
ring compounds v i a charge transfer c o m p l e x e s . e m T h e oxidation of the cyclopropane derivatives ( 7 4 ) o n illuminated Z n S or C d S has been pentane
studied.=,
Irradiation of
for 20 h yields
Change of
solvent
the cyclopropane ( 7 6 . 35%)
the dimers
to benzene
also yields
and
( 7 5 ) in
(77, 15%).
these dimers which
are accompanied by the adducts ( 7 8 ) and the furan (79).'O adducts The
( 7 8 ) are formed
photochemical
derivatives This
by
involves cyclization
the
of
the
carbazole
of
ring-opening
of
The
hydrogen abstraction pathway.
isomerization
(80) a f f o r d s
reaction
followed
VAa
the
spirocyclopropane
derivatives a
resultant
oxidative s t e p must also be operative.
(81).51
cyclopropyl biradical.
bond An
259
11113: Photochemistry of Alkenes, Alkynes and Related Compounds
Me
X
(86 1
(85 1
= H = CH20Me X = C02Me
(87)a: X b: X c:
4
RO QH
X
(88) R
=
Me, Et o r Pr'
(89)
&R
X
Y
V X
(901
(91)
(921
"i
Y
(93)
Y
(941
R
Photochemistry
260
(97)
(96)
&
Ph Ph
H
R2
(101)
'Me
(1021
Mc'
Me' (0I3 )
x
2
= R = H or Me R'= H, R2= Me X = 0,NC0,Et
(1001 R'
(99)
a
BRl
(104 1
11113: Photochemistry of Alkenes, Alkynes and Related Compounds
26 1
The dihydro naphthalene ( 8 2 ) is photochemically reactive. Its irradiation
in
hexane
methylnaphthalene
and
at
temperature
room
the
methylidene
gives
naphthalene
2(83).
Irradiation at -45°C
follows a different path and yields the
three
( 8 4 1 , (85). and
new
products
( 8 6 ) as
well
as
the
methylidene naphthalene ( 8 3 I a s f
Reactions of Dienes. Trienes, and Higher
3
Polyenes The
irradiation
of
the
strained
solution affords the rearranged interpret
this
as
starting material
evidence
diene
(87a) in
product
for
the
alcoholic
(88). The authorssg isomerization
of
(89)
(87a) into the 4-paracyclophane
the which
thermally adds solvent to afford the isolated product. A more detailed
report
of
photoisomerizations of
(91) on
and
this
work
has
included
the
(87 b , c ) which yield mixtures of
irradiation
in
ethanol.
(90)
Spectroscopic evidence
confirms the paracyclophanes ( 8 9 ) as the intermediates in the formation of
the alcohol
addition
products
(88). ( g o ) ,
and
(91).=. Several reports over the past photochemical
cyclizat ion
of
few years have dealt with the dienes
or
enones
of
the
type
represented by (92). The problem with such systems is that i t is often difficult to predict whether straight addition to the biradical preferred.
(93) or crossed addition, biradical Ohsaku*s
has
studied
this
(94).
problem
will and
be has
published a theoretical treatment. A detailed study of the photochemical
reactivity of the diene
( 9 5 ) has been carried o u t . g = The intramolecular cycloaddition
of
the diene
been
used
as
( 9 6 ) to yield a
step
(98).a7 The triene
in
the tetracyclic isomer
the
synthesis
(99) is formed by
of
the
(97)
novel
the photochemical
has
dime ring
opening of the diaza and azaoxa tricyclohexenes (100).30 The d i m e (101) is photochemically reactive and ring opens in the gas
phase
using
280-300
nm
light
to
give
mainly
the
cyclooctatriene (1021, benzene and ethylene. The formation of
t h e triene ( 1 0 2 ) is influenced by the addition of added gases
Photochemistry
262
OH Scheme 5
kc
(106)
(107)
@'
0
Me (108 1
CF3 (109 1
11113: Photochemistry of Alkenes, Alkynes and Related Compounds
263
0
II
cf35' II
0 0
(110)
(111)
(112)
0
./.
dirt r i bution c i s -C- 2 cis- C - 4 (1131 a: R ' = OMc, R2= R3= H b: R 1 = R 2 = R 3 = ti 1
c: R d: R' c: R'
= OMt, R 2 = H. R 3 = F = O M . R2= F. R3= H = OMc, R2= R3= F
70
30
3
97 95 >98 94
5 (2 6
phwo2Mc H
H
Ph h O , O C O R '
,c-\
R3 R2 (114)
R3
(1151
R2
2 64
Photochemistry
and
the
from
authorsgs
a
suggest
vibrationally
that
the
excited
triene
state.
(102) is
formed
Mercury-sensitized
photolysis of (101) affords mainly benzene plus ethylene.
A study of the photochromic behaviour of the stilbene analogue (103)
and
made.
its
reversible
cyclization
to
(104)
has
been
O
The wavelength dependent photochemistry of previtamin D s (105) has been studied. Irradiation at several wavelengths has shown that the quantum yield for the formation of the products shown in
the
5
Schdme
wavelength
used.
is
to
The
it
extent
evidence
that
adequate
explanation for the effect.
that
particular
A
consideration.41 irradiative
doubtful
if
a
vibrational patent
has
isomerization
of
dependent
collected
suggests a
is
some
two
by
the
state
the
authors.'
model
is
,
an
A suggestion was made
manifold
been
upon
worthy
of
lodged dealing with
is
the
7-dehydrocholesterol
into
a
mixture of the three products (106), (107), and ( 1 0 8 ) as well as the starting material.*P A
high yield
the enone
of
(109) is obtained
from the diene
(110) on irradiation in pyridine. The authorsa* the
formation of
product
S-0 bond
process whereby
( 1 1 1 ) and
the
radical
trifluoromethyl
suggest that
from
(109) results
a
radical
fission affords the alkoxy
(112) which
fragments
to
SOP
radical and
the
(111) to
radical. This combines with radical
afford the isolated enone. A
study
sought
of to
the
photoisomerization of
establish
the
involvement
the
of
dienes
( 1 1 3 ) has
zwitterions
in
the
isomerization process and the influence that substitution can have
on
the
reaction.
isomerization about and that
The
results
obtained
indicate
that
the C-2 and C-4 double bonds does occur
the polarity
of
the substituent
plays a n important
role in determining the position of the isomerization in the molecule.
Thus
dominant
and
in
(113a) the effect
influences
the
of
the ester
involvement
of
the
zwitterion (114) leading to isomerization of the C-2
group
is
twisted bond. The
introduction of fluoro substituents on C-2 or C-4 or the use of the aldehyde instead of the ester in (113b-e) changes the
265
IIIl3: Photochemistry of Alkenes, Alkynes and Related Compounds
=w
PhCSC- C E C - C E C-R
(119 1
(120) R
=
Ph or Me
(122 1
(123)
R’ = H, R 2 t A c or Me R’ = 0, R~ = ~e
t$ (1251
(1261
(127 1
(128)
Xm X
(129)
XB
1,co 0
(130)
U
x = CH,. c’,
X
or C=C(CNI,
Photochemistry
2 94
x
0
(49)
(48)
q0
$J
-”
N-
(51)
(50)
(52) X = N , Y = 0
(54) X = N , Y = O
( 5 3 ) X = N , Y = NH
( 5 5 ) X = N , Y = NH
(56) X = N , Y = S
(57) X = N , Y = S
k (58)
267
JllI3: Photochemistry of Alkenes, Alkynes and Related Compounds nature of the zwitterion so that the twisted state (115) is dominant bringing about isomerization of the C-4 bond.** A twisted excited state has also been implicated in the direct irradiation of
the didehydrosqualene
(116) in hexane. This
isomers of the bicyclooctene
treatment affords a ,mixture of
derivative (117). The generality of this (2+2)-intramolecular addition was demonstrated in the reactions of simpler systems such
as
the
tetraene
(118)
which
cyclizes
yielding
the
bicyclooctene (119). The reaction yielding the bicyclooctenes is
thought
generated
to
from
involve the
a
twisted
triene part
of
bisallylic
excited
the molecule.
state
This
then
interacts with a terminal alkene in a n ionic process to yield the observed products.4m excited
state
has
The involvement
previously
been
of such a twisted
proposed
by
Dauben
and
Kel logg . Irradiation
of
the
triyne
(120) in
the
presence
of
2,3-
dinethylbut-2-ene affords the two adducts (121) in 33 and 11 X yield respectively.*l
4
[2+2] Intramolecular Additions
Photoisomerization
of
the
benzothiepine
(122)
yields
the
Thermal elimination of HCl from the
isomeric product (123):.
chloromethylfuran (124) in a gas phase flow reactor affordm the diene (125) as a n observable long lived intermediate. The irradiation of this compound (126) in en Argon matrix using 300 nm light yieldsthe cyclized compound (125). the identity of which was inferred from spectral data.** Irradiation
of
the
dime
(127)
yields
the
cyclobutane
derivative (128) as the sole product. The structure of this was confirmed by X-ray analysis.go Prinzbach )t a J . m a have reported
the intramolecular photochemical
(2+2)-addition
of
the dienes (129) to afford the adducts (130). Cycloaddition is also reported derivatives Alder
to take place on irradiation of
the benzene
(131) where the adducts were isolated as Diols-
adducts
of
the
dienes
(132).
Acetone-sonsitizod
irradiation of the diene (133) results in the rapid conversion
268
Photochemistry
Me0
OMe
Cl
& c
N'/ N
(139)
(140)
( I 4 11
(1421
C l Cl?Mc
& cl
-.
Ac
(143)
(115)
0
0
269
IIll3: Photochemistry of Alkenes, Alkynes and Related Compounds
( 1 4 8 ) R ' = R 2 = R3= R4= H
R2= R3= R4= 1 R 2 = Me, R = R3= R4= R ' = Me,
(149) H H
R 3 = Me, R ' t R2= R4= H R 4 = Me, R1= R2= R3= H R 3 = R 4 = Me, R ' = R2= H
.4-,,
C02R'
CO 2R1 & R ( 1 5 0 ) R' R*
2
= 1 or 2-naphthyl,
=
H o r CO,R
(151 1
1
CO Bun R'
R1
(1521 R'-R4= H or Me R 5 = CHFEt, C F 2 E t or CF,
(1531
(&7g '
(156)
(155 1
\
\
(156 1
Photochemistry
270
q g
Me
(157)
(158)
(159 1
(160)
NO,
C02H
&
P
R
R
(161)
R
= Ph, 0 - and p-CLC&Ib,
-
R
C0,H
(1621
-
2.4 a n d 3 , t C12C6H,
R
a 0
I MeN 0 (163) R
0
=
H or C l
(1 6 4 )
0
271
I I I N : Photochemistry of Alkenes, Alkynes and Related Compounds to the cage compound
Irradiation (254 nm) of
(134).5p
(135)
affords the cage structure (136).sa
The Diels-Alder adduct (137) is photochemically active and can be converted transformed compound
into the cage compound by
hydrolysis
(139).sa
and
The
acetone-sensitized
(2+2)-cycloaddition within hepta cyclic diketone
(138). This product was
decarboxylation
the
diketone
into
the
azo
intramolecular
(140) affords
the
(141). This process was used as a key
step in the synthesis of
the bishomohexaprismane
A
(142).""
study has sdught to establish the constraints present in cage formation
in compounds of
the type represented by
(143) and
(144). The researchers have shown that the diene (143) fails to undergo cage formation. However, the less strained molecule ( 1 4 4 ) is yield
photochemically
the
cage
reactive
compound
and
cyclizes
A
(145).*=
study
smoothly has
to
reported
observations on both the theoretical and experimental problems associated
with
(2+2)-photocyclization of
(146) to yield
the
prismane analogues ( 1 4 7 ) . s 7 The irradiation of the norbornadiene derivatives (148) yields the
quadricyclanes
(149).
These
quadricyclanes
can
be
reconverted to the starting material by treatment with silver ion.se The norbornadienes (150) photochemically ring close to the
quadricyclanes
irradiation were mixture
of
products. The
benzophenone
as
norbornadiene (153).eo
(151).
used but
the
Paquette
direct
reactions
and
(154)
(152)
were
sensitized
cleaner
Irradiation the
have
which
homoconjugation is high. This
much
affords
Racherlasi in
and
irradiation afforded
sensitizer."-
derivative
norbornadiene
Both
the direct
is borne
of
the
quadricyclane
synthesized
is
it
out
a
using
claimed
the that
on acetophenone-
sensitized irradiation in pentane when i t is converted to the quadricyclane
(155).
Prinzbach
and
his
coworkersmP
have
reported o n the photochemical (2+2)-cycloadditive behaviour of adducts
of
sensitized
the
type
(2+2)-cycloaddition to (157)
and
represented
irradiation (158).
of afford
Direct
this a
2:l
by
(156).
compound mixture
irradiation.
The
acetone-
brings of
however,
the
about adducts
follows
a
different path to yield a mixture of the (2+2)-adduct (157) as
272
Photochemistry
p
Ph (167 1
(1 68 1
(169)
p
Ph
Ph
Ph
Ph (17 0 1
(1711
Me Me
(CH,), (1721 n = 2 o r 3,
Ar
(173 1
= p - MeOC6H,
0 Me Me
273
:IIIi3: Photochemistry of Alkenes, Alkynes and Related Compounds well as the isomer (159) which is formed by a norbornadiene quadricyclane type cyclization.
5
Dimerization and Intermolecular Additions
Photochemical dimerization of the diene (160) has been carried out in the solid state.== The styrylisoxazoles (161) are also photoreactive
and
affords
a-truxillic
the
photochemical
yield
(ZtZI-dimers. acids
dimerization
of
Oxidation
( 1 6 3 ) has
of
these
(162). u *
derivatives been
The
reported
to
afford a cyclobutane derivative when irradiated in the solid phase
A
,as
detailed
review
has
surveyed
the
conformation
effects influencing photochemical solid state reactions.Eu
A
mixture
of
four
dimers
benzophenone-sensitized Vacuum
sublimation of
which
was
subsequently
paths
to
the
(8%)
is
obtained
irradiation
of
the
this mixture converted
hydrocarbon
affords
(166).E7
in methanol
solution. This
head-to-head
and
(165)
chemical
Photosensitized
(Rose
(167) has been studied
affords both
head-to-tail
the
(164).
the dimer
conventional
by
Bengal) dimerization of aceanthrylene
from
triene
the
syn- and a n t i -
stereoisomers.
The
results
indicate that there is a slight preference for the formation of the G - a d d u c t s Kaupp and Ringer's stilbene
to
the
.Im
have described the photoaddition of heterocyclic
compound
(168) to
trans-
yield
the
adducts (169) and (170).
6 A
review
Miscellaneous Reactions
lecture
has
dealt
with
the
photosensitized
ring
opening of a w l cyclobutane derivatives such as (171).70 The results
of
a
ring-cleavage
photochemical reactions
of
study some
the
ring-opening
and
aromatic
cyclobutanes
and
of
et el.'* cyclobutenes have been d e s ~ r i b e d .Yamashita ~~
report
that the cage compounds (172) are photochemically unreactive to electron transfer induced reactions. However, the alkenes
2 74
Photochemistry
OH
I
(3 N
-*
2 PhCHO
+
I
Ph CH-CHPh (177 1
H
Scheme 6
0 Ph CHO ( 179)
(1781 R
= Me. Et, P r , Pr‘, But, Ph, 2 - f u r y 1 or 2-thicnyl
Ph
RbcN I
C
111
H2N Nc&cN
Ph
NC CONH, Ph
C
I
CN
(180) R-R = (CH,) or (CH2) 3 4 R = Me
( I 8 11
“‘gCN R
R
Ph
H,N CONH, (183)
(186)
(182 1
(l8tI
(185)
lIll3: Photochemistry of Alkenes, Alkynes and Related Compounds
275
dN CN
NC CN
CN
NC (189)
(190)
(1911
dco2k *'OSi Me3
(192)
(192)
(1931
(195 1
a: R' = H, R 2 = C 0 2 M e b: R' = H, R2 = CH20Ac C: R ' = CH20Ac, R2= H
x (196) X
= I
o r Br
& CL
R'
R2 CL
(198) a: R' = R2 = CL b: R' = Cl, R 2 = H 1 C: R = H , R2= CL
(197) X = Y = H X = OH, OAC, OMS, Cl, Y = H x = ci, Y = O A ~(trans)
=Y = x =Y =
X
CL ftrunsJ C i (cis)
276
Photochemistry
(173)
are
reactive
and
undergo
a
novel
pericyclic
rearrangement. T h u s the irradiation of
( 1 7 3 ) in the presence
of
affords
2.4.6-triphenylpyrylium
perchlorate
the
isomeric
compound
( 1 7 4 ) . T h i s is formed by way of a n electron transfer
mechanism
involving the radical c a t i o n ( 1 7 5 ) which rearranges
to the novel
radical
c a t i o n ( 1 7 6 ) by a
1,2-vinyl migration.
This intermediate is t h e n transformed into the final product ( 1 7 4 ) . Quantum that
the
study
yield
conversion the
of
measurements occurs
by
photochemistry
a
on
the
chain
reaction
indicate
A
detailed
process.
1,2-diphenylbenzocyclobutene
of
under electron transfer conditions has b e e n r e p o r t e d . 7 a Electron acceptor
induced photochemistry
( 1 7 7 ) results in the
fragmentation of
of
the aminoalcohol
the compound
t o yield
the products shown in S c h e m e 6 . " ' T h e photochemical of
( 1 7 8 ) have
react ions of
been
the endo-
studied. The
and
0x0-derivatives
endo-derivatives
rearrange
faster and afford the dioxazocines (179).7LT et a 1 . 7 L have
Armesto
reported
a n e w photochemical
reaction
for the substituted 4H-pyrans ( 1 8 0 ) . T h e irradiation of these compounds(l80) gives
the
through P y r e x
cyclobutenes
products are accompanied by and
in methylene
(181)
The
about
chloride
30%
solution
yield.
These
the fragmentation products
( 1 8 3 ) w h i c h a r e produced
cyclobutene.
in
reaction
(182)
by secondary irradiation of affording
the
the
cyclobutenes
is
presumed to involve bridging of the type illustrated in ( 1 8 4 ) . Collapse
of
this
intermediate
as
illustrated
yields
the
observed products. Irradiation
contrast
the
of
abstraction
from
the
dienyne
solvent
irradiation
(185)
affording of
enyne
results the
in
triene
(187)
results
hydrogen (186). in
In
bond
fission and isomerization yielding the cyclohexene derivative (188).77 single
Irradiation product
(254 nm) o f
(190).
the diene
Sensitized
(acetone)
( 1 8 9 ) affords a irradiation
of
(189) follows a different path and y i e l d s (191). T h e mechanism for
the formation of
initial
adduct
followed by
into
these products cycloheptatriene
involves fission of and
the
tetracyanoethylene
thermal readdition of the ethylene t o afford the
illl3: Photochemistry of Alkenes, Alkynes and Related Compounds
277
CH SnBu3
Bu 3Sn SnBu,
(1991 a: R ' = H, R'= G H ~ b: R ' = H, R =a-naphthyl C: R' = R 2 = C,H,
(200)
/
R2
= H or ~ e x, = 0 , R 2 = H b: R' = H or Me, X = 0, R2= Me0 1 c: R = H. R 2 = MeO. X = CH,
( 2 0 1 ) a: R'
(202)
Ph
(~~),CHCH,CH,OCH,OCH, (203)
(201)
Photochemistry
278 two
products.
multiplicity
The
of
dependence
of
product
the reaction indicates
formation
that
on
the
the singlet and
the triplet states of (189) do not decay along a common path. The
authors7"
suggest
that
the
difference
is
due
to
polarization of the excited states. The photochemical adducts such
as
(192) can
be
converted
in
three
steps
into
the
ring-expanded compounds (193). The key step in this process is the
irradiation
of
mercuric oxide and
the
alcohols
iodine
(194) in
in benzene.
the
presence
of
The reaction involves (195).79 A similar
the homolysis of the resulting hypoiodite
approach has been reported for derivatives of (192) where the ester is replaced by a cyano group.eo A detailed
halides
study of the photochemical behaviour of the alkyl (196)
photophysical
has
data
been
of
the
reported.Oi compounds
out.Oe The photoisomers of D i e l d r i n , are
photoreactive
in
the
example, the
irradiation
dehalogenated
compounds
1:5.e3
been
carried
A l d r i n and E n d r i n ( 1 9 8 )
presence
of
Measurement o f the
(197) has of
photoaldrin
(198b) and
triethylamine.
For
(198a) affords
the
(198c) in
Ionic reactions in photochemistry
a
ratio
of
have been reviewed
by Chow and Wu.Or A
study of
has
the photochemical
reported
the
efficiency
fission of of
the
the stannanes (199)
process
yielding,
for
example, from benzyl stannane (199a), bibenzyl and the alkyl tin
derivative
explained
.by a
(200).
The
radical
reaction
fission
in
benzene
affording
the
is
tin
best
and
the
benzyl radicals.eu The
photochemical
reactions
of
(201 a , c ) in acetonitrile-methanol of 1,4-dicyanobenzene
the
bicyclic
compounds
solution in the presence
have been studied. The irradiation of
(201a) affords the mixture of &--t
methoxy
derivatives
(201b) which are also photochemically reactive under the same conditions. photochemical
The
products
from
(201a)
addition o f methanol
are
to the
formed
furan
by
the
(202). This
furan is formed by production of the radical cation of (201a) followed by deprotonation affording a doubly benzylic radical. The study was extended to the monocyclic system (203) which on electron-transfer-induced
irradiation
afforded
the
acetal
11113: Photochemistry of Alkenes, Alkynes and Related Compounds (204).
In this instance the radical cation undergoes C-C bond
fission and trapping by methanol.e6
279
Photochemistry
280 References
1.
J . McEwen and K. Yates, J . A m . Chem. S O C . , 1987, 109. 5800.
2.
T. S. L e e , C . S. Shim, and S. S. Kim, Bull. Korean Chem.
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H. Al-Ekabi and P. de Mayo. J. O r g . C h e m . , 1987. 5 2 ,
1986, 7, 116 (Chem.
SOC.,
4. 5.
6.
A b s t r . , 1987. 106. 6569).
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D. M . Zeglinski and D. H. Waldeck, Springer S e r . Chem. Phys.
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A b s t r . . 1987. 1 0 7 . 115106).
8.
Y . Ito. Y. Uozu, and T . Matsuura, T e t r a h e d r o n L e t t . .
9.
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V . F. Razumov. A . G. Ivanchenko. A. G . Rachinskii. and M . V . Alfimov. Dokl. A k a d . Nauk S S S R , 1987. 293. 666 (Chem.
11 *
C . Galiazzo, A . Spalletti. G. Bartocci. and G. G . Aloisi,
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H.-D. Becker and K. Andersson, T e t r a h e d r o n L e t t . , 1987,
13.
Y . Hirai, H. Egawa. Y . Wakui, and T. Yamazaki. H e t e r o c y c l e s , 1987, 25. 201 (Chem. A b s t r . , 1987. 107,
14.
D. R. Arnold and S. A . Mines, Cun. J . C h e m . . 1987, 6 5 .
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111/3: Photochemistry of Alkenes, Alkynes and Related Compounds 17.
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28.
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Photochemistry
2x2 37.
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11113: Photochemistry of Alkenes, Alkynes and Related Compounds
283
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4 Photochemistry of Aromatic Compounds BY A. C.WEEDON Introduction
This year's format
last
of
isomerisation,
report on the photochemistry of aromatic compounds follows the year
and
nuclear rearrangements, aromatic
is
arranged
in
sections
covering
addition. substitution, intramolecular cyclisation,
ring
whose
and reactions of reactivity
substituents
derived
is
from
on the peripherary of the
the
Several reviews have appeared during the year. aromatic
compounds
have
mechanistic and structural
of
the
molecules;
been
features
discussed
with
photoactivation
this
contains
chromophore.
of
distal
examples
processes
and
a
*
Many
review
of
special
of
the
attention
governing the outcome of the
ring
reactions
of
arene
radical
groups
of
prior
and
in
the
polyfunctional
non-conjugated
aromatic
excitation
of the
adjacent
involve
electron
transfer
photoreactions ions
to
interaction of
Morrison has published an
functional
substituents whose reactivity is dependent upon arene
presence
The photoaddition reactions
photoexcited arenes with alkenes and other arenes. account
involving
photochemistry") .
( "peripheral
of
reactions
dimerisation, lateral
charge
transfer
phenomena
in
photochemistry has a ~ p e a r e d ;this ~ Includes a discussion of how the ortho versus
mete selectivity in the addition of alkenes to photoexcited arenes is related to the free
energy
change
for
electron
transfer
between
the
excited
arene
and
the
alkene. Also in the area of light-induced
electron transfer processes.
a paper from
Farid's group describes the results of an investigation of the quantitative aspects
of electron transfer sensitised arene photoreactions:
in this article the fate cf the
radical ion pair generated by irradiation of an electron acceptor in the presence of an arene donor was probed by measurement of the quantum yield of separation of the ion pair.
Combination of this with the rate constant for separation of the
ion pair allowed the determination of the rate constant for back electron transfer in the radical ion pair.
This rate constant was correlated with the free energy of
the back electron transfer
reaction for various arenes and sensitisers.
In the
latest volume of the Organic Photochemistry series Mariano has reviewed the light induced electron transfer reactions of the imino group;5
same
as noted In last year's
many of these reactions lead to products of arene substitution.
report.
Issue
oleflns6
a
brings
chapter up
to
devoted date
to
the
recent
photocycllsation revlews
285
of
reactlons
rearrangement
of
In the
conjugated
reactions
of
Photoch ernistry
286
(5)
(7)
(10)
(6)
(8)
(11)
(12)
287
IiIl4: Photochemistry of Aromatic Compounds 5-membered ring aromatic heterocycles7 and the stilbene-dihydrophenanthrene cyclisations.8 derivatives.
as
well
as
summarising
some
of
the
reactions
of
type
styrene
The second edition of the Organic Photochemistry text of Coxon and
Halton has appeared9 and contains sections devoied to aromatic photochemistry of value as an elementary the photochemistry
of
introduction for those unfamlllar with the area. derivatives
of
the N-oxides
of
pyrazine,
Finally.
quinoxaline and
phenazine has been reviewed. lo
isomerisation Reactions
1.
Turro
and
co-workers
benzocyclobutene. ( 1 )
have
investigated
in pentane.
,
the
photochemistry
of
At conversions low enough to ensure little
loss by secondary photochemistry they obtain products (2) and (3).
product
along with
products derived from
respectively.
hydrogen abstraction,
The pentalenes (2) and
in the
ratio 71: 16: 13,
( 3 ) are proposed to arise by way of a
sequence involving formation of the prebenzvalene biradical (4) which
opens to
Hydrogen migration in (5) subsequently produces either (2) or
the carbene (5).
( 6 ) : the latter is then presumed to rearrange to ( 3 ) by successive 1.5-hydrogen
shifts. for
The photochemistry observed for ( 1 ) is in sharp contrast to that observed
derivatives
of
benzocyclobutene where
cyclobutene ring opening to
quinone
dimethides is the norm. It is reported that the bridged Dewar benzene ( 7 )
upon irradiation in a low
temperature matrix produces a product whose U. V. /visible absorption spectra are is trapped to
consistent with the formation of the cyclophane ( 8 ) . l2 Thus (8) give
(9)
formed
i f the from
ethylene.
irradiation is carried out in an alcohol solvent,
(8)
in
a
secondary
photochemical
The more constrained Dewar system ( 1 1 )
rearrangement to the cyclophane when irradiated; ( 1 2 ) is formed,
(15)
shown
presumably y&
in
scheme
1
photochemical
isomerisation
transformations
takes
isomers.
as
outlined
place in
the isomer ( 1 3 ) . have
been
reactions
involving the
the
scheme;
being formed. irradiated
assigned structure in
methanol. l 4
(
is of
The Dewar benzenes (14) and and
corresponding the
(10)
extrusion
does not show evidence of
prepared
all
involving
instead the benzobicyclo-octane
examined, l3
enough to allow characterisation by nmr.
is
step
while
their
thermal
complex
A
prismane
compounds
and
shown
were
stable
A Dewar Isomer is also reported as
interesting
following a simple substitution is observed
of
benzene
16) , when t h e salt of the aminopyridine
An
and
series
for
diversion
from
normal
the anthraquinones
(
(
17)
reactivity
18) -(20). l 5
Irradiation of (18) and ( 1 9 ) cleanly gave the Corresponding Dewar structures (21) and (22) only.
whereas (20)
gave a mixture of products among which were low
yields of compounds assigned structures consistent with their being derived from intramolecular hydrogen abstraction from a tert-butyl carbonyl.
group by the anthraquinone
No Oewar structures were observed in the mixture obtained from (20).
Photochemistry
288
E
t hv
B ut I
But
B Ut
But
hfk
E
But E
-$
But
But
But Scheme 1
289
ilIt4: Photochemistry of Aromatic Compounds
(13)
(16)
(1 7)
WR2WR \
R3
0
(18) R, = R, = R, = B u t (19) R, = R, = But , R, = SiMe3 (20) R, = R, = But , R,= H
But
(23) R = CN (25) R = H
0
R3
Photochemistry
290
1
Ph
Phx
Bu3P
:
h
0
&ph
Ph H
Scheme 2
291
11114: Photochemistry of Aromatic Compounds The
reactivity
of
(20)
is
more
typical
of
anthraquinones
formation of Dewar structures ( 2 1 ) and ( 2 2 ) of reaction for the anthraquinone show
large
perturbations (20) .
anthraquinone extinction bands
in
system.
their
These
which
may
reflect
steric
9-tert-buty1210-cyanoanthracene
dibenzobicyclo[2. 2 . llheptane
photochemistry
of
( 2 6 ) . l7 The
reaction
between
and
(23)
one
which
(25)
its
the
presumably
of
the
with
shifts
and n+nx,
anthraquinone
Anomalous reactivity has also been
( 2 4 ) . l6
9-tert-butylanthracene
latter
while
compared
bathochromic
longest wavelength,
group.
gave
spectra
include
interactions
found for the
absorption
of the
carbonyls and the adjacent tert-butyl
general
The authors note that ( 1 8 ) and (19)
U. V.
perturbations
coefficient enhancements
in
is the first observation of this type
upon
This
which
reversal
irradiation
is
in
forms
have
the
been
at
-20°C
constrast
to
Dewar
examined
the
isomer
for
their
potential for solar energy storage. 18 A
of
number
photoisomerisation
reports reactions
have of
appeared
during
5-mem bered
the
aromatic
year
concerning
heterocycles.
the
Several
mechanisms have been proposed to explain the rearrangement of these species. These include sequences which involve the intermediacy of a Dewar isomer
( I .8 .
a bicyciol2. 1 . Olpentane) , and sequences in which initial ring opening is followed by closure to a carbonyl substituted cyclopropene.
An example of a reaction in
which the former
is the rearrangement of the
mesoionic
thiazollumolate
tributylphosphine product
mechanism is thought to operate
is
gives
proposed
( 27)
the to
which
quinolone
arise
upon
(28)
from
irradiation
as
in
the
presence
desulphurisation
of
the
intermediate
isomer (29) followed by ring opening and closure as shown.
of
2. l9 The
indicated in scheme
Dewar
A similar sequence
i s suggested to explain the formation of the products (30) and (31) obtained on irradiation
the
of
analogous
aminothiazolium
salt
(32)
under
the
same
conditions. l9 Competition is thought to occur between the ring opening pathway and
Dewar
isomer
formation
oxathiazollumolate ( 3 3 ) . 2o
in
the
photochemistry
Thus irradiation of (33)
of
the
mesoionic
frozen in an inert matrix at
low temperatures gave rise to two spectroscopically characterised species; these was assigned the ring opened structure (34) as
The
(35).
Dewar
isomer
production of the
(36) ;
loss
following
latter
was
of
carbon
thiazirine (37) which could open to ( 3 5 ) . the
proportions
of
(34)
and
(35)
yield
of
rearrangement 1.3.4-oxadiazoles results in (40)
of
(34).
Ring
the
opening
1.2.4-oxadlazoles
(39) . 21
ring opening to
product.
dioxide
to the this
formation
would
were
is
also (38)
It is suggested that
If the
substltuents
yield
of
the
phenyl
more vlscous
observed;
or
while softer matrices gave a higher proposed to
give
to
rationalise
the
irradiation of
give a species represented by the
and (41) ; closure of this to (42)
the isolated
ascribed
Interesting environmental effects upon
obtained
harder media favoured the formation of (35) relative
one of
and the other was identified
the
corresponding
(38)
in methanol
resonance forms
and subsequent rearrangement leads to on
(38)
are changed
so that R 2 is
Photochemistry
292
B Ut
MeNk Ph
(2 6 )
Ph
(30)
0
II
P h-C-C
H ,C N Ph
Ph
(32)
(31)
0
+
s
Ph >-N
Ph-CEN-S-
+ (33)
(341
(35)
ph.kJ 0
Ph
S
(36)
\Y S (37)
(38) R, = A r , R, = NH, or NHMc
11114: Photochemistry of Aromatic Compounds
293
N-N
(39) R, = A t , R2 = NH, or NHMe
.AR2 Rl<
0-
Y
R , q -q2 N:
0
(40)
N
0
II
II
P h -C-N
(42 )
fi 0 ’
(44)
Jd (46)
H-C-R,
(43)
0
N
,OMe
d $ 0
(45)
CN
0 (47)
Photochemistry
2 94
x
0
(49)
(48)
q0
$J
-”
N-
(51)
(50)
(52) X = N , Y = 0
(54) X = N , Y = O
( 5 3 ) X = N , Y = NH
( 5 5 ) X = N , Y = NH
(56) X = N , Y = S
(57) X = N , Y = S
k (58)
11114: Photochemistry of Aromatic Compounds
295
phenyl or dimethylamino instead of amino or methylamino, the reaction appears to be diverted at the ring opening stage so that ( 4 0 ) / ( 4 1 )
proceeds to ( 4 3 ) as the
isolated photochemical
structures
represented by ( 4 0 )
product.
The
and ( 4 1 )
Intermediacy of
such
as
that
has been tested by comparlng the photochemistry
of the oxazole ( 4 4 ) with that of the azide ( 4 5 ) . 22
Photolysis of the latter would
be expected to lead to nitrogen expulsion and formation of a nitrene analogous to If this is in fact an intermediate in the photorearrangement of
(41).
the
product
obtained
irradiation of
from
should
(45)
be
identical
In the event irradiation of
(44).
the same product,
the acylazirine ( 4 6 ) .
with
that
and (45)
(44)
However,
( 4 4 ) then
obtained
from
did indeed give
photolysis of
gave an
(44)
additional major product, the diacetylacetonitrile ( 4 7 ) , which was not formed from it was found that the formation of ( 4 6 ) from ( 4 5 ) was inhibited by triplet
(45).
quenchers,
while
sensitisation
of
suppression of the formation of secondary
photoproduct
the
reaction
produced
of
resulted
(44)
in
complete
and Instead gave the oxazole ( 4 8 )
(47)
by
sensitised
isomerisation
of
as a
.
(46)
The
observations can all be accounted for i f a nitrene is assumed to be the reactive a
intermediate,
with ( 4 6 )
singlet nitrene.
.
b d n g derived from the triplet nitrene and (47)
from the In this
Acylazirine formation also occurs for the oxazole ( 4 9 ) . 23
case irradlatlon with 254 nm light gave ( 5 0 ) as a mixture of diastereomers along with
similar
wavelength suggest
amounts light
of
gave
the
the
intramolecular
Paterno-Buchi
oxetane
product
Use
(51).
only.
of
leading the
longer
authors
that acylazirine formation occurs from an upper excited state.
obsorvations
were made in the photochemistry of
wavelength
irradiation
but
rearranged
which was inert to long
(44)
efficiently
to
Similar
when
exposed
to
light
of
wavelength of 254 nm. 22 Benzannelated photoisomerise. which
oxazoles
glvlng ( 5 4 )
proceeds
which,
cleavage
following
observed
subsequent
products. 24
surprising
that
and and
the
closely
as
heteroatoms and
closure
precedents of
(57)
thiazole
and
(52)
also
(53)
and a mechanism is given
between the
related
isomer
such
respectively.
ring
Given the
photochemically to the
diazoles (551,
to
produce
rearrangement. (52)
(56) is
and
biradicai to
the
it is somewhat
(53)
found
a
leads
not
to
rearrange
especially since evidence exlsts suggesting
,
that irradiation results in cleavage of the nitrogen sulphur bond to give a biradicai intermediate. 25
The
evidence
the
thiazole
(56)
that
irradiation of
( 5 6 ) with an alkyne gives a product derived from
mechanism photolysis.26 1.2-addltion
of
by
this
and
the
trapping reaction results
the
observation
occurs
apparently formed
between
comprises
cycloaddltlon
of has
a
rearranged now
suggest
been
that
the
of the alkene or alkyne to the N-S
and that a biradical specks is not, in fact,
and
alkenes
biradical
photochemical
or
aikynes; (581,
intermediate. 25
examined
directly
products are
using
formed
thus
which is
by
The flash direct
bond of the photoexcited thiazole
an intermediate.
296
Photochemistry
0
0
OH
(59)
OH (60)
0 (61)
(62)
9
0 H
(63)
P
h
q
PhCO COPh
(65)
(64)
O
p?Kp Ph
(66)
IIll4: Photochemistry of Aromatic Compounds
297
In last year's report work on the rearrangement of isoxazoles such as (59) to give (60) was mentioned;27 a further account has now appeared in which the mechanism of the reaction has been addressed. 28 of (60)
from (59)
can be sensitised,
I t is reported that formation
indicating triplet excited state reactivity;
it
is also found that the addition of ethyl bromide increases the quantum yield of product formation significantly. of ( 5 9 ) .
although it does not char:ge the fluorescent lifetime
Thus it would appear that the enhancement or the quantum yield is not
due to heavy atom acceleration of inter-system state to the triplet of
(59).
frnrn the singlet excited
crossin,:
To explain these results the authors suggest that
(60) is also formed through the singlet excited state of (59) &y
a singlet nitrene
and that the heavy atom additive acts by increasing the rate of conversion of the singlet nitrene to its triplet.
The triplet nitrene then proceeds to (601, while the
singlet nitrene either proceeds to (60) also.
or reverts to (50).
This explanation
Is supported by the results of experiments in which the nitrene was generated Independently from the azide (61) ; sensitised photolysis of ( 6 1 ) gave (60) while direct irradiation gave both (60) and ( 5 9 ) . Furans can also undergo photolytic ring cleavage and a new example is the photochemistry of (63)
since the
(62)
in which the intermediate is assumed to be the carbene
isolated product
(64)
appears to
result from
its intramolecular
The furan (64) is highly fluorescent and the authors propose its use
trapping. 29
as a photoactivated fluorescent probe. Photoisomerisations in which from
carbon
to
oxygen
rearrangement
of
structure
determined
was
are
an
aromatic
relatively
tetrabenzoylethylene
to
(65)
by X-ray
rlng migrates within
rare.
analysis
One
very
give
the
some
old
lactone ago. 30
years
a
molecule
example
is
(66) ,
the
whose possible
A
mechanism for this reaction involves intramolecular transfer of a phenyl group in excited tetrabenzoylethylene to
Consistent
(66).
crystalline forms.
to give the ketene (67) which then cyclises thermally
with
this
proposal
only one of which
is
the
fact
produces (66)
that
(65)
exists
on irradiation;
in
crystalline form has (65) in a conformation in which one of the phenyls is an adjacent carbonyl,
as shown in the structure
unreactive crystalline form has all the evidence for the intermediacy of (67)
phenyls
replaced
by
those
of
the
(65).
to
whereas
to the carbonyls.
the
Further
has now been found;31 irradiation of, (65)
at 10 K leads to signals in the infra-red consistent with the structure of the
drawn for
two
this reactive
spectrum of the photolysate which are
ketene
lactone
(66).
(67) ; on warming. It
would
the signals are
appear
that
similar
conformational effects can also be observed in solution if conformational Changes are slower than the rate of decay of the excited state; examlned the ketones
photochemistry of
(68)-(70)
and found a mixture of
upon the influence of the a-substltuent molecules'
conformatlons. 32
thus Wagner's group has
compounds such as the
a-substituted
a-mesltyl
reactlvity which appears to
depend
upon the stabilities and mobillties of the
In addltion to the expected
products derived from
Photochemistry
298
(68) R = CH,
(67)
(69) R = CH2CH2CH3 ( 7 0 ) R = Ph
P
n
R
Ph
(71) R = CH,
(72) R = CH,CH2CH, (73) R = Ph
0
0
OPh
0 (75)
y 2
(76)
y
2
(77)
299
11114: Photochemistry of Aromatic Compounds &hydrogen derived
abstraction and a-cleavage.
from
mesityl
group
migration
irradiation of such
as
( 6 8 )- ( 70)
(71)-(73).
yields products
On
the
basis
of
interpretation of nmr spectra and molecular mechanics calculations it Is Suggested slows rotation within the molecule so
that a-substitution in the ketones (68)-(70) that
no conformatlonal
involved,
changes
Consequently,
&hydrogen
occur
during the
lifetime of the
excited
state
in cases where the more stable conformation dlsallows
abstraction but allows aryl group migration from carbon to oxygen,
this latter reaction becomes dominant. photochemical transformation of
(
Phenyl group migration also occurs in the
74) to ( 7 5 ) and the mechanism of the reaction
has been examined;33 it is concluded that the reaction proceeds from the triplet state of ( 7 4 ) . new
A
photochemical
rearrangement
has
been
observed;
irradiation
aqueous solutions of the sodium salt of meta-amlnobenzenesulphonic
of
acid
( 76)
has been found to give the ortho and para derivatives along with aniline. 34
The
reaction shows a pH dependence with maximum efficiency displayed at pH 3 and and lowest efficiency at extremes of
11. 5,
qU~3nChlng and sensitlsatlon experiments excited state;
pH and at pH 9.
suggest the
radical intermediates would
The results of
Intermediacy of
not appear
to
the triplet
be involved since the
appearance of the products was not influenced by the presence of butanethlol. The authors suggest that the reaction takes place by adiabatic protonation of the excited state on carbon followed
by relaxation to the o-complex
(77).
In a
process which represents the reversal of the electrophlllc sulphonatlon of benzene, (77) then either loses the sulphonyl group to give anlilne. rearranges
by
1,2-shifts
to
new
o-complexes
prior
or the sulphonyi group
to
deprotonation
to
the
products. Addition Reactlons
2.
Past work on the addition of simple alkyl-substituted benzene has shown that appear
to
be derlved
the
from
reaction favours inltlal
posltlons of the aromatic ring.
the
bonding between the
produced shows evidence for some separation of Charge. coupling
between
Cornellsse and co-workers
C-1
of
adducts which
alkene and
the
meta
The intermediate species which Is thought to be
the addition of ethylene to benzene. from
alkenes to photo-excited
formation
and
as shown in ( 7 8 ) for
The isolated product. either
C-3
or
C-5
of
8 . 8.
(791,
the
results
intermedlate.
have now described the results of CNDOIS and MNDO
calculations performed for this reactlon. 35
Their results are consistent with initrai
bonding between the alkene and the mete positions of the ring followed by very rapid.
almost
synchronous,
closure of
calculated intermediate corresponds to rather than twltterlonic character: occur in the excited benzene,
the ( 78)
intermediate to '
the
product.
The
except that it possesses blradicaloid
however they find that Charge development does
In the sense shown in ( 7 8 1 , in the early stages of
300
Photochemistry
C H,
&+
2
1
-2
4
(78)
R
(80 1
(81)
R3
( 8 3 ) R, = CF3 , R, = C F 3 , R, = H ( 8 4 ) R, = CF3, R, = CN , R,= ( 8 5 ) R,
=
H
CF3 , R, = H , R, = CN
301
llIl4: Photochemistry of Aromatic Compounds the addltlon.
The same group has also tested the viablllty of various possible
mechanisms
for
the
mete-photoaddition
steady state
combination of
of
cyciopentene
to
benzene
using
a
kinetics and fluorescence quenching experiments. 36
The results confirm that It is the S1 state of the arene which reacts with ground state alkene but do not ailow any concluslon to be made about the intermediacy of an exciplex or any other species along the reaction path. laboratory.
Also in the same
the products of the mete photo-addition of cyciopentene with alkyl and
slze of the
aikoxy benzenes have been determined and the effect of increasing alkyl or alkoxy group examlned. 37
The major product isolated is ( 8 0 ) , although
(81)
more
and
other
isomers
slze
substituent's
Is
become
Increased.
mechanism involving the
Important
The
formatlon
of
results
(82)
for
are
where
alkyi
benzenes
consistent
the
as
with
a
the polar
substltuent stabllises
the
posltlve charge and sterlc Interactions are avoided by the endo orientation of the
Also
cyclopentane. obtained
from
trifluoromethyl products
conslstent with a polar intermediate are the mete
the and
Isolated
of
lrradlatlon nltrlle
were
cyclopentene
substituted those
in
benzenes which
and
cyclohexene
(83) - ( 85) ;
the
maximum
in
all
number
adducts
with
the
cases
the
of
electron
withdrawing substltuents were piaced at positions 3 and 5 in the polar intermediate analogous to produced;
(82) - 3 8
thls
seems
in this serles both ex0 and endo adducts are
However, to
be
in
accord
with
the
Idea that
adducts
endo
preferred (due to secondary orbltal lnteractlons as the reactants approach)
are
unless
substituents on the benzene ring offer steric resistance. In all of 1,3-posltIons
above photoaddltlons meta addition
the
of the arene.
However,
has occurred
to the arene are also formed In some reactlons,
between
between the versus
mete
ortho
exclted
the
and it appears that the ortho
versus meta selectivity can be predlcted by consideration of the Charge transfer
across
ortho adducts resultlng from 1 , 2-addition
arene
and
selectlvity and
the
charge
alkene.
transfer
energetics of The
was
relationship
the
subject
of
several papers discussed In last year's report. and has since been summarised in a revlew. arene formed. full
alkene
becomes,
the
greater
is
transfer
deficient
rather
arenes
than
(83) -(85)
cycloaddltlon
proportion
donor
alkene
photo-adduct
(86)
2,3-dihydrofuran as the
only
are
mentloned
electroneutral alkenes such as cyclopentene. the
the
In the Ilmlt. as the process becomes exergonlc.
electron
electron
less endergOnlC that charge transfer between excited
Essentially. the
and
have
formed.
above
ortho
of
adducts
products resulting from
gave
Thus
mete
while
the
adducts
with
the acceptor arene benzonitrile and been
isolated product. 39
reported With
to
give
the
ortho
1-methoxycycioalkenes
products derived from [2+21 photoadditlon to the nitrile group were obtained. 39
A
similar
of
pattern
cyanoanisoles:
of
reactivity
is
mete
adducts
are
seen
for
formed
the with
photoaddition cycloalkenes,
reactions. while
products
resultlng from ortho addition are isolated when ethyl vinyl ether is used. 40* 4 1 The
groups
of
Gilbert
and
of
Wagner
have
reported
examples
of
Photochemistry
302
CN
(86)
0 -C H,C Hz-
C H =C
R, ( 8 7 ) R, = CN
I
R, = H
(8 8 ) R, = H , R, = CN (89) R, = H , R, = C0,Mc
(99) R , = COCH,
I
R, = H
(100) R, = H , R, = COCH,
(96) R, = CN , R, = H
( 9 7 ) R , = H , R, = C N (98) R, = H ,
R, =
(105) R , = COCH,
C02Me
, R, =
H
(106) R, = H , R, = COCH,
H,
303
IIIt4: Photochemistry of Aromatic Compounds Intramolecular addltlon reactions.
the products of whlch lndlcate a departure from
the normat mechanism of arene addition. 42-44 alkenyloxybenzoates or
benzonltrlies such as
addltlon and ylelds
ortho
these
open
thermally
cyclohexadlenes (90) - ( 92)
to
the
cyclo-octatrlenes
photolysed to the Isolated products ( 9 6 ) - ( 9 8 ) selectivity just described for where
orlentation
mere
similar;
lrradlatlon
dlenes (101)
of
of
Gllbert reports that lrradlatlon of as
the
prlmary
(93)- ( 9 5 )
. 42
and
took
place. 4 0 a 4 1 such
Wagner's
as
(99)
are
100)
gave
(
as primary products which opened thermally to trienes
may also proceed in an Intermolecular fashion slnce pare with
findings
and
(103) and (104) , and were then photolysed to (105) and ( 1 0 6 ) . Irradiated
further
to cyanoanlsoles
Intermolecular addltlon of alkenes addition
products:
are
Is In contrast to the
This result
alkenyioxyacetophenones
and (102)
results In intramolecular
( 8 7 ) - ( 89)
hexene
appears
to
produce
a
triene
The reactlon
methoxyacetophenone
analogous
to
(
103) . 44
Wagner produces convlnclng evldence that it Is the triplet T+n* states of (99) and (100) which are responsible for the reaction43 and this may be the origin of the ortho rather than mete mode of addition for these compounds. additlon
Ortho
to
the
arene
ring
also
occurs
in
cage
geometrical constralnts dlsallow other orientations of addition;
Is
the
intramolecular
photochemical
reaction
cycloaddltion
which
adducts. 45
A
Diels-Alder
norbornadlene-naphthoquinone has been reported
in which the
spiro-fused ring on the bridge:
thus
(
systems can
new
occur
example
norbornadiene fragment
107) gives
(
where
a common example In
of
this
possesses a
108) on irradiation. 46
Alkenes add photochemically to naphthalenes, normally to give products from 1 . 2 addition to the ring.
In a report whlch appears to be a further example of
this reaction Chow and co-workers reveal that lrradiatlon of mixtures of naphthols.
or their
methyl
ethers.
additlon of
the
enol
1-naphthol
gives
the
product ( 1 1 0 ) . fact
that
reactlon
of
acetyl
of
the
enolised
closely
acetone
yield
diketone to
cyclobutanol
However,
the
more
and
form
(
109)
products
the
which
derived
from
naphthalene ring.47
retro-aldolises
the
to
1,2 Thus
Isolated
the authors show that the excited state Involved Is In acetyl
acetone
resembles
de Mayo
acting as the alkene component.
rather
than
the
naphthol;
photocycloaddltion with
thus
the
the
naphthol
A different group has irradiated the silyl ethers
of 1- and 2-naphthol in the presence of methyl acrylate and obtained products of which show a degree of regioselectivity. 48
1,2-addition gives
(
111)
while
2-siioxynaphthaiene
described suggest that in this which
is
involved.
desiiylated
and
The
case it is the
authors
converted to
gives
their
further
( 112) ;
irradiation
condltions
naphthol sllyi ether exclted state
describe
hypoiodites:
Thus 1-siioxynaphthalene the
how
photolysis
the of
adducts these
can
be
then yields
products derived from ring expansion of the cyclobutyloxy radicals produced. Gilbert's addition
of
group
report some new results for
poiarised
bichromophoric system
alkenes (
to
the
naphthalenes. 49
interIt
and
Is
intramolecular
found
113) Undergoes intramolecular addition to give
that (
the
114) while
304
Photochemistry
(107) n = 2 , 4
(109)
CO,CH, I
(108) n = 2 , 4
(1101
@
CO,CH,
OSiMc3
(111 1
(112)
IIIl4: Ptiotochemistry of Aromatic Compounds
305
R (114) R = H (118) R
(119)
(120)
= CN
(121 1
(122) R
1
(123) R = 2
-
naphthyl
- naphthyl
(124) R = 9 - p h t n a n t h r y l
Photochemistry
306 the isomer and
(
(115)
is inert.
respectively,
119) ,
The cyano derivatives
studied
authors
attempt
greater
charge
However,
give
1,2-addition
density
at
not all of their
naphthalene
with
bichromophoric
and the
the
respectively.
products
interpret this,
to
and (117)
with
Thus each one of the
high
regioselectivity
non-reactivity
1-position
results,
of
the
of
dihydrofuran,
support
this
system
to
the
However,
naphthalene
ring
and
state.
rationalisation.
In
another
photochemistry both
the
has
( 122)
been
and
123)
(
of the enone double
reactions
are
regloselectlve.
as with the naphthol/acetyl acetone palrs described
above.
it is probably the enone chromophore which is excited.
report
that
the
excited
and for
whose
again
the
(117).
photoadducts resulting from 1,2-addition
in these systems,
and
in terms of
(1161,
reported50 the alkene partner is a 3-phenylcyclopentenone:
bond
(1151,
naphthalene
particularly those for
naphthalene-alkene
give intramolecular
give (118)
while dihydropyran and dihydrofuran add to naphthalene
itself to give predominantly (120) and (1211, systems
(116)
5-( phenanthrylmethyl) cyclopentenone
124)
(
The authors also
also
Undergoes
the
reaction. 50 Two examples of In one, of
l14-addition to the naphthalene ring have been reported.
the substltuent effects upon the reaction between the triplet excited state
1-acetylnaphthalene
while
in the
other,
and
the
variously
substituted alkenes
1.4-addition
of
a-methyl
has
styrene
been examined, 51
and
of
1. 1-dlphenyl
ethylene to the phthalimlde (125) is shown to proceed by electron transfer from alkene to
the
which
is
the
excited state
isoelectronic
irradiated with
with
stilbene. 53
of
the
phthalimide. 52
naphthalene, The
also
addition
The azaindene
forms
products
addition
are
(126),
products
assigned the
when
structures
(127) and ( 1 2 8 ) . Many examples exist of the reaction of anthracenes with alkenes and dienes to
give
products
anthracene 'ring. (129)
resultlng
from
addition
whic,h are then
across
reaction to
Yang has used this
the
9, 10-positions
generate the
converted to the novel para.para'
of
the
[4+41 adducts
linked species
(130).
These compounds are chemllumlnescent on thermolysis and yield benzene and. the case of
R=H.
singlet
excited anthroic
acid. 54
in
The [4+21 photoaddltion of
maleate and fumarate esters to anthracenes has been reported previously: 55 the lntrarnolecular version of thls reaction has now been examined. 56 ester
(1311,
R=Me.
yields
the
adduct
(132)
with
low quantum
The fumarate efficiency;
the
same product is formed from the corresponding maleate ester
and the authors
show
is
that
(131)
is
intermediate
in
the
reaction.
Evidence
presented
to
suggest that both esters react to give intermediates which revert to the fumarate ester (131) more efficiently than they proceed to the product (132), and that this accounts for the low quantum efficiency as well as the formation of (132) both maleate and fumarate esters.
from
Some diastereoselectivity i s also observed in
the reaction if chiral esters are used ( e . 8. i f R i s bornyl or menthyl) . 5 6 Photoaddition
of
alkenes
to
phenanthrenes
also
occurs
across
the
307
l l l i 4 : Photochemistry of Aromatic Compounds
HF
PhO'
Ph
(127)
(126)
Ph (128)
x'
(129) R = H , C 0 2 H
'h
(130) R = H , CO,H
Photochemistry
308
(1 31)
(132)
(133)
qvD \N
0
ElH
(135)
(136)
I'
(137)
Q I
CI
309
11114: Photochemistry of Aromatic Compounds 9, 10-position and an example of this was cited above for structure ( 1 2 4 ) . 50 tetra-azaphenanthrene
is no exception;
(133)
The
it is found to give high yields of
cyciobutane adducts when irradiated in the presence of chlorinated aikenes. 57 The photoreduction of arenes is also an addition reaction and two examples have appeared during the period of this report.
Irradiation of the 2.2’-quinoxalyl
in acidic solution leads to the formation of a blue species for which the
(134)
structure
( 135)
isopropanoi
is
gives
suggested, the
while
dihydrophthaiazine
phthalazine (137)
(
and
when
136)
the
dimer
irradiated (138) ;
it
in is
proposed that these are formed from a common phthaiazinyl radical produced by hydrogen abstraction from
the
solvent
by the
excited
phthalazine. 59
bases will add to photochemically produced arene radical cations; of
phenanthrene
in
the
presence
of
an
electron
acceptor
ammonia leads to 9-amino-9, 10-dihydrophenanthrenes y& cation.
and
Nitrogen
thus excitation an
amine
or
the phenanthryi radical
The mechanlsm of this reactlon has been examined for phenanthrene.
anthracene and naphthalene derivatives. 6O when either
naphthalene or
state to give
(
A similar process may be operating
phenanthrene i s irradiated with indoie in the solid
1-indolyi) -dihydroarene products. 6 1
Addition has also been shown to occur when the pyridinium iodide (139) is irradiated. reaction
The product is assigned the structure (140) and the relevance of this to
the
discussed. 62
photoreactlvity
of
Kosower
solvent
polarity
probes
has
been
The use of osmlum tetroxide to hydroxyiate alkenes is a well known
procedure which is often carried out in aromatic solvents.
These arene solvents
form charge transfer complexes wlth the osmium tetroxide and the photochemistry of these has now been examined.63
it is shown that with benzene and aikyl
benzenes isoiable adducts are formed;
that from
benzene is assigned structure
(141).
3.
Substitution Reactions
Aromatic rings which possess an electron Withdrawing substltuent can undergo photosubstitution of
tMs
or
other
substltuents
on the
ring if
irradiated
in the
presence of a nucleophile. A considerable number of papers have appeared over the years reporting the results of studies almed at gaining an understanding of the
mechanism
and
hence
allowing
prediction
of
the
regiochemistry
of
the
photosubstitution reactlon in cases where more than one group can be displaced. The
reaction
operate.64 S N ~A r *
is cornpllcated by the For example,
fact that
more than
one
mechanism can
direct displacement of a substituent can occur
mechanism). or electron transfer mechanisms can be Involved.
(the These
include electron transfer from the excited arene to an acceptor followed by attack of a nucleophile upon the arene radical cation.
or electron transfer from the
nucleophiie to the excited arene and coupling of the radical ion pair produced. Consequently.
structural changes
in the
arene or
nucleophile can Change the
310
Pho loch emistry
OCH, (141)
(142)
6CH, (143)
OCH3
I
OCH, I
N0, (144)
X ( 1 4 5 ) X = 4-NOz
( 1 4 7 ) X = 3-NO,
(146) X = 3 - N 0 ,
(148) X = 4-NO,
Ph
(149)
.3.
bNH2 mNHA Ar
(150)
But
(1 51 1
(152) X
OH
But
= N,CH
31 1
IIIi4: Photochemistry of Aromatic Compounds mechanism operating and the nature and reglOChemiStrleS of the products.
One of the more heavily studied systems is nltroveratroie ( 1 4 2 ) , and several further papers have appeared this year concerning its photosubstitution reactions. These reports are consistent with those which have appeared previously in that they find that irradiation of
presence of hydroxide or primary or
in the
(142)
secondary amines leads to displacement of one of the methoxy groups.
it is
found that whereas hydroxide and primary amines yield products from substitution of the methoxy group situated mete relative to the nitro group. displace the methoxy group in the per@ position. 65-67
secondary amines
On the basis of Solvent.
quenching and p~ effects it is suggestecF.66 that hydroxide and primary amines
vie
displace the methoxy group
an S N Ara ~ mechanism, with the former attacking
the triplet excited state of the arene. excited state.
and the latter interacting with the singlet
The secondary amlne is proposed to react instead
electron
transfer to the triplet excited state of the arene and subsequent coupling of the radical ion pair.
is replaced by a cyan0 or acetyl
If the nitro group of (142)
group then it is found that the mete selectivity of the photosubstitution reaction with
hydroxide
is
unchanged
the
(I. 8 .
methoxy
mete
group
efficient and proceeds with much lower quantum yield. 68 is
used
as
the
nucieophiie
the
to
the
electron
although the reaction i s less
Withdrawing substituent is still the one displaced), regioselectivity
is
However, when cyanide lost
and
products
from
displacement of the methoxy group pare to the electron withdrawing substituent are also
formed. 68
fluorescence when
in
addition.
when
cyanide
hydroxide
was
the
nucieophiie.
This
hydroxide displaces the leaving group (143)
substitution
used
of
photoiysis one
of
consistent
of
a
methoxy groups
by
the
the
the
nucieophiie.
with
the
idea
that
in the case of the amide substituted
presence
in
the
is
as
in contrast to the situation
an S N ~ Ar* mechanism involving attack
upon the triplet excited state of the arene. veratrole
is
qU~3nChing of the arene is observed,
primary
amine
amine.69
resulted
Both
in
possible
regloisomers were obtained but substitution of the methoxy group mete to the nitro group was favoured. detailed
A
study
1 -methoxy-4-nitronapthaiene
amlneS
finds
that
while
of (
the in
144)
primary
amlneS replace the methoxyi. 70
photosubstitution
the
presence
amines
displace
of the
reactions
primary nitro
of
and
secondary
group.
secondary
Both reactions are found to involve attack of the
amine upon the triplet excited state of the naphthalene and it is concluded that the mechanism is S N ~ Ar*
for primary amines,
while with secondary amines an
electron transfer occurs from the amine to the excited arene. followed by coupling of the radical Ion pair.
A study of the dimethoxynitrobiphenyls ( 1 4 5 ) - ( 1 4 8 )
has
been reported71 whose purpose was to deduce whether the nitro group in one ring could effect any influence over the regiOCht3miStry of the photosubstitution of methoxyi ( 146)-(
by
148)
hydroxide. the
methoxyi
in
no
(145)
mete
to
regloselectivity
the
nitrophenyi
was ring
observed. was
but
for
preferentially
Photochemistry
312 displaced.
The nitro group of 4--nltrophenol is also displaced by water to give
hydroquinone
but
in
photosubstitution
of
very
low
quantum
by
methanol
chloride
bromide by chloride in mete-bromo
yield. 72 in
In
meta-chloro
related
reactions
toluenes73 and
n l t r ~ b e n z e n e have ~~ been reported.
latter case it is concluded that the displacement occurs
of
In the
a S N ~ Ar* mechanism
in which chloride ion attacks the triplet excited state of the bromonitrobenzene. In contrast,
the displacement of bromlde by chloride in para-bromo nitrobenzene
via electron transfer from chloride to the exclted state of
has been found to occur the substrate. 75
Several reports have appeared concerning photostlmulated S R N ~reactions of aryl halides.
In these processes substitution occurs
a chain mechanism as
follows:
Ar-X Ar. (Ar-Nu):
(Ar-X)% t N u *
Nu-
t
(Ar-X)'
+
-
___)
Nu-
t Ar-X
-+
A r * t X(Ar-Nu)' Ar-Nu
(Ar-X)'
t
The photochemical step Is initiation of radical anion formation by electron transfer from the state.
nucleophile to the aryl halide.
one of the two being in the exclted
Thus amino acid substltuted diary1 thioethers have been prepared In high
yields by irradiation of
an aryi iodide in the
Similarly,
benzene thlolate in the presence of halogen substltuted
irradiation of
presence of a benzene thiol. 76
thiophenes glves phenyi thlenyl thioethers. 77 but only in low to moderate yields. With halogenated nitrogen heterocycles. such as pyrldlnes. qulnollnes. and pyrazines. good yields
of
pyrimidines
irradiation in the presence of the anlon of phenyl acetonitrile gives coupled
2-bromopyrldine. 78
products;
for
Resonance
example,
stabilised
(149)
whlch
nucleophlles
can
is
obtalned from
exhibit
ambident
reactivity; thus irradiation of aryl iodide/naphthylamide combinations is found79 to produce mainly the C-arylation N-arylatlon product
(
151) .
product
Slmilarly.
(150)
and only small amounts
lrradlatlon of pare-chloro
pyrldlne In the presence of 2,6-di-tert. -butyl
of
the
cyanobenzene or
phenolate yields80 the blaryl
(
152) .
The S R N ~reaction has been revlewed.*l Blaryls
are also
commonly
prepared
photolysls
by
of
aryl
halides
in the
presence of arenes and several examples have appeared during the period of this report.
Photolysls
of
lodothiophenes
in
the
presence
of
thlophene
glves
2 , 2 ' - b i t h I e n y l ~ ~and ~ thls has been applied to the synthesis of several naturally occuring
compounds. 83
For example,
irradiation of
dehyde in the presence of 2-bromothiophene yleld. aldehyde
2-iodothiophene-2-carbal-
glves the blthienyl (153)
In 99%
Thls Is then converted Into a series of natural products In whlch the and
bromo
functions
of
(
153)
are
modified. 83
Similarly,
313
11114: Photochemistry of Aromatic Compounds
0
COzEt
I
a R
(155) R = c y c l o h c x y l
Q?y COzEt
H
(156)
3 14
Photochemistry can
4-iodolndole-3-carbaldehyde
be
converted
to
the
4-phenyl
or
4-( 2-furyl)
derlvatlves by photoiysls in benzene or furan. respectively. 84 in reasonable yields. A reaction whlch also yields coupled products but which presumably operates by a different
mechanism
is
the to
2,3-dichloronaphthoquinone correlation
between
the
thiophenes
studied
was
coupling give
reaction found
of
thiophene
compounds
of
efficiency and
the
and
is
consistent
the
derivatives
type
ionisation
with
a
(
with
154) . 85
A
potential of
mechanism
the
involvlng
electron transfer from the thiophene to the quinone in the excited state followed by coupling of the radical ion palr and loss of HCI. 85 Aryl-carbon photochemically.
to
aikyi-carbon
Thus
the
bond
photoiysls
formation
can
also
be
of alkyi iodides in aromatic
solvents gives low yields of the alkylated arenes. 86 not preparatively useful slnce the alkyl
induced
hydrocarbon
However, the reactions are
groups are rearranged in some of the
products while secondary and tertiary aikyl halides give the alkylated arenes less efficiently. 86
It
Is argued that the reaction proceeds by homolysis of the alkyi
iodide followed by electron transfer in the radical pair to give a carbocation. 86 Arenes can also be alkylated by photolysis in alkanes and a discussion of the mechanism involved in the formation of cyclohexyiarenes when pyrene and perylene are irradiated in cyclohexane using 185 nm light has appeared. 87 carboethoxy-substituted cyclohexyl-substituted
quinoiines
cyclohexane
derivatlve
1,4-dihydro-4-cyciohexyl derivative
products are
formed;
8.
8.
(
( (
The reaction is thought to proceed
also
Irradiation of
reported
to
yleid
155) while 3-carboethoxyquinoline gives
156) .
from
157)
is
In the case of 4-carboethoxyqulnoiine
quinoline products. 88
the product is the 2-cyclohexyl the
in
In
alcohol
solvents
4-carboethoxyquinollne
in
analogous
isopropanol.
hydrogen abstraction from the solvent by
the singlet excited state of the quinoline. 88 Last year’s
report described
an
account
of
the
reductlve carboxylatlon of
arenes to give dihydroarene carboxylic acids when they were presence of carbon dloxide and amlnes. 89 blphenyl and 2-phenyl-N-methylindole
lrradlated
in the
Another group has now reported that
both undergo carboxylatlon In very low yield
when irradiated in the presence of carbon dioxide and anilines. Mixtures of benzophenone and diphenylamine in the solid state give rlse to Charge
transfer
absorptlon
photochemistry is observed;
bands:
when
these
transitions
are
irradiated
however irradlation at shorter wavelengths
no
Is reported
to allow the isolation of tetraphenyi hydrazine and the coupled product
(
158) . 91
The authors suggest that the benzophenone radical anion is formed, which is then protonated and couples with diphenylamine.
-N-nitroso-dimethylamine
Irradiation of polycyclic phenols with
yields quinone mono-oximes
reaction has been inVt3Stlgated. 92
and the mechanism of the
It is concluded that the reaction proceeds by
proton transfer from the excited state of the phenol to the nitrosamlne followed by homoiysis
of
the
latter.
presumably
within
a
phenolate-protonated
3xcipiex. and coupling of the phenolate with the NO radical.
nltrosamlne
lIIl4: Photochemistry of Aromatic Compounds
315
Two papers have appeared concernlng the lrradlatlon of polycycilc aromatlc hydrocarbons
In the
presence
products. nltroarenes. 93,94 to
occur
when
morphoilne
or
of
nltrogen
dioxide
to
give.
along
with
other
Is also reported
while arene-nltrogen bond formation
Is Irradiated wlth secondary nitrogen bases such as
benzene
piperazlne.
but
to
give
products
of
addltion
rather
than
substltution. 95 The environmental problems associated with chlorinated a r o m a b s continue to stlmuiate interest in reactlons involving photochemical replacement of chlorine by hydrogen.
The
efflclency
of
photochemical
dechlorination
of
some
tetrachlorodloxInsg6 and of p e r c h l o r ~ d i b e n z f u r a n ~ and ~ of various chlorobenzenes and chlorophenols under environmentalg8 condltlons have been determined. effect
of
substltuents
upon
the
efficiency
chlorobenzenes has been examined:
it
of
photodechlorination
of
The
substituted
Is found that in general ortho-substituted
chiorobenzenes are more reactive with respect to
photodechlorinatlon than their
mete or para isomers.99 Some
years
dechiorlnated
ago
when
It
was
Irradiated
reported
in
the
that
4-chlorobiphenyi
presence
of
was
efficiently
trlethyiamine. O0
Potential
applications of this reaction are hindered by the fact that short Wavelength light must be used.
The same group now report thelr findlng that the reaction can
be performed using near U. V. reaction. Io1The
authors
or blue visible light If anthracene propose that
electron
Is present in the
transfer from
the
amlne
to
photoexclted anthracene occurs to give the anthracene radical anion; endothermlc electron transfer from the latter to the chiorobiphenyl is then followed by rapid and irreversible loss of chloride from the biphenyl radlcal anion to give biphenyl radical whlch
then abstracts
hydrogen from
Photodechiorination of chiorophenylbenzoxazole
the (
medium to
give the
product.
159) In the presence of amines is
also found to proceed by electron transfer from the amine to the excited state of (
159). Io2
The
mechanism
of
the
photodechlorlnation
haiogeonaphthols has been investlgated. lo3
and
debromination
The authors suggest
that
for
of the
chloronaphthols electron transfer occurs from the triplet excited state of naphthol to a
ground state
naphthol and that
dechlorlnation then
chloride from the radical anion produced. they conclude that C-Br Instead.
A
similar
pentachiorobenzene. Io4
bond homoiysls v&j mechanism
is
proceeds & v
loss of
in the case of the bromonaphthois the singlet excited state takes piace
proposed
for
the
photodechiorinatlon
of
in this case it is SUggc3Sted that a Charge transfer dimer
is formed between the triplet excited state and a ground state molecule and that dechiorination occurs when this separates into a radical Ion pair.
The quantum
yield of dechiorlnation in this reaction was found to be increased by the addition of sodium borohydride. lo4
addition of
The enhancement of reaction efficiency following the
borohydride has been seen previously in other systems and varlous
mechanisms have been proposed to account for its effect: these
mechanistic
possibilities
and conclude from their
the authors examine
own data
that
electron
eC Photochemistry
316
CN OCH,
CH,O
\
OAc
OCH,
OCH,
( 1 61)
(162)
%%
0
OAc Rl OC H,
R, OCH,
(163) R, = OCH, (164) R, = H
I
R, = H
R, = OCH,
(1 6 7 )
CH30 OCH,
(165) R, = OCH, (166) R, = H
(168)
I
R, = H
R, = OCH,
iiIf4: Photochemistry ofAromatic Compounds
317
transfer from borohydrlde to the triplet excited state of the pentachlorobenrene is The effect of added borohydride and also of triphenyl alkyl borates implicated. lo4 upon the photoreduction of halo-
and cyanonaphthalenes has been examined by
via
Schusterlo5 who also concludes that the reaction proceeds
electron transfer
from the additive to the excited states of the substrates. An interesting result has been obtained in a study of the dechlorination of polychlorobenzenes dechlorination.
meta
positions
by
to
irradiation
resulting from
their
ortho-dichlorobenzene amounts
direct
products
original
in
acetonitrile: lo6
rearrangement
point
of
of
attachment
the are
in
to
addition
chlorlne
atoms
observed.
to
Thus
was found to yield mainly chlorobenzene along with small
of pere-dichlorobenzene;
the authors speculate that the
rearrangement
products are formed by recombination of an aryl-chlorine radical pair.
in another
novel result photolysis of pentachlorophenol in acetonitrile is found to give small amounts of the benroxazole
( 160)
Irradiation of tryptophan
. lo7
and related compounds
hydrogen exchange at the 4-position
amino group is implicated in the process. lo*
other
4-deuterated
indoles whlch
preparation 4-deuterated
have a
3-(2-aminoethyl)
irradiation of the fully protiated compounds in D20. log and
Saito
have
collaborated
reaction. l o *
in
known to result in
This exchange reaction has now
been used as a synthetlc procedure for the and
is well
of the indole nucleus and the side chain
a
detailed
They conclude that
study
side
chain
by
The groups of Shizuka
of
intramolecular
tryptophan
the
mechanism
electrophilic attack
of
the
by side
chain ammonium ion of tryptophan and tryptamine derivatives upon the 4-position of the indole nucleus is the origin of the exchange and that this is a major route
for the radlationless deactivation of the indoie chromophore excited state in these compounds.
4.
The synthetic
lntramoiecular Cvciisation Reactions
stllbene-dlhydrophenanthrene appllcations.
photocycllsatlon
The Mra-OXygenated
reaction continues
to
methyl phenanthrene skeleton
(
find 1611
has been prepared by photocyclisation of the stilbene (162);
aromatisation of the
intermediate
methanol. l2
dihydrophenanthrene
photocyclisation
was
observed
occurs in
the
by
elimination
absence
of
of
the
cyano
group
in
No this
compound112 although the closeiy related structures (163) and (164) are said to cyciise to the phenanthrenes anti-tumour
compounds;
a
(
165) and series
(
166) . 113
of
these
Triaryiethylenes are important
have
been
converted
to
the
corresponding phenanthrenes by irradiation in the presence of iodine as oxidant, and
the
anti-tumour
properties
of
the
phenanthrenes
photocyclisation of styryi pyridinium salts such as ( 1 6 7 ) to give arenes such as systems such
as
styryl
(168)
examined.
has been successfully applied to
quinolinium
salts; 11!5*
the
The
in the presence of iodine
reaction
is
more complex found
to
be
Photochemistry
318
x* Ar
AT
Ar
(172)
p Ph h)f
X (173)
Ph m r $ P h
1176)
(177)
lIIi4: Photochemistry of Aromatic Compounds
C H ( S P h )z
I
(1 78)
3 19
PhSCH-
CHSPh
i
(179)
(181)
(182)
( 1 84)
(183)
Photochemistry
320
regloselectlve for those compounds where the ortho positions of the arenes are non-equlvalent. the
The authors interpret their results by making the assumption that
reactlon
cycllsatlons,
Is
mechanism
similar
to
of
that
stllbene-dlhydrophenanthrene
but note that aryl iminium systems are also known to cycllse
electron transfer mechanism. 15
whlch has been reported this year is the reaction of (171). 117 products,
Phenanthrenes are also formed. in the sensitised Irradiation of
examined
the
photocyciisation
(
(169)
to give (170) and
but in low yleld and along with other
172) . l8 Somers and Laarhoven have
reaction
of
a
series
1,2-diphenylcycIopentenes possessing the structure the substituents
an
An example of the latter type of photocyclisation
(
of
para
substituted
173) . l9 They conclude that
have no influence upon the efficiency of the photocyclisation to
the intermediate dihydrophenanthrenes
(
174)
of formation of the phenanthrenes (175)
and that variations in the efficiency
arise from the effect of the substituents
upon the rate of the thermal reversion of (174) to (173)
and upon the ease of
of ( 174) to ( 175) , l 9 The closely related structure 1,2-diphenylcyciobutene. ( 176) , also photocycllses in good chemical yield to the
oxidation
corresponding phenanthrene. 120 low.
However. the quantum yield of formation is very
While it is tempting to ascribe this inefficiency to an effect of ring slze,
would apeear
from the authors description that
no oxidant was
reaction
so
reactlvlty
and
the
reported
relative
of
lack
of
it
present in the
(176)
may
reflect
efflcient reversion of the dlhydrophenanthrene intermediate to the starting material. The photocyclisatlon of the triarylimidazole
(
177) to a phenanthrene product has
been performed in a polymer matrix and the reaction Is found to proceed much
less efficiently than in solution. 121 Photolysls of the dlthloacetal of in homolysls polycycllc
and coupling to
aromatic
9-phenanthryl
hydrocarbon
analogue
his-( 2-naphthyl)
of
For
mlnutes.
(
182)
intermediate
whlch
is
of
did
not
ethylenes
reactlon
on
the
the
In which
the
proceeds
as
a (
ortho
potential
( 185)
light
and
The to
photochromic
photocycllses to the to the
analogue
stable
and
(183) which
gives only
a
coloured
reverts
to
dihydro
on
(1831
The COrreSpOndlng bis-thienyl ethylenes and
cyano
groups
are
replaced
by (
methyls
show
184) . 123
The
also photocyclise to give coloured species which are presumed
to be dlhydrophenanthrenes. vlslble
the
positions
prevent oxidation
similar behavlour as does the thienyl substituted malelc anhydride cyclophanes
for
produces
irradiation. 122
181) ,
methyl groups
analogue
is thermally unstable and reverts to (181) in
thienyi
thermally
further
substituted
1,2-dImesityl-2-butene. In whlch
also
2-naphthyl
fully
investigated
178) , apparently results
(
on further photolysis gives the
the
cyclise
possessing
irradiation with long WaVel13ngth light. bis-fury1
The
however.
Compound (182)
Irradiation
which
180) .
been
example,
dihydrophenanthrene aromatic system.
which
has
(
1-naphthaldehyde, (179)
178) :
(
stilbenes
dihydrophenanthrenes system. 123
of
ethylene
photocyclisation
give
the
length
These revert both thermally and on lrradlation with of
the
bridging
methylene
chain
was
found
to
IIIl4: Photochemistry of Aromatic Compounds
&o
32 1
o&+ -
0
0
0 (1 87)
6" (188 1
(190) R, = H , R,= OCH, or R, = OCH,
, R, =
(191) H
322
Ph ofochemiistry
(192)
(193)
0 (195)
(194)
0-q
H N\C/X
cJ$? 0 N\
H3
0
IIS
(197) X = O R
(1 96)
(198) X = NHR
0 (199) X = OR (200) X = N H R
323
IIIl4: Photochemistry of Aromatic Compounds determine the rate of the thermal reversion;
for n=2 the
photoisomer reverted
after 15 minutes of heating at 60°C whereas when n=3 or 4 the decay was three orders of magnitude faster and the diydro compounds could only be observed by flash photolysls. 124 Fulglcides such as
(
186) show well characterlsed photochromic behavlour and
yield photocyciised specks such as (187) whlch can be reconverted to (186) irradlatlon with ll8ht of approprlate Wavelength.
by
This photochromic system has
been applied as an actlnometer for lasers125 while the effect of the size of the R group In (186)
upon the quantum yield of the photocyciisatlon has also been
determined: 126
It was found that increasing the size of R favoured the formation
of (187).
The photochromic behaviour of analogues of (186) in which the furan
rlng is replaced by either ~ h e n y i or l ~ lndole128 ~ rlngs has also been examined. The
mechanism
fluorenyi radlcal
of (
photocycilsation
of
the
triaryimethyl
radical
(
188)
to
the
189) has been lnVeStigatt3d. 129
Enamldes of varlous structural types can be photochemically cyclised to give aikaiold ring systems;
this year,
dlmethoxyprotoberberlnes
(
190)
for
example.
have been
It has
prepared
been reported that
by irradlatlon of
(
the
1911
in
Is an N-vinyl benzamide whlch cyciises non-regloselectively
which the enamide
onto the non-equivalent
orrho-posltlons
structurally slmilar system
(
of the benzamide phenyi ring. 130
192) excellent yields of
(
In the
193) are obtained, while the
dehydro derivative (194) is formed if the irradiatlon is carried out In the presence of lodlne. (192)
in the absence of the aryi substltuent
photo-Fries
reactivity
Is
observed
upon the vinyl group of
Instead.
Systems
in
which
the
benzamlde portion of the enamide is modified by the use of furan carboxyiic acid instead
benzolc
of
acid
have
also
been
successfully
photocycllsed
to
give
analogous products132 and the use of these to syntheslse ergot alkaloids has now been described. 133
i f the enamide is further modified so that the amide nitrogen
is phenyi rather than vinyl-substituted
then compounds with structure
(
195)
are
obtained whlch will also cyciise on irradiation to give stereoisomers of (196) in poor yield. 134 Two
groups
have
reported
3-chiorobenzthiophene-2-carboxyllc (
acid
197) 135 and the thiourea system
rlng containing compounds . (199) yield.
Similarly,
the N-aryi
(
their
results
amldes.
with
The
N-substituted
thlocarbamate
system
198) 136 both to glve the benzothlenothiazine
and
(200), respectlveiy.
systems (201)
parent benzthlophene analogues. 138
the former
in hlgh
photocycilse to (202) 137 as do the
The reglochemistry of these reactlons was
not. however, fully dlscussed. 137* 138 A new example of the photocycilsatlon of orrho-vinyl
In
which
the
qulnolone; l 3 9 under
trlpiet
.confirmed
the
vlnyl
phenyi
unit
is
replaced
by
a
biphenyls has appeared vinyl
qulnoline
or
vinyl
an examination of the reaction mechanism by laser flash photolysis sensltlslng previqusiy
condltlons proposed
uslng
the
reaction
lsopropenyl
fluorene
mechanism140
which
( 203)
Is
that
has It
Photochemistry
324
I
s 0 OCH,
NH C 0 CH C I,
HO@ c 002 c H 3
ti
OH
11114: Photochemistry of Aromatic Compounds
325
(211) R = H , R’ = C02CH, (212) R (213) R
= H , R’ = OCH, = CH,, R‘ = OCH,
(220) R = CH,, R’
I
OH
C H,O
Photochemistry
326
H
H
H
(222)
(221)
( 2 2 3 ) R , R’ = H I a l k y l
NC
(224)
H
327
11114: Photochemistry of Aromatic Compounds
proceeds adiabatically to the triplet excited state of the Intermediate (204) which then rearomatises either by air oxidation or by a 1.5-hydrogen shift. The 2,2-dimethyi-2H-benzpyran anti-juvenile
system is the parent skeleton of a number of
hormone compounds;
this ring system has now been prepared by
electron transfer sensitised irradiation of alkoxy-substituted In
another
synthetic
phySl0lOglCally (2051,
application
active
of
photochemical
clnnamyl alcohols. 142
cyciisatlon
N-(dlchioroacetyl) tryptophan
compounds,
leading
methyl
to
ester,
cyciises on irradiation to give (206) ; the second chlorine substituent is
Use of the
presumed to be replaced by hydroxyi during work-up and Isolation. monochioroacetyl tryptophan 2-position
of
the
indole
resulted
in
large
nucleus. 143
The
an
interestlng
application
of
cycilsation
reaction has been
synthesis of the indole alkaloid indolactam V.
in
of
amounts
onto
the
applied to
the
(207). 144
high
intensity
laser
photochemistry,
2-methylbentophenone has been converted to the anthrone (208) ; 145 the reaction proceeds
via
-Z-isomer
by photoenolisation of the parent ketone.
the E-enoi
which Is produced along with the shorter lived
(209)
The lifetime of the E-en01 Is
several seconds whlch is long enough to allow sufflcientiy high concentrations to be attained that it can absorb light and undergo further photochemistry to give the cyciised intermediate (210) which is converted to (208) by air oxidation. 145 5.
Dimerisation Reactions
There are very few Becker
and
Andersson
papers to report upon under this heading this year. have
published the
the
anthracene
rings
intramoiecuiarly and, bond,
of
paper
isomers
upon
the
of
(21 1)
yielded
compound
(212)
gave
Only
aikene (213).
[4+21
mainly
[4+41 adduct
on
these
substltuent
either [4+41 or [4+21 adducts are obtained.
derivative adduct.
&
the
depending
full
their
ethyienes (21 1) - ( 213) . 146
photochemistry of the 1 ,2-dianthryl
adducts the
only.
was
compounds
upon
on
the
the
dimerise
llnking
double
The carbomethoxy substituted while
[4+41 adduct
(215)
work
When irradiated,
the
(214)
obtained
methoxy
substituted
along with
some
the
susbstituted
from
doubly
[4+21
The [4+21 adducts from (211) and (212) were asslgned structures
(216) and (217 ) , respectively: the spectroscopic evidence did not, however. rule out the alternative possible structures (218) favours
the
former.
photochemistry
of
Becker
the
and
and (219) , but chemical precedent
Andersson
hydroxy-substltuted
undergoes a novel rearrangement to the product arise original
(222) ;
preliminary
communication
(221)
further (220) . 146
whlch
on
the This
is presumed to
reporting
this
reaction
where
the
authors
to the rearrangement product in whlch the methyiene and
carbonyl groups of (221) were interchanged. 147 the
report
aikene
these structural assignments are revisions of those given in the
assigned a structure irradiation of
also
dianthryi
9-substituted
anthracenes
(223)
It has also been reported that yields
an
insoluble material
Photochemistry
328 wpich the authors speculate may be an anthracene dimer. 148 Many examples of
anthracenes
photodlmerisatlon
have been reported,
there are relatively few examples of naphthalene photodimerlsatlon. co-workers
but
Alblni and
have re-examined the photochemistry of 2-cyanonaphthalene
and have
Isolated two products Identified as the cage dlmers (224) and (225) ; the position of the cyano group on the benzene ring in (225) was not asslgnable from the data obtained. 149
A slmllar cage dlmer was formed between 2-cyanohaphthalene
and naphthalene, while irradiation of 2-cyanonaphthalene wlth anthracene gave a [4+41 adduct.
On the basis of qUenChlng and sensitlsation experiments. as Well
as chemical
precedent,
the authors
suggest
that the
naphthalene dlmerisatlon
via a
reactions proceed from the singlet excited state of 2-cyanonaphthalene adduct:
Is
thls
then
2-cyanonaphthalene
sensitised
into
its
triplet
exclted
state
$4+41
by
the
and Undergoes closure to the cage product. 149
Lateral Nuclear Rearrangements
6.
This section reports those reactlons In which an arene slde chain undergoes cleavage and the fragments recombine by bondlng of the non-arene fragment to the arene ring. photo-Frles
One of the
rearrangement:
using pere-methoxyphenyl found for labelled
180.
probed the
mechanibm
acetate as the substrate.
production of
the
wlth
most common examples of this
Shine has
13C
are
l4C
consistent
this
reactlon
The kinetic isotope effects from
2-acetyl-4-methoxyphenol
and
process is the of
wlth
the
phenyl acetate
product
formation
by
recombinatlon of a Caged radical pair originating from the singlet excited state of the ester. The
photo-Fries
3-acetylindoles; synthesis of 5acetone
reactlon
the
51
and
of
application
N-acyllndoles of
the
favours
reactlon to
indoles has now been described. 152
irradiation
of
4-acetyllndollne
gave
7-acetylindoline in 12% and 11% ylelds. respectively. 152
into
the
of
for
the Thus
5-acetyl-
and
Smaller amounts of the
derivatives of these products along wlth unspeclfled amounts of
were also formed. yield
formation
7-substituted
sensitised
N-acetyl
the
N-acetylindoline
lndole
Further lrradiatlon of the products converted them in high corresponding
indoles. 52
rearraf18~?113nt of
Photo-Fries
N-aroylcarbazoles has also been reported; 153 it is stated that irradiation wlth short
Wavelength
light
(254 nm)
gives
3-aroylcarbazoles
(226)
as
rearrangement product while use of longer wavelength llght (366 nm)
(226) and the l-aroylcarbazoles hydroxamic
acid
(228)
found
(227). no
products,
but
the
(229)
rearrangement. 154
formation
cleavage Is occurlng:
benzanilide formed underwent further photochemistry which Included. photo-Fries
major
A study of the photochemistry of the
photo-Fries
benzanilide in the product mixture suggests that N-0 expected.
the
gives both of the
as would b e
In the case of the nitramino pyridines
photolysls is reported to lead to photo-Fries
type products In which the
lIIi4: Photochemistry of Aromatic Compounds
329
AOC J ? J - @ H
COAr
(22 6 1
(227)
0
II
Ph-C-N
/OH ‘Ph
(2 2 8 )
(229)
OH
(230)
(231)
+
P h,As C H, iFF4
330
Photochemistry
p”’” R
q+y
(235)
X
(236)
(238)
(237) OC H3
I
CH30 OCH,
0 CH3 (2391 OCH3
I
OC H,
I
OCH3
OCH,
OCH3
OCH3
33 1
11114: Photochemistry of Aromatic Compounds nitro group has migrated
into the
imperatorin
photolysis
(230)
upon
pyridine
ring. 155 while the
gives,
along
with
natural product
other
products,
the
rearranged compound (231) $ 1 5 6 The photolysis of aryl onium salts can also give photo-Fries type products. Some group V salts have been investigated by Saeva who reports that the aryl arsonium salt (232) ammonium
and
yields the rearranged product (233) ; 57 the corresponding
phosphonlum salts
although these
also
give
products
arising
from
do not arise from recombination of the fragments.
cleavage.
A very similar
reaction of triphenyl sulphonium salts gives biphenyl phenyl suiphlde; reaction solvent
Is sensitised then cage
iodonium
slnce
salts
the
diphenyl
photolyse
inltialiy formed
sulphide
to
glve
radicals appear to
becomes the
mixtures
if the
58
escape the
maJor product. 159
which
include
Diary1
iodobiphenyl:
the
mechanlsm of this process has been investigated by flash photolysis. 6o Systems in which carbon-carbon
bond cleavage in an aryl substituent leads
to products in which the cleaved substituent is bonded to the arene ring include the
aikylated
dibenzyl
ketones
(234).
Ramamurthy
has
compared
the
photochemistry of these compounds when Irradiated in solutlon with that obtalned when they are irradiated in the presence of 8-cyclodextrin. B-cyclodextrin
Type
cleavage
I
occurs
and
the
In the absence of
radicals
obtained
following loss of carbon monoxide to give dibentyl ethanes. amounts
of
Type
II
products
are
formed.
However,
recombine
In addltion.
when
the
small
reaction
is
performed in the presence of B-cyclodextrin a remarkable change in the fate of the
radical fragments occurs
species
(235).
since the
Excited
state
major
product Isolated is the
cleavage
1- ( N. N-dimethylamino) -2,2-dlphenyiethane
of
the
carbon-carbon
also leads to products of
coupled bond
in
photo-Fries
rearrangement as minor components of the reaction mixture. 162
of
Photolysis
small
aryl-substituted
rlngs
can
subsequent closure by cyclisation onto the arene. such as
(236)
upon direct
irradiation are
result
in
converted to
diradicalold species whlch can be wrltten as (238). 163 upon the aryl groups has now been examined
rlng opening
and
Thus 1 , 1-diaryicyclopropanes lndanes
(237)
a
The effect of substituents
and it is found that electron
donating groups slow the reactlon while electron withdrawing groups accelerate the reaction. 164
This rlng opening-closure
sequence can also occur under electron
transfer sensitlsed conditions and an example has been reported this year for a diarylcyclobutane (239). 165
system
in
a
synthesis
of
the
natural
product
magnoshinin,
In this route the cyclobutane (240) was irradiated In the presence of
phthalic acld as the electron acceptor: this is presumed to give the radical cation (241) which closes to glve.
eventually.
(239).
The cyclobutane (240)
is itself
prepared by electron transfer sensitlsed dimerisation of the appropriate &methyl styrene and this
reaction is also presumed to proceed
process
in
occurs
the
semiconductor
( CdS)
9
sensitised
(241).
A similar
photodlmerlsation
1. 1-diarylethylenes to glve dihydro- and tetrahydronaphthalenes. 166
of
332
Photochemistry
no-0 - 0 N O -.
CN
(242)
N' 0
+
(243)
(244)
( 245)
(246)
OH
I
NHCH2CH20H
(249)
333
11114: Photochemistry of Aromatic Compounds Aromatic amine
oxides
have a
large
reaction of this functionality is transfer position.
The x-oxide
photochemical
literature and a
major
of the oxygen from nitrogen to
a ring
literature includes many contributions from Albini's group
and this year they have reported the results of a study of the photochemistry of simple
substituted
N-oxide
pyridine
N-oxides.
The
67
products
when the reaction is performed under basic conditions. is obtained.
(242)
flash
from
formation
structures
of
a
a high yield of the anion
the authors suggest that
species
and
(243)
which
can
this
then
(244) ;
be
the
reaction
represented
either
by
rearranges
Oxygen
tranfer
is
seen
also
in
polymer matrix has been examined. 169
the
and also as an i n
photochemical
a nitro-nitrite is
which In this
the
rearrangement
of
of this reaction in a
efficiency
The nitroimidazole ( 2 4 8 ) . which is used radioiysis activated anti-cancer
vivo
rearranges photochemically to the oxadlazole (249) . 170
which
(245) which
phenyi. or benzyi.
azoxybenzenes to ortho-hydroxyazobenzenes:
an anti-bacterial
to
The same
The latter were obtained in proportions which
were found to be dependent upon the nature of the substltuent X . study was hydrogen, nitrile.
by
Contributing
( 2 4 2 ) . 167
group has investigated the photochemistry of phenanthridine N-oxides rearrange to (246) and ( 2 4 7 ) . 168
proceeds
the
polymerises.
or in basic media is deprotonated to give
formyipyrrole,
via
pyridine however.
Based upon the nature of the products and the results of
photolysis experiments
initial
formed
itself are low yields of formylpyrroie and large amounts of tar;
agent,
This i s probably formed
ester photochemical rearrangement leading to the OXime t 250)
converted
to
(249)
by
a
hydrolytic
ring
opening-ring
closure
sequence. 170
7.
Peripheral Photochemistry
This section deals with the photochemistry of arenes in which Changes occur in a substituent which originate from excitation of the arene chromophore. most common class of substituents.
The
reactions in this category are the
irradiation
of
benzyi
alcohols
in
reactions of
aqueous
leads to photosolvolysis and the formation of benzyl ethers;
The
benzylic
alcoholic
solution
this has been shown
to proceed from the singlet excited state of the arene which loses hydroxide ion to (
form
a
benzyl
1-naphthylmethyi)
The
carbocation. 17'
trimethyiammonium
salts
has
corresponding been
analysed
reaction in
competing heteroiytic and homolytic cieavage of the naphthyimethyl-ammonium bond in the singlet excited state of the salt. 172
for
terms
of C-N
Homolytic cieavage is thought to
dominate in the photolysis of benzyi tributyi stannanes to give products of coupling of the
intermediate benzyi and tributyi tin
phenol-formaldehyde
resins
alkaline
proposed to
solution
is
excited state of the
in the
radicals, 173
photolysis proceed
phenolate (251)
by
of
while the formation of
ortho-hydroxy
elimination
of
benzyl alcohol hydroxide
to give ortho-quinonemethide
from
(252).
in the The
Photochemistry
334
CHZOH
0(252)
(251)
I
(251)
CHZOH
polymer
t
hV
0Scheme 3
6
t
+
Nu’
NO2
1
-
\
Nu-
J
Schcmcr 4
Nu’
IIIl4: Photochemistry of Aromatic Compounds
335
OH (253)
X
i$
0
Ro
C H3
N0,
(254)
Ph &Ph
(258)
(259)
n--J ap OCH,
(260)
(261)
Photochemistry
336
mPh Ph
X
R
R (263) R = H ( 2 6 4 ) R = OCH,
11114: Photochemistry of Aromatic Compounds phenolate ( 2 5 1 )
337
and (252) then condense as shown in scheme 3 and continue The photolysis of the para-benzoyl
to react as indicated to form the polymer. 174 benzyl phosphonic proceeds
via
acid
(253)
to
give
the
benzophenone
(254) 175
probably
cleavage of the carbon-phosphorus bond to give a benzyl carbanion.
as is the case for the corresponding para-nitrobenzyl benzophenone (254) on further irradiation photochemical
reactivity,
the
phosphonic
photodegradable surfactants. 75
phosphonic acids: 76
the
Is photoreduced. and because of their acids
(253)
are
Benzyl carbanion formation
proposed
is also
as
involved
in
the photodecarboxylation of diaryl acetic acids to give diaryl m e t h a n e ~ land ~ ~ in the photo-retro-aldol
reaction of 1-phenyl-2-( nitrophenyl) ethanols. 78
Arene side chain reactions can also b e transfer
as
in
the
photosubstitution
derivatives (255) and (256). 179
of
induced by photochemical electron
para-nitrobenzyl
chlorides
and
nitro
This substitution is a chain process initiated by
llght absorptlon by the charge transfer complex formed
between the
nucleophile
and (255) or (256) as shown in scheme 4.
The formation of aryl aldehydes by
photo-oxldatlon
naphthalenes
of
alkyl
benzenes
and
alkyl
in
the
presence
of
electron acceptors is rationallsed by a mechanism in which a singlet excited state electron transfer occurs from arene to acceptor to give a radlcal’ Ion pair;
proton
transfer then gives a benzyl radical which is intercepted by oxygen. 180
It has
been shown previously that Irradiation ,O,B-dlphenyl ethyl ethers such as (257) in the presence of electron acceptlng photosensitisers gives products resulting from C-C
bond cleavage in the radical cation of
and
an
a-0x0-carbocation. 181
It
to give dlphenylmethyl
been reported
also Undergo the
that
the
radical
analogous
cyclic systems (258)
and
and (261)
The lack of reactivity of the latter pair i s ascribed to the
do not.
(259)
(257)
has now
orthogonal orientation of the C-C singly
occupled
(261).
molecular
reaction 182 but that
(260)
bond normally prone to cleavage relative to the
orbital
(SOMO)
This assumes that the SOMO
Is
of
the
radical
cation
of
(260)
and
malnly associated with the fused phenyl
ring. Benzylic C-C
bond cleavage In a’ photochemically produced radical cation is
also seen when the dlphenylcyclobutene (262) electron
acceptors:
the
radlcal
cation of
is irradiated in the presence of
(262)
opens stereospecifically
ortho-qulnone dimethide whlch is trapped by Diets-Alder
to
an
dienophiles. 183
lrradlatlon of arenes containing leaving groups on remote positions of a side chaln can lead to products derlved from lonisatlon of the leaving group. has examlned the bicyclo-octane both of the substltuents X and Y
systems
(263)
and
(264),
Crlstol
in which either or
are potential leavlng groups. and argues that the
observed reactions are the result of electron transfer from the excited arene to the
u* orbltal of the C-X or C-Y bond to glve an intramolecular radical ion pair x or Y can tonise. 184 A similar process may be occuring in ?he
from which
photolysis of 4-phenyl-1-lodobutane
to glve 4-phenyl-1-butene. 185
Photochemistry
338 References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
25. 26. 27. 28. 29. 30. 31. 32. 33 * 34.
J . J. MCCullough. Chem. Rev., 1987, 87, 811. H. Morrison, Rev. Chem. Intermed., 1987. 8, 125. J. Mattay. AngeW. Chem., Int. ed. E n g l . , 1987. 26. 825. I . R. Gould, D. Ege, S.L. Mattes and S. Farld. J. Amer. Chem. S O C . , 1987, 109. 3794. P. S. Mariano, Organic Photochem., 1987. 2, 1. W. H. Laarhoven, Organic Photochem., 1987. 2. 129. W.A. Rendall, M. Torres, E . M . Lown and O.P. Strausz. Rev. Chem. lntermed., 198516, S . 335. F. C. Mallory and C. W. Mallory, O w . Reactions, 1984. 30, 1. Organic Photochemlstry, J . M . Coxon and B. Halton, 2nd Ed. , Cambridge Unlv. Press, 1987. S. Lin, Youll Huaxe. 1987, 418; Chem. Abstr., 1988, 108. 1 1 2 2 7 3 ~ . N . J . Turro, 2. Zhang, W.S. Trahanovsky and C.H. Chou. Tetrahedron Letters, 1988. 29. 2543. T.Tsuji and S. Nishlda, J. Amer. Chem. SOC., 1988. 2157. H . Wingert, H. Irngartinger. D. Kailfass and M. Regitz. Chem. B e r . , 1987. 120. 825. J. Krzeczek, T. Szurgot and P. Tomasik. Pol. J. Chem., 1986. 2,1259. S. Miki, K . Matsuo. M. Yoshida and 2. Yoshlda, Tetrahedron Letters. 1988, 29, 2211. J. Meng, X. Yao, H. Wlng, T. Matsuura and Y . Ito, Tetrahedron. 1988, 44, 355. I . Kralzlc, M. Mintas. L. Klasnic. F. RanOgaIeC and H. Gusten. Nouveau J . Chim., 1983. 1 , 239. A . J . Abdul-Ghani. N . O . T . Bashi and S . N . Maree. J. Solar Energy 1987, 3 , 53. H. Kato, K . Wakao. A. Yamada and Y. Mutoh, J. Chem. S o c . , Perkin I . 1988, 189. N. Harrit. A. Holm, I . R. Dunkin. M> Poliakoff and J.T. Turner, JChem. S O C . , Perkin I I . 1987. 1227. S. Buscemi. M.G. Cicero, N. Vivona and T. Caronna. J. Chem. S O C . , Perkin I . 1988. 1313. R . R . Sauers and S . D . Van Arnum. Tetrahedron Letters. 1987. 28, 5797. R . R. Sauers, A . A . Hagedorn. S. D. Van Arnum. R. P. Gomez and R . V . Moquin, J. OrR. Chem., 1987. 52. 5501. H. Tlefenthaler, W. Dorscheln, H. Goth and H. Schmidt, Tetrahedron Letters, 1964, 2999; K . H . Grellmann and E. Tauer. J. Photochem., 1977, S . 365. M. Sindler-Kulyk. D. C. Neckers and J. R. Blount, Tetrahedron, 1981, 37, 3377. D. C. Neckers, M. Slndler-Kulyk. J. C. Scalano. L. 1 0 . Stewart and D. Welr, J. Photochem., 1987, 39. 59. F. M. Dmitriev, L. M. Gornostaev. N. P. Gritsan and A. V. El'tsov. & O m . Khlm., 1985, 21. 2452. A.V. El'tsov, F. M. Dmitriev, L. M. Gornostaev and N. I. Rtishchev. O r g . Khlm., 1986. 22. 2361. R. T. Cummlngs. J. P. DlZio and G. A. Krafft, Tetrahedron Letters. 1988. 19.. 69. J. R. Cannon. V.A. Patrick, C. L. Raston and A. H. White, Aust. J. Chem.. 1978. 31, 1265. M . B . Rubin and W.W. Sander, Tetrahedron Letters, 1987. 28. 5137. P. J. Wagner and 8. Zhou, J. Amer. C,hem. S O C . , 1988. 110. 611. Y. P. Strokach. V. A. Barachevskii, N. T. Sokolyuk and Y . E. Gerasimenko. Khlm. F i r . , 1987. 3. 320. J. M. Lalley and W.J. Spillane. J. Chem. S o c . , Chem. Commun., 1987, 1571.
E,
m,
339
11114: Photochemistry of Aromatic Compounds 35. 36. 37. 38. 39. 40. 41. 42. 43. 44, 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71.
J . A . Van der Hart, J. J. Mulder and J. Cornellsse. J. Mol. Struct. (Theochem. 1 , 1987. 151. 1. E.M. Osselton, J . J . van Dljk-Knepper and J. Cornellsse. J. Chem. Soc.. Perkln 11, 1021. P. de Vaal, E . M . Osselton. E.S. Krljnen, 0. Lodder and J. Cornellsse, Recl. Trav. Chlm. Pays-Bas, 1988. 107. 407. G. Weber. J. Runsink and J . Mattay, J. Chem. Soc., Perkin I . 1987. 2333. J. Mattay. J. Runsink, R. Heckendorn and T. Wlnkler. Tetrahedron, 1987. 43. 5781. A. Gilbert and P. Heath, Tetrahedron Letters, 1987. 3.5909. N. Al-Jalal, A. Gilbert and P. Heath, Tetrahedron, 1988, 44, 1449. K . 6. Cosstlck, M . G . B . Drew and A. Gilbert, J. Chem. SOC.. Chem. Commun., 1987, 1867. P . J . Wagner and K. Nahm. J . Amer. Chem. S o c . , 1987, 109. 4404. P. J. Wagner and K. Nahm, J. Amer. Chem. SOC., 1987. 109. 6528. A. S. Kushner, Tetrahedron Letters. 1971, 3275. V. K . Singh, B . N . S . Raju and P.T. Deota, Svnth. Commun., 1987, . 17, 1103. Y.L. Chow, G. E. Buono-Core, X . Y . Liu. K. It0 and P. Qian. Chem. SOC.. Chem. Commun., 1987, 913. H. Suglnome, M. ltoh and K . Koboyashl. J. Chem. S O C . , Perkin i. 1988. 491. A. Gilbert. P. Heath, A. Kashoulis-Koupparis, G. C. R. Ellis-Davles and S. M. Firth, J. Chem. S O C . , Perkin I. 1988. 31. M . T . M . Clements and T.B.H. McMurry, Can. J. Chem., 1987. 1810. D. Dopp and R. Memarian. Nato ASi S e r . , Ser. C. 1986, 189. C. Somich, P. H. Mazzocchi and H. L. Ammon. J. O r g . Chem., 1987. 52. 3614. G. Kaupp and E. Ringer, Tetrahedron Letters, 1987. 3.6155. N.C. Yang and X. Yang, J. Amer. Chem. S o c . , 1987. 109. 3804. G.,Kaupp, Lleblgs Ann. Chem., 1977. 254. K. Okada, F. Samizo and M. Oda. Tetrahedron Letters, 1987. 3, 3819. S. Park, S. KI and C. Sang, Bull. Korean Chem. SOC., 1987. 8, 27; Chem. Abstr., 3. 75345~. I . Baranowska. Monatsh. Chem., 1987, 118, 569. H. Inoue, T. Sakurai, K. Tomoyama, R. Sano. M. Oshio. T. Hoshi and J. Okubo, Bull. Chem. SOC. Japan, 1988, 893. M. Yasuda, Y. Matsuzaki, K. Shima and C. Pac, J. Chem. S o c . , Perkin 11. 1988, 745. J. Meng, Y. Ito and T. Matsuura. Tetrahedron Letters, 1987. 28. 6665. Y . Hui. H. Kong. X. Cheng and Y. Gai. Huaxue Xuebao. 1987. 43. 926; Chem. Abstr., 108, 2 0 4 0 5 3 ~ . J. M. Wallis and J. K. Kochi, J . O r e . Chem. , 1988. 53. 1679. H. C. H . A . van Riel. G. Lodder and E. HaVlnga. J. Amer. Chem. SOC., 1981. 1 0 3 . 7257. A. Cantos, J. Marquet and M. Moreno-Manas, letrahedron Letters. 1987. 8.4191. A. Cantos. J. Marquet. M. Moreno-Manas and A. Castello. Tetrahedron, 1988. 44, 2607. P. Kuzmic, L. Paviickova, J.Velek and M. Soucek. Coll. Czech. Chem. Comm., 1986. 51. 1665. P. Kuzmic and M. Soucek, Coll. Czech. Chem. Comm., 1987, 52. 980. P. Kuzmic, L. Pavlickova and M. Soucek. Coil. Czech. Chem. 1780. Comm., 1987, N. J. Bunce. R. Cater, J . C . Scaiano., and L. J. Johnston. J. Orb?. Chem., 1987, 52. 4214. J. Urban, P. Kuzmic. D . Saman and M. Soucek. Coll. Czech. Chem. Comm., 1987, 52. 2482.
-
m.
a.
-
z.
Photochemistry
340 72. 73. 74.
A. Ailf, P. Boule and J. Lemaire. Chemosphere. 1987, 16. 2213. T. Ichlmura, M. lwai and Y. Mori, J. Photochem., 1987. 39. 129. G.G. Wubbels, D . P . Susens and E . B . COUghlin. J. Amer. Chem. S O C . , 1988, 111. 2538. G.G. Wubbels. E. J. Snyder and E . B. COUghlln. J. Amer. Chem. Soc., 1988. 110. 2543. D. W. Hobbs and W.C. Still. Tetrahedron Letters, 1987, 28. 2805. M. Novi, G. Garbarino, G. Petrillo and C. Dell'Erba. J. OrR. Chem., 1987, 52. 5382. C. K. F. Hermann, Y. P. Sachdeva and J. F. Wolfe. J. Het. Chem., 1987. 24. 1061. A. 6 . Pierinl, M. T. Baumgartner and R. A. Rossi, Tetrahedron Letters. 1987, 28, 4653. C. Combellas, H. Gautier, J. Simon, A. Thiebault. F. Tourniihac, M. Barzoukas, 0. Josse. I. Ledoux. C. Amatore and J . - N . Verpeaux. J. Chem. SOC., Chem. Commun.. 1988. 203. M . G . Kuzmin and V . L. ivanov. Izv. Sib. Otd. Akad. Nauk SSSR. Ser. Khim. Nauk, 1987. 40; Chem. Abstr., 108. 3 6 8 5 7 ~ . M. D'Auria, A. D e Mico. F. D'Onofrio and G. Piancatelli, J. Chem. SOC., Perkin I. 1987. 1777. M. D'Auria, A. De Mico. F . 0. D'Onofrio and G. Piancatelli. J. Ore. Chem., 1987, 52. 5243. M. Somei, H. Aarl and Y. Makita. Chem. Pharm. Bull., 1986. 34. 3971. K . Maruyama and H. Tamiaki. Bull. Chem. SOC. Japan. 1987, 60. 1847. M. E. Kurz. T. Noreu1l.J. Seebauer, S. Cook, 0. Geier. A. Leeds. C . Stronach. B. Barnickei. M. Kerkemeyer. M. Yandrasits. J. Witherspoon and F . J. Frank, J. Orn. Chem. , 1988. 53. 172. M. Lamotte, J. Rereyre. J. Joussot-Dubien and R. Lapouyade. J. Photochem., 1987, 3,177. I. Ono and N. Hata, Bull. Chem. SOC. Japan, 1987, 2891. S. Tazuke, S. Kazama and N. Kltamura. J. Org. Chem., 1986. 51, 4548. Y . Ito. Y. Uozo and T. Matsuura. J. Chem. Soc.. Chem. Commun., 1988. 562. K.S. Sidhu, W . R. Bansal and S.K. Jaswal, Ind. J. Chem., 1986, 258, 910. Y . L. Chow and Z.Z. Wu. J. Amer. Chem. S O C . , 1987. 109, 5260. H . Barlas and H. Parlar. Chemosphere. 1987. E, 519. H. Barlas, Chim. Acta T u r c . , 1986. 14, 109; Chem. Abstr., 107, 144768s. A. Gilbert. S. Krestonosich. C. Martinez and C. Rlvas, Rev. Latinoam Quim, 1987, 18, 40; Chem. Abstr., 107, 154298t. G . G . Choudhry and G . R . B . Webster. Chemosphere. 1986. 3,1935. M. Koshioka, H. lizuka. J. Kanatawa and T. Murai. Agric. Biol. C h e m . , 1987, 31, 949. N. J. Bunce. J. P. Landers. J . A . LangShaW and J . S . nakai. Proc. APCA Annu. Meet., 1987. 80th (Vol. 6) 87/96. 2; Chem. Abstr., 108. 1726398. W. Augustyniak. J. Wojtctak and M. Sikorski, J. Photochem. Photobiol. , A, 1988. 43. 21. M. Ohashi, K . Tsujlmoto and K. Seki. J. Chem. SOC., Chem. Commun.. 1973. 384. Y . Tanaka, T. Uryu. M. Ohashi and K. Tsujimoto. J. Chem. S O C . , Chem. Commun., 1987. 1703. S. Fery-Forgues. 0. Lavabre and N. Paillous, J . OrR. Chem.. 1987. 52. 3381. V . L. lvanov and L. Eggert, Zh. Org. Khim., 1986. 22, 1933. P. K . Freeman and N. Ramnath. J. OrR. Chem., 1988. 53. 149. M. Kropp and G . B . Schuster. Tetrahedron Letters, 1987. 28. 5295.
-
75. 76. 77. 78. 79.
80. 81. 82. 83. 84. 85.
86.
87. 88. 89. 90. 91 92. 93. 94 I
95. 96. 97. 98
99 100. 101. 102. 103. 104. 105.
so.
IIIi4: Photochemistry of Aromatic Compounds 106. 107. 108. 109. 110. 111. 112. 113. 114. 115.
116. 117. 118. 119. 120. 121. 122. 123. 124. 125. 126. 127. 128.
129. 130. 131. 132. 133. 134.
135. 136. 137. 138. 139.
34 1
K. Morisaki, Y. Miura, K. Abe, M. Hirota and M. Nakada, Chemistry Letters. 1987, 1589. G . G . Choudhry. N . J . Graham and G . R . B . Webster. Can. J. Chem., 1987. 65. 2223. I . Saito, H. Sugiyama, A. Yamamoto, S. Muramatsu and T. Matsuura, J. Amer. Chem. S o c . , 1984. 106. 4286. M. S. Morales-Rios and P. Joseph-Nathan. J. Het. Chem., 1986. 23. 1617. H. Shizuka, M. Serizawa. H. Koboyashi. K . Kameta, H. Sugiyama. T. Matsuura and I. Saito, J. Amer. Chem. SOC., 1988, 110. 1726. H. Shizuka, M. Serizawa, T. Shimo. I. Saito and T. Matsuura, JAmer. Chem. SOC., 1988, 110, 1930. A.A. Finnie and R . A . Hall. J . Chem. Res. Synop., 1987, 78. N. S. Narasimhan and I. S. Aidhen. Tetrahedron Letters, 1988, 3, 2987. M.R. Schneider and C.D. Schilier. Arch. Pharm., 1987, 320, 159. S . Arai. T. Takeuchi. M. Ishikawa. T. Takeuchi. M. Yamazaki and M. Hlda. J. Chem. SOC., Perkln I. 1987, 481; see also J. Chem. SOC., Perkin I, 1988, 415. M. Hida. Kenkyu Hokoku Asahi Garasu K O R ~ O Gijutsu Shoreikai. 1986. 49, 315; Chem. Abstr., 108, 9 4 3 6 7 ~ . I . -S. Cho and P. S. Mariano, J. Ore. Chem. , 1988, 53. 1590. K. R. Gopidas. 6. B. Lohray. S. Rajadural. P. K. Das and M.V. George. J. OrR. Chem., 1987, 52. 2831. J. 6. M. Somers and W. H . Laarhoven, J . Photochem. Photobiol. , A, 1987, 9. 125. Y. Kawamura. M. Thurnauer and G. 6 . Schuster. Tetrahedron. 1986. 42'. 6195. A. C. Tetsa. J. Photochem. Photobiol. , A, 1988, 43, 105. A. Sugimoto. M. Okada and S. Yoneda. Chem. Express. 1987, 2, 425; Chem. Abstr., 108, 1 3 1 2 5 0 ~ . M. lrie and M. Mohri, J. Ore. Chem., 1988. 803. S. Murakami. T. Tsutsui. S. Salto. A. Miyazawa. T. Yamato and M. Tashiro. Chemistry Letters, 1988, 5. V . Wintgens. L. J. Johnston and J . C . Scaiano. J. Amer. Chem. Soc., 1988, 110. 511. Y. Yokoyama. T . Goto. T. inoue. M. Yokoyama and Y. Kurita. Chemistry Letters, 1988, 1049. H.-D. llge, J. Suhnei, D. Khechinashvlli and M. Kaschke. J. Photochem., 1987, 38, 189. V . I. Mlnkin, E . A . Medyantseva, O . T . Lyashik. A.V. Metelitsa. I . M . Andreeva, M. I. Knyazhanskl and N. V. Voibushko, Khim. Geterotsikl. Soedin., 1986, 1569; Chem. Abstr., 107, 5 8 7 8 0 ~ . M. A. Fox. E. Gaillard and C. -C. Chen. J. Amer. Chem. SOC., 1987, 109, 7088. P. Chinnasamy. K. Iwasa. S. Von Angerer. C. Weimar and W. Wlegrebe. Arch. Phar., 1987, 320, 790. A. Couture and P. Grandclaudon. Svnthesis. 1986, 576. I . Ninomiya, C. Hashimoto, T. Kiguchi and T. Naito, J. Chem. S O C . , Perkin I. 1984, 2911. I. Ninomiya, C. Hashimoto. T. Kiguchi and T. Naito, Chem. Pharm. Bull., 1986, 2 ,2799. R. 6. Bates. V . V . Kane. A.R. Martin. R. 6 . Mujumdar. R. Ortega. Y. Hatanaka, K. San-nohe and Y. Kanaoka. J. Ore. Chem., 1987, 52, 3178. P. Kutschy, J. Imrich. J. Bernat and P. Kristian. Coll. Czech. Chem. Comm. , 1986. 31, 2002. P. Kutschy. J. imrlch, J. Bernat. P. Kristian. 0. Hrltzova and T. Schoffmann, Coll. Czech. Chem. Comm., 1986, 51. 2839. S. Pakray and R.N. Castle, J. Het. Chem.. 1987. 24. 231. J. D. McKenney and R. N. Castle, J. Het. Chem., 1987, 24. 1103. K. Veeramani and P. Shanmugam, ind. J. Chem., 1987, 268. 116.
a,
-
342
Photochemistry
140.
S. Lazare. R. Lapouyade and R. Bonneau. J. Amer. Chem. S o c . , 1985. 1 0 7 . 6604. R. Bonneau, Nouveau J. Chim., 1986, 10. 425. G. Pandey and A. Krishna. J. Ors. Chem., 1988. 53. 2364. M.. Mascal and C . J . Moody, J. Chem. S o c . , Chem. Commun., 1988. 587. M. Macal and C. J. Moody, J . Chem. S o c . , Chem. Commun. , 1988. 589. R. M. Wilson, K. Hannemann. K. Peters and E.-M. Peters. J. Amer. Chem. S O C . , 1988. 109, 4741. H . - 0 . Becker and K . A n d e r s o n . J. Org. Chem., 1987. 52. 5205. H . - 0 . Becker and K . A n d e r s o n . Tetrahedron Letters, 1987. 1323. H. J. Timpe. U. Lammel and L. Fisera. J. Prakt. Chem., 1986. 328. 824. A. Albini, E. Frasani and A. Gamba. J. Photochem. Photobiol. A, 1988, 41 215. H. J. Shine and W. Subotkowska, J. Org. C h e m . , 1987. 52, 3815. Y. Ban. K . Yoshida. J. Goto. T. Oishi and E. Takeda. Tetrahedron, 1983. 39, 3657. M. Akagi and K. Ozaki, Heterocycles, 1987. 3.61. S. Ghosh. T . K . Das. D . B . Datta and S. Mehta. Tetrahedron Letters, 1987, 28. 4611. E. Lipczynska-Kochany and J. Kochany. J. Photochem. Photobiol., A. 1987. 38. 331. J. Seplol and P. Tomasik. Acta Chim. Hung.. 1986. 121. 333; Chem. Abstr., -107, 96556n. M. M. Abou-Elzahab, M. A. Metwally. A. M. Dawldar. M. Abdel-Mogib and E . A . Abu-Mustafa, Bull. Chem. SOC. Japan, 1987. 60. 4433. 0. T. Breslin and F. 0. Saeva, J. OrR. Chem.. 1988. 53. 713. J . L . Dektar and N. P. Hacker, J. Chem. S O C . , Chem. Commun., 1987, 1591. J. L. Dektar and N. P. Hacker, J. Org. Chem. , 1988. 53. 1833. R . J . Devoe. M.R.V. Shahyun. N. Serpone and D.K. Sharma. Can. J. Chem., 1987, 65. 2342. B. N. Rao. M . S . Syamala, N. J. Turro and V . Ramamurthy. J. Org. Chem.. 1987. 52. 5517. D. D. M. Wayner and L. Gravelle, Tetrahedron Letters, 1988, 29, 431. E. W. Valyocsik and P. J. Sigal. J . Org. Chem., 1971. 36, 66. S . S . Hlxson and L . A . Franke, J . Org. Chem., 1988. 2706. S. Kadota. K. Tsubono. K. Makino. M. Takeshita and T. Kikuchi, Tetrahedron Letters, 1987. 28, 2857. H. Al-Ekabl and P. de Mayo, J. O m . C h e m . . 1987. 52. 4756. C. Lohse. L. Hagedorn. A. Albini and E . Fasani. Tetrahedron. 1988, 44, 2591. A. Alblnl, E. Fasanl and V. Frattini. J. Chem. SOC., Perkin 11. 1988. 235. N. J . Bunce, C. R. Montgomery and J. L. Hunt, J. Photochem. Photobiol. A, 1988. 43. 207. 8. J. Wllklns, 0. J. Gainsford and D. E . Moore. J . Chem. S o c . , Perkin 1, 1987. 1817. P. Wan and B . Chak, J. Chem. S o c . , Perkin I t . 1986. 1751. B. Foster. B. Gaillard. N. Mathur. A. L. Pincock. J. Pincock and C. Sehmbey. Can. J. C h e m . , 1987, g . 1599. N. Soundararajan and M . S . Platz, Tetrahedron Letters, 1987. 28, 2813. P. Wan and D. Hennig. J. Chem. S o c . , Chem. Commun., 1987. 939. Y. Okamoto. H. Yoshlda and S. Takamuku. Chemistry Letters, 1988, 569. Y. Okamoto, N. lwamoto and S. Takamuku. J . Chem. SOC.. Chem. Commun.. 1986. 1516. I . McAuley, E. Krogh and P. Wan. J. Amer. Chem. S O C . , 1988, 110, 600.
141. 142. 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 165. 166. 167. 168. 169. 170. 171. 172. 173. 174. '175. 176. 177.
a,
S T
11114: Photochemistry of Aromatic Compounds 178. 179. 180. 181. 182. 183. 184. 185.
343
S. Muralidharan and P. Wan. J. Chem. S O C . . Chem. Commun., 1987, 1142. P . A . Wade, H.A. Morrison and N. Kornblum, J. Org. Chem., 1987, 52. 3102. A. Aibini and S. Spreti. 2. Naturforsch., 8: Anorg. Chem. OrR. Chem., 1986, 418, 1286. A. Okamoto. M . S . Snow and D . R . Arnold, Ietrahedron, 1986. 42. 61 75. D. R . Arnold. 6.J. Fahie. L.J . Lamont. J. Wierzchowski and K . M . Young, Can. J. Chem., 1987, B. 2734. Y . Takahashi and J . K . Kochi. Chem. B e r . , 1988, 121, 253. S . J. Cristol, E . 0. Aelling. S. J. Strickier and R. D. ito. J. Amer. Chem. S O C . , 1987. 109, 7101. K . V . Subbarao. N . P . Damodaran and S. Dev, Tetrahedron. 1987, 43. 2543.
5 Photo-reduction and -oxidation BY A. COX 1. Introduction Review8 have appeared of data available on singlet oxygen quantum yields, 8 inglet
' chemiluminescent reactions with participation of
oxygen and dioxetanes ,
photoox idat ion of unsaturated
fatty acids,3 and the photooxidation of furans.4 2. A
Reduction of the Carbonvl G r o w
study of proton transfer reactions involving the triplet
state of benzophenone in aqueous MeCN has shown that there is no proton-induced protonat ion is
quenching (n,n*).
and
that
the
reactive
state
for
Hydrogen transfer from 1-naphthol to
ground-state benzophenone has been reexamined and an earlier suggestion6 that this occurs within a preequilibr ium-controlled concentration of triplet exciplex is challenged .7
Simple enols
have been generated flash photolytically by oxidation of the corrxmponding alcohols using either acetaldehyde or acetone, enabling some keto-enol equilibrium constants to be determined. The Cu(J1) complexes of acetylacetone, l,l,l-trifluoroacetylacetone, and 1,1,1,5,5,S-hexafluoroacetylacetone all quench the triplet excited state of benzophenone.
Increases in the number
of CF3 groups and the H-atom donating ability of the solvent bring about
an
increase in the
limiting quantum
efficiency.
Photoreduction of 1,6- and 1,8-pyrenedione, has been described'' and the quenching of triplet benzophenone by 2,4,6-tri-tert-butylphenol and the kinetics of phenoxy radical formation have been
344
1111.5: Photo-reduction and -oxidation
345
reported.ll The kinetics of geminal recombination of radicals formed on photoreduction of 4-RCgHqCOCgHqR'-4 = Me1 R = Br, R '
is
reported
p-benzoquinone micelles,
R'
H; R
=
R'
2 in a 0.34 T magnetic fieldI2 and
6
to
accelerate
the
photoreduction
of
in SDS and CTAB micelles; in Aerosol OT reversed
the
reaction
anthraquinone-2-sulphonate irradiation of
-;i
H) by various donors in viscous solvents are
=
decreased by a factor of pressure
(R
is
retarded.13
radical
anion
The
(AQS)'
yie-ld generated
of
by
in aqueous acetonitrile containing propan-2-01
AQS
has been found to depend on the water concentration and to follow Perrin's
equation. l4
Complexation of aryl alkyl ketones with
p-cyclodextrin leads to changes in the ratio of the products of elimination and cyclisation which resu3t from reaction of the 1,4-biradicals
arising
in
the
Norrish
type
11
hydrogen
abstraction pr0ce~ts.l~This appears to be a consequence of the steric constraints l,&biradical
imposed on the rotational motions of the
by the cyclodextrin cavity.
An ESR study of the
photogenerat ion and photodispropor t ionat ion of hydroxyphenoxyl radicals
formed
in
crystals
of
3,5-di-tert--butylpyrocatechol
containing 3,5-di-tert-butyl-~-benzophenone has appeared,l6 and
in the solid
state,
irradiation
of
(p_-MeC6Hq)2C0 leads
to
intermolecular H abstraction followed by dimeriaation, whereas (m-MeC6H4)2CO,
g-MeC6H~coC6H~Me-a and
R-MeCgHqCOPh
are
phot08table.l~ This difference has been accounted for in t e r m of bond distance data.
Photoenhanced reduction of conjugated enones
with sodium borohydr ide is reported to occur through zwitter ionic species formed from the 3(n,n*) state of the conjugated enones,
followed by hydride attack to yield unsaturated or saturated alcohols. l8 Enant ioselect ive photodeconjugat ion of @-unsaturated
Photochemistry
346
HO
(2) R
=
Me, R ‘ = Me, PhCH,
1
( 4 ) R = R3= Me$, R = R 2 = H
OH
NC
eNCONH 2
HO
-! I
CH,Ph
R’
(8) R
t
R =
Ph. R‘= H, CF3 G-NCC6H4, R ’ = H
IIIl.5: Photo-reduction and -oxidation
347
esters of the form Me2CHCH:CR2C02R’
(R’, R2
=
various
aLkyl
groups) by ( + ) - and (-)-ephedrine appears t o be determined by major interactions in the transition state which develop between the inductor and the p-carbon of the intermediate dieno1.l’ The same authors have also investigated how the nature of the chiral agent affects the reaction.20,21
The laser-jet method has been
used in the generation and subsequent photolysis of the photoenol (1)
of
2-methylben~ophenone~~and
photoenolisat ion of ap-unsaturated
dienols
produced
by
ketones have been directly
observed, and activation parameters for dienol reketonisation via a 1,s-hydrogen shift obtained .23 Measurements have been made of the
rates
of
reketonisation
of
dienolates
by
photochemical
enolisatlon of e a l k y l ap-unsaturated ketones in aqueous basic solution,24 and the same group has used photoenolisation in a synthesis of the S a n Jose scale pheromone.25 Direct observation of
acetophenone
phenylacetylene
enol
has
been
formed
by
reported,
photodehydration and
the
rate
of
of its
reketoni sat i on measured accurately .26 3.
Reduction of Nitroaen-containina COmDOUnds
The mechanism of the electron transfer reaction for xanthene dye-sensit ized formation of the methyl viologen radical has been invest igated27 and conditions have been published for achieving the optimal quantum yield
in the photosensitized reduction of
methyl viologen by eKythKOSlrN?.28 A variety of systems have been described
which will
also photoreduce
methylviologen
to
its
cation radical, and which, In the presence of colloidal platinum will reduce water to generate molecular hydrogen. 29 Complexation of negatively charged zinc tetraphenylporphyrin sulphonate with positively charged viologens has been investigated along with the
Photochemistry
348 ro1.e
this
pl.ays
in
the
aena Ct.i.xed
photoreduct, i.on
of
methy1.viol.ogen. 3o Some water -sol.iibl.e x i.nc porphyr i.na capab1.e o f a c t i n g both as photoasnsi,ti.xer and e1.ect.ron c a r r i e r moLecu1.e have been
used
i n a phot,oi.ndiiced
hydrogen evol.iit. i.on
process. 31- The phot~oredtiction of met-hylv i.ol.ogen t.o radical. i n pol.ymer m a t r i c e s
iit3in9
i.n t h e same
i.t..a ca.ti.on
visi.bl.e l.i.9ht and aensi.ti.xera
such as dyes and porphyri.ns,32 a new method for det,ermi.ning t-he qiiant-urn yie1.d
of
the
porphyr i.n-sensi.t.i.zt4
photorednct.i.on
of
met.hyl.vi.ol.oqan, 33 t-ha so1.i.d sita.t.e photo1.ysi.s o f met-hyl.vi.ol.ogen,34 and t h e abi.1 i.ty o f 3.,7-diaxapyreni.am ca.t,i.on ( 3 . ) t o firnct,i.on a.8 a. methy1.vi.oloqen anal.oq11e3’ have a.l.l. been r e p o r t e d . can be phot-orediiced by benzophenone t.ripl.et,a
atom donors
.in d e o x m e n a t e d
c3.ipheny.l carhino1
rad.ica.le.
MeC!N.36
a c r i.dine - 39
’’
5-deaxaP.1 a v i na ,
Metal.
i.n t h e preaence o f H reackjon
syat-emfi which
Other
phot.orducsd inc.1lids t,he. NAnH model nj cokjnamjde, 37
The
Met,hyl.ene R 1.118
,
occiirs
have
via been
1 -hsnxy.l -1 ,4-d .ihydro-
and 9,l O - d i hyrlro-3 0-met.hy.l-
phthal.ocyani.ne-sens it,i.xed
photmradiicti.on o f
dimethyl 4 - n i t r o p h t h a l . a t s by ascorbi-c a c i d has been i.nvest-igated
and the correspond inq amimo- and hydroxy1.ami.no compounds shown t.o
be products of the primary photmreaction .40 The phot.nreduct..ion o f
several aromat..ic d i n l i k r o compounds by Ek3N gives n l kroan.i.1jnaa and on khe hapl.ie of R J ~ J N ~ O ca.lcillakjon% / ~ a mechaniatlc Acheme has
bean proposed; t-hi.s scheme al.so embraces some photosirbat i.t-11ti o m . 41. 4.
Ni.acell.aneoiis Reduct. ions
Phn tor duct-.i ve deha.1ogenat-i on
of
khe
i nPrect. i c .id e
hromoclan
has been descr li bed. 4 2 5
-
Sina.1et O x y q e ~
S ing let oxygen i.s generated by exc i.t-atton o f po 1.ymet.hi.ne dyea
11115: Photo-reduction and -oxidation
349
in solut 1 o d 3 and also when some photoexcited p-carbolinee react with oxygen. formed
in
In this latter case, superoxide radical anion is addition.44
It
has
also
been
reported
that
pteridin-2,4,7-trione absorbs singlet oxygen smoothly to produce pteridin-2,4,7-trione 6,8’-endopetoxide, a stable solid which can be stored indefinitely at room temperature and which on warming reverts to the parent trione with liberation of singlet oxygen.45 Quantum yields oxygen
using
for the photosensitized porphyrins
and
generatjon
metalloporphyrins
of singlet in
nonpolar
solventsQ6 and media effects on the quantum yield of generation of singlet oxygen by anthracene have been reported.47 New methods
have been described for measuring singlet oxygen luminescence quantum yields in organic solvents and water,48 for identifying singlet
oxygen
in
photochemical
spectroscopic
t e ~ h n i q u e , ~ ’ and
biliverdin
the examination of
€OK
reactions limitations
by
a
Ge-based
in
the
use
JR
of
oxygen participation in
B inglet
oxidation reactions have been stipulated - 5 0 Deactivation of lo2 by solvent molecules is a collisional E V+RtT
energy transfer
process;
+
it occurs by coupling of the
highest fundamental vibrat Fonal mode X-Y of the acceptor molecule with
an
o2(uag,
v
=
0)
+
(3%-,
v
=
m)
transition.51
Singlet-tr iplet annihilation of singlet oxygen and xanthone dyes in their triplet state has been observed in liquid solution52 and singlet oxygen photooxidations sensitized by anionic species such
as Rose Beriyal can be readily performed jn an aqueous-organic two-phase
system
in
the
quaternary onium salts.53
presence
of
catalytic
amounts
of
Both singlet oxygen and the oxygen
radical anion are thought to participate in the photooxidation of electron-r ich compounds by 9,10-dicyanoanthracene, and to involve
350
Phorochenzistry
a CT complex between the donor and acceptor upon excitation.54 A further
report
has
buta-1,3-dienes
as
appeared
demonstrating
mechanistic
probes
for
the the
utility
of
reactjons
of
singlet oxygen and other e l e ~ t r o p h i l e s ,and ~ ~ rate constants have been measured for the reactions of singlet oxygen with radicals and
molecules
in
the
gas
phase.56
Rate
constants
quenching of the luminescence of singlet molecular
for
the
oxygen by
substituted derivatives of pyrrole depend on the structure of the heterocycle. 57
The
inclusion
of
pyrrole
into
porphyr in
quenching.
macrocycles leads to a strong decrease of
The
same workers have also carried out similar quenching studies using 1,4-diaminoanthraquinone. 5 8 6. Oxidation of AliDhatic ComDounds
Alkanes have been photooxidised
in aqueous solutions of
Hg( I t ) salts59 and their use on a preparative scale described.60 An
experimental study and theoretical modelling of methane CH
Moog has appeared6'
bond photoactivation by Moo3 and Cu2+-doped and
cyclohexane
photooxidised autoxidation
and
using of
1,4-dimethylcyclohexane
pyr idine
adamantane,
photochemically
promoted
temperature.63
Tracer
dehydrogenation
of
by
norbornane,
and
(NH4)2Ce(N02)6
studies
methanol
The
N-oxide .62
have
have
oxidation
shown
that by
hydroxyl H is the source of the evolved H2.64
and
cyclohexane
in MeCN
photocatalysed
been
is
at
room
in
the
Pt-Ti02,
the
Rates of carbonyl
compound formation have been used to compare the reactivities of MeOH,
EtOH,
propan-1-01
and
propan-2-01
as
a
function
of
temperature using platinised anatase, prepared by impregnation and hydrogen reduction, and by p h o t ~ d e p o s i t i o n .Propan-2-01 ~~ has also been photocatalytically dehydrogenated uaing niobium oxide
35 1
11115: Photo-reduction and -oxidation
on porous
WCOK glass
66 Photo induced ox idat ion of normal and
branched alcohols chemisorbed onto y-alumina has been studied according to the characteristics of the W irradiation source, nature of the alcohols, and pressure of oxygen.67 The wavelength dependence of the photooxidation of formaldehyde in excess oxygen study of the rates of methylene blue
has been studied.68
A
photooxidation
terpenes
of
stereoelectronic autoxidation of
has
and linoleate
been
accounted
for
in
the benzophenone-photosens it ized
in solution and
aulphate micelles has been shown t o
in sodium dodecyl by a free-radical
OCCUK
autoxidation rather than by a process involving singlet oxygen. 70 A
convenient
one-pot
synthesis
of
epoxy
alcohols
via
photooxygenation of olefins in the presence of a Ti(1V) catalyst has
Fsr
appeared.
example,
Me2C:CMe2
has
been
successfully
photooxidised to (3) in 84% in the presence of Ti(OCHMe2)471 and dicyclopentadiene similarly gives 3,4-epoxy-5-hydroxycyclopentene. 72 A stereochemical investigation of the photoepoxidat ion
of olefin (4) using singlet oxygen in the presence of to
proceed
via
a
perepoxide. 73
dispiro[2.0.2.4]deca-7,9-diene tetr m e t h y l
analogues
1,4-endoperoxidea. 74 gel-supported lsobutylene
The
acetone
of
gives
has
catalysts been
appears
Photooxidation its
monospiro
the
photocatalytic
zirconium oxide to
and
SO2
of and
corresponding
activity
of
silica
in the oxidat ion of
correlated
with
their
luminescence intensity, and the binding related to the mechanism of active centre formation in the catalysts.75 The influence of
the active sites and structure of
inorganic supports on the
oxidative cleavage of olefine with oxygen in dry media has been i n ~ e s t i g a t e d and ~ ~ poisoning experiments have been used to show
352 that
Photochemistry both
acid
and
base
sites
are
involved
in
the
room
temperature photocatalytic dehydrogenation of propan-1-01 over a Pt/Ti02 catalyst, the dominant role being played by base sites.77 Cyanoaromatic-sens it ized photooxidat ions of alkenes some of which involve
singlet
of
oxygenation
oxygen
appeared. 78 79
have
adamantylidenecyclopropanes
Photosensitized is
substituent
dependent and gives either the corresponding 4-methylene-1,2dioxolane, or lactone and cyclic ketone. 8o These observations suggest the initial formation of a zwitteronic peroxide followed by
its
conversion
carbonyl
to
oxide.
an
allylic
Singlet
oxygen
( E ) -I-propyl[ 1, 1, l-2H3]oct-4-ene d isubst ituted formation
of
s ide81 the
photooxygenation
and
in
unconjugated of
cation
occur polar
type
ene
zwitterion or reactions
prodominantly solvents,
hydroperoxide
is
at
of the
preferential reported
on
3,4-dihydro-6-methyl-2H-pyran-5-carboxylic
acid ethyl ester with singlet oxygen.82 Matrix isolation of the trisdioxetane (5) occurs on photooxidation of 2,5-dimethylhexa-2, 3 , 4 - t ~ i e n e .Singlet ~~ oxygenation of 2-[hydroxy(4-nitrophenyl)methylltropone gives 6,7-dioxabicyclo[3.2.2]nona-3,8-dien-2-one, and
an
observed
change
in
regioaelectivity
due
to
a
high
oxygenation rate in MeOD compared with MeOH has been explained in terms of quenching of singlet oxygen by the free OH group at the reaction site. 84 Both acetoin and biacetyl are photocatalytically oxidised by [NBuJ4[W10032] in MeCN.
However, it is reported that
oxidat ion of biacetyl does not ar ise from the redox cycle of the decatungstate, but from photoexcitation of the complex formed between the polyanion and substrate. 85
2 The
yield8
of
ring
cleavage
products
from
the
NO-air
IIll5: Photo-reduction and -oxidation
353
photoox idat ions of a ser ies of aromatic hydrocarbons have been reported.86
In the preaence of bromine compounds, toluene and
ethylbenzene have cyanoanthracenes
been have
photooxidised been
used
to
by
aira7
and
several
photooxidise
various
methyl-substituted aromatics in M e w . 88 Quenching rates of some aromatic olefin radical cations by oxygen and superoxide anion
.
have been measur ed 89 Some other compounds photoox id ised include Ph2C:CHMe
in
the
presence
of
benzil,90
various
e-dimethoxybenzene derivatives which give quinone epoxidaa,91 2',4,4'-trihydroxychalcone
which gives products identical with
those arising from enzyme ~xidation,'~ and substituted indenes at low temperatures which leads to the format.ion of 1,2-, 1,4-, and ene products, whose distribution is shown to be solvent dependent.93
Photooxidat ive alkylat ions of
d icyanonaphthalene
with a l k y l t r iphenylborate salts proceeds with homolyaia of the bond
C-B
and
generation
10-methylacridinium,
an
NAD+
of
alkyl
model
radicals,94
compound,
and
selectively
photoconverts benzyl alcohol into the corresponding aldehyde in a process which is initiated by electron-transfer to the singlet excited state of the heterocycle.95 Light-induced oxidations have been reported f o r L - ~ - l - p - n i t r o p h e n y l - 2 - a c e t y l a m i n o p r o p a n 1 , 3 - d i 0 1 , ~a~ variety of aromatic a-keto alcohols in the presence of benzoyl peroxide and N-bromoauccinimide,97 phenol aensl tized by
2,2'-bipyridyl
and
its
complexes
with
Cr(I11),98
and
stereoselective oxygenation of 2,3-diaryloxiranes by irradiation of electron donor-acceptor complexes of TCNE has been observed.99 A
number of
substituted furans have been photooxidised.
These include the low-temperature photooxygenation of some furan derivative8 which, following treatment with Me2S and Me3SiCN,
.
354
Ph otoch ernistry
(9) X
= Cl.
OMe, OH
HE
HoaHO
Me
- NMe (12 1
R
0
R
S
I
C0,Et (13) R
R
'
= Me, R'= H , Me
=
OMc, R ' t H
I
R0
355
111l.5: Photo-reduction and -oxidation r~ive
CH20Ac,
CH20Rz,
R'
CHMeOH;
H, Me, CH20Ac,
=
t.o 4-cyanobuteno.1ides
can he oxidised
(R
H,
=
and which
CH20Rz),
(7).'On
CH20H,
Other
examp.les
of g-lycosylfurans to gjve g1ycoay-l
include the photooxidation
and of tetrabzomofuran in benzene to give a mi.xtiire
acrylates"' of
(6)
2-cyano-5-hydroxy-2,5-d ihydrofurans
tetrabroml actone
eJectronic
and
substi t u t e n t s
influence of
oxygenation
anhydride. '.03.
di bromoma-lsic on
the photosensitized
S-(hydroxymethyl)-2-f urf ura.1
of
The
has
heen
di~cuased.~*~ 8,
O x i.dation of Nitroaen-contai.ni.naComnoiinds
Hydrogen-abstracted
radjcals are formed on irradiation of
amide-FeClg complexes at 313 nm, hut at 366 nm acyl radicals are Photosens it ixed oxygenat i.on o f 3-
produced in larger amounts.
and 6-substituted 2-pyr idones in the presence of methyl.ene hl.iie
g ives
pyz id i.nediones,
intermed iate, lo'
thymine
aqueous
of
suspension
[ Ru (bpy)3 1
v i.a
probably has
been
Ti02,1.07
and
an
endoper ox i.de
photmoxyqenatsd i.n
i.n an
presence
the
'+
of
as sena it izer , photo Lys is of the 4-al.ky1.ated NADH
model (8) induces electron transfer to t.he inorganic comp-lex.1.08 SolvoJytic cleavage of oxime carbamates (9, x
= C1,
OMe, OH) has
been achieved by dye-sens it ized photooxygenat i.on i.n the presence
of MeOH and Rose Rengal. to give Me02CNHC6H4X-2 and cyclohexanone
'
ox ime , O9
and
the
photosens it ized
s ing1.e-el.ectron
t-ra,nafer
oxidation of N-hydroxylamines t o gi.ve cyc1.i.c ni.t-rone8 ha.8 been reported. 'lo yields
benzoxazinone
photooxidation mixture
Dye-sensitized
of
of
(30)
photooxi.dation o f and
the
new
dimer
5,6-dlhydroxy-l-methylindole
fluorescent
compound8
2-phenyl.i.ndo1.e
among
(JI),'.''.
and
glves a comp.lex which
is
2,4'-biindolyl (32), isolated as i t s acetoxy derivative;'12
the the
Photochemistry
356
photooxidation of 5.6-dihydroxyindole has also been diacuassd,'13 Photochemical
oxidation
the
of
tryptophan
aide-chain
by
pyrimido[S,4-g] pteridine N-oxide,314 the 3-methyl group in some carbazole alkaloids315 and l-methyl.-2,4,5-triphenyl.imidazol.e in the solid state116 have a l l . been recorded, the photosens it ized oxygenat ion of show
an
that
pyrazoline
electron-transfer
cation
radical
Kinetic studies on
I., 3,5-tr i.aryl.-~-lpyraRol.i.nea
reaction
and
occurs
auperoxide
khe
to give
pair.
ion
Photosensitized oxygenation of the diazepines (13) (R
=
H, Me; R
= H, CHO),
=
OMe,
R'
= H)
gives pyrrolinones (14) (R'
*
and RC0CH-CR'NR2C02Et''
R2NHC02Et
step . on
dye-sensJ tized
serve
as
=
and systems containing hot.h
oxazole and selenide units yie1.d @-unsaturated singJe
Me, R '
tr iamides i.n a
photooxidation
precursors
to
to
produce
a@-unsaturated
substrates
which
lactones.
The oxidation of methylviologen has been carried out
photocatalytically in the presence of Ti02 and gives two strongly fluorescent products, the 1',2'-dihydro-l,l'4,4'-bipyridyl ium
cation
dimethyl-3-0x0-4,4
and
dimethyl-2'-oxo3,4-dihydro-l, 1 ' -
the
' -bipyridyJ ium cation; I 2o the reaction
appears
to be initiated by homogeneously distributed or surface-adsorbed hydroxyl radicals 9.
-
Miscellaneous Oxidations
Charge-transf er
photooxygenat ion
of
sulphides
has
been
studied in a cryogenic oxygen matrix and I R evidence obtained f o r
an
intermediate which
zwitterion. 12'
A
is best
formulated
as a
persul.phoxide
SpiKodiOXathiiKdne is formed as an intermediate
in the photosens it ized oxygenat ion o f biadamantyl.idenethiirane,122 and the same workers have reported the first example of
epoxidation
of
olefins
by
the
active
oxidiaing
species
357
11115: Photo-reduction and -oxidation
on
generated
photonxj da t. i on
photmoxygenatjon
of
r aac t i ona
m e s o .ion .ic
of
th.i i
a
The
d i t h i1 .iumo1 a t.e ,
thiazoliumolat.e, and related heterocycle3 have haen at.iid.ied..13.4
Photooxidation of sulphur at pentacova 1 snt. phosphorus has heen sensi t.ized by many .1,2-dicarhony.l compotindn; hot.h ainq.l ett oxyqen and diacyJ peroxidea are exc.liided aa intermediates.
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Photoreactions of Compounds containing Heteroatoms other than Oxygen BY S. T. REID 1.
N i t r o g e n - c o n t a i n i n g Compounds
Few i f any n o v e l p h o t o r e a c t i o n s have been r e p o r t e d i n n i t r o g e n c o n t a i n i n g s y s t e m s d u r i n g t h e p e r i o d c o v e r e d by t h i s r e p o r t . P u b l i c a t i o n s have i n most c a s e s d e a l t w i t h e x t e n s i o n s t o known p r o c e s s e s , d e f i n i n g more c l e a r l y t h e scope and mechanism o f these reactions. Rearrangements.- ? , & - P h o t o i s o m e r i z a t i o n o c c u r s r e a d i l y i n i m i n e s and i n a z o compounds. The s y n - i s o m e r ( 1 1 , f o r example, i s t h e major p r o d u c t o f i r r a d i a t i o n o f n i t r o f u r a z o n e ( 2 ) i n s o l u t i o n and i s formed t o g e t h e r w i t h t h e c o r r e s p o n d i n g a z i n e on exposure t o The p h o t o i s o m e r i z a t i o n of azobenzene laboratory illumination. d e r i v a t i v e s i n s o l u t i o n , i n membranes, i n h o s t - g u e s t complexes o f c y c l o d e x t r i n s , and i n polymers c o n t i n u e s t o a t t r a c t a t t e n t i o n . The r e v e r s i b i l i t y o f L , E - p h o t o i s o m e r i z a t i o n o f azobenzene i n c y c l o hexane s o l u t i o n h a s been e s t a b l i s h e d , 2 and t h e J j / & - r a t i o s g e n e r a t e d by i r r a d i a t i o n of v a r i o u s azobenzene d e r i v a t i v e s a d s o r b e d on h y d r a t e d s i l i c a g e l have been d e t e r m i n e d . 3 E , L - P h o t o i s o m e r i z a t i o n h a s a l s o been o b s e r v e d i n c e r t a i n dithia-diazaIn.2lparacyclophanee n e s ,4 and d i r e c t o r b e n z i l - s e n s i t i z e d E , Z - i s o m e r i z a t i o n o f 2,4,6isopropyl-3’-(phenylazo)azobenzene h a s been shown t o be u n s e l e c tive. D e t a i l s o f f l u o r e s c e n c e and p h o t o i s o m e r i z a t i o n s t u d i e s o f aqueous b i l a y e r a g g r e g a t e s o f a z o b e n z e n e - c o n t a i n i n g a m p h i p h i l e s have been p u b l i s h e d , ‘ and a p h o t o c h e m i c a l l y induced p h a s e t r a n s i t i o n h a s been o b s e r v e d i n a m i x t u r e of 4-cyano-4’-n-pentylbiphenyl and A new t y p e o f photochromic Langmuir4 - b u t y l - 4 ’ -methoxyazobenzene. B l o d g e t t f i l m c o n t a i n i n g azobenzene d e r i v a t i v e s i n a h o s t - g u e s t i n t e r a c t i o n w i t h a m p h i p h i l i c B - c y c l o d e x t r i n s h a s been p r e p a r e d , 8 and n o v e l a z o b e n z e n e - c o n t a i n i n g p h o t o r e s p o n s i v e p o l y p e p t i d e s have been The a g g r e g a t i o n p r o p e r t i e s of a z o b e n z e n e - c o n t a i n i n g described. ” p h o t o r e s p o n s i v e ‘ t a i l ( a m m o n i u m ) - b i t i n g ’ crown e t h e r s have been
’
’’
examined, and t h e a m p h i p h i l i c s a l i c y l i d e n e a n i l i n e d e r i v a t i v e , N-[4-(dodecyloxy)salicylidene]-4-carboxyaniline, i n c o r p o r a t e d i n a
3 66
11116: Photoreactions of Compounds containing Heteroatoms other than Oxygen
(11
(21
hV
McCN
I
R
(41
R
=
Me or PhCH,
R3
co*-
(51
(61
(7 1
R' Me
R2 Me
R3 Me
Et
Me Me Me
Me
Me
Ph
Me
eu'
Me Ph Me
- (CH2I4-
Me
Et Me
Me
367
Photochemistry
368
cop I hv
ROyN-Co2Et
R o\ eN-C0,Et
-N-C0,Et Ph (8)
Ph
Ph
NH -C02Et
RO
NH-C0,Et
Si02 4
R = SiMe2But
Ox$\
C02Et
Ph
(91
Scheme 1
c 1(13 1
‘C0,Et Ph
11116: Photoreactions of Compounds containing Heteroatoms other than Oxygen
369
Langmuir-Blodgett film, exhibits photochromic behaviour. A method for the measurement of temporary light-induced changes in pXa has been developed and applied to the z,gphotoisomerization o f 2-hydroxyazobenzenes. Derivatives of l-phenylazo-2-naphthols also undergo photoisomerization in a polymer matrix. 14 Examples of photorearrangement arising by 4 ~ and 6nelectrocyclic pathways have again been reported. The Z-azabicyclo[2.2.0]hex-S-en-3-ones ( 3 ) have been prepared in good yield by 15 irradiation of the 4,-t-butylpyrid-2-ones (4) in acetonitrile; surprisingly, [lr4+ 41 photodimerization does not occur as in other pyrid-2-ones, even at high concentration. The ‘Dewar’ pyrimidin-4-ones ( 5 ) are intermediates in the conversion of the 2,3,6-trialkylpyrimidin-4-ones ( 6 ) into the tetraalkylpyrimidinium5-carboxylates (7) on irradiation in acetic acid,16 and Z-aminopyridinium sulphate, phosphate and arsenate are converted into the corresponding aminoazobicyclo[2.2.O]hexadienes in 20-40% yield on irradiation in rnethan01.l~ Full details of the related electrocyclic ring opening of oxaza- and diaza-tricycloheptenes 18 to oxazepines and diazepines have now been published. Photochemically induced electrocyclic ring opening has also been reported for the l,Z-dihydro-1,2-pyridazine ( 8 ) which on irradiation and desilylation on silica gel is converted into the pyrrolinone ( 9 ) by the route shown in Scheme 1 .” The first report of photochromic behaviour in liquid crystal polysiloxanes containing i n d o l i n o s p i r o b e n z o p y r a n s has been published,” and it has been independently shown that a bilayer membrane provides an effective medium for regulating the isomerization of analogous photochromic i n d o l i n o s p i r o b e n z o p y r a n s . 2 1 Other new mono- and 22 b i s - i n d o l i n e s p i r o b e n z o p y r a n s have been prepared. 6n-Electrocyclization occurs readily in the 4-phenyl-3vinylquinoline (10) to give the benzo[k]phenathridine (1 1) ,23 and the indolizino[3,4,5,6-&] quinoxaline (1 2) is the major product o f irradiation of the l-styrylpyrrolo[l,2-a]quinoxalinoxalin-lO-ium chloride (13) in methan01.’~ A synthesis of the isobacteriochlorin ring system has been developed in which a key step is an 25 181~-photocyclization. A recent review of the photochemistry of enamides draws attention to the ease with which enamides undergo 1,3-acyl shift on absorption of light, whereas dienamides prefer to follow a 6n-photocyclization pathway.26 N-Aroylcarbazoles are converted on
3 70
Ph otochemistry
hV ___)
0 (14) R
6 R
(16) R
=
R ‘
H O
= H o r Me
QN
@
Me or Me0
(15)
hV
qJj \
(17) R
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
371
(221
(20 1
lhV R = Me, Ph, 4 - MeOC6H4, 3 - MeOC6H4'
m=n=l
m
= 2, n = 1
4 - CF3C$i4 or a-napht hyl
R = 4-MeOC@, R
m=n=3
=
Me
0
6
NKC02CHMc2 I H (23 1
hV
EtZO
h C 0 12 C H M e 2 H (24 1
Photochemistry
372
/I MeOzC R (27) R
= p-MeOC6H,
Me
Me
Me
Me
hV ___)
Ph
Ph
ph& (30 1 N'R
Me
Me
Me hV ___)
sens.
Me
3,
Ph
Ph
OAc
1116 Photoreactions of Compounds containing Heteroatoms other than Oxygen
373
i r r a d i a t i o n i n methanoluiacompeting a r o y l migrations i n t o 1 - and 3 - a r o y l ~ a r b a z o l e s . ~6 -~r - P h o t o c y c l i z a t i o n i s , h o w e v e r , more common i n e n a m i d e s t y p i f i e d by t h e f u r a n c a r b o x a n i l i d e s ( 1 4 ) w h i c h on i r r a d i a t i o n i n b o t h p r o t i c and a p r o t i c s o l v e n t s y i e l d t h e isomeric f u r o q u i n o l i n o n e s ( 1 5 ) a s p r i m a r y p h o t o p r o d u c t s . 2 8 The 4 - a r o y l - 4 azahomoadamantanes ( 1 6 ) a r e s i m i l a r l y c o n v e r t e d i n t o t h e i s o q u i n olin-5(7H)-ones (1 7) Enamide p h o t o c y c l i z a t i o n h a s p r o v e d t o 30-32 and be of p a r t i c u l a r v a l u e i n t h e s y n t h e s i s of a l k a l o i d s , t h e r e l a t e d r e d u c t i v e p h o t o c y c l i z a t i o n , accomplished i n t h e p r e s e n c e o f h y d r i d e i o n , h a s . b e e n employed i n t h e s y n t h e s i s o f a depyrrolo analogue of reserpine33 and i n t h e conversion of t h e enamide ( 1 8 ) i n t o p r o d u c t ( 1 9 1 , a k e y s t e p i n a r e c e n t s y n t h e s i s of ( + ) - h i r ~ u t e i n e . ~ An~ a l t e r n a t i v e c y c l i z a t i o n pathway i s followed i n t h e dienamides (20) a f f o r d i n g t h e spiro-oxazines ( 2 1 ) i n high y i e l d ; 3 5 iminol tautomers ( 2 2 ) have been proposed a s intermediates. The r e l a t e d p h o t o c y c l i z a t i o n s o f d i v i n y l a m i n e s t o p y r r o l e s and o f d i a r y l a m i n e s t o d i h y d r o c a r b a z o l e s a r e w e l l e s t a b l i s h e d i n t h e l i t e r a t u r e . A f u r t h e r example o f t h i s t y p e o f
.”
behaviour h a s been r e p o r t e d i n t h e N - u n s u b s t i t u t e d divinylamine ( 2 3 ) which i s c o n v e r t e d on i r r a d i a t i o n i n d i e t h y l e t h e r i n t o t h e h e x a h y d r o i n d o l o n e ( 2 4 ) . 36 I n c o n t r a s t , x a n t h o n e - s e n s i t i z e d e x c i t a t i o n o f l-(l-phenylvinyl)-3,4-dihydroisoquinoline ( 2 5 ) y i e l d s t h e s p i r o b e n z y l i s o q u i n o l i n e ( 2 6 1 , b u t i n o n l y 6 % y i e l d . 3 7 The presence o f v i t a m i n C d u r i n g t h e photo-induced rearrangement of o t h e r spirobenzylisoquinolines i s r e p o r t e d t o s u p p r e s s t h e 38 accompanying f o r m a t i o n o f o x i d a t i o n p r o d u c t s . A 1,3-acyloxy migration i s implicated i n t h e pyrenep h o t o s e n s i t i z e d r e a r r a n g e m e n t o f N-(1-naphthoy1)-g-(p-toluoyl)N - p h e n y l h y d r o x y l a m i n e , 39 a n d a 1 , s - t r a n s f e r o f a m e t h o x y c a r b o n y l g r o u p a p p e a r s t o be r e s p o n s i b l e f o r t h e c o n v e r s i o n o f t h e 3(2;)i n d o l o n e (27) i n t o t h e i s o m e r ( 2 8 1 , a p r o c e s s which i s p r o b a b l y i n i t i a t e d by p h o t o c h e m i c a l l y i n d u c e d Z,E-stereoisomerization. 4 0 An a n a l o g o u s a c y l g r o u p t r a n s f e r h a s b e e n o b s e r v e d i n a c y l a t e d h y d r a z o n e s o f 3-hydroxybenzo [&I thiophene-2-carboxaldehyde , 4 1 a n d 1 , 3 - b e n z o y l m i g r a t i o n a n d L , E - i s o m e r i z a t i o n p a t h w a y s compete on i r r a d i a t i o n o f c e r t a i n 4-acyloxy-2-azabuta-l,3-dienes, t h e p r e f e r r e d r o u t e b e i n g d e t e r m i n e d by t h e n a t u r e o f t h e 3- a n d 32 4-substituents. 1-Aryl d e r i v a t i v e s ( 2 9 ) o f 3,3-dimethyl-5,5-diphenyl-la z a p e n t a - I , 4 - d i e n e u n d e r g o a z a - d i - n - m e t h a n e r e a r r a n g e m e n t on
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exposure t o l i g h t and y i e l d t h e corresponding cyclopropylimines ( 3 0 ) . 4 3 R e l a t e d i m i n e s w i t h a low i o n i z a t i o n p o t e n t i a l r e a c t l e s s e f f i c i e n t l y . Oxime a c e t a t e s h a v e now b e e n shown t o u n d e r g o a z a - d i rr-methane r e a r r a n g e m e n t more r e a d i l y t h a n oximes due t o t h e increased i o n i z a t i o n p o t e n t i a l , t h u s minimizing t h e p o s s i b i l i t y o f i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r . The oxime a c e t a t e ( 3 1 1 , f o r e x a m p l e , i s c o n v e r t e d i n t o t h e c y c l o p r o p y l i m i n e (32) on i r r a d i a t i o n 44 i n b e n z e n e , p r e s u m a b l y by t h e pathway o u t l i n e d i n Scheme 2. Di-IT-methane p h o t o r e a r r a n g e m e n t i n t h e 5,8-dihydro-5,8-methano45 q u i n o l i n e system h a s a l s o been observed. P h o t o i s o m e r i z a t i o n o f five-membered h e t e r o c y c l e s commonly takes place r i n g - c o n t r a c t e d i n t e r m e d i a t e s . The Z H - a z i r i n e ( 3 3 ) i s formed i n t h i s way f r o m t h e i s o x a z o l e ( 3 4 ) a n d i s f u r t h e r c o n v e r t e d t h e r m a l l y i n t o two o x a z o l e s . 4 6 The p o s s i b i l i t y t h a t s u c h p h o t o r e a r r a n g e m e n t s p r o c e e d via v i n y l n i t r e n e i n t e r m e d i a t e s was examined by c o m p a r i n g t h e p h o t o c h e m i s t r y o f 3 - a c e t y l - 5 - m e t h y l i s o x a z o l e w i t h t h a t o f Z-3-azidohex-3-en-2,S-dione which would b e e x p e c t e d t o p r o d u c e t h e same v i n y l n i t r e n e by p h o t o e l e m i n a t i o n o f nitrogen." Both compounds g a v e t h e same e x p e c t e d 2 H - a z i r i n e on i r r a d i t i o n ; v a r i a t i o n s i n p r o d u c t d i s t r i b u t i o n were a t t r i b u t e d t o d i f f e r e n c e s i n t h e m u l t i p l i c i t y o f t h e e x c i t e d s p e c i e s . Ring c o n t r a c t i o n h a s a l s o been observed i n t h e f u s e d d i h y d r o f u r a n s (35) on t r i p h e n y l e n e - s e n s i t i z e d i r r a d i a t i o n a n d l e a d s t o t h e f o r m a t i o n of 5 , 7 - d i a z a s p i r o I 2 . S I o c t a n e s ( 3 6 ) .48 A n o v e l p h o t o r e a r r a n g e m e n t h a s , however, been d e s c r i b e d f o r t h e f u s e d i s o x a z o l e , a n t h r a n i l o p a p a v e r i n e (371, which on i r r a d i a t i o n i s c o n v e r t e d i n a l m o s t q u a n t i t a t i v e y i e l d i n t o t h e isoquino[l,2-b]-quinazoline (38) .49 Although i s o x a z o l i n e s g e n e r a l l y undergo photodecomposit i o n t o a v a r i e t y o f p r o d u c t s , s e l e c t i v i t y c a n b e a c h i e v e d by t h e i n t r o d u c t i o n o f a n oxygen atom i n t h e B - p o s i t i o n w i t h r e s p e c t t o t h e i s o x a z o l i n e o x y g e n . New e x a m p l e s o f t h i s r e a r r a n g e m e n t l e a d i n g t o t h e f o r m a t i o n of enamino a l d e h y d e s h a v e b e e n r e p o r t e d i n m o n o c y ~ l i ca~n d~ i n b i c y c l i ~ ~i s ~o x-a z~o ~l i n e s . Endo- a n d E - i s o x a z o l i n e s (391, f o r example, a r e c o n v e r t e d i n t o t h e d i o x a z o c i n e s ( 4 0 ) by t h e pathway o u t l i n e d i n Scheme 3 . 5 5 , 5 6 1~-Benzo[~lpyrazolo[l,2-alcinnolinesh a v e b e e n p r e p a r e d a s n o v e l p h o t o c h r o m i c compounds; "-the dicyano d e r i v a t i v e ( 4 1 ) , f o r e x a m p l e , a f f o r d s t h e c o l o u r e d b e t a i n e ( 4 2 ) via a p h o t o c h e m i c a l l y induced c o n r o t a t o r y 1 , s - e l e c t r o c y c l i c r i n g opening. Photochemically induced r i n g c l e a v a g e h a s a l s o been observed i n t h e endo- o r
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d i h y d r o t r i a z o l e ( 4 3 ) l e a d i n g , p r e s u m a b l y via t h e d i p o l a r i n t e r 58 mediate (441, t o t h e 2lj-azirine ( 4 5 ) . O x a z i r i d i n e s a r e formed by p h o t o c y c l i z a t i o n o f b o t h a c y c l i c and c y c l i c n i t r o n e s . S t a b l e t r i a r y l o x a z i r i d i n e s have been p r e p a r e d i n t h i s way f r o m polyfluorotriarylnitrones ,” a n d t h e n i t r o n e ( 4 6 ) i s c o n v e r t e d i n 78% y i e l d i n t o t h e o x a z i r i d i n e ( 4 7 ) on i r r a d i a t i o n ( A > 302 Limited e n a n t i o s e l e c t i v i t y has p r e v i o u s l y b e e n a c h i e v e d by t h e i n t r o d u c t i o n o f a c h i r a l s u b s t i t u e n t i n t o t h e n i t r o n e o r by t h e u s e o f a c h i r a l s o l v e n t . Much b e t t e r e n a n t i o s e l e c t i o n o f up t o 1 0 0 % e n a n t i o m e r i c e x c e s s h a s now b e e n o b t a i n e d by i r r a d i a t i o n i n a c r y s t a l l i n e i n c l u s i o n complex o f t h e n i t r o n e a n d o p t i c a l l y a c t i v e 1,6-di(~-chlorophenyl)-ly6diphenylhexa-2,4-diyne-1,6-diol. 61 The mechanism o f t h e r e l a t e d p h o t o r e a r r a n g e m e n t o f h e t e r o c y c l i c N-oxides i s s t i l l a m a t t e r f o r d e b a t e . Evidence t h a t r e a r r a n g e m e n t o f t h e p h e n a n t h r i d i n e N - o x i d e s ( 4 8 ) t o t h e Es u b s t i t u t e d phenanthridones (49) and t h e dibenzo[d,f] -1,3o x a z e p i n e s ( 5 0 ) p r o c e e d s by way o f b i r a d i c a l i n t e r m e d i a t e s r a t h e r t h a n o x a z i r i d i n e s h a s been p u b l i s h e d . 6 2 Dehydroperloline h a s b e e n s y n t h e s i z e d by a n a n a l o g o u s p h o t o r e a r r a n g e m e n t o f t h e N-oxide 63 o f 5 - (3,4-dimethoxyphenyl)benzo [ g ][ 2 ,7 l n a p t h y r i d i n - 4 (3H) - o n e . The p h o t o c h e m i c a l b e h a v i o u r o f s i m p l e p y r i d i n e N - o x i d e s h a s a g a i n b e e n shown t o b e e x c e p t i o n a l . I r r a d i a t i o n o f p y r i d i n e N-oxide ( 5 1 ) i n a q u e o u s b a s e , f o r e x a m p l e , a f f o r d s t h e a n i o n of 5 - h y d r o x y p e n t a d i e n e n i t r i l e ( 5 2 ) . 6 4 The n i t r e n e ( 5 3 ) h a s b e e n p r o p o s e d a s t h e most l i k e l y i n t e r m e d i a t e i n t h i s t r a n s f o r m a t i o n . The p h o t o r e a c t i o n s o f pyrazine-1 , 4 - d i o x i d e , q u i n o x a l i n e - 1 , 4 - d i o x i d e a n d phenazine-9,lO-dioxide have been reviewed. 65 P y r i d i n i u m y l i d e s a n d r e l a t e d s p e c i e s a r e known t o u n d e r g o a n a l o g o u s p h o t o r e a c t i o n s . The c y c l o a l k a n e - a n n u l a t e d p y r i d i n i u m N-aminide ( 5 4 ; n = 2 ) i s c o n v e r t e d i n t h i s way, p r e s u m a b l y v i a t h e d i a z i r i d i n e (551, i n t o t h e cyclopenta[cl-1,2-diazepine (56) .66 A competing 1 , s - e l e c t r o c y c l i z a t i o n i s p r e f e r r e d , however, on i r r a d i a t i o n of t h e N - a m i n i d e s ( 5 4 ; n = 3 o r 4 ) a n d l e a d s t o t h e 3 - a z a q u i n o l i z i n o n e s ( 5 7 ; n = 3 o r 4 ) by t h e pathway shown i n The s p i r o b e n z y l i s o q u i n o l i n e ( 5 8 ) h a s b e e n p r e p a r e d by Scheme 4 . i r r a d i a t i o n o f t h e o x i d e ( 5 9 ) ; 6 7 t h e l i k e l y pathway i s shown i n Scheme 5 . O x a z i r i d i n e s have been proposed a s i n t e r m e d i a t e s i n t h e photo-Beckmann r e a r r a n g e n e n t o f oximes. A r e i n v e s t i g a t i o n o f t h e p h o t o c h e m i s t r y o f ( + ) - c a m p h o r oxime ( 6 0 ) h a s r e v e a l e d t h a t t h e
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l a c t a m s ( 6 1 ) a n d ( 6 2 ) a n d t h e amide ( 6 3 ) a r e , a s e x p e c t e d a n d c o n t r a r y t o e a r l i e r r e p o r t s , t h e major p r o d u c t s of i r r a d i a t i o n i n m e t h a n o l . 6 8 T h i s i s i n a g r e e m e n t w i t h r e s u l t s o b t a i n e d f o r (+Ifenchone and f o r o t h e r b i c y c l o [ 2 . 2 . l ] h e p t a n o n e oximes. Regios p e c i f i c photorearrangement h a s s u r p r i s i n g l y been observed i n (!)and (Z)-cholest-4-en-3-one oximes, i n (E)-2,2-dimethyl69 c h o l e s t - 4 - e n - 3 - o n e oxime a n d i n ( g ) - c h o l e s t - S - e n - 7 - o n e oxime. Two t y p e ? o f p h o t o r e a r r a n g e m e n t h a v e b e e n r e p o r t e d i n n i t r o compounds, t h e f i r s t a r i s i n g by i n i t i a l n i t r o - t o - n i t r i t e r e a r r a n g e m e n t a n d t h e s e c o n d by i n t r a m o l e c u l a r h y d r o g e n a b s t r a c t i o n . The a n t i b a c t e r i a l d r u g m e t r o n i d a z o l e ( 6 4 ) i s c o n v e r t e d via t h e n i t r i t e ( 6 5 ) i n a w e l l documented f a s h i o n i n t o t h e u n s t a b l e oxime ( 6 6 ) on i r r a d i a t i o n i n a q u e o u s s o l u t i o n . 70 I n i t i a l n i t r o - t o n i t r i t e rearrangement i s a l s o r e s p o n s i b l e f o r t h e photodecomposition o f 1 - n i t r o p y r e n e . 7 1 The c o n v e r s i o n o f n i t r o n a t e a n i o n s i n t o hydroxamic a c i d s i s c l e a r l y a r e l a t e d p r o c e s s i n v o l v i n g i n i t i a l c y c l i z a t i o n t o a n o x a z i r i d i n e . Complete r e t e n t i o n o f c o n f i g u r a t i o n h a s been observed i n t h e photorearrangement of t h e anion of t h e n i t r o c y c l o h e x a n e (67) t o t h e a z e p i n e ( 6 8 ) . 7 2 Norbornyl a c i n i t r o 73 nate anion follows a similar reaction course.
o - N i t r o b e n z y l s y s t e m s a r e known t o u n d e r g o r e a r r a n g e m e n t as t h e r e s u l t of photochemically induced i n t r a m o l e c u l a r hydrogen ( 6 9 ) was a b s t r a c t i o n . !-(a-Hydroxy-2-nitrosobenzyl)-l-naphthamide o b t a i n e d i n t h i s way by i r r a d i a t i o n o f : - 2 - n i t r o b e n z y l , - l naphtharnlide ( 7 0 ) a t -78 "C , 7 4 a n d a new 2 ' - n i t r o b e n z h y d r y l p o l y s t y r e n e r e s i n h a s b e e n d e v e l o p e d a s a p h o t o s e n s i t i v e polymer s u p p o r t f o r p e p t i d e s y n t h e s i s . 75 Analogous s y s t e m s h a v e b e e n employed a s p h o t o l a b i l e c h e l a t o r s f o r t h e r a p i d r e l e a s e o f d i v a l e n t c a t i o n s 7 6 a n d a s p h o t o c h r o m e s . 7 7 s 7 8 The h y d r o g e n atom a b s t r a c t e d on i r r a d i a t i o n o f 2 - n i t r o - t - b u t y l b e n z e n e s h a s now b e e n i d e n t i f i e d by X - r a y ~ r y s t a l l o g r a p h y , ~a' n d t h e e f f i c i e n t p h o t o c h e m i c a l s i n g l e - s t r a n d c l e a v a g e o f DNA by 9 - ( 4 - n i t r o b e n z a m i d o polymethylenelaminoacridine i s b e l i e v e d t o b e t h e r e s u l t o f a n e q u i v a l e n t i n t e r m o l e c u l a r hydrogen a b s t r a c t i o n . 8 0 I n i t i a l c y c l i z a t i o n t o t h e 1,2,4-oxadiazete-Z-oxides ( 7 1 ) i s r e s p o n s i b l e f o r t h e photochemically induced conversion of t h e nitrohydrazones ( 7 2 ) i n t o t h e n i t r o s a m i n e s ( 7 3 ) ; 8 1 n i t r o a l k e n e s a r e known t o undergo an analogous c y c l j z a t i o n . Rearrangements o f n i t r a m i n o p y r i d i n e s have a l s o been r e p o r t e d , 8 2 and t h e intermediacy of a r a d i c a l - i o n p a i r h a s been proposed i n t h e photo-Smiles r e a r r a n g e 83 inent o f [ 2 - ( 4 - n i t r o - 1- n a p h t h o x y ) e t h y l ] a n i l i n e .
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111f4: Photoreactions of Compounds containing Heieroatoms other than Oxygen
383
Rearrangements in nitrogen-containing carbonyl compounds merit brief discussion in this section as well as in Part 111, Chapter 1 . Type I1 photocyclization has been widely used in the synthesis of B-lactams. The achiral a-oxoamide, N,N-di-isopropylphenylglyoxylamide (741, forms chiral crystals which on irradiation in the solid state are converted into optically active 3-hydroxyl-isopropyl-4,4-dimethyl-3-phenylazetidin-2-one ( 7 5 ) in high optical and chemical yield.84 Products arising by an analogous 6-hydrogen abstraction have previously been observed in N,Ndialkyl 6-oxoamides, but the related unsaturated 6-oxoamide (76) has now been shown to undergo an unusual reductive cyclization on irradiation in the presence of triethylamine to give the lactam (77) .85 Pyrrolo[l ,2-~]pyrazineshave been prepared by photocyclization o f N-acylsuccinimides ,86 and remote hydrogen abstraction has been employed in the synthesis of 8,14-dioxo-13hydroxyaporhoeadane.87 2- (~-Acyl-~-alkylamino)cyclohex-2-enones (78) are convkrted on irradiation in acetone into the spirolactams (79) ,88 and an unprecedented photocyclization has been reported for the B,y-unsaturated amides (80) leading to the lactams (81), presumably via the 1,6-biradicals ( 8 2 ) formed by 1,s-hydrogen transfer.89 Addition Reactions.-A section on heterocyclic compounds is included in a recent comprehensive review o f the photoaddition react ions of aromatic compounds.90 Numerous examples of intermolecular and intramolecular r a 2 + 21 photocycloaddition to carbon-carbon double bonds in nitrogen-containing systems have been reported. [T2 + T2] Photodimerization has been observed in 3-styrylisoxazolo [3,4-d]pyrida~in-7(6kJ)-ones,~~and the use of smectic liquid crystalline media significantly enhances the stereoselectivity and the rate o f photodimerization in uracil derivatives Intramolecular photocycloaddition of two dibenz[b,f] azepine units linked by a polymethylene chain of two to thirty carbon atoms has been described .93 Intermolecular[T2 + T2]photoreactions reported include the addition of 3-aminocyclohex-2-enone to ethoxyethylene,94 the addition of Ij-vinylcarbazole to 3-cyanostyrene ,” and the acetonesensitized addition of 5-fluoruracil to methyl vinyl ether, 2methoxypropene and ketene dimethyl acetal to give good yields o f the corresponding 8,8-disubstituted 6-fluoro-2,4-diazabicyclo[4.2.0]0ctane-3,5-diones.~~ Particular attention has been devoted
.’*
Photochemistry
384
-o &l (CH,),CH=CH,
'0
hV
I
I
H
H
(92 1
(93)
Me
Me
I
+
I
Ph
Me
- a?? hV
=
Ph
(95)
+
Ph
(97)
(96)
iHz
hV
C
II 0 (99)
(98 1
- q$$ hv
(100 1
0 (1011
llIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
385
to the [T2 + T21 photoreactions of 4-ethoxy-carbonyl-5-phenyl-lfipyrrole-2,3-dione (83), the major products of addition to alkenes with electron-donating substituents being the isomeric cyclobutanes (84) and ( 8 5 1 , formed with high regio- and stereo'-selectivity.9 7 The analogous additions of (?I- and (El-d-styrene have been shown to take place antarafacially. 98 [T2 + 23 Photoadducts are also formed from 1,4,SY8-tetraazaphenanthrene and halogenated alkenes,99 and the [ T 2 + n21 cycloaddition of 4-substituted quinol-2-ones to 1,l-dichloroethylene has been employed as the key step in a method developed to introduce the 2,2-dichloroethyl group into the 3position of the quinoline ring system. l o o The first documented photocycloaddition reaction of an indolizine has been reported; irradiation of indolizine ( 8 6 ) with trans-stilbene (87), for example, gave the 1:l-adduct ( 8 8 ) and the 1:2-adduct ( 8 9 ) with Theoretical studies o f high regio- and stereo-selectivity. lo' the photocycloaddition of psoralen to thymidine have been described. 102 Examples of the equivalent intramolecular cycloaddition have also been reported. The conversion of enaminone ( 9 0 ) into the tetracyclic amine (91) has been used in the construction of a taxane BC intermediate, l o 3 and indolizine and quinolizine derivatives have been prepared by intramolecular [ T 2 ?+ l21 photoadditions in w-alkenylisoquinolinones and w-alkenyl;,yridinones.104 The regioselectivity o f analogous cycloadditions in 4-(alkeny1oxy)quinolin-Z-(lH)-ones is determined by the chain length;105 irradiation o f quinolone (92; n=1), for example, gave the adduct (93), whereas the related quinolone (92; n=3) was converted photochemically into the adduct (9'4). Intramolecular [ T 2 + 21 photocycloaddition has also been employed in the preparation of photoresponsive c y c l o b u t a n e - 1 , 2 - d i c a r b o n y l - c a p p e d [ 2 . n ] d i a z a c r o w n ethers. 106 In contrast to addition to alkenes, photocycloaddition to the carbon-nitrogen double bond is relatively rare. During the period covered by this report, however, further examples o f this process have been reported and the requirements for successful addition are becoming more clear. Intermolecular addition is favoured in cyclic imines in which the carbon-nitrogen double bond is conjugated with an electron-withdrawing group. Addition of the quinoxalin-2-one (95) to 1,l-diphenylethylene (961, for example takes place regiospecifically to give the azetidine ( 9 7 ) in 249, yield. l o 7 Analogous additions of benzoxazin-2-ones to
Photochemistry
386
%-& hv
(102)
(103) X
=
N H or 0
CH,, NCO,Et,
Me
Me
Me
I
I
MeOH
I
OMe
,
OMe
-- Ph
--Me
Me
Ph
(105)
(104)
(106)
(107)
r
1
I
H
c104-
(100)
(109)
%C=C", H H
(1111
+
OPh I
CH2C3CH
H
H
(112 1 Schtuk 6
(110)
lllJ6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
387
a r y l a l k e n e s have been r e p o r t e d , and t r i f l u o r o m e t h y l d e r i v a t i v e s of b o t h q u i n o x a l i n - Z ( l H ) - o n e a n d o f 1 , 4 - b e n z o x a z i n - 2 - o n e a d d t o e l e c t r o n - r i c h and e l e c t r o n - d e f i c i e n t a l k e n e s . l o 8 Addition of 3trifluoromethylquinoxalin-Z(l!)-one (98) t o ketene a f f o r d s t h e azetidin-2-one ( 9 9 ) . l o g D e t a i l s of t h e c r y s t a l s t r u c t u r e s of a z e t i d i n e s d e r i v e d by p h o t o c y c l o a d d t i o n o f 1 , 3 - d i m e t h y l - 6 azathymine t o v a r i o u s a l k e n e s have been p u b l i s h e d . 1 1 0 Analogous i n $ r a m o l e c u l a r a d d i t i o n s h a v e a l s o b e e n described. The i m p o r t a n c e o f t h e t r i f l u o r o m e t h y l g r o u p i n i n f l u e n c i n g t h e c o u r s e o f a p h o t o r e a c t i o n h a s a g a i n b e e n demons t r a t e d i n t h e c o n v e r s i o n o f 3-(but-3-enyl)-2-trifluoromethyl-4(3H)quinazolinone (100) i n t o t h e i n t r a m o l e c u l a r adduct ( 1 0 1 ) ; l l 1 t h e corresponding 2-unsubstituted quinazolinone is reported t o be photostable. Intramolecular a z e t i d i n e formation has a l s o been o b s e r v e d on i r r a d i a t i o n o f pyrimidine/6-azapyrimidine a n a l o g u e s o f dinucleotides,’” a n d t h e f i r s t [ a Z + .rr2] p h o t o r e a c t i o n s o f a t h r e e membered r i n g a n d a n a z o g r o u p h a v e b e e n d e s c r i b e d ; l l 3 t h e a z o compounds ( 1 0 2 1 , f o r example a r e c o n v e r t e d i n t h i s way i n t o t h e a d d u c t s ( 1 0 3 ) on i r r a d i a t i o n i n a c e t o n i t r i l e . R e g i o i s o m e r i c o x e t a n e s a r e formed by P a t e r n o - B u c h i p h o t o a d d i t i o n o f 3-acetyl-2,3-dihydro-2,2-dimethyloxazole t o a c e t o n e a n d benzophenone, and t h e p r e p a r a t i o n of i s o x a z o l i n e s an unusual p h o t o a d d i t i o n of n i t r i l e o x i d e s t o a l k e n e s h a s been d e s c r i b e d . ’ l 5 I n i t i a l t T 2 + n2] p h o t o a d d i t i o n of a n i t r i l e t o a carbon-carbon d o u b l e bond h a s b e e n p r o p o s e d t o a c c o u n t f o r t h e p h o t o r e a c t i o n s o f b e n z o n i t r i l e ’ l 6 and c e r t a i n cyanoanisoles. 1 1 7 The p h o t o a d d i t i o n o f p h t h a l i m i d e s a n d r e l a t e d d i c a r b o x imides t o a l k e n e s has been t h e s u b j e c t o f d e t a i l e d s t u d y over t h e years. In t h e presence of added methanol, t h e p h o t o r e a c t i o n s o f d i c a r b o x i m i d e s w i t h a l k e n e s a l s o r e s u l t i n t h e f o r m a t i o n of m e t h a n o l i n c o r p o r a t e d p r o d u c t s . The e f f i c i e n c y o f a l c o h o l t r a p p i n g b y t h e N-methylphthalimide-alkene r a d i c a l i o n p a i r , which i s i n v o l v e d i n t h i s a d d i t i o n , h a s r e c e n t l y b e e n shown t o b e a f u n c t i o n o f b o t h s o l v e n t p o l a r i t y and a l c o h o l n u c l e o p h i l i c i t y . l 8 In c o n t r a s t , a n o v e l a n d u n u s u a l p h o t o a d d i t i o n o f N-methyl-1,8-naphthalimide ( 1 0 4 ) t o a-methylstyrene (105) h a s been observed i n methanol l e a d i n g t o t h e i s o m e r i c t e t r a c y c l e s (106) and ( 1 0 7 ) . l 9 D e u t e r i u m - l a b e l l i n g s t u d i e s h a v e shown t h a t t h e p h o t o a d d i t i o n o f p h e n y l c y c l o p r o p a n e r a d i c a l c a t i o n t o 2-methylphthalimide r a d i c a l anion i s a two-step p r o c e s s i n v o l v i n g a n i n t e r m e d i a t e b i r a d i c a l . l Z o The e a s e o f e l e c t r o n t r a n s f e r from a l k e n e
t o p h t h a l i m i d e c a n b e reduced by t h e
388
Photochemistry
6 I
4- Et,N-CH2-SiMe3
"
&NEtz
&NEt2
+
Me Me
Me Me SiMe,
(117)
(116)
Me Me
(118)
(119)
hV ___)
EtOH
CHOH
I
Me (1201
(121 1
hV
RJ
A
E t20
R
0
\N R
A,
/
WR CHOEt
I
(122 1 R
= Ph or 4 - MeC&
Me (123)
11116: Photoreactions of Compounds containing Heteroatoms other than Oxygen
389
use of t h e phthalimide a n i o n ; i n t h i s c a s e , a d i f f e r e n t r e a c t i o n pathway p r e d o m i n a t e s , w i t h i r r a d i a t i o n o f sodium p h t h a l i m i d e and c y c l o h e x e n e l e a d i n g t o t h e f o r m a t i o n i n methanol o f t h e c o r r e s 121 ponding b e n z a z e p i n e d i o n e a n d 3 - h y d r o x y i s o i n d o l i n o n e . S i n g l e e l e c t r o n t r a n s f e r from a v a r i e t y o f s u i t a b l e d o n o r s i s a l s o r e s p o n s i b l e f o r t h e e x c i t e d s t a t e c h e m i s t r y o f iminium s a l t s . A l l e n e s h a v e now b e e n shown t o p a r t i c i p a t e i n t h i s e l e c t r o n t r a n s f e r a d d i t i o n ; i r r a d i a t i o n o f 2-phenyl-1-pyrrolinium perchlora t e ( 1 0 8 ) a n d a l l e n e (109) i n methanol gave t h e e t h e r (1101, t h e a l l e n e ( 1 1 1 ) a n d t h e a l k y n e (112) via t h e i n t e r m e d i a t e a l l e n e c a t i o n r a d i c a l a s shown i n Scheme 6. 2 2 I n t r a m o l e c u l a r p h o t o c y c l i z a t i o n s o f 1 - b e n z y l - 1 - p y r r o l i n i u m p e r c h l o r a t e s have a l s o been described. I r r a d i a t i o n o f t h e b e n z y l p y r r o l i n i u m p e r c h l o r a t e (1131, 123 f o r example, gave t h e i s o m e r i c p y r r o l i z i d i n e s (114) and ( 1 1 5 ) . The c o r r e s p o n d i n g i n t e r - a n d i n t r a - m o l e c u l a r a d d i t i o n s o f a l l y l s i l a n e s t o iminium s a l t s g i v e r i s e a f t e r d e s i l y l a t i o n t o s y n t h e t i c a l l y u s e f u l b i r a d i c a l i n t e r m e d i a t e s . Evidence f o r t h e e x i s t e n c e of two mechanisms f o r s u c h r e a c t i o n s , d i f f e r i n g o n l y i n t h e t i m i n g o f c a r b o n - s i l i c o n bond c l e a v a g e a n d c a r b o n - c a r b o n bond f o r m a t i o n , h a s been d e s c r i b e d l Z 4 Analogous e l e c t r o n t r a n s f e r p h o t o c h e m i s t r y f o l l o w e d by d e p r o t o n a t i o n o r d e s i l y l a t i o n h a s been o b s e r v e d i n t h e a-silylamine-cyclohexenone s y s t e m . 2 5 I r r a d i a t i o n o f s i l y l a m i n e (116) and c y c l o h e x e n o n e ( 1 1 7 ) gave t h e a d d u c t ( 1 1 8 ) and t h e d e s i l y l a t e d amine (1191, t h e r a t i o o f p r o d u c t s b e i n g d e p e n d e n t on t h e p o l a r i t y o f t h e s o l v e n t u s e d . P h o t o i n d u c e d a d d i t i o n of t e r t i a r y amines t o c y c l o h e x - 2 - e n o n e h a s a l s o been 126 reported. S o l v e n t a d d i t i o n o c c u r s r e a d i l y on i r r a d i a t i o n o f 1 , 2 , 3 , 6 - t e t r a h y d r o p y r i d i n e s i n methanol a n d y i e l d s t h e c o r r e s p o n d i n g Solvent incorporation i n ethoxycarbonyl4-methoxypiperidines. s u b s t i t u t e d q u i n o l i n e s i s t h e r e s u l t of a photochemically induced hydrogen a b s t r a c t i o n by t h e r i n g n i t r o g e n ; e t h y l q u i n o l i n e - 4 c a r b o x y l a t e (1201, f o r e x a m p l e , i s c o n v e r t e d i n t h i s way i n t o t h e 2 - s u b s t i t u t e d q u i n o l i n e ( 1 2 1 ) on i r r a d i a t i o n i n e t h a n o l . l Z 8 I n t e r m o l e c u l a r hydrogen a b s t r a c t i o n by a n imino g r o u p i s a l s o r e s p o n s i b l e f o r t h e c o n v e r s i o n of t h e l-alkyl-4,6-diarylpyrimidinZ ( l g ) - o n e s ( 1 2 2 ) i n t o t h e a d d u c t s (123) on i r r a d i a t i o n i n t h e p r e s e n c e o f a hydrogen donor s u c h a s d i e t h y l e t h e r , ” ’ and i n i t i a l hydrogen a b s t r a c t i o n i s p r o b a b l y i n v o l v e d i n t h e p h o t o r e a c t i o n s o f p h t h a l a z i n e i n propan-2-01’ 30 a n d o f d i p h e n y l m e t h a n i m i n e i n T h e r e i s s t r o n g e v i d e n c e , however, t h a t p h o t o m e t h a n o l . 13’
”’
. a d d i t i o n of N , N - d i m e t h y l a n i l i n e - t o p - b e n z o q u h o n e d i i m i n e
Photochemistr
390
hV
(126)
Scheme 7
AcoQ AcO
OAc (129)
"OQAcO
OAc (130)
I I I b Photoreactions of Compounds containing Heteroaroms other than Oxygen
(132
391
(I311 R ' = Ac or Me, R 2 = H 2
R ' = Me, R = D
(13 C 1
(135)
R = Cl, OMc, OEt or SCN
(136)
I
dPh Ph-N&
Ph
Ph
I
H (137 1
(138)
Scheme 8
SPh
(139)
R = Me, E t , CH2CH=C$or
Ph
SPh
(1401 CH2Ph
Photochemistry
3 92
132 d e r i v a t i v e s p r o c e e d s by way o f a n e l e c t r o n t r a n s f e r mechanism. Other miscellaneous photoadditions r e p o r t e d include r e a c t i o n of 5,7-dimethoxycoumarin w i t h adenosine ,133 t h e a d d i t i o n o f n i t r o g e n d i o x i d e t o n a p h t h a l e n e , ’ 34 t h e f o r m a t i o n o f 1 - ( 1 , 4 dihydro-1-naphthy1)indole by a d d i t i o n o f i n d o l e t o n a p h t h a l e n e i n t h e s o l i d s t a t e , l 35 and t h e c o n v e r s i o n of 2 -amino-l,4-naphtho136 quinone ( 1 2 4 ) i n t o ‘ t h e t r i m e r i c s p e c i e s (125). M i s c e l l a n e o u s R e a c t i o n s . - The p h o t o r e a c t i o n s o f ! - s u b s t i t u t e d 137 2(1H)-pyrimidinones have been reviewed. I r r a d i a t i o n of non-8-enyl n i t r i t e (126) l e a d s h o m o l y s i s o f t h e n i t r o g e n - o x y g e n bond a n d 1 , s - h y d r o g e n t r a n s f e r a s shown i n Scheme 7 t o t h e a c y c l i c a n d c y c l i c n i t r o s o - a l c o h o l s ( 1 2 7 ) and (128).138 N i t r o s a t i o n of p o l y c y c l i c phenols h a s been a c c o m p l i s h e d by i r r a d i a t i o n i n t h e p r e s e n c e o f N - n i t r o s o d i m e t h y l amine,13’ a n d t h e p r o d u c t s o f p h o t o d e c o m p o s i t i o n o f s o l i d ( + ) - l o bromo-2-chloro-2-nitrosocamphane a r e b e l i e v e d t o a r i s e & y an i n i t i a l c a r b o n - n i t r o g e n bond h o m o l y s i s . Nitrenium and a l k y l n i t r e n i u m i o n s , g e n e r a t e d by p h o t o l y s i s o f 1 - ( a m i n o ) - a n d l-(alkylamino)-2-methyl-4,~diphenylpyridinium t e t r a f l u o r o b a t e s , 141 h a v e b e e n u s e d i n t h e d i r e c t a m i n a t i o n o f a r o m a t i c compounds. An u n u s u a l b u t e f f i c i e n t c o n v e r s i o n o f t h e p y r i d i n i u m c h l o r i d e ( 1 2 9 ) i n t o t h e h i g h l y f l u o r e s c e n t b e t a i n e ( 1 3 0 ) h a s been 142 o b s e r v e d on i r r a d i a t i o n i n a q u e o u s s o l u t i o n . 2.
S u l p h u r - c o n t a i n i n g Compounds
A wide v a r i e t y o f p h o t o r e a c t i o n s h a v e b e e n r e p o r t e d i n s u l p h u r -
c o n t a i n i n g compounds, w i t h p a r t i c u l a r a t t e n t i o n b e i n g p a i d t o t h e photochemistry of thiones. E l e c t r o c y c l i c r i n g c l o s u r e t o t h e c y c l o b u t a b e n z o [b] t h i o p h e n e s (131 ) i s t h e p r i n c i p a l r e a c t i o n o b s e r v e d on i r r a d i a t i o n o f t h e m o n o - s u b s t i t u t e d 1 -benzot h i e p i n e s ( 1 32 1 . 1 4 3 P h o t o r e a r r a n g e m e n t o f t h e 2 - m e t h y l - 1 , s - b e n z o t h i a z e p i n e s (133) t a k e s a d i f f e r e n t c o u r s e and a f f o r d s t h e isomeric b e n z o t h i a z e p i n e s ( 1 3 4 ) p r e s u m a b l y y& t h e d i p o l a r i n t e r m e d i a t e s ( 1 35). 144 I r r a d i a t i o n of t h e mesoionic triphenylthiazolium-4o l a t e (136) i n t h e p r e s e n c e of t r i b u t y l p h o s p h i n e gave t h e q u i n o l i n o n e ( 1 3 7 ) . 14’ T h i s r e s u l t c a n b e s t b e e x p l a i n e d a s shown i n Scheme 8 by i n i t i a l p h o t o c h e m i c a l l y i n d u c e d v a l e n c e i s o m e r i z a t i o n f o l l o w e d by d e s u p h u r i z a t i o n a n d r i n g o p e n i n g t o t h e k e t e n e ( 1 3 5 ) . Four n o v e l p h e n y l d i t h i e n o i n d o l e d e r i v a t i v e s h a v e b e e n
lIlI6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
Me
SMe
hv ___)
MeCN
(141 1
(142 1
hv ___)
(1431
hV
4 (145)
s5fj$: S
(146)
hV ___)
MeOH
“C
*c (1171 hV
Scheme 9
1
cyclopentcnc
393
394
Phorochemistry
Me
(155) R
=
H or Me
(156)
hV
S
H
(758)
R2 R3
R'qs + R2
hV
R3
NN ,
R
1
'N
I
H
(159 1
R'
=
(1611 H o r Mc.RG H, Me, OEt o r OAc, R3= R4=H o r Me
(160 1
~
R
4
11116: Photoreactions of Compounds containing Heteroatoms other than Oxygen
3 95
prepared by the oxidative photocyclization of dithienylpyrroles, and enamide photocyclization followed by elimination of H C 1 has been observed in 3 - c h l o r o - ~ - p h e n y l b e n z o [ b ] t h i o p h e n e - Z carboxamides.147,148 Ally1 sulphones (139) undergo a 1,3-sulphonyl shift on irradiation in solution to give the isomeric sulphones (140). 149 Direct irradiation of 9-dimethylsulphonium fluorenylide (141) in acetonitrile or tetrahydrofuran yields primarily the Stevens rearrangement product 9-methyl-9-(methylthio)fluorene (1421,150 and a 1,Z-shift of a sulphonic acid group is thought to be involved in the photoisomerization of the sodium salt of metanilic acid (m-aminobenzenesulphonic acid). 51 Photoinduced rearrangement of 4,5-(ethylenedithio)-l,3-dithiole-Z-thione (143) to the isomeric 4,5-(ethylenedithio)-l,Z-dithiole-3-thione (144) has been reported.152 Intramolecular [.,r2 + T 2 ] photoadditions in sulphurcontaining systems have been employed in studies directed towards the total synthesis of dicyclopenta[~,~lcyclooctaneterpenoids153 and in the conversion of the tetrathiadiene (145) into the propellane (146), a process in which the ease of reaction is attributed to the close proximity of the two carbon-carbon double bonds. lS4 Irradiation of the 2(5H)-thiophenone (147) in methanolcyclopentene affords the diasteroisomeric thiatricyclo[6.4.0.02 "1 dodec-10-enes (148) and (149) via the ester (150) formed by photosolvolysis of the thiophenone as shown in Scheme 9.l" Detailed studies of photoaddition of thiocarbonylcontaining compounds have been reported. A molecular orbital analysis of such additions has been undertaken and the results have proved useful in rationalizing observed regiochemistries.156 1,1,3-Trimethyl-2-thioxo-l,2-dihydronaphthalene adds to electronr i c h alkenes such as 2,3-dihydrofuran, ethyl vinyl ether, v i n y l acetate and tetramethylethylene to give thietanes and 1,4-dithianes on excitation to either the S 2 ( ~ n * )or the S, (nT*) state. 157 Cycloaddition of the same thione (1 51) to the electron-deficient an upper alkene acrylonitrile (1521, however, takes place excited singlet state to give an 8:1-mixture of stereoisomers (153) and (154);158 an exciplex has been proposed as an intermediate in this addition. Thiocoumarin is reported to add to both electronrich and electron-deficient alkenes the lowest triplet excited state. 59 An analogous intramolecular addit ion has been described in the 4-vinyl-l,3-thiazole-5(4H)-thiones (1 55) and leads to the
*
Photochemistry
3 96
Me$H2SH
$ + (167 1
(168)
(166)
R
= CN or C0,Me
I
R' (169 1
S
+ R'= Ph, PhCH,. 6un, Me or H R2= R3= Me, Ph or (CH215 Scheme 10
I
R'
(170 1
II
Me-C-"Et,
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
3 97
tricyclic thietanes (1 56) ,160 and the first stable 1,2-dithiethane (157), a yellow-orange crystalline compound, has been prepared by irradiation of the dithiocarbonyl lactone (158). 161 The study of thioimides has attracted particular attention and the photochemistry of cyclic thioimides has been reviewed.1 6 2 Thietanes are the primary products of most photoadditions of thioimides to alkenes. The additions of pyridine-2-thione, quinoline-2-thiones and isoquinoline-1-thione to vinyl ethers have been reported,163 and the 312Ij)-pyridazinethiones (159) are converted into the thieno[2,3-clpyridazines (160) on irradiation with alkenes (161). 164 Irradiation of N-methylmonothiophthalimide (162) in the presence o f thietane (163) gave the 1,2-dithiane (164) and the 1,3-dithiane (165) the previously reported formation o f 1,Z-dithianes in the photoaddition o f N-methylmonothiophthalimide to styrene can now be explained in terms of an intermediate spirophthalimidethietane. Thietanes are also intermediates both in the conversion o f the pyridine-4-thione (166) into the 4-substituted pyridines (167) on irradiation in the presence of alkenes (168)'66 and in the photoadditions of pyrimidine-4 (3H) -thiones and quinazoline-4(3H) -thiones to alkenes.167 Indoline-2-thiones undergo desulphurization to the corresponding indole derivatives on irradiation in benzene, intermediate thiiranes.168 Irradiation of the same possibly indoline-2-thiones (169) in the presence of triethylamine, however, affords the indolines (170) ;16' a pathway involving electron transfer and the formation of the zwitterions (171) has been proposed and is outlined in Scheme 10. The photodecomposition o f 5,s-diethyl-2-thiobarbituric acid in various alcohols has been described 170 Other miscellaneous additions reported include the photoaddition of thiocarboxylic acid to 3,4-diallyl-l,6-propano-lH,6H171 3a-thia(S IV )-1,3,4,6-tetraazapentalene-Z ,5(3!,4€j)-dithione, the Paterno-Btichi addition of methyl vinyl sulphides to benzophenone to give 3-methylthio-oxetanes stereoselectively and regiospecifically,' 72 and the stereospecific addition of 1,Znaphthalenedicarboxylic thioanhydride (172) to 2-but-2-ene (173) to give the naphthothiepinedione (1 7 4 ) ,l 73 a transformation analogous to that previously reported in certain arene dicarboximides. a-Cleavage reactions also occur on irradiation of thiones. Norrish Type I cleavage in thiones has been examined using the
.
Photochemistry
398
(176)
(17 5 1
?F
";k.:.
H
Me
Me
NC
Me
CN (177)
Scheme 11
Me
3 99
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
(179 1
(1801
hV
( Mc2Si l6
Me2Si:
(181)
16
Me
(182 1
&II
Si --H
(1831
Me
I
(1851 Scheme 12
CMe3
Me3C
I / Si /\
Me$
-/Si-Si \- W e 3 CMe3
CMe3
hV L
Me&
\
Sit
/
Mc3C
R-CZN
Mc3C CMe, \ / R
/\
Mc3C
(mi
(186)
(188) R
=
CMe,
Me or Ph
Photochemistry
400
H,
SiMe3
Me,Si
R’xe3 \
,OEt
/
Et O H
hY
Me3C
sxM
’
Me 3C
CN3
(190) R = mesityl
CMe,
(189)
Me M
hv wMe-M
e
Me-
Si-Si
I
I
+
&-@Me
-Me Me
/
Si,
Me Me
(194 1
(195 1 hV
Me Me
I
PhZCO
Me Me
Me’
Me2Si:
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
401
MIND0/3-CI method, 7 4 and both photophysical and photochemical studies of cyclobutanethiones have been undertaken. The thione (1751, for example, is converted into the isomeric cyclobutanethione (176) on irradiation in benzene and into the cyclic thioacetals (177) and (178) in the presence of methanol; the proposed pathways are shown in Scheme 11. Type I1 behaviour is observed, however, in the cyclic dithioimides (179) and leads on irradiation in solution to the bicyclic thiols (180). 176 3.
Compounds containing other Heteroatoms
The majority of the reports included in this section are concerned with the photoreactions o f organosilicon compounds. In particular, the generation and reactions of silylenes (silanediyls) have been the subject of much interest. A variety of organosilylenes have been prepared in a 3-methylpentane glass at 77K by irradiation of cyclosilanes or linear trisilanes.177 Diarylsilylenes can be generated in a similar fashion from 2,2-diaryl-1,1,1,3,3,3hexamethyltrisilanes and add non-stereospecifically to cis- and trans-but-2-enes to give the correspondingly substituted cyclopropanes. 78 The addition of photochemically generated dimethylsilylene (181) to B-pinene (182) takes place on the lesshindered face and affords the allysilane (183) and the methoxysilane (184) via the unstable silirane (185) as shown in Scheme l2,l7’ and addition and insertion products have been obtained from c y c l o p r o p y l p h e n y l s i l y l e n e , the product of photodecomposition of 2 - c y c l o p r o p y l - 2 - p h e n y l h e x a m e t h y l - t r i s i l a n e . 180 Silylene itself reacts rapidly with alkenes but is virtually unreactive towards alkanes. 181 Di-t-butylsilylene (186), generated by photolysis o f hexat-butylcyclotrisilane (187), adds readily to the nitrile group of acetonitrile or benzonitrile to give the 3,6-disila-3,6-dihydropyrazines ( 1 881,’82 and the first phosphasilirene has been prepared by the analogousaddition of a silylene to a phospha-alkyne.183 A high yield of the expected silylene insertion product (189) was obtained on irradiation o f the cyclopropenyltrisilane (190) in ethanol;184 the failure of this silylene (1913 to undergo rearrangement is surprising in view of the comparable reactivity of analogous nitrenes and carbenes. Silylene rearrangement is observed, however, on photodecomposition o f the same trisilane in a 3-m th 1 entane glass at 77K and yields the novel but unstable 7 y p
’
Photochemistry
402
M
e
w Me
Me2Si,S,Si
e
w
M
Si
’
Me
‘Me
(1981
Et2
-si \
h-si
M
Me,
(197 1
/se Et,Si
+
+ hv IMe2Si=S1
hv
st /
I Et,Si =Sl
i-
Et,S(
Se )SiEt2 Se
Et2
(200)
(199)
(2011
Me
Si
/ \
Me
Me (2031
1
butadicne
Me
I
,CH,Si
Me2CH=CH,
(204)
Mt
e
IIIl6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
Me
I
Me
Me I
Me
Me
(206 1
(207)
Me Me
(2091 R
=
Me Me
Me Me
mesityl
(2081
-
0
R,ll 0 Me%
hV
0
N-Ph
II
R-P*
+I]
(2101
+ -
R,P-CEN-O
(2121
[
0
“Ph
(211 1
S
+
hV
S II
R,P-
N=C=O
(213 I
403
404
Photochemistry
s i l a c y c l o b u t a d i e n e ( 1 9 2 ) which c a n b e t r a p p e d a s t h e a d d u c t ( 1 9 3 ) 185 by r e a c t i o n w i t h e t h a n o l . Reaction of photochemically generated d i - t - b u t y l s i l y l e n e w i t h dimethylsulphoxide i n t h e p r e s e n c e of w a t e r gave a t e t r a s i l oxane. In addition t o dimethylsilylene extrusion t o give the dibenzosilacyclopentadiene ( 1 9 4 ) , t h e d i s i l a c y c l o h e x a d i e n e ( 1 9 5 ) u n d e r g o e s a n o v e l p h o t o r e a c t i o n w i t h benzophenone t o y i e l d t h e i n i t i a l h o m o l y s i s o f t h e s i l i c o n - s i l i c o n bond. 1 8 7 adduct (196) The p r a c t i c e of s u r r o u n d i n g r e a c t i v e d o u b l e b o n d s w i t h b u l k y s u b s t i t u e n t s h a s made i t p o s s i b l e t o i s o l a t e d i s i l e n e s a s ’ thermally s t a b l e , yellow o r orange coloured, c r y s t a l l i n e species. Many methods f o r t h e p r e p a r a t i o n o f d i s i l e n e s a r e p h o t o c h e m i c a l i n n a t u r e . 88 T e t r a m e t h y l d i s i l e n e h a s p r e v i o u s l y b e e n o b t a i n e d by p h o t o f r a g m e n t a t i o n of dibenzotrisilacycloheptadiene; a p p l i c a t i o n o f t h i s a p p r o a c h t o t h e s u l p h u r - c o n t a i n i n g a n a l o g u e (197) gave d i m e t h y l s i l a t h i o n e ( 1 9 8 ) which was t r a p p e d w i t h 1 , 1 , 3 , 3 - t e t r a -
methyl-2-oxa-1,3-disilacyclopentane. 18’ Analogous e x t r u s i o n o f d i e t h y l s i l a n e s e l o n e (199) h a s been proposed t o account f o r t h e c o n v e r s i o n o f hexaethylcyclotrisilaselenane ( 2 0 0 ) i n t o t e t r a e t h y l 190 c y c l o d i s i l a s e l e n a n e ( 2 0 1 ) on i r r a d i a t i o n i n h e x a n e . T e t r a k i s [ b i s ( tr i m e t h y l s i l y l ) m e t h y l ] d i s i l e n e u n d e r g o e s d i s s o c i a t i o n 191 t o t h e c o r r e s p o n d i n g s i l y l e n e on i r r a d i a t i o n . S i l e n e s can be g e n e r a t e d by a v a r i e t y of photochemical p r o c e s s e s . The c y c l o a d d i t i o n r e a c t i o n s of c e r t a i n s t a b l e s i l e n e s , p r e p a r e d b y i r r a d i a t i o n o f a c y l s i l a n e s , h a v e b e e n e x a m i n e d , 192 a n d i r r a d i a t i o n o f t h e 1,2-divinyl-l,Z-disilane (202) a f f o r d s t h e m o n o s i l e n e (203) which on r e a c t i o n w i t h b u t a d i e n e i s f u r t h e r c o n v e r t e d i n t o t h e s i l a c y c l o b u t a n e (204) and t h e s i l a c y c l o h e x e n e (205). l g 3 V a r i o u s o t h e r u n r e l a t e d e x a m p l e s of r e a c t i v i t y i n s i l i c o n c o n t a i n i n g compounds h a v e b e e n r e p o r t e d . Hexamethyl-1 , 4 - d i s i l a b e n z e n e ( 2 0 6 ) h a s b e e n p r e p a r e d by i r r a d i a t i o n o f t h e a n t h r a c e n e adduct (207) and i t s thermal r e a c t i o n s w i t h a l k y n e s , methanol and oxygen d e s c r i b e d . l g 4 The s i l a c a r b o n y l y l i d e ( 2 0 8 ) c a n b e g e n e r a t e d by p h o t o l y s i s o f t h e o x a s i l i r a n e ( 2 0 9 ) , l g 5 a n d s i n g l e e l e c t r o n t r a n s f e r i s involved i n t h e photochemically induced d e s i l y l a t i o n 196 of t r i m e t h y l s i l y l enol e t h e r s . An i n i t i a l t r i p l e t r a d i c a l p a i r h a s b e e n i d e n t i f i e d i n t h e p h o t o l y s i s of benzoyltriethylgermane. l g 7 Dialkyl- and d i a r y l germylenes, g e n e r a t e d photochemically from digermanes, r e a c t w i t h 3,s-di-t-butyl-2-quinone t o g i v e 2 - g e r m a - 1 , 3 - d i o x o l a n e s . l g 8 O t h e r r e a c t i o n s o f d i m e t h y l g e r m y l e n e , o b t a i n e d by p h o t o f r a g m e n t a t i o n o f
11116: Photoreactions of Compounds containing Heteroatoms other than Oxygen
405
406
Photochemistry
7-germanorbornadiene, have also been described. 199 The photoreactions of ally1 and benzyl phosphites have been reviewed. Photochemical1y induced carbon -phosphorus bond cleavage has been reported in substituted (benzy1)phosphonic acid derivatives ,201 and the highly reactive N,N-dimethylamino metaphosphoramidate (210; R=NMe2) and ethyl metaphosphate (210; R=OEt) have been prepared by photofragmentation o f the corresponding 2,3-oxaphosphabicyclo[Z.2.2]oct-S-enes (211). 202 The A s phosphorus-substituted nitrile oxides (212) are reported to and undergo photorearrangement to the isocyanates ( 2 13) ,'03 5-methyl-2-phenyl-l,2,3-diazaphosphole is converted in low yield into a dehydro dimer. 204 A novel lY4-methyl migration has been observed on irradiation of the selenanaphthalene (2141, yielding the ketenimine (215) in 178 yield.205 Irradiation o f the 1 ,2,3,4,5-pentaselenepin (216) in the presence o f norbornadiene (217) gave the adduct (2181, presumably via the corresponding 1 ,2-diselenoneYzo6 and photodeselenation has been employed in the preparation o f [2.2]cyclophanes from diselena[3.3]cyclophanes. 207 Irradiation of sodium tetraphenylborate in acetonitrile or tetrahydrofuran does not, as previously claimed, result in the formation of a diphenylborene anion; stilbene derivatives which are formed on irradiation o f sodium tetraphenylborate in the presence of diphenylacetylene have now been shown to arise via an electron transfer pathway from tetraphenylborate anion. 2 0 8
IIll6: Photoreactions of Compounds containing Heteroatoms other than Oxygen
407
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108,
2,
E,
Photochemistry
408 39 40 41
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108,
107,
42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
28,
120,
(w.
108,
107,
108,
121,
106,
lIlJ6: Photoreactions of Compounds containing Heteroatoms other than Oxygen 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110
2, 108,
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Q.,
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2,
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410
Photochemistry
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11116: Photoreactions of Compounds containing Heteroatoms other than Oxygen
41 1
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325,
2,
108,
2,
27,
108,
E,
60,
2,
7 Photoelimination BY S. T. REID This Chapter is principally concerned with the photoinduced fragmentation o f organic compounds, accompanied by the formation of small molecules such as nitrogen, carbon dioxide and sulphur dioxide. Photodecompositions resulting in the formation of two or more sizeable fragments are reviewed in the final section. Fragmentations arising by Norrish Type I and Type I 1 reactions of carbonyl-containing compounds are considered in Part I11 Chapter 1 . 1.
Elimination of Nitrogen from Azo-compounds
Alkyl radicals are readily generated from azoalkanes by photochemically induced elimination of nitrogen. 1-Adamantyl radicals can be obtained in this way by photolysis of azo-1,l'-adamantane in acetonitrile; the products are derived principally by hydrogen abstraction from the solvent although radical addition to the nitrile group is also important. The effect of solvent viscosity on the photoisomerization and photodecomposition of trans-azo-1,l'adamantane has also been examinedY2 and the products of photolysis of 2 - , 3 - , and 4 - p h e n y l a z o a m i n o p y r i d i n e s have been described. 3 More attention has been paid to photoelimination of nitrogen from cyclic azoalkanes. Diazirine is a special case and undergoes decomposition via an identifiable carbene, with evidence in some cases for the intermediacy of a linear diazoalkane. The infrared spectra of phenylbromocarbene and phenyltrifluoromethylcarbene, generated by photolysis of the corresponding diazirines in argon matrices at 12K, have been r e ~ o r d e d . ~Irradiation of 3 - b e n z y l - 3 - c h l o r o d i a z i r i n e ( 1 ) in methanol affords B-chlorostyrene (2) and phenylacetaldehyde dimethylacetal (31, the ratio o f products being dependent on diazirine concentration. Chlorostyrenes are also formed along with cyclopropanes on photolysis of 3 - c h l o r o - 3 - b e n z y l d i a z i r i n e in the presence o f alkenes ; evidence has been presented for the formation of a carbene-alkene complex. Results obtzined from a study o f the addition of photochemically generated phenylhalocarbenes to alkenes are also consistent with 413
Photochemistry
414
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a
/L\ PhCH,
(2 1
C1
N=N
Me
+
hV
,-b
+ HC 1
MeO-?-Ph
-N2
%OH Me Me
Me
Ph
Me -Me
OMe
16)
C0,Me
"
'
0
(7) R
=
2 N+ X PhCH,OCO
-Meo2c C0,Me
hV
- N2
(8)
415
llIl7: Photoelimination
N= N (10)
zN
(91
hV
L
- N2
N
(111
(121
OH
hv
- N2
I
OH (171
(18)
Me
Photochemistry
416
t h e formation of a carbene-alkene complex, and g - c h l o r o a c r y l o n i t r i l e h a s b e e n shown t o b e a n e x c e l l e n t s u b s t r a t e t o d e m o n s t r a t e 8 t h e ‘ l a t e n t n u c l e o p h i l i c i t y ’ of phenylhalocarbenes. Carbene r e a r r a n g e m e n t p r o d u c t s a n d i n s e r t i o n p r o d u c t s a r e formed on p h o t o e l i m i n a t i o n o f n i t r o g e n f r o m a p h e n y l m e t h y l -
diazirine-B-cyclodextrin complex. Methoxyphenylcarbene, g e n e r a t e d by p h o t o l y s i s o f t h e c o r r e s p o n d i n g d i a z i r i n e a t - 1 O ” C , a d d s r a p i d l y t o v a r i o u s a l k e n e s ; i n t h i s c a s e , n o e v i d e n c e was f o u n d f o r t h e Methoxyphenylcarbene p a r t i c i p a t i o n o f methoxyphenyldiazomethane. h a s b e e n shown t o p o s s e s s u n u s u a l n u c l e o p h i l i c s e l e c t i v i t y ; i r r a d i a t i o n of t h e d i a z i r i n e ( 4 ) i n 2,3-dirnethylbut-Z-ene c o n t a i n i n g t r a c e s o f t h e a l c o h o l ( S ) , f o r e x a m p l e , a f f o r d s t h e O-H i n s e r t i o n p r o d u c t ( 6 ) t o g e t h e r w i t h a low y i e l d o f t h e c o r r e s p o n d i n g c y c l o D i a z i r i n e s have been s y n t h e s i z e d f o r u s e i n photopropane.” affinity labelling. y 1 The p h o t o e l i m i n a t i o n o f n i t r o g e n from l - p y r a z o l i n e s provides a valuable r o u t e t o l Y 3 - b i r a d i c a l s and products d e r i v e d therefrom. The h i g h y i e l d c o n v e r s i o n o f t h e p y r a z o l i n e ( 7 ) i n t o t h e c y c l o p r o p a n e ( 8 ) h a s b e e n u s e d i n t h e s y n t h e s i s o f 2,3-methano-
’
analogues of g l u t a m i c a c i d and pyroglutamic a c i d , l 4 and t r i c y c l o [3.2.1.02”]oct-3-ene ( 9 ) i s t h e major photoproduct of t h e azoalkane (101.’ N i t r o g e n e x t r u s i o n from t h e b i s - a z o a l k a n e ( 1 1 ) t a k e s p l a c e i n a s t e p w i s e f a s h i o n a n d on p r o l o n g e d i r r a d i a t i o n y i e l d s t h e t h r e e isomeric b i c y c l o [ 2 . 1 .O]pentanes ( 1 2 1 , (13) and ( 1 4 ) ; l 6 no s p e c t r o s c o p i c e v i d e n c e f o r t h e i n t e r m e d i a c y o f a t e t r a r a d i c a l c o u l d be o b t a i n e d i n t h i s c a s e . The l i f e t i m e s 1 7 a n d e x p e r i m e n t a l h e a t s o f f o r m a t i o n 1 8 of v a r i o u s l y 3 - c y c 1 o p e n t a d i y l b i r a d i c a l s have been measured, and p h o t o d e c o m p o s i t i o n o f t h e spirocyclopropylpyrazoline ( 1 5 ) i n an o r g a n i c m a t r i x a t 4-35 K a f f o r d s t r i p l e t 2 - a l k y l i d e n e - 1 , 3 Oxygen t r a p p i n g o f t r i p l e t b i r a d i c a l s cyclopentanediyl (1 6 ) . g e n e r a t e d by benzophenone s e n s i t i z e d l a s e r p h o t o l y s i s o f a z o c y c l o a l k a n e s p r o v i d e s a n e f f e c t i v e method f o r e s t i m a t i n g l i f e t i m e s o f t h e s e t r a n s i e n t s p e c i e s , 2 o and i n t r a m o l e c u l a r t r a p p i n g of t h e 1 , 3 - d i y l formed on i r r a d i a t i o n o f t h e l - p y r a z o l i n e ( 1 7 ) l e a d s t o t h e t r i c y c l e ( 1 8 1 , a t r a n s f o r m a t i o n which i s a key s t e p i n t h e r e c e n t l y r e p o r t e d t o t a l s y n t h e s e s o f ( 5 ) - c o r i o l i n and ( ? I h y p n o p h i l i n . 2 1 I r r a d i a t i o n o f A 2- p y r a z o l i n e s i s a l s o r e p o r t e d t o r e s u l t i n p h o t o e l i m i n a t i o n o f n i t r o g e n a n d t h e f o r m a t i o n of c y c l o p r o p a n e d e r i v a t i v e s . 2 2 Not s u r p r i s i n g l y , t h e p h o t o d e c o m p o s i t i o n of azoalkanes takes a d i f f e r e n t course i n concentrated
11117: Photoelimination
417 Me hV
Me
J
(19 1
(20)
___)
Me Mey
Me (221
e (21 1
Scheme 1
418
Phorochemistry
- 4? hV
CH20Ac
-N2
0
(31)
(35)
IIIi7: Photoelimination
419
sulphuric acid;z3 as expected, the azoalkane (19) is converted on irradiation in benzene into the bicyclo [ Z . 1 .Olpentane (20) , but in concentrated sulphuric acid, excitation leads to the formation of a protonated 3-isopropylpyridazine (21). The likely intermediate ( 2 2 ) is shown in Scheme 1. Triplet ground state 2,2-dimethyl-4,5dimethylene-l,3-~yclopentanediyl (231, generated by irradiation of the azoalkadiene (24) in an argon matrix at 1 0 K , has been characterized spectroscopically;24 react ion products include the cyclobutane ( 2 5 ) and various dimeric species. The 1,4-biradicals 1 ,4-perinaphthadiy125 and 1 -phenylcyclohexa-l,4-diy126 have been obtained in a similar fashion from the appropriate 6-membered azoalkanes, and evidence for an intermediate diazenyl biradical has been found in the conversion of labelled 2,3-diazabicyclo[2.2.2]oct-2-enes into the corresponding bicyc10[2.2.0]hexanes.~~ An unusual ring opening of a photochemically generated cyclohexane-1,4-diyl radical has been observed in the azoalkane ( 2 6 ) and leads to the diene (27) in addition to the bicyclo[2.2.0]hexane ( 2 8 ) , 2 8 and irradiation of 2-(2'-butylallylidene)-6,7-diazabicyclo[3.2.2]nona-3,6-diene affords the triplet 8 ~ r non-Kekule polyene, 4-(2'-butylallylidene)cyclohept-Z-ene-1,S-diyl.
29
3H-Pyrazoles readily undergo photochemically induced elimination of nitrogen to yield the corresponding cyclopropenes, often by way o f detectable vinyl diazo intermediates. The first example of a cyclopropapyridine ( 2 9 ) has been obtained in this way along with the isopropenyl pyridine (30) by irradiation of the pyrazole (31),30 and cyclopropene esters have been prepared in a similar manner from the corresponding pyrazole esters .31 The cyclopropanimine (32) is produced quantitatively by irradiation of the dihydromethylene-l,2,3-triazole (33). 32 The photoelimination of nitrogen from triazoles, tetrazoles and other related heterocycles has also been examined and a number of useful synthetic applications have been reported. l-Aryltriazoles are converted regiospecifically on irradiation into functionalized indoles. This procedure has been employed in a total synthesis o f 7 - m e t h o ~ y m i t o s e n e . ~The ~ triazoline (34) is analogously converted into the azatricyclodecenone (35) on irradiation in methanol,3 4 and further examples of the preparation of imidazoles by photoelimination o f nitrogen from l-vinyltetrazoles have been rep~rted.~' The cyclohexenyltetrazole ( 3 6 ) , for example, affords the tetrahydro-3aH-benzimidazole (37), presumably via the imidoyl nitrene ( 3 8 ) .
Photo chemistry
420
Me
Me 4
Me Me
Me Me
hV
- N2
\ Me Me&
Me
Me@ Me
( 4 31
(42)
scheme 2
( 4 51
11117: Photoelimination
0
42 1
Li +
6 -1s
Li fN--TS
hV
___, -N2
r
1
N-N-TS
Cope NHNHTs
Scheme 3
Me I
Me3Si-Si-C-
I II Ma N2 (511
H
hV ___I)
- N2
Me I
0.
Me3Si-Si-C
-H
I
Me
(50)
Mc,Si=CH-SiMc,
(491
Photochemistry
422 Me
I
Me3Si-Si-C-
I II
C02Et
Si Me,
, CO,Et
/
Me2Si=C
Me N2 (521
(531
Me ,Si
Me Si
\
c=c=o
0
'OEt
MeCHO
+
(MeO2CI2C=N2 155 1
hV
4
- N2
Me H
( C02Me l2
(57)
1
McCHO
Illl7: Photoelimination
423
The isolation of a stable selenirane (39) has been achieved by addition of furan to the selenirene (401, generated photochemically from the 1,2,3-~elenadiazole(41) ,36 and the first 2H-phosphirene ( 4 2 ) has been prepared along with l-phosphacyclopent-1-ene (43) by photoelimination of nitrogen from the 3H-1 ,2,437 diazaphosphole (44) as shown in Scheme 2 . Spectroscopic and chemical evidence for the formation of azetes on irradiation of fluorinated 1,2,3-triazines has been published;38 the triazine (45), for example, affords the azete dimer (46) in quantitative yield. Photolysis of lithium 3-[(ptolylsulphonyl)amino]-l,2,3-benzotriazin-4(3~)-one (47) in methanol gave the ester (48) and not 2-methoxybenzoic acid tosylhydrazide as previously reported;39 a pathway involving an azetidinoneiminoketene intermediate has been proposed and is shown in Scheme 3. 2.
Elimination of Nitrogen from Diazo-compounds.
The photoelimination of nitrogen from diazo-compounds provides a simple and versatile route to carbenes. Rearrangement to the silene (49) is observed in the carbene ( S O ) , derived from the diazomethane (51).40 The silene (52), generated in a similar fashion from ethyl pentamethyldisilanyl diazoacetate (531, undergoes ethoxyl group migration with the formation of the ethoxyketene (54) .41 Silyl migration is observed along with other rearrangement pathways in the carbenes derived from diazo-2-silacyclohexa-3,5-dienes .42 Triplet 4,5-benzocycloheptatrienylidene has been identified as a product of irradiation of 4,5-ben~odiazocycloheptatriene i n a Z-methyltetrahydrofuran matrix at 4 K,43 and singlet dicarbomethoxycarbene, obtained by photoelimination of nitrogen from dimethyl diazomalonate (55), reacts with acetaldehyde to give the dioxolane ( 5 6 ) 9the ylide ( 5 7 ) .44 Photolysis of 4-diazo-l,1,1,2,2-pentafluoro3-(pentafluoroethyl)-3-(trifluoromethyl)butane, however, affords the corresponding azine.4 5 Aryl and diarylcarbenes are easily prepared by irradiation of the corresponding diazo-compounds. Topics studied include the effect of ring substituents on the fluorescence spectra of substituted diarylcarbenes,46 the search for heavy atom effects in the reaction of 2,7-dihalofluorenylidenes with methanol ,47 and the photochemical rearrangements of isomeric tolylmethylenes which have been shown to interconvert via methylcyclohepta-1,2,4,6-tetraene intermediates.48
Photochemistry
424
Me
**
hV
6
Me2C=C=CH2
(621
(61 1
(63)
(66)
SOaNa (681
(67)
S0,Na
S0,Na
(69 1
iiil7: Photoelimination
425
A r y l c a r b e n e s g e n e r a t e d i n t h i s f a s h i o n r e a c t w i t h a wide v a r i e t y of r e a g e n t s . Both s i n g l e t and t r i p l e t d i p h e n y l c a r b e n e 49 r e a c t w i t h diphenyldiazomethane t o g i v e t h e c o r r e s p o n d i n g a z i n e , b u t t h e p r o d u c t s d e r i v e d from l - n a p h t h y l c a r b e n e and e i t h e r c y c l o hexane o r t o l u e n e a r e c o n s i s t e n t w i t h s i n g l e t r e a c t i ~ i t y . ~ ' A t r i p l e t 1,1,3,3-tetra-arylpropane-l,3-diyl ( 5 8 ) h a s been d e t e c t e d on h i g h - i n t e n s i t y l a s e r - j e t i r r a d i a t i o n o f diphenyldiazomethane (59) i n t h e p r e s e n c e of a 1 , l - d i s u b s t i t u t e d s l k e n e (60) ," and a d d i t i o n of p h o t o c h e m i c a l l y g e n e r a t e d d i a r y l c a r b e n e s t o benzene A d d i t i o n o f t h e c a r b e n e d e r i v e d from h a s now been o b s e r v e d . 5 2 4 - p y r i d y l d i a z o m e t h a n e (61) t o 1 , l - d i m e t h y l a l l e n e ( 6 2 ) gave t h e 53 methylenecyclopropane ( 6 3 ) . The p h o t o r e a c t i o n s o f 9-diazo-1,8-diazafluorene ( 6 4 ) a r e dependent on t h e wavelength of l i g h t employed;54 IT+IT* e x c i t a t i o n ( A = 310nm) r e s u l t s i n r e a r r a n g e m e n t t o t h e i s o m e r i c d i a z i r i n e (65) f o l l o w e d by l o s s of n i t r o g e n and i s s i n g l e t d e r i v e d , whereas nwr* e x c i t a t i o n ( A = 420nm) a f f o r d s t r i p l e t a s w e l l a s s i n g l e t s p e c i e s . The photochemical b e h a v i o u r of 9-diazo-3,6-diazafluorene i s s i m i l a r t o t h a t of t h e 1 , 8 - d i a z a isomer b u t d i f f e r s s i g n i f i c a n t l y from t h a t o f t h e p a r e n t 9 - d i a z o f l u o r e n e . 5 5 The r e a c t i o n s o f p h o t o c h e m i c a l l y g e n e r a t e d s i n g l e t 3H-1,2,4-triazol-3-ylidenes w i t h s u b s t i t u t e d 56 benzenes have been d e s c r i b e d . The s t u d y o f t h e photodecomposition o f or-diazo k e t o n e s continues t o a t t r a c t attention. The s t r o n g and weak t r i p l e t s i g n a l s o b s e r v e d i n t h e e . s . r . s p e c t r u m on p h o t o l y s i s of c r y s t a l l i n e a z i stereob e n z i l a t 7 7 K have been a s s i g n e d t o t h e 2-2 and t h e Trapping experii s o m e r s of ground s t a t e benzoylphenylmethylene. 57 ments w i t h h e x a f l u o r o b u t - 2 - y n e p r o v i d e e v i d e n c e t h a t t h e k e t o c a r b e n e s o b t a i n e d on g a s p h a s e p h o t o l y s i s of h e x a f l u o r o - 3 diazobutan-2-one, octafluoro-2-diazopentan-3-one and o c t a f l u o r o - 3 d i a z o p e n t a n - 2 - o n e e q u i l i b r a t e via t r a n s i e n t o x i r e n e s . 58 Photoc h e m i c a l l y g e n e r a t e d k e t o c a r b e n e s r e a d i l y undergo r e a r r a n g e m e n t t o k e t e n e s ; t h e h y d r a t i o n o f such s p e c i e s h a s been examined u s i n g f l a s h p h o t o l y s i s . 59 Photo-Wolff r e a r r a n g e m e n t o f t h i s t y p e h a s a l s o been u s e d i n a number o f s y n t h e t i c s e q u e n c e s . The d i a z o k e t o n e (661, f o r example, i s c o n v e r t e d i n t o t h e e x p e c t e d e s t e r ( 6 7 ) on i r r a d i a t i o n i n methanol i n c o n t r a s t t o t h e u n u s u a l b e h a v i o u r e x h i b i t e d by t h e same compound on d e c o m p o s i t i o n w i t h rhodium ( 1 1 ) a c e t a t e . 6 0 Photo-Wolff r e a r r a n g e m e n t s have a l s o been o b s e r v e d i n c y c l i c B , y - u n s a t u r a t e d d i a z o m e t h y l k e t o n e s , 6 1 and 8 - d i a z o d i b e n z o i s r e p o r t e d t o undergo [ ~ , , ~ ] t r i c y c l o [ S ..0.02'10]deca-3,5-dien-9-one S
2-E
Photochemistry
426
0
0
N2
11 II
nu
R-C-C-SiMe2SiMe,
___)
R-C-
-N2
(70 1
11
SiMe,
II
C-
SiMe3
(73)
Me
\ /
Me,Si f i
0-Si-Me
I
Me
- oKR
o-si
R
Me
/\
Me (71) R
=
CMe, or 1-odamantyl
(72) R
5:
SiMe, Me
Me or CHMe,
J
11117: Photoelimination
R-CH,
427
,
NH
hV
N3
R-C@
____)
- N2
OMc
OMe (82)
(811
R
= Et.
\
CHMc, or PhCHMe
Mc3Si N3 \ / Si
./
Me3Si
\
N3
Mc,Si
- N = Si =N - Si Me, (83)
Scheme 4
Photochemistry
428
hV ____)
- N2
(85)
(86)
Scheme 5
hV
- N2
(89)
(90)
429
llIi7: Photoelimination
an analogous photochemical r i n g c o n t r a c t i o n .62 Spectroscopic e v i d e n c e f o r t h e i n t e r m e d i a c y o f a n o x i r e n e h a s b e e n o b t a i n e d by l a s e r f l a s h p h o t o l y s i s o f sodium l-oxo-2-diazonaphthoquinone-Ss u l p h o n a t e ( 6 8 ) i n w a t e r a t 298 K ; two t r a n s i e n t s p e c t r a h a v e b e e n 63 o b s e r v e d , t h e f i r s t b e i n g a s s i g n e d t o t h e o x i r e n e (69). Carbene r e a r r a n g e m e n t o f a d i f f e r e n t t y p e i s p r e f e r r e d i n t h e (pentamethyldisilanyl-diazomethyl) k e t o n e s ( 7 0 ) w h i c h a r e c o n v e r t e d on i r r a d i a t i o n i n t o l-oxa-2-silacyclobut-3-enes ( 7 1 ) a n d 1,5-dioxa-2,6-disilacyclo-octa-3,7-dienes ( 7 2 ) via t h e u n s t a b l e 3-oxa-1-silaprop-1-enes (73) .64 3 - D i a z o a c e t y l r e t i n a l s have been 65
synthesized f o r use i n photoaffinity labelling. C a r b e n e s d e r i v e d by p h o t o e l i m i n a t i o n o f n i t r o g e n f r o m 1 , 4 - b e n z o q u i n o n e d i a z i d e s u n d e r g o r e a c t i o n w i t h oxygen t o f o r m 67 1,4-benzoquinone C-oxides6' and add t o benzene. P h o t o d e c o m p o s i t i o n o f sodium a n d l i t h i u m s a l t s o f p-
toluenesulphonylhydrazones g i v e s r i s e , i n g e n e r a l , t o t h e f o r m a t i o n o f c a r b e n e s by way o f d e t e c t a b l e d i a z o i n t e r m e d i a t e s . The b i c y c l o [2.1.0]pentane (74) and t h e cyclopropane (75) a r e formed i n t h i s way i n 4 0 a n d 35% y i e l d s r e s p e c t i v e l y f r o m t h e t o s y l h y d r a z o n e ( 7 6 ) The c y c l o h e p t a t r i e n e s ( 7 8 ) a n d ( 7 9 ) h a v e v i a t h e carbene (77).68 a l s o b e e n o b t a i n e d by i r r a d i a t i o n o f t h e t o s y l h y d r a z o n e s a l t ( 8 0 ) , and photochemically generated benzocycloheptat r i e n y l idenes a r e c o n v e r t e d by p r o t o n a t i o n a n d r e a c t i o n w i t h a l c o h o l s i n t o 7 - a l k o x y 7H- a n d 5-alkoxy-5~-benzocycloheptatrienes.7 0 The r e a c t i o n s o f 3- a n d 5 - m e t h y l b i c y c l o [ 2 . 1 . l ] h e x - 2 - y l c a t i o n s 7 ' a n d of 2-oxa-5and 2-oxa-6-norbornane diazonium i o n s , 7 2 g e n e r a t e d i n a s i m i l a r f a s h i o n from p - t o s y l h y d r a z o n e d e r i v a t i v e s , h a v e b e e n d e s c r i b e d . 3.
E l i m i n a t i o n o f Nitrogen from Azides.
The p h o t o r e a c t i o n s o f a z i d e s c a n i n most c a s e s b e r a t i o n a l i z e d i n t e r m s o f t h e i n i t i a l f o r m a t i o n o f n i t r e n e s which t h e n u n d e r g o rearrangement, i n s e r t i o n o r a d d i t i o n r e a c t i o n s . Nitrene rearrangement i s t h o u g h t t o b e r e s p o n s i b l e f o r t h e c o n v e r s i o n o f t h e a - a z i d o e t h e r s (81) i n t o t h e imino e t h e r s ( 8 2 ) , 7 3 and t h e f i r s t s i l a n e d i i m i n e (83) t o b e d e s c r i b e d h a s been p r e p a r e d i n a s i m i l a r Intraf a s h i o n f r o m t h e d i a z i d e ( 8 4 ) a s shown i n Scheme 4 . 7 4 molecular n i t r e n e a d d i t i o n t o s u i t a b l y aligned nitrogen-nitrogen d o u b l e b o n d s h a s b e e n employed i n t h e s y n t h e s i s o f t r i a z i r i d i n e s . 7 5 s 76 An u n u s u a l l y s t a b l e t r i a l k y l t r i a z i r i d i n e ( 8 5 ) h a s b e e n p r e p a r e d by i r r a d i a t i o n of t h e a z i d e (86) i n a c e t o n i t r i l e . Vinyl a z i d e s a r e c o n v e r t e d by p h o t o e l i m i n a t i o n o f n i t r o g e n i n t o 2H-
430
Photochemistry
(92)
(91)
1
morphol inc
Scheme 6
hV
- N2
(96 1
(95)
(98 I
(971 R’ = H or ~ a R*= , H, MC or c%Et R3= H, Me or OMe
mN3
43 1
11117: Photoelimination
h V , NaOMe
R
\
"2
R
(100 1
(991 R = H, Me or Ph
$gR1
- R$xR1
R2
hV
I
N3
MeOCH20Cb
- N2
lCiY
MeOCH20
0
0
X'Me
O X 0
I&
M e M e (1011 R ' = $=H or Me
(102)
R ' z H, R2= Me R'
=
Me, R2= H
Et
Et
I
hv
@N
____)
- N2
N3
'
N"2
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o b t a i n e d i n t h i s way f r o m e t h y l a-azido-6-(2-methylthionaphth-1-y1)a c r y l a t e on i r r a d i a t i o n a t 0°C.77 S t e p w i s e l o s s o f n i t r o g e n h a s been o b s e r v e d i n 2,3-diazidopenta-lY3-diene ( 8 7 ) l e a d i n g t o t h e e v e n t u a l f o r m a t i o n o f t h e 3 , 3 ' - b i - 2 H - a z i r i n e ( 8 8 ) a s shown i n Scheme 5 . 7 8 V i c i n y l v i n y l d i a z i d e s h a v e b e e n u s e d a s n o v e l p r e c u r s o r s f o r l Y 4 - d i c y a n o compounds;the d i a z i d e ( 8 9 ) , f o r example, i s c o n v e r t e d on i r r a d i a t i o n i n t o t h e d i n i t r i l e ( 9 0 ) . 79 Recent experiments have e s t a b l i s h e d w i t h a f a i r degree of c e r t a i n t y t h a t 1,2-dehydroazepines a r e intermediates i n t h e p h o t o d e c o m p o s i t i o n o f a r y l a z i d e s . The d e h y d r o a z e p i n e ( 9 1 ) , f o r e x a m p l e , h a s b e e n d e t e c t e d a t room t e m p e r a t u r e by t i m e - r e s o l v e d i n f r a r e d s p e c t r o s c o p y on f l a s h p h o t o l y s i s o f 4 - ( d i m e t h y l a m i d o ) p h e n y l a z i d e ( 9 2 ) . 8 0 The w e l l documented a l t e r n a t i v e e x p l a n a t i o n i n v o l v i n g an a z i r i n e a s an i n t e r m e d i a t e h a s been advanced t o account f o r t h e c o n v e r s i o n o f 5-azido-2H-benzimidazole ( 9 3 ) i n t o t h e 4 , s d i - s u b s t i t u t e d 2 H - b e n z i m i d a z o l e ( 9 4 ) on i r r a d i a t i o n i n t h e p r e s e n c e o f m o r p h o l i n e (Scheme 6 ) . 8 1 P h o t o l y s i s o f p - a z i d o a n i l i n e i n t o l u e n e o r h e x a n e s o l u t i o n a t room t e m p e r a t u r e g a v e t h e c o r r e s p o n d i n g a z o b e n z e n e d e r i v a t i v e , 8 2 a n d b e n z [c,dIi n d a z o l e ( 9 5 ) h a s b e e n p r e p a r e d i n a s i m i l a r manner by a t w o - p h o t o n K r F p u l s e d - e x i m e r l a s e r photodecomposition of 1,8-diazidonaphthalene (96). 83 Competing s i n g l e t - a n d t r i p l e t - d e r i v e d c y c l i z a t i o n s h a v e b e e n observed i n t h e photodecomposition o f Z-(aryloxy)-l-azido-4h y d r o x y a n t h r a q u i n o n e s . 84 A s t u d y o f 3- a n d 4 - n i t r o p h e n y l a z i d e s h a s shown t h a t t h e
r e a c t i v i t y of photochemically generated i n t e r m e d i a t e s i s profoundly i n f l u e n c e d by t h e n i t r o g r o u p . 8 5 The c h o i c e o f n i t r o s u b s t i t u t e d a r y l a z i d e s f o r u s e a s p h o t o a f f i n i t y l a b e l s may n o t , t h e r e f o r e , b e w i s e . O t h e r a r y l a z i d e s h a v e b e e n employed f o r t h i s p u r p ~ s e . ~ ~ - ~ ' The p h o t o r e a c t i o n s o f h e t e r o a r y l a z i d e s h a v e a l s o b e e n examined i n d e t a i l . L o s s o f n i t r o g e n f o l l o w e d by r i n g e x p a n s i o n t o g i v e t h e 4 - m e t h o x y - 5 ~ - 1 , 3 - d i a z e p i n e s ( 9 7 ) o c c u r s on i r r a d i a t i o n of t h e 3 - a z i d o p y r i d i n e s ( 9 8 ) i n t h e p r e s e n c e o f sodium m e t h ~ x i d e . ' ~ 4 - A z i d o p y r i d i n e s a r e s i m i l a r l y c o n v e r t e d i n t o 5-methoxy-6H-1,4d i a z e p i n e s Y g 4 a n d 1H-1 , 4 - b e n z o d i a z e p i n e s c a n b e o b t a i n e d i n t h e same way f r o m 4 - a z i d o q ~ i n o l i n e s . ~I r~r ~a d~i ~a t i o n o f t h e 3 - a z i d o q u i n o l i n e s (99) i n t h e p r e s e n c e of sodium methoxide a l s o r e s u l t e d i n r i n g e x p a n s i o n a n d t h e f o r m a t i o n o f t h e 3-methoxy-3!-1,4b e n z o d i a z e p i n e s ( 1 0 0 ) . 9 7 Analogous c o n v e r s i o n s h a v e b e e n d e s c r i b e d i n 5 - , 6 - , 7- a n d 8 - a z i d o d e r i v a t i v e s o f f u r o [ 2 , 3 - b ] - , t h i e n o [ 2 , 3 98 b ] - a n d pyrazolo[3,4-~]-quinolines.
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E f f i c i e n t i n t r a m o l e c u l a r n i t r e n e i n s e r t i o n r e a c t i o n s have b e e n r e p o r t e d i n 3-benzyl-4-azido-coumarin a n d q u i n o l - 2 - o n e d e r i v a t i v e s ” a n d i n t h e 6 - a z i d o u r i d i n e s (101 1 which a r e c o n v e r t e d i n t o p h o t o p r o d u c t s ( 1 0 2 ) . l o o Quantum y i e l d s f o r t h e p h o t o decomposition o f 2-azidobenzothiazoles have been determined, l o ’ and p h o t o e l i m i n a t i o n of n i t r o g e n from a z i d o - l Y 3 , 5 - t r i a z i n e s i n t h e p r e s e n c e o f a i r g a v e t h e c o r r e s p o n d i n g n i t r o t r i a z i n e s . lo’ V a r i o u s p r o d u c t s i n c l u d i n g t h e amine ( 1 0 3 ) were o b t a i n e d on i r r a d i a t i o n o f t h e a z i d i n i u m s a l t ( 1 0 4 ) . 103 N i t r e n e a d d i t i o n t o t h e c a r b o n - c a r b o n d o u b l e bond f o l l o w e d by a z i r i d i n e r i n g o p e n i n g a s shown i n Scheme 7 i s b e l i e v e d t o b e r e s p o n s i b l e f o r t h e p h o t o r e a c t i o n o f e t h y l azidoformate (105) w i t h ketene s i l y l a c e t a l (106) t o g i v e t h e d i e s t e r ( 1 0 7 ) i n 7 5 % y i e l d . O4 D i r e c t and t r i p l e t s e n s i t i z e d i r r a d i a t i o n of 6-naphthoyl a z i d e gave n i t r e n e - d e r i v e d p r o d u c t s c h a r a c t e r i s t i c of r e a c t i o n o n l y from t h e s i n g l e t s t a t e . 105 4.
P h o t o e l i m i n a t i o n o f Carbon D i o x i d e
Evidence h a s been o b t a i n e d t h a t t h e photodecarboxylation of b e n z a n n e l a t e d a c e t i c a c i d s i n a q u e o u s s o l u t i o n p r o c e e d s via c a r b a n i o n i n t e r m e d i a t e s ; O6 5E-diben zo ,g]c y c l o h e p t e n - 5 - c a r b o x y l i c a c i d , f o r e x a m p l e , u n d e r g o e s p h o t o d e c a r b o x y l a t i o n w i t h a quantum e f f i c i e n c y o f c l o s e t o u n i t y . The r e a c t i o n s of t h e p - n i t r o b e n z y l a n i o n , g e n e r a t e d by p h o t o c h e m i c a l l y i n d u c e d l o s s o f c a r b o n d i o x i d e f r o m p - n i t r o p h e n y l a c e t a t e a n i o n , h a v e b e e n examined a n d a mechanism proposed t o account f o r t h e formation of t h e corresponding
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bibenzyl d e r i v a t i v e . Reductive d e c a r b o x y l a tion of c a r b o x y l i c a c i d s i n c l u d i n g a-, 6- a n d y-amino a c i d s c a n b e a c h i e v e d by i r r a d i a t i o n o f t h e i r benzophenone oxime e s t e r s i n 2 - p r o p a n o l i n t h e p r e s e n c e o f t - b u t y l m e r c a p t a n p r e s u m a b l y b y way o f i n i t i a l n i t r o g e n oxygen bond h o m o l y s i s ; l o 8 t h e amide ( 1 0 8 ) , f o r e x a m p l e , i s f o r m e d i n t h i s way f r o m e s t e r ( 1 0 9 ) i n 8 0 % y i e l d t o g e t h e r w i t h benzophenone a n d benzophenone a z i n e . D e c a r b o x y l a t i o n o f a c i d s by p h o t o l y s i s o f t h e i r N-hydroxyp y r i d i n e - 2 - t h i o n e e s t e r s h a s b e e n t h e s u b j e c t o f much s t u d y . The r e a c t i o n p r o c e e d s S y way o f a r a d i c a l c h a i n pathway a n d i n v o l v e s l o s s o f c a r b o n d i o x i d e . l o g Carbon r a d i c a l s g e n e r a t e d i n t h i s way h a v e b e e n d e t e c t e d by e . p . r . s p e c t r a ’ ” a n d a r e w i d e l y u s e d i n synthesis. R a d i c a l a d d i t i o n t o a l k e n e s ’ 1 1 - ’ l 3 a n d t o q u i n o n e s 114 h a s , f o r e x a m p l e , b e e n d e s c r i b e d a n d a modest d e g r e e o f a s y m m e t r i c
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I r r a d i a t i o n o f t h e r e l a t e d N-hydroxypyridine2 - t h i o n e c a r b a m a t e ( 1 1 0 ) i n t h e p r e s e n c e o f a h y d r o g e n d o n o r gave i n a d d i t i o n t o o t h e r p r o d u c t s t h e p a r e n t amine ( 1 1 1 ) a n d t h e p y r r o l i d i n e ( 1 1 2 ) . ’ 1 8 H i g h e r y i e l d s o f c y c l i z e d p r o d u c t s were o b t a i n e d i n t h e p r e s e n c e of a c e t i c o r t r i f l u o r a c e t i c a c i d . A c a r e f u l r e i n v e s t i g a t i o n h a s shown t h a t t h e m a j o r pathway f o l l o w e d on p h o t o l y s i s o f h y d r o b e n z o i n c a r b o n a t e i s l o s s o f c a r b o n d i o x i d e a n d t h e f o r m a t i o n o f a 1 , 3 - b i r a d i ~ a l ;t h~ u~s ~ , t h e +-carbonate (113) gave t h e o x i r a n e s ( 1 1 4 ) and (115) t o g e t h e r with diphenylmethane and deoxybenzoin. Photoelimination of carbon d i o x i d e h a s a l s o been r e p o r t e d i n t h e c y c l i c c a r b o n a t e 4-phenyl1 , 3 - d i o x o l a n - Z - o n e . 1 2 0 The r e l a t i v e y i e l d s o f b e n z o n i t r i l e s u l p h i d e ( 1 1 6 ) a n d phenyl(nitrosothio)ketene ( 1 1 7 ) , o b t a i n e d by i r r a d i a t i o n o f 4-phenyl-l,3,2-oxathiazolylium-S-olate ( 1 1 8 ) a t c r y o g e n i c t e m p e r a t u r e s , a r e d e p e n d e n t on t h e v i s c o s i t y o f t h e medium. 2 1 The p r o p o s e d p a t h w a y s t o t h e s e p h o t o p r o d u c t s a r e o u t l i n e d i n Scheme 8 . Examples o f e l i m i n a t i o n o f c a r b o n d i o x i d e on p h o t o l y s i s 122-125 of d i a c y l p e r o x i d e s have been r e p o r t e d .
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P h o t o f r a g m e n t a t i o n of t h e c y c l i c t e t r a s u l p h i d e ( 1 1 9 ) i n b e n z e n e i n t h e p r e s e n c e of n o r b o r n e n e a f f o r d s t h e 1 , 4 - d i t h i i n ( 1 2 0 ) , p r e s u m a b l y by way o f t h e i n i t i a l l y f o r m e d 1 , 2 - d i t h i o n e ( 1 2 1 ) . 1 2 6 1 , 2 - S e l e n o x o t h i o n e d e r i v a t i v e s c a n b e g e n e r a t e d i n a s i m i l a r manner f r o m lY2,3,4-tetrathia-5-selenepines. C a r b o n - s u l p h u r bond h o m o l y s i s i s commonly o b s e r v e d i n t h e p h o t o c h e m i s t r y o f s u l p h u r - c o n t a i n i n g compounds. 5 - A l k y l a n d 2 - a c y l x a n t h a t e s , f o r e x a m p l e , a r e v a l u a b l e s o u r c e s o f a l k y l and a c y l r a d i c a l s . 2 7 I n t r a m o l e c u l a r t r a p p i n g of s u c h r a d i c a l s h a s b e e n o b s e r v e d a n d i s e x e m p l i f i e d by t h e c o n v e r s i o n a c h i e v e d i n 70% y i e l d of t h e 5 - a c y l x a n t h a t e ( 1 2 2 ) i n t o t h e chromanone ( 1 23) C a r b o n - s u l p h u r bond h o m o l y s i s i s t h e i n i t i a l s t e p i n t h e c o n v e r s i o n o f t h e Z ’ - p h e n y l t h i o m e t h y l d e r i v a t i v e (124) i n t o t h e 8 , 2 ’ - m e t h a n o a d e n o s i n e ( 1 2 5 ) b y p h o t o l y s i s f o l l o w e d by
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r e s p o n s i b l e f o r t h e p h o t o r e a c t i o n s of bis(pheny1thio)methylc o n t a i n i n g compounds. Diphenyl s u l p h i d e i s t h e major p r o d u c t of Initial t r i p l e t s t a t e t r i p h e n y l s u l p h o n i u m s a l t p h o t o c h e m i s t r y . 13' s u l p h u r - h y d r o g e n bond h o m o l y s i s a p p e a r s t o b e i m p l i c a t e d i n t h e p h o t o c y c l i z a t i o n o f t h e t h i o c a r b o x y l i c a c i d 7 - t h i o g i b b e r e l l i n A3 i n t o t h e c o r r e s p o n d i n g 7 , l S a - t h i o l a c t o n e , 33 a n d t h e a l k o x y c a r b o n y l n i t r e n e s ( 1 2 6 ) h a v e b e e n p r e p a r e d by i r r a d i a t i o n o f t h e t e t r a c h l o r o t h i e n y l 5 , l j - y l i d e s (127). 134 Type I 1 p h o t o r e a c t i o n s o f p h e n a c y l s u l p h i d e s , s u l p h o x i d e s a n d s u l p h o n e s h a v e b e e n examined i n d e t a i l . 3 5 y 1 36 T h i o a l d e h y d e s h a v e b e e n g e n e r a t e d by p h o t o l y s i s ' o f p h e n a c y l s u l p h i d e s a n d r e a c t r e a d i l y w i t h a l k e n e s a n d d i e n e s . 3 7 The n i t r o g e n - c o n t a i n i n g phenacyl s u l p h i d e s (128) undergo analogous photoinduced c l e a v a g e t o t h i o a l d e h y d e s ( 1 2 9 ) which c a n b e t r a p p e d a s t h e c y c l o a d d u c t s ( 1 3 0 ) by r e a c t i o n w i t h t h e e l e c t r o n - r i c h d i e n e ( 1 3 1 ) . 138 A u s e f u l s y n t h e s i s o f t h e h o m o p e n i c i l l i n (132) h a s b e e n a c h i e v e d by p h o t o f r a g m e n t a t i o n o f t h e B-ketosulphoxonium y l i d e ( 1 3 3 ) i n a c e t o n i t r i l e ; ' 39 a mechanism i n v o l v i n g i n i t i a l c l e a v a g e t o t h e c a r b e n e ( 1 3 4 ) f o l l o w e d by r e a r r a n g e m e n t t o t h e k e t e n e ( 1 3 5 ) h a s b e e n p r o p o s e d on t h e b a s i s o f t h e known p h o t o r e a c t i o n s o f s u l p h o x o n i u m y l i d e s . Loss o f s u l p h u r monoxide t o E i v e a z i n e s h a s b e e n o b s e r v e d on i r r a d i a t i o n o f 2,5-dihydro-1,3,5-thiadiazole 1 - o x i d e s , 140 a n d a new p r o c e d u r e f o r t h e r e d u c t i v e p h o t o d e s u l p h o n I r r a d i a t i o n of y l a t i o n o f O-keto s u l p h i d e s h a s b e e n d e v e l o p e d . 1 4 ' t h e s t e r o i d a l d i e n o l t r i f l a t e (136) i n p y r i d i n e r e s u l t s i n l o s s o f sulphur dioxide and t h e formation of t h e 6B-trifluoromethyl d e r i v a t i v e (137) , 1 4 2 whereas e x t r u s i o n of s u l p h u r d i o x i d e from t h e 2,6-dithia-adamantane bis-sulphone (138) i s accompanied by r e a r r a n g e m e n t a n d y i e l d s t h e t r i c y c l i c s u l p h o n e ( 1 3 9 ) e v e n on p r o l o n g e d i r r a d i a t i o n . 1 4 3 S u l p h u r d i o x i d e i s a l s o formed t o g e t h e r w i t h a v a r i e t y o f o t h e r p r o d u c t s on p h o t o d e c o m p o s i t i o n o f arenesulphohydroxamic a c i d s . 144 6.
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h o m o l y s e s h a v e b e e n employed t o g e n e r a t e t h e 1 , l ’ - t r i m e t h y l e n e b i s ( p y r i d i n y l ) b i r a d i c a l ,14‘ t h e 1 ,1 - e t h y l e n e b i s [ 4 - ( n e t h o x y c a r b o n y l ) p y r i d i n y l ] b ‘ .a d i c a l a n d t h e 1 -me t h y 1- 3 -met h o x y c a r b o n y l p y r i d i n y 1 r a d i c a l . 148 Carbonyl y l i d e s can be d e r i v e d photochemically from c e r t a i n o x i r a n e s . The y l i d e s ( 1 4 0 ) , o b t a i n e d f r o m t h e o x i r a n e s ( 1 4 1 1 , u n d e r g o s t e r e o s p e c i f i c b u t u n c h a r a c t e r i s t i c a l l y nonr e g i o s e l e c t i v e a d d i t i o n t o unsymmetrical e l e c t r o n - d e f i c i e n t dipolarophiles, w h e r e a s d i r e c t i r r a d i a t i o n o f t h e a ,B - u n s a t u r a t e d y,B-epoxy n i t r i l e ( 1 4 2 ) a f f o r d s p r o d u c t s ( 1 4 3 ) t o ( 1 4 6 ) d e r i v e d f r o m t h e y l i d e ( 1 4 7 ) a n d t h e c a r b e n e ( 1 4 8 ) . 150 H e t e r o l y t i c c a r b o n - n i t r o g e n bond c l e a v a g e i s r e s p o n s i b l e f o r t h e e x c i t e d s t a t e c o n v e r s i o n o f N,N-dimethyl-2,2-diphenylethylamine i n t o d i p h e n y l m e t h a n e i n m e t h a n 0 1 T ’ ~ ’ a n d b o t h h o m o l y t i c a n d h e t e r o l y t i c c l e a v a g e pathways a r e found i n (1-naphthylmethy1)trimethylammonium c h l o r i d e . l S 2 Amine d e m e t h y l a t i o n h a s b e e n o b s e r v e d i n s u b s t i t u t e d a m i n o b e n z o q u i n o n e s , ’ 53 a n d t h e u s e o f t e r t i a r y n i t r o s o a l k a n e s d i s s o l v e d i n s o l i d polymer m a t r i c e s a s m a t e r i a l s f o r holographic recording with semiconductor l a s e r s i s b a s e d on a p h o t o c h e m i c a l l y i n d u c e d c a r b o n - n i t r o g e n bond h o m o l y s i s . l S 4 The c o n v e r s i o n o f hydroxamic a c i d s i n t o t h e c o r r e s p o n d i n g amides i s b e l i e v e d t o i n v o l v e i n i t i a l formation of amidyl r a d i c a l s by n i t r o g e n - o x y g e n bond h o m o l y s i s . 5 5 P h o t o d e c o m p o s i t i o n o f h y d r o p e r o x i d e s , 56 p e r o x i d e s ’ 5 7 a n d o z o n i d e s ’ 58 h a s a l s o b e e n examined. + T 2 ] c y c l o r e v e r s i o n of t h e Photochemically induced bicyclo[Z.Z.O]hexadiene (149) h a s been u s e d t o g e n e r a t e t e t r a m e t h y l c y c l o b u t a d i e n e ( 1 5 0 ) which c a n b e t r a p p e d a s t h e a d d u c t o f 1 , 3 d i p h e n y l i s o b e n z o f u r a n o r a s t h e s y n - d i m e r . 159 f T 2 + 21 C y c l o r e v e r s i o n h a s a l s o been observed i n t h e c y c l o b u t e n e (1511, o b t a i n e d by a n o v e l p h o t o c h e m i c a l r i n g c o n t r a c t i o n o f 4H-pyran ( 1 5 2 ) , and a f f o r d s t h e a l k e n e ( 1 5 3 ) a n d t h e a l k y n e ( 1 5 4 ) . T60 P h o t o c l e a v a g e of t h e c y c l o b u t a n e r i n g i n a NyN’-dibuty1bis(2-hydroxyphenyl)cyclobutanedicarboxamide i s s o l v e n t a n d w a v e l e n g t h d e p e n d e n t . 161 Examples o f c y c l o b u t a n e r i n g c l e a v a g e i n t h e p r e s e n c e o f a n e l e c t r o n a c c e p t o r h a v e a l s o b e e n documented. 162-164 The p h o t o s e n s i t i z e d m o n o m e r i z a t i o n o f t h y m i n e d i m e r s h a s been a c h i e v e d i n t h e p r e s e n c e of reduced f l a v i n , 1 6 ’ and pyrimidine d i m e r s u n d e r g o c l e a v a g e by l i g h t - u t i l i z i n g enzymes which a r e t h o u g h t 166 t o a c t by a p h o t o i n d u c e d e l e c t r o n t r a n s f e r mechanism. A number o f r e p o r t s of p h o t o c y c l i z a t i o n a c c o m p a n i e d by e l i m i n a t i o n of HG1 and HBr have appeared i n t h e l i t e r a t u r e although
’
443
I11/7:Photoelimination
R'
-
R2*NH
0
hV
- HBr
R4
JYo 0
RS (158)
R3
R'
R2
R3
R4
OH OH
OMe
H
O M OMc
OMe
OH H
OM
H H
OCH,O H H
OMe
OH
OMe OMe
R5
(157)
I H 2 0 , hV MrCN M c. . -* lc
Cl
cl@
Cl
OH Cl
CL
(160)
(162 1
(159)
(161 1
(164) R
=
H o r PhCH=CH
444
Photochemistry
d e t a i l s o f t h e mechanism a r e n o t a l w a y s c l e a r . I r r a d i a t i o n of t h e dichloroacetaltryptophan methyl e s t e r (155) gave, a f t e r r e a c t i o n w i t h n u c l e o p h i l e s , t h e p y r r o l o b e n z a z o c i n e s ( 1 5 6 ) . 1 6 7 An a n a l o g o u s c y c l i z a t i o n h a s b e e n employed i n t h e s y n t h e s i s o f ( - ) - i n d o l a c t a m The m e t a - b r i d g e d l a c t a m s ( 1 5 7 1 , o b t a i n e d by i r r a d i a t i o n of t h e amides (1581, a r e u s e f u l i n t e r m e d i a t e s i n t h e p r e p a r a t i o n of homoaporphines. P h o t o c y c l i z a t i o n s w i t h l o s s of HC1 have a l s o b e e n r e p o r t e d i n 1-( 3 - c h l o r o - 2 - b e n z o [b] t h i e n o c a r b o n y l ) -Elmonosubst i t u t e d t h i o u r e a s ' 7 0 a n d i n O - a l k y l N- ( 3 - c h l o r o - 2 - b e n z o [b] thienylcarbony1)monothiocarbamates. 1 7 1 I n t e r m o l e c u l a r e l i m i n a t i o n o f HX a l s o o c c u r s on i r r a d i a t i o n . Notable examples i n c l u d e t h e c o n v e r s i o n of 6 - i o d o u r i d i n e s i n t o 6-aryl and 6 - h e t e r o a r y l - u r i d i n e s , 72 t h e s y n t h e s i s of b i t h i e n y l s 1 7 39 1 7 4 a n d t h i e n y l n a p h t h o q u i n o n e s l 7 5 f r o m h a l o g e n a t e d t h i o p h e n e s , a n d t h e f o r m a t i o n o f 4-phenylindole-3-aldehyde f r o m 4 - i o d o i n d o l e 2-Methyl-4,5,6,73 - a l d e h y d e by i r r a d i a t i o n i n b e n z e n e . 17' t e t r a c h l o r o b e n z o x a z o l e ( 1 5 9 ) i s u n e x p e c t e d l y f o r m e d on i r r a d i a t i o n 177 of p e n t a c h l o r o p h e n o l ( 1 6 0 ) i n a q u e o u s a c e t o n i t r i l e . Many o t h e r p h o t o c h e m i c a l l y i n d u c e d d e c o m p o s i t i o n s a r i s e by c a r b o n - h a l o g e n bond c l e a v a g e . The m a j o r i t y o f t h e s e r e a c t i o n s a r e r a d i c a l p r o c e s s e s w i t h l i t t l e photochemical s i g n i f i c a n c e and a r e not t h e r e f o r e included i n t h i s Report. I n some i n s t a n c e s , i o n i c s p e c i e s a r e i n t e r m e d i a t e s i n t h e s e t r a n s f o r m a t i o n s ; examples i n c l u d e 4 - p h e n y l - l - i o d o b u t a n e a n d 4-phenyl-1 - b r o n o b u t a n e l 78 a n d c e r t a i n a - i o d o c y c l o a l k a n o n e s . 17' The d i k e t o c a r b e n e ( 1 6 1 ) i s b e l i e v e d t o
v. 1 6 8
b e formed i n i t i a l l y on i r r a d i a t i o n o f t h e iodonium y l i d e 1162) i n t h e presence of alkenes (163); t h e f i n a l products are h e x a h y d r o b e n z o f u r a n s ( 1 6 4 ) . 180 Numerous p h o t o i n i t i a t e d S R N l r e a c t i o n s h a v e b e e n d e s c r i b e d 181-197 i n t h e l i t e r a t u r e d u r i n g t h e p e r i o d c o v e r e d by t h i s R e p o r t . P h o t o c h e m i c a l l y i n d u c e d n i t r o g e n - h a l o g e n bond h o m o l y s i s 198 i s t h e i n i t i a l s t e p i n t h e a d d i t i o n of N - h a l o a m i d e s t o a l k e n e s 199 a n d i n t h e c y c l i z a t i o n o f b e n z y l N-bromo-N-methylcarbamates. The 3,3-di-t-butyloxaziridinyl r a d i c a 1 2 0 0 - a n d t h e e t h o x y a n d t r i m e t h y l s i l y l o x y iminyl r a d i c a l s 2 0 1 have been p r e p a r e d i n a s i m i l a r manner by p h o t o l y s i s o f t h e c o r r e s p o n d i n g N - c h l o r o compounds. The p h o t o c h e m i c a l g e n e r a t i o n o f a l k o x y l r a d i c a l s f r o m hypoiodites h a s a t t r a c t e d widespread a t t e n t i o n i n r e c e n t y e a r s and i s of p a r t i c u l a r value i n s y n t h e t i c s t u d i e s . Reactions involving 6 - s c i s s i o n of t h e a l k o x y l r a d i c a l have t h e g r e a t e s t p o t e n t i a l i n
445
11117: Photoelinzination
Me
Mt
(166)
(1651
CN
CN
Scheme 9
Photochemistry
44 6
synthesis. The conversion of the cyclopentanol ( 1 6 5 ) into the iodo ketone ( 1 6 6 ) by photolysis of the hypoiodite has, for example, been used in the synthesis of exaltone,202 and the [.,r2 + T 2 1 photocycloaddition-@-scission sequence shown in Scheme 9 affords good yields of the benzocyclo-octanone ( 1 6 7 ) . 203 13-Scission Qf photochemically generated alkoxyl radicals has also been employed in the synthesis of medium-ring lactones, 204 benzohomotropones 20 5 and phthalidesZo6 and in the synthesis and modification of steroid molecules. ’07-‘ Examples of intramolecular hydrogen abstraction by alkoxyl radicals 21 - ” and intramolecular addit ion of alkoxyl radicals to alkenes214 have been reported.
’
llIi7: Photoelimination
447
References. 1 P. S. Engel, W. K. Lee, G. E. Marschke, and H . J. Shine, J. Org. Chem., 1987, 52, 2813. 2 W. K. Chae, B u l l . Korean Chem. S O C . , 1987, 5, 5 2 (Chem. Abstr., 1987, 175547). 3 E. E. P a s t e r n a k , P. Tomasik, and W. Zawadzki, Pol. J. Chem., 1986, 9, 767. 4 A. K. Mal'tsev, P. S. Zuev, and 0. M. Nefedov, Izv. h a d . Nauk SSSR, Ser. K h i m . , 1987, 463 (Chem. Abstr., 1987, 235908). 5 ET. H. Liu and R. Subramanian, J. Chem. S O C . , P e r k i n Trans. 2, 1988, 15. 6 M. T o H. Liu, M. S o u n d a r i r a j a n , N. P a i k e , and R . Subramanian, J. Org. Chem., 1987, 52, 4223. 7 N . J. Turro, M. Okamoto, I. R . Gould, R . A. Moss, W. Lawrynowicz, and L. M. Hadel, J. Am. Chem. Soc., 1987, 109, 4973. 8 R. A. MOSS, H. Fan, L. M. Hadel, S. Shen, J. Wlostowska, M. Wlostowski, and K. Krogh-Jespersen, Tetrahedron L e t t . , 1987, 28, 4779. 9 C. J. Abelt and J. M. P l e i e r , J . Org. Chem., 1988, 53, 2159. 1 0 R. A. MOSS, S. Shen, L. M. Hadel, G. Kmiecik-Lawrynowicz, J. Wlostowska, 4341. and K. Krogh-Jespersen, J. Am. Chem. S O C . , 1987, 11 R . A. Moss and J. Wlostowska, Tetrahedron L e t t . , 1988, 9, 2559. 12 U. Sonnewald and S. S e l t z e r , J. L a b e l l e d Compd. Radiopharm., 1987, 24, 787. 1 3 D. L. Ladd, P. B. Harrsch, and L. I. Kruse, J. Org. Chem., 1988, 417. 14 L. F. E l r o d , E. M. H o l t , C. M a p e l l i , and C. H . Stammer, J. Chem. Soc., Chem. Commun., 1988, 252. 15 W. Adam, M. D b ' r r , J. Kron, and R . J . R o s e n t h a l , J. Am. Chem. SOC., 1987, 109, 7074. 16 W. Adam, K. Hannemann, E. M. P e t e r s , K. P e t e r s , H. G . Von Schnering, and R. M. Wilson, J. Am. Chem. SOC., 1987, 5250. 17 W. Adam, E. G h t h e r , P. Hossel, H. P l a t s c h , and R. M. Wilson, T e t r a h e d r o n L e t t . , 1987, 4407. 18 M - S . Herman and J. L. Goodman, J. Am. Chem. SOC., 1988, 2681. 19 R. J a i n , L. McElwee-White, and D. A. Dougherty, J. Am. Chem. S O C . , 1988, 110, 55220 W. Adam, P. H%ssel, W. Hhmer, H. PLatsch, and R. M. Wilson, J . Am. Chem. SOC., 1987, 7570. 2 1 L. Van H i j f t e , R. D. L i t t l e , J. L. P e t e r s e n , and K. D. Moeller, J. Org. Chem., 1987, 52, 4647. 22 A. Khemiss anFM. Franck-Neumann, J. S O C . Chim. Tunis, 1986, 2, 3 Abstr., 1987, 107, 77691). 5498. 23 W. Adam and M. A. Miranda, J. Org. Chem., 1987, 24 W. R. Roth. U. Kowalczik. G. Maier. H. P. Reisenauer. R. Sustmann. and W. M;ller,*Angew. Chem. I n t . Ed. Engl., 1987, 1285. 25 M. N. B u r n e t t , R. Boothe, E. C l a r k , M. G i s i n , H. M. Hassaneen, R. M. Pagni, G. P e r s y , R. J. Smith, and J. Wirz, J. Am. Chem. Soc., 1988, 2527. 26 W. Adam, S - Grabowski, R. M. Wilson, K. Hannemann, and J. Wirz, J. ~ m . Chem. S O C . , 1987, 7572. 27 A. J. F. Edmunds and C. J. Samuel, J. Chem. Soc., Chem. Commun., 1987, 1179. 28 M. C h r i s t l , S. Freund, H. Henneberger, A. K r a f t , J. Hauck, and H. I r n g a r t i n g e r , J. Am. Chem. S O C . , 1988, 3263. 29 P. B. Ayscough, R. J. Bushby, C. J a r e c k i , K. D. S a l e s , D. Oduwolet, and J. Tann, Tetrahedron L e t t . , 1988, 2719. 30 R. Bambal, H. F r i t z , G. Rihs, T. Tschamber, and J. S t r e i t h , hgew. Chem. I n t . Ed. Engl., 1987, 26, 668. 3 1 M. Franck-Neumann, M. Miesch, and H. Kempf, Tetrahedron, 1988, 44, 2933. 32 H a Quast and and G. Meichsner, Chem. Ber., 1987, 2, 1049. 33 P. A. Wender and C. B. Cooper, Tetrahedron Lett., 1987, 6125. 34 A. G - S c h u l t z , R. R. S t a i b , and K. K. Eng, J. Org. Chem., 1987, 52, 2968. 35 M. Casey, C - J. Moody, and C. W. Rees, J. Chem. S O C . , P e r k i n Trans. 1, 1987, 1389. 36 W. Ando, Y. Kumamoto, and N. Tokitoh, T e t r a h e d r o n Lett.., 1987, 2867.
107,
107,
109,
53,
109,
-
28,
110,
-
-
109,
-
(m.
2, 26,
110,
109,
110,
2,
28,
2,
Photochemistry
448 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67
Maas, and M. R e g i t z , Angew. Chem. I n t . Ed. Engl., 1987, 26, 1257. R. D. Chambers, M. Tamura, T. Shepherd, and C. J . Ludman, J. Chem. SOC., Chem. Commun., 1987, 1699. M. G. Reinecke and E . S - Brown, J. Org. Chem., 1988, 53, 208. A. Sekiguchi and W. Ando, O r g a n o m e t a l l i c s , 1987, 1857. A. S e k i g u c h i , T. S a t o , and W. Ando, O r a n o m e t a l l i c s , 1987, 6, 2337. G. Mh-kl, W. S c h l o s s e r , and W. S . Shelgdrick, T e t r a h e d r o n L e t t . , 1988, 29, 467. J. E. Chateauneuf, K . A. Horn, and T. G . Savino, J. Am. Chem. SOC., 1988, 110, 539. R. P. L’Esperance, T . M. Ford, and M. J o n e s , J . Am. Chem. SOC., 1988, 110, 209. P. L. Coe, M . I . Cook, N . J . Goodchild, and P. N . Edwards, J . F l u o r i n e Chem., 1986, 34, 191. J . C. S c a i a n o and D. Weir, Can. J . Chem., 1988, 66, 491. S. F. Rak, S. C. l,apin, D. E. Falvey, and G. B . S c h u s t e r , J . Am. Chem. SOC., 1987, 5003. 0 . L. Chapman, J. W. Johnson R. J . McMahon, and P. R. West, J . ~ m . Chem. SOC., 1988, 501. D. G r i l l e r , M. Majewski, W. G. McGimpsey, A. S. Nazran, and J . C. Scaiano, J . Org. Chem., 1988, 53, 1550. G. W. G r i f f i n and K. A. Horn, J. Am. Chem. SOC., 1987, 4919. R. M . Wilson, and K. A. Schnapp, J. Am. Chem. SOC., 1988, Q, 982. K. Hannemann, Angew. Chem. I n t . Ed. Engl., 1988, 27, 284. X. Creary and M. E. Mehrsheikh-Mohammadi, T e t r a h e d r o n L e t t . , 1988, 29, 749. Y . - Z . L i and G. B. S c h u s t e r , J. Org. Chem., 1987, 2, 4460. Y.-2. L i and G. B. S c h u s t e r , J. Org. Chem., 1987, 52, 3975. J. G l i n k a , D. F i s c u s , C. B. Rao, and H . S c h e c h t e r , T e t r a h e d r o n L e t t . , 1987, 28, 3221H. Murai, I. S a f a r i k , M. T o r r e s , and 0. P. S t r a u s z , J. Am. Chem. SOC., 1988, 110, 1025. P. G . Mahaffy, D. V i s s e r , M. T o r r e s , J. L. Bourdelande, and 0. P. S t r a u s z , J. Org. Chem., 1987, 2, 2680. A. D. A l l e n , 4. J . Kresge, N . P. Schepp, and T. T . T i d w e l l , Can. J . Chem., 1987, 65, 1719. A. Padwa, S. P. C a r t e r , H. Nimmesgern, and P. D. S t u l l , J. Am. Chem. SOC., 1988, 110, 2894. B. Saha, G. B h a t t a c h a r j e e , and U. R. Ghatak, J . Chem. S O C . , P e r k i n Trans. 1, 1988, 939. M - Banciu, M. E l i a n , A. Banciu, C. D r a g h i c i , and E. Cioranescu, Rev. Roum. Chim., 1986, 3,1019 (Chem. A b s t r . , 1988, 37363). K. T a n i g a k i and T. W. Ebbesen, J. Am. Chem. S O C . , 1987, 109, 5883. G. Maas, K. S c h n e i d e r , and W. Ando, J. Chem. SOC., Chem. Commun., 1988, 72. H. Ok, C. Caldwell, D. R. Schroeder, A. K. Singh, and K. N a k a n i s h i , T e t r a h e d r o n L e t t . , 1988, 2275. W. W. Sander, J. Org. Chern., 1988, 53, 2091. A. 2 . Yankelevich, A. M. Sergeev, S. V. Rykov, V . K. Potapov, and G. A. N i k i f o r o v , I z v . &ad. Nauk SSSR, Ser. Khim., 1986, 2680 (Chem. Abstr., 1987, 96253). U. H. B r i n k e r and W. E r d l e , Angew. Chem. I n t . Ed. Engl., 1987, 26, 1260. R. G l e i t e r , H. Zimmermann, W. Sander, and M. Hauck, J. Org. Chem., 1987, 52, 2644. W. Kirmse and H. D. Sluma, J. Org. Chem., 1988, 53, 763. W. Kirmse, K.-H. Kampmann, and V. Zellmer, Chem. Ber., 1987, 1301. W. Kirmse and U. Mrotzeck, Chem. Ber., 1988, 121, 485. A. Hassner, R. F i b i g e r , and A. S . Amarasekara, J. Org. Chem., 1988, 53, 22. S. S. Z i g l e r , K. M. Welsh, and R. West. J. Am. Chem. SOC., 1987, 4392. 0. K l i n g l e r and H. P r i n z b a c h , Angew. Chem. I n t . Ed. Engl., 1987, 26, 566. W. M a r t e r e r , H. F r i t z , and H. P r i n z b a c h , T e t r a h e d r o n L e t t . , 1987, 5497. 0. Wagner, G.
a,
-
-
109,
110,
109,
-
108,
2,
107,
68 69 70 71 72 73 74 75 76
-
120,
109, 2,
449
11117: Photoelimination 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
101
w.
Isomura, M - S a k u r a i , T. Komura, M. S a r u w a t a r i , and H. T a n i g u c h i , 1987, 883. K. B a n e r t , Chem. Ber., 1987, 120, 1891. K. B a n e r t , Angew. Chem. I n t . Ed. Engl., 1987, 2, 879. C. J. S h i e l d s , D. R. C h r i s o p e , G. B. S c h u s t e r , A. J. Dixon, M. P o l i a k o f f , and J. J . T u r n e r , J. Am. Chem. SOC., 1987, 109, 4723. H. S u s c h i t z k y , W. Kramer, R. N e i d l e i n , and H. Uhl, J. Chem. Soc., P e r k i n Trans. 1, 1988, 983. E. A. P r i t c h i n a , N . Pa G r i t s a n , and N . M. B a z h i n , Izv. Akad. Nauk, SSSR, S e r . Khim., 1986, 1749 (Chem. A b s t r . , 1987, 153993). A. Yabe, A. Ouchi, and H. Moriyama, J. Chem. Soc., Chem. Commun., 1987, 1744. A. V. E l ' t s o v , F. M. D m i t r i e v , L. M. G o r n o s t a e v , and N . I. R t i s h c h e v , Zh. O w . Khim., 1986, 22, 2361 (Chem. A b s t r . , 1987, 107, 58268). T. Y. Liang and G . B. S c h u s t e r , J ; Am. Chem. SOC., 1987, 7803. S. K. R i c h a r d s o n , A. J e g a n a t h a n , R - S. Mani, B. E . Haley, and D. S. Watt, T e t r a h e d r o n , 1987, 43, 2925. G. Dupuis, Can- J. Chem., 1987, 65, 2450. H. K e s s l e r , A- Haupt, M. Frimmer, and K. Z i e g l e r , I n t . J. P e p t - P r o t e i n R e s - 9 1987, 2,621S . K. Arora, E. J. Kattelman, C. T . L i m , G . C. Le B r e t o n , and D. L. Venton, J. Med. Chem-, 1987, 30, 918. C. Q. Earl, A. P a t e l , R. H. C r a i g , S. M. Daluge, and J. Linden, J . Med. Chem-, 1988, 2,752. G. Cooper, D. Delmer, and C - N i t s c h e , J. L a b e l l e d Compd. Radiopharm-, 1987, 24, 759. G. G a c a , E - F e l l i o n , B . P. Roques, R . G e n e t , J. L. Morgat, and P. Fromageot, J. L a b e l l e d Compd. Radiopharm., 1987, 24, 867. H. S a w a n i s h i , K. Tajima, T. T s u c h i y a , Chem. Pharm. B u l l . , 1987, 35, 4101. H. S a w a n i s h i , K. T a j i m a , and T. T s u c h i y a , Chem. Pharm- B u l l . , 1987, 35, 3175. H. S a s h i d a , A. F u j i i , and T. T s u c h i y a , Chem- Pharm- B u l l - , 1987, 2, 3182. H. S a s h i d a , M. Kaname, and T - T s u c h i y a , Chem- Pharm- B u l l . , 1987, 35, 4676. H. S a s h i d a , A- F u j i i , and T - T s u c h i y a , Chem- Pharm. B u l l . , 1987, 35, 4110. R. Hayes and R . K. Smalley, J. Chem. R e s e a r c h ( S ) , 1988, 14. W. S t a d l b a u e r , Monatsh- Chem-, 1987, 1297. T. Miyasaka, H - Tanaka, K. S a t o h , M. Imahashi, K. Yamaguchi, and Y. I i t a k a , J. H e t e r o c y c l . Chem., 1987, 24, 8 7 3 V. Ya- Pochinok, L. M. Y a g u p o l ' s k i i , P. A. Kondratenko, V. I. Popov, N . V. Kondratenko, A. V. Pochinok, V. N . Skopenko, and L. I . Medvedenko, Ukr. K h i m . Zh.(Russ E d - ) , 1987, 53, 308 (Chem- A b s t r - , 1988, 55317). T. 4. Andreeva, V. P. K r i v o p a l o v , V. I. E r o s h k i n , and V . P. Mamaev, Izv & a d - Nauk SSSR, S e r . a i m - , 1987, 1196 (Chem. Abstr., 1983, 108, 75348). H - B a l l i , M H u y s - F r a n c o t t e , and F. S c h m i d l i n , Helv. Chim. Acta, 1987, 2045. M. M i t a n i , 0 . Tachizawa, H . T a k e u c h i , and K. Koyama, Chem- L e t t . , 1987, 1029 * T. Autrey and G. B. S c h u s t e r , J . Am. Chem. SOC., 1987, 109, 5814. 1. McAuley, E. Krogh, and P. Wan, J. Am. Chem. Soc., 1988, 110, 600. B. B . C r a i g and M. D. Pace, J - Chem- Soc., Chem. Commun., 1987, 1144. M. Hasebe and T. T s u c h i y a , T e t r a h e d r o n L e t t . , 1987, 28, 6207. D. H. R. B a r t o n , D. B r i d o n , I. F e r n a n d e z - P i c o t , and S. 2. Zard, T e t r a h e d r o n , 1987, 43, 2733. K- U. I n g o l d , J. L u s z t y k , B. M a i l l a r d , and J. C. Walton, T e t r a h e d r o n L e t t . , 1988, 29, 917. D. H. R. B a r t o n , E. da S i l v a , and S. Z. Zard, J. Chem. SOC., Chem. Commun-, 1988, 285. D- H. R - B a r t o n , A. G.-Olesker, S. D. Gero, B. Lacher, C. T a c h d j i a n , and S. Z. Zard, J. Chem. SOC., Chem. Commun., 1987, 1790 D. H. R . B a r t o n , Y. Herve, P - P o t i e r , and J . T h i e r r y , T e t r a h e d r o n , 1987, 43, 4297. K.
Lett.,
107,
109,
-
118,
108,
102
103 104 105 106 107 108 109 110 111 112 113
-
2,
Photochemistry
450 114 115 116
D. H. R. Barton, D. Bridon, and S. 2. Zard, Tetrahedron, 1987, D. Crich and J. W. Davies, Tetrahedron L e t t . , 1987, 28, 4205. D. H. R. Barton, B. Lacher, B. Misterkiewicz, and S. Z. Zard,
43,
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52,
24,
.
110, 110,
(w.
108,
53,
109, 109,
53,
53,
121,
2,
28,
108,
148 149 150
2,
P. Clawson and D. A. Whiting, Tetrahedron L e t t . , 1987, 3155. K. I s h i i , M. Abe, and M. Sakamoto, J. Chem. S O C . , P e r k i n Trans. 1, 1987, 19 37 1 5 1 D. D- M. Wayner and L. G r a v e l l e , T e t r a h e d r o n L e t t . , 1988, 29, 431. 152 B - F o s t e r , B. G a i l l a r d , N. Mathur, A. L. Pincock, J . A. Pincock, and C. Sehmbey, Can. J. Chem., 1997, 65, 1599. 1 5 3 H. 3. Kallmayer and C. Tappe, Pharmazie, 1986, 2,832. 1 5 4 J. P i n g l , M. Gehetz, A. Reggel, and C. B r i u c h l e , J. Am. Chem. SOC., 1987, 6479. 155 B. D. Hosangadi, P. N. Chhaya, M. M. Nimbalkar, and N . R. P a t e l , Tetrahedron, 1987, 43, 5375.
109,
ii117: Photoelimination 156
V. V-Shibanov, G. N. Volkova, V. A. Smirnov, and
S. V. Gorbacheva, Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 1987, 2,34 Abstr., 1988, 55333). Ya. N. Malkin, S . V . Rykov, and E. V. Skakovskii, Izv. &ad. Nauk SSSR, Ser. Khim., 1986, 2815 (Chem. Abstr., 1987, 107, 154004). C. Kashima, A. Tomotake, and Y. Omote, J. Org. Chem., 1987, 52, 5616. I. G . P i t t , R. A. R u s s e l l , and R. N. Warrener, Synth. Commun., 1986, 16,
157 158 159
451
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(w.
1627. 160 161
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165 166
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167 168 169
M. Mascal and C. J. Moody, J. Chem. SOC., Chem. Commun., 1988, 587. M. Mascal and C. J. Moody, J. Chem. SOC., Chem. Commun., 1988, 589. 0. Hoshina, H. Ogasawara, A. Takahashi, and B. Umezawa, H e t e r o c y c l e s ,
162 16 3 164
S.
2,
58,
2685.
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Phorochemistry
452
193 R. Beugelmans, M. Bois-Choussy, and Q. Tang, J. Org. Chem., 1987, 52, 3880. 194 M. Novi, G. Garbarino, G . P e t r i l l o , and C. Dell'Erba, J. Org. Chem., 1987, 52, 5382. 195 R. Beugelmans and M. Bois-Choussy, Heterocycles, 1987, 2,1863. 196 C. K. F. Hermann, Y. P. Sachdeva, and J. F. Wolfe, J. Heterocycl. Chem., 1987, 24, 1061. 197 M. G . Kuzmin and V. L. Ivanov, Izv. Sib. Otd. &ad. Nauk SSSR, Ser. Khim. Nauk, 1987, 40 (Chem. Abstr., 1988, 36857). 198 J. T u a i l l o n , Y. Couture, and J. L e s s a r d , Can. J. Chem., 1987, 65, 2194. 199 P. F. Dicks, S. A. Glover, A. Goosen, and C. W. McCleland, J. Chem. S O C . , P e r k i n Trans. 1, 1987, 1243. 200 G. G . Lazarev, S - V - Varlamov, A. I. Prokofev, R. G. Kostyanovskii, and Ya. S . Lebedev, IZV.Akad. Nauk SSSR, Ser. Khim., 1987, 699 (=. Abstr., 1988, 37082). 201 S. A. Glover and A. L. J. Beckwith, Aust. J. Chem., 1987, 40, 701. 3963. 202 H. Suginome and S. Yamada, Tetrahedron L e t t . , 1987, 203 H. Suginome, M. I t o h , and K. Kobayashi, Chem. L e t t . , 1987, 1527. 204 H. Suginome and S. Yamada, 205 H. Suginome, M, I t o h , and K. Kobayashi, J. Chem. S O C . , P e r k i n Trans. 1, 1988, 491. 206 K. Kobayashi, M. I t o h , and H. Suginome, Tetrahedron L e t t . , 1987, 28, 3369. 207 H. Suginome and S. Yamada, Bull. Chem. Soc. J n., 1987, 60, 2453. n m e t t . , 1987, 783. 208 H. Suginome, J. B. Wang, a 209 C. G. F r a n c i s c o , R. F r e i r e , M. S. Rodriquez, and E. Suarez, Tetrahedron L e t t . , 1987, 2,3397. 210 G u g i n o m e , H. Senboku, and S. Yamada, Tetrahedron L e t t . , 1988, 29, 79. 2 1 1 K. F u r u t a , T. Nagata, and H. Yamamoto, Tetrahedron L e t t . , 1988, 29, 2215. 2 1 2 S. D. Burke, L. A. S i l k s , and S. M. S. S t r i c k l a n d , Tetrahedron L e t t . , 1988, 2,2761. 213 H. Suginome and S. Yamada, Chem. L e t t . , 1988, 245. 214 G. A. Kraus and J. Thurston, Tetrahedron L e t t . , 1987, 2,4011.
-
108,
108,
2,
Part IV POLYMER PHOTOCHEMISTRY By N. S. ALLEN
Polymer Photochemistry BY N. S.ALLEN
1. Introduction This report follows the same format as the previous one. Academic and industrial interest in this field continues with a strong emphasis on new photocrosslinkable polymers and new monitoring techniques especially for electronic applications. The optical and luminescence properties of polymers continue to maintain interest although still more from a mechanistic point-of-view rather than any commercial implications. In the areas of photodegradation and stabilisation the approaches appear to be varied from new techniques to mechanistic studies and in the case of the latter hindered piperidine molecules continue to rank as the most efficient systems although an explanation for their high efficiency remains unsolved. Dyes and pigment photochemistry related to polymers continues to have interests with regard to light stability although the efforts in this direction are much less active.
2. Photopolymerisation The field of photopolymerisation and radiation curing continues to expand in many areas and this is yet again reflected in the large number of reviews and related industrial articles of interest which have appeared. The mechanisms of photoinitiated polymerisation have been actively covered in this regard and include cationic types for epoxy resins, radical types for photocross-linking, ’ the curing of diolefin silicones,‘O”’ polyimides12 and the use of dyes as catalysts. l 3 The applications of poly@-vinylphenol) in electronic components has been covered in some detailf4 as have U V curable inks and adhesives. ’ A number of commercial articles have concentrated on UV curable laquers and their safety,18 wood finishes, photoresponsive polymers2’ and photografting,21 while others have concentrated more specifically on the use of sulphonium salts for epoxy Several new techniques have appeared for monitoring photopolymerisation reactions and include the use of 455
Photochemistry
456
chemical probes,24 differential p h o t o ~ h e m i s t r y ,spectrosensito~~ metry26 and a microwave dielectric method2’ as well as a general review on equipment design. 28 More specialised methodologies in the field include the determination of hydroxyl values2’ and the use of dilatometry. 30 Finally, Decker3’ has presented an excellent review on the problems and future of radiation curing while Guillet32 has covered the photochemistry and radiation chemistry of polymer materials. 2.1 Photoinitiated Addition Polymerisation Chromium (VI) ions undergo a photoredox process to give chromium (V) ions by a charge-transfer mechanism which involves the formation of active HCr04 ions that effectively initiate the photopolymerisation of a ~ r y l o n i t r i l ewhile ~~ 2,4,6-trimethylbenzoyldiphenylphosphineoxide has been found to promote the cationic photopolymerisation of tetrahydrofuran and butyl vinyl ether.34 In the cationic polymerisation of butylvinyl ether in the presence of an g- 4,4-azobis (4-cyanopentanoyl)] bisdibenz ( b , f ) azepine whilst the presence of an iodonium salt generated a polymer with a small fraction of photoactive dibenzazepine end-groups. An aromatic carbonyl compound such as benzophenone resulted in a high yield of photoactivated endgroups. 35 Monomer reactivity ratios have been determined for cresyl glycidyl ether, butyl blycidyl ether and propylene oxide in the presence of the salt P F ~ - .Ph3 +.36 The photoconversion of the monomers was found to be determined by their basicity. The photopolymerisation of thioethers on the other hand such as triethylene glycol dithiol with ethylene glycol divinyl ether gives antiMarkovnikov structures in the presence of the cationic initiator oxide has been observed to undergo ( M ~ c 12 ~ ~H +~ ~ ~37 6 - Cyclohexene . a novel ring-opening anionic photopolymerisation in the presence of titanium (IV) isopropoxide and p-nitrobenzyl-p-chlorophenyl ether as a catalyst the yield of which increased with increasing titanium (IV) concentration. 38 In the cationic photopolymerisation of p-tertbutylphenyl glycidyl ether in the presence of di-(2-tert-butylphenyl) iodonium hexafluorvantimonate the HSbF6 produced was apparently only slightly dissociated3’ while the cationic polymerisation of oxetane derivatives of carbazole have been found to give high melting polyoxyalkylenes. 40 Using pulse radiolysis to study the cationic photopolymerisation of tetrahydrofuran the presence of hexafluoro salts have been found to scavenge solvated electrons which normally
-
c
IV: Polymer Photochemistry
nRCO(CN)C =CH-CH=CH
457
a-
CH=CH-CH
=C(CN)COR
R O-C-CH=CH2
+ CHZ=C
I
R +CH2-CH%
I
I
c=o
R'
I
0 I
Scheme 3
TX T X = Thioxanthonc
CH2
+
I
0-TX
+ HC 1
I
NH2-CcL.nn-x
I
R'
458
Photochemistry
neutralise the cations responsible for initiating polymerisation.41 Solid state photopolymerisation continues to attract interest and in this respect the polyaddition of&-benzenedithiol to p-diethylbenzene has been found to be a topotactic reaction which is controlled by the crystal lattice of the mixed monomers.42 This is also true of alkyl esters of A-phenylenediacrylic acid43 and 5,5' - 1 ,4phenylene-bis( 2-cyano-2,4-pentadienoic acid). 44 In the latter case the crystals were observed to undergo an interesting photoreversible topochemical photopolymerisation with light below 300 nm. With light wavelengths above 340 nm polymerisation occurs as depicted in Scheme 1. The solid-state photo2olymerisation of 5,7-dododecadiyne 1,12-bis(butoxycarbonylmethylurethane) occurs by a double homogeneous and heterogeneous process45 while the photoreactivity of black copolymers of diacetylene with urethanes, esters, ureas and amides has been found to depend on the activity of the monomer unit, the stack widths of the diacetylene groups and the degree of phase separation in the films.46 Of the monomers studied those based on urethanes were found to be the most photoactive due to hydrogen bonding shortening the distances between the planes of the diacetylene crystals. Under hydrostatic pressure the topochemical photopolymerisation of 1,6-bis(p-toluenesulphonato)-2,4-hexadiyne resulted in a polymer in which the distance between neighbouring molecules is larger than that between units of an unperturbed planar chain whereas crystals of 1,6-dicarbazolyl-2,4-hexadiyne gave the reverse effect due to valence angle d e f ~ r m a t i o n . ~In ~ the solid state photopolymerisation of 1,3,5-trithiane oxygen was necessary for the reaction to occur48 and the photoisomerisation of pendant norbornadiene units to quadricyclane has been determined in polystyrene.49 The mode of action of carbonyl containing compounds continues to be widely studied in many respects. Trialkylbenzophenones have been prepared and found to be highly efficient photopolymerisation initiators for acrylic monomers in the presence of tertiary amine synergist^.^' Their efficiency was associated with their ability to form triplet exciplexes with the amines with the 2,4,6-trialkyl derivatives being the most effective. In the photoinduced polymerisation of acrylamide by water soluble benzophenones the interaction between their triplet states and the monomer have been found to differ significantly from that of benzophenone itself.51 In other studies 3-benzoy1co~mari.n~~ and 4-benzoyl-N,N,N-trimethylbenzene-
I V : Polymer Pho!ochemistry
459
methanaminium chloride53 have been found to be more effective photoinitiators than benzophenone. Dibenzyl ketone has been found to initiate the photopolymerisation of styrene in micro-emulsions with the rate being highly dependent on the particle size of the latex5' and mercaptans have been found to enhance the photopolymerisation of methyl methacrylate initiated by benzophenone and triethylamine.5 5 Phenazines and benzophenones have been found to operate as effective photoinitiators through the formation of an excited-state complex whose stability depended very much on the electron-acceptor properties of the benzophenones.56 Laser flash photolysis studies have been used to investigate the mode of action and a mathematical exofO C , & d i p h e n y l a c e t o p h e n o n e pression has been derived to calculate the rate of photopolymerisation of methyl methacrylate in the presence of benzoin methyl ester using polychromatic light .58 Energy transfer and electron transfer have been ruled out as important mechanisms in the photoinduced polymerisation of methyl methacrylate by 3,3',4,4'-tetrakis ( tert-butyldioxycarbonyl) benzophenone5' and the kinetics of the photopolymerisation of diethylene glycol bis(alky1 carbonate) The initiated by #,<-dimethoxydioxybenzoin have been established. quinoline-bromine donor-acceptor complex initiates the photopolymerisation of acrylonitrile to give high molecular weight polymers61 with terminal bromine atoms.62 High copolymer yields have also been observed with other monomers such as 1-vinylpyrrolidene and again bromine residues were found to be present .63 Water soluble photosensitive polymers which undergo a cyclic acetal arrangement on irradiation have been prepared from poly(viny1 alcohol) containing arylideneacetophenone residues and the photopolymerisation activity of polymers containing benzophenone and amine moieties is greatest when both groups display a large'conformational mobility. 6 5 Halogen substitution in4-phenylbenzoin has been found to significantly enhance photoinitiator activityd6 while the presence of tert-butyl hydroperoxide acts as a chain-transfer agent and inhibits the photoinduced polymerisation of vinyl acetate by benzoin. 67
derivative^^^
The alternating copolymerisation of methyl methacrylate .and styrene in the presence of borontrichloride proceeds in the homopolymerisation of aternary molecular complex composed of all three systems68 while under visible light the photopolymerisation of methyl methacrylate is induced by methyl tetraphenylporphinato aluminium through indirect excitation of the porphyrin rings .69
460
Photochernistr'Y
In the laser induced photopolymerisation of methyl methacrylate on an aluminium surface the kinetics have been found t o be controlled mainly by the initiation of active particles in the adsorbed monomer layer and by radical recombination7' while excimer laser-induced radical polymerisation has enabled the determination of all rate constants over a wide range of conditions after a single Ions width laser p ~ l s e . ~ ' ESR spectroscopy has also been found to be valuable in the latter respect with regard to the photopolymerisation with maleic anhydride72 and the lamellar structure of liquid crystals of lecithin and 2-hydroxyethyl methacrylate are retained after photopolymerisation as studied by X-ray diffraction. 73 Azobis-isobutyronitrile has been found to be effective for the photopolymerisation of thin films of derivatives of 1,3,5-triazine-2,4-dithiol monosodium salts.7 4 'Ihe conversion rate however, decreases with increasing thickness of the monomer film. Vinyl ether polymers with thiol moieties have been prepared using benzophenone and Michler's ketone as photo initiator^^^ whilst bis( isopropy1xanthogen)disulphide has been found to be an effective photoinitiator for various vinyl monomers. 76 Remaining with thio compounds, the photoaddition polymerisation of 1,8-dithio-3,6-dioxaoctane with dialkyl phthalate ~~ occurs in a stepwise process with little or no r e c o m b i n a t i ~ nand thiobenzoates undergo photolysis reactions that are capable of initiating the photopolymerisation of glycol acrylate.78 In the latter case the efficiency of photopolymerisation was enhanced by the introduction of a 4-benzoyl group on the benzoate ring due to the photochemical formation of active benzoyl radicals which are Vinyl acetate has been capable of undergoing direct substitution. observed to photopolymerise in the presence of calcium containing zeolites7' and the photopolymerisation of acrylamide aerosol particles has been monitored by using auramine 0 as a fluorescent tracer.8o Photopolymerisable cationic oligourethanes have been prepared by terminating propylene glycol and toluene diisocyanate diurethane with diethylethanolamine and then subsequently quaternising the amine group with alkyl halides8' while several nitrobenzaldehyde polymers have been converted to acetals by reaction with ethylene glycol, and 2-hydroxyethylsalicylate which on irradiation give -nitrosobenzoate polymers.82 Poly(l-vinylcarbazole) has been obtained in high yields by photopolymerisation of the monomer in chloroform solution83 and poly (1-trimethylsilyl-2-propen-1-one) has been successfully prepared
I'J~:Polymer Photochemistry
46 1
from the corresponding monomer by a free radical photopolymeri ~ a t i o n . One ~ ~ particular feature of the latter work was the apparent formation of a colourless transparent polymer from a deep yellow monomer. Films of hexafluorobenzene, A-vinylpyrrolidene and 85 chloroacrylonitrile have been prepared by a plasma polymerisation and polymers with pendant tris(2,2'-bipyridyl) ruthenium (111) groups have been prepared by the radical copolymerisation of 4vinylpyridine with R~(2,2-bipyridyl)~(4-methyl-4-vinyl-2,2'Using pyrene fluorescence as a probe polystyrene bipyridyl)2+.86 microlattices prepared from rodlike micellar solutions have been found to be similar to those prepared from micro-emulsion solutionsg7 whilst sodium 10-undecanoate has been found to photopolymerise over a given concentration range which is controlled by the formation of micelle cores .88 Polymer-bound diaryliodinium salts have been prepared through the iodination of polystyrene followed by treatment with permetic acid, toluenesulphonic acid and then KA5F6 or KPF6.89 They proved to be effective cationic photopolymerisation initiators. Novel quaternary ammonium amphiphilic methacrylates have been prepared which give oligmeric species that behave with micellar-like properties'' while the photodimerisation of 2-anthracenesulphonic acid proceeds stereoselectively in aqueous media in the presence of p- or cyclodextrins.91
8-
In the triplet sensitised stepwise photopolymerisation of a polymethylene having terminal dibenz(b,f) azepine groups indicates that there is a critical chain length beyond which the linear oligmer actually undergoes photopolymerisation. With increasing chain length the intrinsic rate of deactivation of the terminal reactant groups exceeds the propagation rate and polymerisation ceases. The critical chain length was found to be 3 for this system. Bivalent photoinitiation involving electron transfer to onium salts has been critically assessed93 and in the photopolymerisation of dibenzoyl peroxide with azobisisobutyronitrile chain termination was found to be bimolecular and diffusion c ~ n t r o l l e d . ~Trichloro~ acetic acid and dimethylaniline have been found to initiate the photopolymerisation of methyl methacrylate through a complexg5 while aniline itself forms a complex with arylonitrile and photoinitiates polymerisation of the monomer via proton tran~fer.'~ In the case of the VOCl induced photopolymerisation of isobutene, the presence 3 of naphthalene was important for any observable polymerg7 and in the photoinduced polymerisation of N , J j - ' - m e t h y l e n e b i s a c r y l a m i d e the
'*
Photochemistry
462
presence of uranyl ions were found to operate as initiators and not chain terminators. 98 A pyridine-bromine charge-transfer complex has also been found to be effective f o r the photoinduced photopolymerisation of vinyl monomers via the formation of the bromine radical.” Bromine radicals have also been implicated in the photoinduced polymerisation of methyl methacrylate by bromobenzenel” and vinyl monomers by an 1-vinylpyrrolidone-bromine charge-transfer complex. l o ’ In the photoinduced polymerisation of 2-vinylnaphthalene with maleic anhydride electron transfer takes place with the resultant formation of a copolymer whereas in the presence of benzophenone a cycloadduct of 2-vinylnaphthalene is produced which then reacts with the maleic anhydride. l o * Other studies of interest include macromolecular growth in laser-induced photopolymerisations,I o 3 reaction of gases with irradiated films of acylamide, 105 shear mechanical relaxation processes of irradiated monomolecular layers of monomers,lo6 the photopolymerisation of methyl methacrylate by peroxydiphosphatelo7 and acryloni trile by l-alkylcarbazoles. 108
2.2 Photocrosslinking The area of photocrosslinking is a subject of considerable industrial importance with several new types of polymers and monomers being continuously discovered. Polyvinyl alcohol containing styrylpyridinium and styrylprinolinium groups has been synthesised. 109-1 12 Both polymers undergo rapid photocrosslinking, with the former group being the most photoactive in solution whereas in the bulk both groups had the same activity. The same workers have also prepared polymers with p e n d a n t p - p h e n y l e n d i a c r y l a t e groups which exhibit high photosensitivity to 488 nm light from an argon-ion laser with Similar photosensitivity has a quantum efficiency of 0.44. been observed f o r polymers with methacryloyl side groups using p-dimethylaminobenzylidene as a photoinitiator’ l 4 and the same workers have yet again prepared polymers with pendant e(dialky1amino)benzylideneacetophenone groups whose photosensitivity increase dramatically in combination with vinyl monomers and a cationic photoinitiator. l 5 High resolution photoresists have been prepared from pyromellitic dianhydride and ry-(2-nitrophenyl) ethanol. The product from this reaction polymerises with diamines to give poly116,117 amic acids which do not swell during the development process.
’’
’
The kinetics of free radical polymerisation in the photocuring of resins has been covered in depth’” and radical trapping in some
IV: Polymer Photochemistry
463
’’
acrylated resins has resulted in a post polymerisation effect.’ Ultra-violet curable resins are excellent for coating optical fibres12’ and the surface hardening of polyacrylates has been Hydrogen polysiloxanes have been successfully modified studied. 12’ with cinnamic photosensitive groups for photoresists’22 and acrylated and methacrylated silicones have been prepared as ultraviolet curable sealants. ’23 New organosilicon deep UV positive resists have been prepared using poly(&-disilanylenephenylene). 124 Aromatic ketones and quinones continue to attract interest as initiators of photocuring. Several commercially available aromatic carbonyl compounds have been examined in detail and their photochemistry, photophysics and photopolymerisation efficiencies related. 125 In this case, the triplet state was considered to be important in inducing the photopolymerisation of n-butylmethacrylate and a similar conclusion was also made by the same workers on the photopolymerisation activity of a range of novel propoxy substituted thioxanthones. 126 In the latter case photoactivity was determined by the electron donating ability of the amine cosynergist indicating the involvement of a triplet exciplex. Evidence was also provided to show that in the photocuring of acrylated resins with carbonyl-amine exciplexes it is the alkylamino radical which is the photoinitiator. The same group of workers have also recently prepared novel 2-acryloylthioxanthone by reaction of 2-hydroxythioxanthone with acryloyl chloride as shown in Scheme 2. This novel monomer will copolymerise effectively with other acrylic monomers to give highly photocrosslinkable polymers as shown in Scheme 3. Polystyrene was also tagged with thioxanthone by reaction o f 2-hydroxythioxanthone with p o l y ( p c h l o r o m e t h y 1 s t y r e n e ) (Scheme 4). The latter polymers photocrosslink rapidly at a thioxanthone concentration greater than 4% by weight o f the polymer. Thioxanthones have been found to be excellent photosensitisers for the crosslinking of poly( vinylcinnamate)‘ 2 8 and halogenated polystyrenes. 12’ Vinyl acetate-isopropenyl acetate copolymers are effectively photocrosslinked by 2-benzoquinone’30 as are 2-hydroxyethyl methacrylates. 13’ In the former case however, the polymers have the advantage of being water soluble on hydrolysis. Poly(propargy1 methacrylate) has been prepared and photocrosslinked with 2-alkylanthraquinones and 4-morpholino-2,5-dibutoxybenzenediazonium salts’32 while benzoin isopropylether has been found to initiate the photopolymerisation of 1,4-butanediol dimethacrylate in layers of poly(vinylpyrro1idone)
Photochemistry
464
under aerobic conditions.133 In the latter case a related study on the photocuring of acrylic epoxy resins found that the.presence of 1-vinylpyrrolidone as a reactive diluent markedly reduced oxygen inhibition. 34 The photosensitised crosslinking of 3,4-polyisoprene -2,6-bis(4’-azidobenzal) cyclohexanone by benzophenone has been associated with an addition reaction between dinitrene and externally activated double bonds ’ 36 and a photocrosslinkable polyamide has been prepared from cyclopentanone-2,5-dipropanoic acid and oxydianiline using l-chloro-2-phenyl-4-methyl-1,2-dihydro-l,5,2,3,phosphoxadiazole as a condensation agent. 137 In the photochemical crosslinking of poly(phenylquinoxalines1 nitrenes are formed at atmospheric pressures ( 1 - 3 Pa by a non-radical reaction from the lowest excited ~ i n g l e t - s t a t e lwhile ~~ in the photovulanisation of cyclised isoprenerubber using aromatic azido compounds the number of crosslinks were linearly related to the number of azido In the latter study bisazide compounds were found to groups. be more effective although their photolysis did not contribute toward the gelation of the polymer and there was a limiting concentration for vulcanisation of 7 % weight/weight beyond which the photovulcanisation efficiency decreased. Several studies have concentrated on the commercial properties of photocured resins. These include humidity and solvent resistance lof epoxy-acrylates,140 microhardness and shrinkage of diacrylates, viscosity and solvency of methoxy ether acrylates,1 4 2 sanding properties of polyweathering of acrylic varnishes’44 and hardness esters on wood, and solvent r u b testing o f acrylates.145 Other studies have shown that 2-ethylhexyl-~-(dimethylamino)benzoate is an effective nonyellowing co-initiator with benzophenone’4 6 and the application of a magnetic field enhances the photocrosslinking of butadienestyrene rubber partially modified by a Friedel-Crafts reaction. 147 The ultraviolet irradiation of 2,5-dibenzylidenecyclopentanone and its nickel complex has been shown to result in a 2 + 2 dimerisation of the exocyclic double bond causing crosslinking.148 Other types of novel resins synthesised include phenoxy resins having p-azidobenzoyloxy groups14’ and poly 4-(vinyloxyethoxy)styrene prepared by a phase-transfer catalyst.’’O Studies on the structure of amine co-synergists in the photocuring of acrylate resins has shown that dimethylsubstituted types are more effective for scavenging oxygen than diethyl-substituted types. 15’ ’ 152 Here oxidation of the methyl groups adjacent to the nitrogen is an important function.
’
”’ ’
’”
’”
IV: Polymer Photochemistry
465
Several studies have concentrated on the photocrosslinking of epoxybased resins. Using differential scanning calorimetry the photocuring of epoxy and acrylic prepolymers has been disturbed by the nature of the polymer networks and at high acrylic concentrations some phase separation was observed. 1 5 3 In the photocuring of epoxy resins using bis 4-(diphenylsulphon'ic)phenyl sulphide bis(hexafluorophosphate) as photoinitiator gelation was found to decrease with increasing molecular weight of the resin15' and soluble photocrosslinkable polymers have been prepared from poly(glycidy1 methacrylate) with esters having chalcone moieties using tetraethylammonium bromide salts as a catalyst. 155 The extent and rate of ultraviolet induced crosslinking of 3 , 4 - e p o x y c y c l o h e x y l m e t h y l - 3 ~ , 4 ~ epoxycyclohexane carboxylate has been found to increase with increasing temperature and irradiation intensity 56 and the properties of photocurable cycloaliphatic epoxides have been altered through the incorporation of polyethylene and PTFE powders. 157 Epoxy-acrylic resins have been developed with good adhesion prope r t i e ~ 'while ~ ~ a novel ultraviolet curing technique has been developed for impregnating fabrics with monomers without the need The cationic ring-opening polymerisation of for solvents. 15' epoxides and diglycidyl ethers in the presence of iron-arene photoinitiators proceeds in aligand exchange of arenes by epoxides resulting in the formation of cyclic polyethers and crosslinked epoxy resins16' and the reaction of methacrylic acid with the telomer of 2,3-epoxypropyl methacrylate and dodecanethiol gives highly photocrosslinkable polymers which have good adhesion to aluminium. Polyurethane-acrylate films cured by an electron beam has been shown to have better properties than that cured by ultraviolet light 6 2 while the crosslinking of tetraethylene glycol diacrylate is dependent on the rate of photopolymerisation.1 6 3 Photosensitive azido polymers have been found t o undergo a coupling reaction 164 involving nitrenes formed from the photolysis of azido groups whilst the alternating copolymerisation of maleic anhydride with an ally1 acetate involves the formation of a charge-transfer complex. 165 The properties of unsaturated diazoester acrylurethanes have been examined165 and have the strength properties of glass fibre reinforced unsaturated polyesters 168 and thermochromism of novel polydiyne materials. 6 9 Photocrosslinkable poIyisoprene and isobutylene-isoprene copolymers have been prepared with cyclic structures.17' In the case of the latter thermal stability was
466
Photochemistry
found to be dependent upon the isobutylene content. Other studies of interest include telomers from 2,3-epoxypropylmethacrylate, 17' ultraviolet curable varnishes, 172 electrochemical characterisation and ~ of photocured coatings, 173 thickness effects in p h o t ~ c u r i n g ' ~ the photoaddition of terephthalaldehyde to poly(rnethy1 methacrylate). 175 2 . 3 Photografting Studies on photografting appear to have declined in interest. The presence of acid has been found to enhance the photografting of styrene onto polypropylene and cellulose with dimylbenzene giving good synergism. 176 Both methyl methacrylate and methacrylic acid have been found to photograft onto nitrocellulose whereas styrene and vinyl acetate would not. 177 Interestingly, photografting increased with increasing nitrogen content of the nitrocellulose. In the photografting of methyl methacrylate onto chitosan polymerisation proceeded via photolysis of amine groups. 78 Methyl methacrylate has also been photografted onto nylon 6 using pyronin G as a photoinitiator in the presence of a phosphate-nitrate buffer. 179 The photografting of styrene onto cellulose triacetate has been studied as a reverse osmosis membrane18' while the adhesion of p o l y e t h y l e n e t e r e p h t h a l a t e to Cu metal is improved by photografting Polydiacetylenes have been photografted onto alumina monomers. l 8 and silica' 8 2 and styrene has been photografted onto diethylenetriamine modified oxycellulose using potassium persulphate as a catalyst. "3
3. Optical and Luminescence Properties Several review articles of topical interest have appeared. Donoracceptor interactions in charge-transfer complexes between low molecular weight compounds and polymers have been reviewed with A book has been compiled emphasis on poly(J-vinylcarbazole). on fluorescent polymers' and light induced effects have been covered by two separate groups of workers. 8 5 9 87 Other reviews include excimer formation in cyclodextrins'88 and monitoring the curing of resins by fluorescent probes. 189 A whole series of papers have been compiled from a NATO Advanced Science Conference, many of which are review articles o r papers of topical interest.lgO These include reviews on fluorescence characterisation of biopolymers,191 energy transfer dynamics, l g 3 singlet photochemical effects, energy migration, 94 fluorescent probes, 195 cis-trans photoisomer-
IV: Polymer Photochemistry
467
isation, molecular diffusion, fluorescence quenching in conformational probes in polyacrylics, electronic polystyrene, excitation transport measured by fluorescence depolarisation2" and polymer blend thermodynamics.201 Articles of special interest include fluorescence polarisation of anthracene labelled polystyrene,2029 2 0 3 diffusion in poly( propylene oxide) ,204 dynamics in dye-labelled polymethyl methacrylate and poly(viny1 acetate), 205 time-resolved fluorescence analysis, fluorescent probes based on p-(N,N-dialkylamino)b e n z y l i d e n e m a l ~ n i t r i l e s ,excimer ~~~ formation in rubber208 and rotational dyad statistics in blends o f polystyrene and poly(viny1 methyl ether) .209 Other typical papers include a review on the anisotropic properties of the Durham route polyacetylene,210 effects of ammonia gas on the optical properties infra-red dichroism o f drawn polyof p o l y ( p p h e n y l e n e v i n y 1 e n e ) , monitoring o f interfacial polycondensation by ultraviolet spectroscopy,2 1 photochromic properties of polyvinyland the use of derivative absorption spectroscopy for the analysis of copper-humic acid complexes.215
' ''
Fluorescence lifetimes of melamine-formaldehyde resins have been measured and concluded not to be important in the photodegradation M of the resins.216 Circular dichroisrn studies on E-poly(N -phenylazobenzoyl-L-lysine) have shown that conformational changes are associated with a partial reversible transition from a F-rich form structure to a random coil rich structure.217 Energy transfer in polyoxyethylene surfactants has shown that the micelles are subject to ageing2' while the photobehaviour of end-labelled poly(ethy1ene oxide) in solution has indicated that. specific solution effects must be considered for bound chromophores when compared to unbonded molecules. 2 1 9 The temperature dependence of the fluorescence of poly(benzy1 acrylates) has shown that there are transitions associated with activation energies of the benzyl group220 and a study on benzoylated polystyrene beads has indicated that a high degree of functionalisation suppresses triplet sensitisation due to a higher incidence o f intra-molecular energy transfer.221 The photophysics and photochemistry o f p - d i m e t h y l a m i n o b e n z o y l a t e d polystyrene indicates low photoreactivity when compared with that of Michlers ketone due to a high rate of intra-molecular self quenching.222 In the bichromophoric molecule 9-@ - (8-carbazoyl)propyg -9-methyl -2,7-dinitrofluorescence fluorescence quenching is associated with intramolecular energy transfer.
Photochemistry
468
The dispersion of resonantly-enhanced Roman modes with excitation energy have been examined in Durham poly(acety1ene) .223 The results showed that within the amplitude-mode formalism of Horovitz the defects that terminated the straight sequences in unstretched materials did not impose a preferred sense of bond alternation on the chain. Defects introduced through chemical doping or photoexcitation showed the characteristics of soliton-like states with a single midgap electronic absorption feature at much higher energies than for stretched Durham or Shirakawa type polymer. The photoinduced infra-red spectra of trans-poly(acetylene1 have been interpreted in terms of a lattice dynamical calculation in which the polymer is treated as an infinite dimerised chain,2’24 Interband transitions have been measured for poly(3-methylthiophene) with different dopant levels225 and photoinduced active vibrations in polyacetylene showed enhanced bound-mode infra-red activity coexisting with translational-mode infra-red activity. 2 2 6 Transient reflectance changes in polydiacetylene toluenesulphonate have been associated with the lowest excited triplet state formed by the recombination of charge carriers.227 The formation and decay of a triplet state in a polydiacetylene single crystal has been directly observed by pulsed ESR after optical excitation. 2 2 8 The unusual spin polarisation properties of the observed triplet indicated the formation of a triplet soliton pair. The photoredox behaviour 2129 of various substituted polypropylenes has been examined. Photoisomerisation processes particularly those utilising an azo group continue to attract much interest. An azobenzene modified poly(1-methyl L-glutamate-co-L-glutamic acid) has been prepared and irradiated in bilayer membrane vesicles of distearyl-dimethylammonium chloride. 230 Trans-cis isomerisation of the polymer resulted in transfer of the polypeptide from the hydrophobic bilayer membrane interior to the hydrophilic surface. This property caused an observed decrease in the ion permeability through the bilayer membrane and the resultant formation of intervesicular adhesion. Azobenzene and stilbene compounds have been examined as molecular ~ ’ found to be sensitive to the probes in p ~ l y m e t h y l m e t h a c r y l a t e ~and local free volume. The miscibility of blends of poly(methy1 vinyl ether) with polystyrene has been studied by monitoring the-trans isomerisation of pendant stilbene groups on the latter isomerisation of polymer.232 On the other hand, the trans-* stilbene has been photosensitised by polymer bound OrthQ and w-
-
IV: Polymer Photochemistry
469
Photochemical Transformat ions in Rose 8engal End Capped Polystyrenes
-
J
mcthylcne chloride
1
toluene
Scheme 5
470
Photochemistry
benzy l~xybenzaldehyde~ while the photoviscosity of poly(dimethy1siloxane) may be controlled through the incorporation of azobenzene residues in the main chain.234 A photopolychromic system based on (E)-~2,5-dirnethoxyphenyl-substituted)methylene] is ppropylidenesuccinnic anhydrides undergo marked colour changes on irradiation235 and photosensitive membranes have been prepared from an aromatic polyamide and a cinnamate acid containing a liquid crystalline component.236 The latter have been observed to undergo a cycloaddition reaction on irradiation. Fluorescent crown ethers have been prepared from erbium chloride and poly(2-meth~cryloyloxymethyl1 8 - c r 0 w n - 6 ) ~and ~ ~ Rose Bengal bound to the ends of a polystyrene chain have been observed to undergo a photoconformational change from monomeric to aggregate structures238 as shown in Scheme 5. The absorption spectra of polysilanes have been found to be dependent upon steric effects of the substituents as a consequence of strain 240 on the Si-Si backbone bonds239 as have their fluorescence spectra. Phosphorescence emission above 400 nm from poly(pheny1 methyl silane) has been associted with photodecomposition products in the polymer241 while a new mechanism for excimer dissociation has been proposed in this polymer.242 Arrhenius plots of the excimer to monomer emission intensities of a dimer 1,3-diphenyltetramethyldisiloxane reproduces those of the polymer whilst a monomeric anologue does not. Both the polymer and dimer plots show isobestic points below the transition temperature which disappear above it. It is concluded that below the transition temperature the monomer intensity increases with increasing temperature due to excimer dissociation to excited-state monomer. Above the transition temperature the excited-state equilibrium is apparently broken because the thermal energy is sufficient to activate excimer non-radiative decay by dissociation to ground-state monomer. Consequently, the monomer emission no longer increases with increasing temperature and the isobestic point disappears. Pyrene has been usedas a fluorescent probe to monitor the conformational state of maleic acid with alkyl vinyl ethers with cationic surfactants.2 4 3 Here changes in the fluroescence intensity reveals a transition from a microdomain to a hydrated conformation. Polyvinylalcohol has been found to be non-luminescent above 420 nmZ4' while the emission anisotropics of fluorescent chromophores in an adhesive layer on poly (ethyleneterephthalate) are markedly controlled by the thickness245 of the layer. The structure of polymer complexes stabilised through
47 1
IV: Polymer Photochemistry
hydrogen bonds have been shown to be markedly influenced by the presence of non-active groups on the polymer chains246 and hydrophobic association of ~-benzyl-1,4-dihydronicotinamide with poly (sodium styrene---sulphonate) results in more effective fluroescence quenching than with l-benzyl-nicotinamide. 2 4 7 However, the fluorescence of polymers of the latter is more effectively quenched due to the formation of poly(electro1ytes). The photoreductive properties of copper complexes of non-cyclic urea oligomers have been studied248' as have the photochromic properties of liquid crystalline polysiloxanes. 249 Interestingly, the fluorescence of 1a m i n o - 8 - n a p h t h a l e n e s u l p h o n i c acid is markedly enhanced when bound to a polymer chain due to enhanced molecular rigidity.2 5 0 New fluorescence complexes of Cerium (111) ions with PVC have been prepared251 arid the wettability of poly butyl methacrylate-c0-W (2-hydroxylphenyl)4-(4-vinylphenyl)benzyl alcohol is enhanced on irradiation due to a reversible isomerisation process . 2 5 2 The optical emission from ablated foams has been related to the laser f l ~ e n c e and ~ ~the ~ mechanooptical properties o f polymers has been investigated by a photoelasticity method. 254 The molecular mobility in poly(epoxide) networks has been studied by both fluorescence and phosphorescence emission spectroscopy and a striking correlation has been seen between the transitions observed and those obtained from mechanical property Using pyrene as a fluorescent probe the manufacture and curing of acrylic composites has been monitored. 2 5 6 Homopolymers from four isomeric acetonaphthyl methacrylates have been synthesised and found to exhibit intense phosphorescence at 77 K 2 5 7 while long-range energy transfer has been observed from covalently linked phenanthryl groups onto a polyanion to methylviologen bound electrostatically onto the peripheral of hydrophobic aggregates around the former.258 The rate of fluorescence quenching of the excited state of acrylic acid-4-methyl-4'-vinyl-2,2'-bipyridine copolymer containing pendant ruthenium bipyridyl complexes by methyl viologen has been found to increase with increasing molecular weight of the copolymer.2 5 9 At low molecular weights quenching was associated with a dynamic process whereas at higher molecular weights both dynamic and static quenching processes were observed.
measurement^?^^
The methyl nitrite quenching of pyrene fluorescence in polyacrylic acid is dependent upon the polyelectrolyte properties of the latter especially at high pH 9 . 260 This was associated with ionisation
472
Photochemistry
of the carboxylic acid groups which expanded the polymer chain thus exposing the bound pyrene molecules to the aqueous phase and the quencher. Polymers prepared from 1,2-bis(2,4-octadecadienoyl) g l y c e r o - 3 - p h o s p h o c h o l i n e containing 5(6)-carboxylfluorescein as a probe are more stable than that of the monomer261 whilst poly (1-ethyl-4-vinylpyridinium bromide) had no significant quenching effect on the fluorescence of labelled poly(sodium methacrylate) .262 The polarisation of the fluorescence of l-phenyl-4-(4-cyano-Inaphthylmethy1ene)piperidine increases strongly during the polymerisation of methyl methacrylate indicating that the rotational motion of the former is shorter than that of its fluorescence lifetime.2 6 3 Using the same technique ion-pair aggregates have been observed in ionomers containing fluorenyl-sodium when present as pendant chromophores at a mole fraction 0.02. 264 Excimer emission from poly(9-vinylanthracene) has been used to probe the electrochemical polymerisation of the monomer265 whilst fluorescent probes have been successfully used to monitor the nature and movement of species in polyelectrolytes266 as has the hydrolysis of gel phases of divinylbenzene with diisopropenylbenzene styrene copolymer. 267 Electrostatic interaction of p o l y ( d i m e t h y l d i a l k y l a m r n o n i u m chloride) with dibromofluorescein causes a red shift in the fluorescence emission wavelength maximum of the latter268 while a fluorescence quenching study of tris(2,2'-bipyridine) ruthenium bound onto a hexyl vinyl ether-maleic anhydride copolymer indicated the formation of large hypercoiled conformations containing small intramolecular micelles .269 Intramolecular photodimerisation of bis (9-anthrylmethyl) ether in polystyrene and poly(viny1 acetate) is governed by the degree of free volume in the p01ymer-s~~' and the molecular size of latexes have been determined using optical turbidity Polarised fluorescence and laser Raman scattering spectra.27 have been used to measure elastic constants of polymers272 whilst carbon disulphide has been found to quench the fluorescence of anthracene labelled poly(methylmethacry1ate) in poly(l2-hydroxystearic acid). 273 Electrochromic studies on a copolymer of 2-phenyl enediamine resorcinol diglycidyl ether containing nitroanilines indicated energy transfer was occurring274 and laser Raman photon spectroscopy has been used to study intramolecular vibrations in 1 ,4-bisrp-pipridyl(2) vinyg benzene.275 Photoresponsive membranes have been prepared from polyacrylamide gels with triphenylmethane leucohydroxide.276
IV: Polymer Photochemistry
473
The micropolarity and aggregation of polymers bound onto silica have been studied by using pyrene as a fluorescent probe277 while the same probe has been used to study the microenvironment in a perfluorosulphonate membrane278 and the effect of hydrocarbon chain length on intramolecular micelle formation in maleic anhydride-loctadecene copolymer.2 7 9 Excimer emission from polymers continues to attract widespread interest particularly with regard to segmental motion in polymers. Intramolecular excimer formation of meso-2,4-di(~-carbazoyl)pentane dissolved in poly(propy1ene oxide) is shown to be controlled by the segmental motions of the polymer involved in the glass transition phenomenon28o and similar work in fluorescence anisotrcpy of diphenylhexatriene in the same polymer281 has shown marked differences in behaviour between the monomer and polymer indicating intramolecular constraints lead to much more catastrophic coupling of motions than intermolecular ones. A naphthalene diisocyanate based polyurethane has been found to form intramolecular excimers between chromophores in the polymer backbone. 2 8 2 In this case a triple exponential fit to the fluorescence decay kinetics of the polymer in solution was interpreted by an isolated monomer model scheme. Steady-state fluorescence spectra were directly correlated with the intrinsic viscosity of the solution thus providing useful information on polymer solubility characteristics. Using the site selective excitation method localised excitons have been found to be generated below the energy of the exciton absorption bound in poly(N-vinylcarbazole). 283 In the solid state the localised excitons hop into the excimer former sites giving excimer emission. The efficiency of excimer formation in protonated poly(2-vinylpyridine) in solution is highly dependent on the degree of polymerisation (DP). 2 8 4 9285 Intramolecular interactions of neighbouring protonated pyridine chromophores with a DP ?/95 are effective and favoured for both dimer and normal excimer formation and an analysis of the decay curves indicates that both excimers occur independently regardless of the degree of polymerisation. Intramolecular excimer formation has been observed for 1O,1O1-diphenyl-bis-9-anthrylrnethyl oxide and meso-2,4-di(~-carbazolyl)pentonein cyclic poly(dimethy1siloxane)286 and various elastomers.287 In the latter case intramolecular conformational change required for excimer formation is controlled by the segmental motions of the polymer matrix involved in the glass transition phenomenon. A detailed study on the excited-
474
Photochemistry
state kinetics of diastereo-isomers of 2,4-di(2-pyrenyl)pentone and bis 1-(2-pyrenyl)ethyI ether indicates that the substitution pattern of the chromophores is important. 288 For pyrene end-labelled polyethylene glycols excimer formation decreases with an increase in the molecular weight of the polymer. 289 However, the formation of excimers was found to be greater than that predicted by diffusion controlled end-to-end cyclisation. Enhanced excimer formation in this case was attributed to a strong hydrophobic attraction between the pyrene molecules. The energies of meso and racemic diol conformations have been determined in polystyrene which indicate that interactions between the phenyl groups in the ground-state do not result in dimer formation and in the excited-state do not result in dimer formation and in the excited-state only the former diol gives rise to excimer formation. 2 9 0 In the case of pyrenelabelled poly(2-ethylhexyl methacrylate) bound onto polyvinylacetate particles excimer emission is reduced due to non-emissive complex formation. 291 Similar experiments have been carried out on naphthalene-labelled polymethylmethacrylate bound to polyisobutylene. 2 9 2 9 293 The nature of the polymerisation process controlled the type of naphthalene substitution with environmental factors controlling the mean-lifetime of the fluorescence. The same group of workers have also developed a theoretical model for excitation trapping in p o l y ( P J - v i n y l c a r b a z o l e ) . 294'2 9 5 The degree of interpolymer penetration has been investigated by studying the fluorescence of carbazole and anthracene labelled polystyrenes in mixed polymer systems. 296-298 The nature of the solvent used was found to be important. Intra and intermolecular interactions have also been studied in naphthyl and phenylcarbonyl terminated polystyhas been found to exhibit r e n e ~ while , ~ ~ poly(pentaf1uorostyrene) ~ no excimer e m i s ~ i o n ~ ~has ~as poly 2-( 9-carbazolyl) ethyl methacrylate ,3 0 1 and poly( 4-vinylpyridine) and 4-vinylpyridine-methyl methacrylate copolymers.302' 303 In the latter case the lowest excited state was stabilised by a strong interaction with the solvent. Polyindene and polyacenaphthylene on the other hand form excimers through a long-range interaction. 304 The conformational characteristics of polymer chains have been concluded to be important in controlling excimer formation in polyesters305 as well as hydrogen transfer in P-naphthol-labelled polycarboxylic acids. 3'06 In the case of anthracene labelled water soluble polymers hydrophobic interactions enhanced intramolecular excimer f ~ r m a t i o n ~while "~ in ion-pair complexes of poly(2-vinylfluorene) both electrostatic and
IV: Polymer Photochemistry
475
steric effects were found to influence intramolecular energy migration. 3 0 8 Copolymers of methyl methacrylate with 2-vinylnaphthalene exhibit both monomeric and excimeric fluorescence component~~' while ~ the fluorescence lifetime of pyrene in acrylamide copolymer solutions was dependent on the intrinsic viscosity of the In I-( 2-hydroxypropyl) methacrylamide polymers labelled medium. 31 with 2-amino-1,3-di(2-naphthyl)propane the activation energy for intramolecular excimer formation was found to be independent of the The compatibility of blends distances between the chromophores. 31 of polystyrene with polymethyl methacrylate have been studied using excimer fluorescence of p o l y ( N - v i n y l - 2 - p y r r o l i d ; o n e ) 3'12and intramolecular excimer formation has been investigated in anthracene labelled &-vinylpyrrolid,one and &-vinyl-caprolac tam copolymers.'31 Micellar interactions have been studied in dipotassium salts of maleic anhydride-1-octadecene alternating copolymer systems using pyrene as a molecular probe. 3 1 4 Polarised fluorescence has been used to study the orientation of and a fluorescence technique non-crystalline polymer has been developed to quantify the amount of microgel in polyacrylamide. 31 Time resolved photoluminescence analysis of polyk-phenylenevinylene) has shown that the rate of non-radiative decay increases with an increase in the chain conjugation length indicating a high degree of biomolecular recombination. 318 Conformational transitions in monostoichiometric polyelectrolyte complexes from sodium acrylates with poly(N-ethyl-4-vinylpyridinium bromide) and hydroxyethyl quaternised poly(4-vinylpyridine) have been studied by luminescence analysis and found to be unaffected by the addition of sodium chloride indicating the absence of any electrostatic interactions?19 The quenching of the excited-state of ruthenium bipyridyl labelled copolymers by methylviologen has been found to be solvent dependent320 and an expression has been develcped to determine the orientation function in *-isoprene networks. 321 The temperature dependence of the diffusion coefficient of polypropylene oxide has been determined by tagging the polymer with a fluorescent dye and monitoring the fluorescence redistribution after photobleaching. 322 A survey of the luminescence of ninety-eight polymers indicated that in general their emission is due to charge recombination of photoejected electrons from adventitious and the HubbardPeierls Hamiltonian has been applied to the low lying excited states of several novel conjugated polymers.'324 The extent of shearing in
chain.^^^^''^^^
476
Photochemistry
poly(acry1ic acid) sodium salt has been measured by using the fluorescence probe Auramine 0325 while electronic transition energies have been calculated for the singlet and triplet states of several lignin models.326 Other studies of interest include the quenching of singlet oxygen in polymethyl methacrylate,327 chain-segment interactions in polymethyl methacrylate using a nitroxyl spin probe, 328 photochemical transients in poly( e t h y l e n e t e r e n a p h t h a l a t e ) powders,329 electron traps in polystyrene330 and electrical tree initiation in p ~ l y e t h y l e n e . ~ ~ ’
4. Photodegradation and Photooxidation of Polymers Several reviews have appeared covering general as well as specific areas of interest. Rabek332 has produced a very comprehensive text covering all photophysical and photochemical processes in polymer systems while O ~ a w has a ~ produced ~ ~ a review dealing with certain selected thermoplastics. The mechanisms involved in the weathering of polymers have been covered with emphasis on localised failures334 as well as a more specific article on polyolefins and polyvinylchloride. 335 Plastics pollution has been reviewed with emphasis on photodegradable polymers336y337 while other articles have dealt more specifically with photosensitised singlet oxygen formation in rubbers, 338 participation of singlet oxygen in the photooxidation of rubbers339 as well as the role of hydroperoxides 340 zinc oxide, 3 4 1 v u l ~ a n i s a t i o nand ~ ~ ~copolymer systems343 all compiled by the same author. A new approach has been developed toward polymer photooxidation using oxygen uptake344 and a new ultraviolet fluorescent lamp has been tested for the accelerated weathering of polymers. 345 Photooxidation products on the surface of polymers a r e apparently readily extracted by water 346 and durability testing of polymers has been reviewed and various important features highlighted .347 Problems in the measurement of impact resistance of photooxidised polymers have been evaluated348 and a fundamental approach has been considered in reviewing the photooxidation mechanisms of elastomers. 349 Research work on the different classes of polymers will now be considered separately. 4 . 1 Polyolefins The photooxidation mechanisms of polyolefins continues to attract much interest and controversy. A comparison of the photooxidation rates of linear low density polyethylene with low density polyethylene indicates that catalyst levels in the former have little, if
IV: Polymer Photochemistry
477
any, activity.350 In the case of high density polyethylene other workers have found that polymer made by the Zeigler process is much more photostable than that made by the Phillips route.351 This was associated with higher levels of unsaturation in the latter polymers and not catalyst levels. This result was essentially confirmed by an analysis of the photooxidation ratio and extents of crosslinking in a range of polyethylenes. 3 5 2 In this case the interaction between dienes and oxygen is considered to be important in initiation of the photooxidation process and this was found to be most marked in the linear low density material which conflicts with the findings of the above article.350 An analysis of peroxy radicals in post-irradiated polypropylene indicates that many of them are actually trapped in the crystalline region and that, in time, these regions slowly oxidise. 353 This conclusion appears to be consistent with that of Margolin et al.354 who have analysed the decay kinetics of peroxy radicals and found that they could only be interpreted in terms of an uneven distribution of radicals in the polymer. Re-extrusion of polyethylene enhances the rate of photooxidation of the polymer355 while the photochemical chlorination of polypropylene results in the replacement of methyl groups by hydrogen atoms. 356 Blends of polypropylene with photooxidised polypropylene show rheological and mechanical properties which are strongly dependent on the composition.357 In the case of benzophenone photosensitised oxidation of an ethylene-propylene copolymer the ketone acts as the primary initiator whereas in the later stages the ketones sensitise decomposition of the hydroperoxides. 358 Irradiated low density polyethylene doped with anthraquinone derivatives shows evidence for changes in mechanical properties during dark storage which are closely related to recrystallisation. 3 5 9 Other studies of interest include tensile strength changes in polypropylene, 360 photooxidat ion of polyethylene blends, 36 photodegradation of polyethylene mulches, 362 an NMR study on irradiated poly(ethy1ene carbon monoxide copolymer),363 and the quinone photoinitiated crosslinking of polyethylene. 364
’
4.2 Poly(vinylha1ides) Variable wavelength effects on the photooxidation of copolymers of vinyl chloride indicate the formation of two light absorbing products at 270 and 310 nm which are interconvertible.365 Both products are considered to be isomers of*-dichlorotriene and under polychromatic irradiation the photoproduct distribution is dependent
478
Photochemistry
on spectral distribution of the light source. The photodehydrochlorination of polyvinylchloride has been monitored conductimetrically and quantum yields determined 366 and crosslinked regions in the same polymer have been found to be more photostable than uncrosslinked regions. 367 The mechanism of p h o t o d e h y d r o c h l o r i n a t i o n has been confirmed to be free radical in nature368 and plasticisers accelerate the process. 369 The effect of conformation on polyene growth has been studied during the photodegradation of poly(viny1 chloride). 370 F o r isotactic polymer the length of polyene sequences was limited by chain conformation whereas in syndiotactic material no effect of chain conformation was observed.
4.3 Polystyrenes The kinetics of polystyrene photooxidation have been monitored and the ultraviolet absorbing products achieve a photothermal equilibrium. 371 Iron and cobalt acetylacetonates sensitise the photooxidation of high impact polystyrene372 and the rates of photooxidation of blends of poly(viny1 methyl ether) with polystyrene increase with an increase in the former component.373 The incorporation of up to 15% w/w of 2-naphthylmethacrylate to styrene and methylmethacrylate as a comonomer markedly improves their photostability.374 4.4 Polyacrylics Hindered phenolic compounds have been found to have little effect on the sensitised photooxidation of poly(methy1 methacrylate) copolymer with isoprene and styrene in the presence of nitroxyl radicals.3751 A chain mechanism has been proposed for the photooxidation of poly(acry1ic acid) and p ~ l y a c r y l a m i d eand ~ ~ ~the ultraviolet absorption of polymethylmethacrylate has been observed to increase during photooxidation with little change in molecular weight. 377 The moisture resistance and durability of radiation cured oligo(carbonate methacrylates) have been studied378 as have the mechanical properties of poly(methy1 methacrylate) and copolymers with methyl vinyl ketone. 379 The latter acted as photosensitisers. Gamma and light irradiation of poly(methy1 methacrylate) results in damage to the polymer only in defect regions3" while ultrashort pulses of laser light improves ablation to the same polymer. 3 8 1 Dyed polymethylmethacrylate has been suggested as a suitable astinometer for monitoring the dosage of photons and correlation of light stability tests. 382
IV: Polymer Photochemistry
479
4.5 Polyamides The photooxidation rates of nylon polymers have been monitored using Fourier Transform Infra-red spectroscopy. 383 Norrish type-I1 reactions of carbonyl groups were considered to be the most important process. Another group of workers have studied the photooxidations rates of a nylon 6- polypropylene glycol copolymer.384 In this case polyether sequences are the major source of free radical attack resulting in high levels of hydroperoxides. Irradiation of nylon and polyester fibres with an excimer laser resulted in the formation of structural irregularities385 while other workers have directed their interests toward the accelerated weathering of nylon 6 and 6,6 fish nets.386
4.6 Poly(0rganosilanes) The photodegradation of poly 1,4-bis(chloroethylmethylsilyl)benzene involves scission of the silicon-silicon bonds followed by the formation of silicon-carbon unsaturated compounds and hydrosilanes.3877388 Copolymers of several alkyl silanes which contain a high ratio of phenyl, cyclohexyl and isopropyl groups have been found to undergo more rapid photodegradation than those simply containing di-methyl and n-propyl groups389 while polysilanes with ferrocenyl groups were remarkedly photostable. 390 The quantum yields of side group photolysis have been measured by monitoring the formation of gaseous products in silicone rubbers and cross linking reactions occur by the hydrogenation of vinyl side groups.’’’ 4.7 Rubbers and Polyurethanes The effect of crystallinity and backbone chain flexibility has been examined on the photodegradation rates of aromatic polyurethanes. 392 In general the extent of degradation decreases with an increase in both parameters and it is concluded that such physical parameters play an equally important role in controlling polymer photodegradation as the photoreactive aryl carbamate moiety. The ester sequencies in copoly(ether-ester) have been shown to be responsible f o r their photoyellowing phenomenon particularly when exposed to shorter ultraviolet wavelengths.393 Contrary t o much earlier work the photooxidation of poly c&-1,4-butadiene and polychloroprene has been found to be inhibited by the well-known singlet oxygen sensitising dye methylene blue and the effect was synergistic with carotene.394 The photosensitising effects of
P
480
Photochemistry
benzophenone and its derivatives have been studied in ethylenepropene-diene rubbers both free and grafted. 3 9 5 ’ 3 9 6 In the latter case there was enhanced formation of oxidation products and chain scission with respect to crosslinking when compared to that of the former case with blended compounds. A similar study was also carried out on the effect of phenylacetophenone where, in this case, photocrosslinking was the dominant process. Interestingly, the photodegradation of yulcanised isoprene rubber has been closely related to its oxidative degradation under mechanical stress 398 while in the case of cis-1,4-polyisoprene microfragmentation was predominant in photooxidation giving rise to several aldehyde/ketone products. 399 In solution the photooxidation of --I, 4-butadiene rubber results in the formation of high levels of hydroperoxidised gels induced by solvent radicals4’’ and pyrene formation is believed to occur in the photodegradation of butadiene-styrene rubber films A photocolourimetric method has but not in photooxidation.‘O’ been developed to monitor the effect of ultraviolet irradiation on plasticisers in styrene-butadiene rubber402 and indirect evidence has been produced for the existence of quinoid-type products in the photodegradation of aromatic based polyurethane elastomers . 4 0 3
4.8 Natural Polymers The photodegradation of wool for upholstery fabrics in cars has been reviewed ‘ 0 4 and the quantum yield of the photomechanical degradation of silk has been found to increase with an increase in the tensile strength of the yarn.405 The quantum yield also decreased from 365 to 254 nm and may be associated with the screening of light by the amide functional groups. Rewinding agents based on nonionic surfactants and sodium phosphates inhibit the photoyellowing of silk fibres406 and the photodegradation of methyl cellulose results in photoyellowing which is consistent with ketone formation. ‘ 0 7 In the photodegradation of cellulose the kinetics of free radical formation and termination have been found to be dependent on the Chainpolymer sample and different regions with the polymer. ‘08 breaking acceptors based on nitroxyl free radicals were found to effectively inhibit chain scission reactions. The photochemical reactivity of non-phenolic benzyl aryl ether units of lignin have been studied is based ons(-(2,4,6-trimethylphenyl)-3,4-dimethoxyltoluene.409 ’ ‘lo Photoyellowing products based on methylenequinones and their derived products were identified and initiated from a benzylic cleavage in the lignin. The photodegradation of dioxane-
IV: Polymer Photochemistry
48 1
lignininduced by the enzyme ligninase has been found to be very dependent on the activity of the latter4” and carbon dioxide and water are the main products in the photooxidation of lignin with the reaction rate being enhanced by the presence of ferrous ions. 4 12
4.9 Miscellaneous Polymers An in-depth study on urethane and bisphenol-A epoxy acrylate resins indicates that electron beam cured films are more photostable than those cured by ultraviolet irradiation due to the presence of residual photoinitiator in the latter case. 4 1 3 Amine terminated acrylates undergo strong photoyellowing due to the formation of unsaturated carbonyl groups. The surface photooxidation of phenoxy resins involves a reaction of the aliphatic ether portion of the polymer which, during the early stages, is associated with crosslinking.4 1 4 Oxidation of the phenyl groups also occurs as suggested by ESCA and similar reactions were observed in polyetheretherketone. Photooxidation of poly(vinylacetate1 results in the loss of acetate side groups and the formation of polyenes together with a high degree of crosslinking and chain scission.415 In the case of ethylene-vinyl acetate copolymers photooxidation results in the conversion of the ester groups into ketone groups and the rate Azomethenes varies linearly with the vinyl acetate content. 4 1 have been found to inhibit the photooxidation of cellulose triacetate; the effect increasing with increasing conjugation. ‘17 The effects of photooxidation on several polymers have been considered and concluded to be very dependent on manufacturing history418 and a related study on morphological effects has been carried out using NMRfl’ as well as surface resistivity. 420 Using GC-mass spectrometry the photocleavage products of a weathered polycarbonate have been identified and confirmed as arising from a photo-Fries reaction together with that of side-chain oxidation.4 2 1 ’ 422 The wavelength dependence of product formation during the irradiation of a polycarbonate has been established423 and pendant phenol groups have been introduced on polymer chains by a photo-Fries rearrangement./424 The 254 nm irradiation of poly(viny1acetophenone) resembles the photoreactions of substituted polystyrenes.‘259’426 The main photolysis products were carbon monoxide and acetaldehyde formed through Scheme 6 while with light wavelengths ) 3 0 0 nm main chain scission was the dominant process. In copolymers containing l-(4-carbethoxyphenyl)-2-propene-l-one self quenching is concluded not t o be an important process in deactivation of the triplet-state
Photochemistry
482
CH- C H 2 a
Q c=o 1
-<
+
CH3
CH,w
CH3
Scheme 6
1 H
4
or SCl
or S.
$ II -Y=O
$
I
OH
1 II -P-OO*
I
II
+ -P-OOH \ T, ( n . l c ' )
Scheme 7
IV: Polymer Photochemistry
483
of the carbonyl group 427 and the photoreduction of poly(propy1viologens) is unaffected by the presence of poly(viny1 alcohol). 4 2 8 undergoes main In solution poly bis(4-benzoy1phenoxy)phosphazine chain scission due to the presence of peroxy radicals as indicated in Scheme 7.429 The latter are formed by reaction of oxygen with phosphorous macroradicals derived from unreacted P-C1 groups. Laser flash photolysis also confirms the initial production of ketyl radicals as shown in Scheme 7. The photodegradation of !-substituted polyethylenimines, sensitised by benzophenone, has been studied as a function of branching, &-substitution by methoxycarbonylmethyl groups and phenyl groups. 430 The branch formed is significantly more unstable than that of the linear polymer. The photoinduced discolouration of paper is improved by pre-treatment with polyethylene while the surface crazing of epoxy resins on photooxidation is greater for filled than unfilled ones!32 Excimer lasers have been used to modify the surface property of polymer fibres 4339434 and the diffusion of oxygen has been examined in the dye-sensitised photooxidation of butyl vinyl ether-butyl methacrylate methacrylic acid copolymer. 435 Irradiation of polymethylmethacrylate enhances its adhesion to metals436 while the photodegradation of melamine-acrylic coatings is enhanced when coated onto aluminium and subjected to mechanical stress.437 The surface properties of polyamidorinides are markedly influenced by p h o t o o ~ i d a t i o nwhereas ~~~ flame retardants have been found to accelerate the photodiscolouration of many curtain-based fibres. 439 Photosensitive polyimides have been found to be more useful for integrated circuit applications440 and polyimides undergo main chain scission on photolysis. 44 1
5. Photostabilisation Processes Several review articles have appeared on various aspects of polymer photostabilisation. These include metal soap stabilisers for polyvinyl chloride,442 photostabilisers for coatings443’ 444 and polyethylene greenhouses,4 4 5 mechanistic action of hindered piperidine molecules,4469“‘l uses of benzophenone type absorbers,448 resorcinol based absorbers449 and general oxidation inhibitors for polymers. 450’ Articles of a more commercial interest show that hindered piperidine molecules are the most effective systems45 1-455 while the light stability of flame retardant formulations is improved by doping the polymer with titanium dioxide pigment. 456 Hindered piperidine compounds are also effective in filled poly-
Photochemistry
484
ethyleneq5?'and as derivatives of diphenyl acrylic acid on the surface of polypropylene458 whereas other workers have shown that 2-hydroxy-4-n-octoxybenzophenone is more effective in retaining the strength of polypropylene. 459 The mechanistic behaviour of absorbers based on 2-hydroxybenzophenone, 2 - h y d r o x y p h e n y l b e n z o t r i a z o l e and salicylates continues to attract much interest. Salicyloyl (3,5-di-tert-butyl-4-hydroxybenzy1)amine is claimed to be the most effective light stabiliser to date for polyethylene 460 while effective polymer bound stabilisers based on 2-(2-hydroxyphenyl)-2H-benzotriazole have been made for reaction with glycidyl groups. 461 Cerium salicylate has been reported to inhibit the photodegradation of polystyrene462 while 2 - h y d r o x y p h e n y l b e n z o t r i a z o l e s havebeen effectively copolymerised 9464 with methyl m e t h a ~ r y l a t e . ~ ~ ~ A detailed photochemical study sulphonate on sodium 2-(2'-hydroxy-5'-methylphenyl)benzotriazole indicates that their molecule exists in two forms in both solution and polymer substrates. 465 One form exists in a strongly hydrogenbonded form with water, is non-planar and does not contribute to photostabilisation whereas the intramolecular planar form in the excited-state is more effective. Hindered phenolic anti-oxidants have been found to synergise effectively with sulphonated 2-hydroxyphenyl b e n z o t r i a ~ o l e sand ~ ~ ~dibenzoylmethane is claimed to be just as effective as 2 - h y d r o x y - 4 - n - o c t o x y b e n z o p h e n o n e . 467 The photoprotection rule for absorbers has been examined experimentally and found to be dependent on the total energy absorbed by the polymer rather than upon the near surface energy absorption properties. 468 Mixtures of iron and nickel dialkyldithiocarbamates have been found useful for the time-controlled stabilisation of polypropylene. 469 Thus, whilst the latter imparts photostability to the polymer the latter induces photodegradation. Diamagnetic diacetyl-monoxime benzoylhydrazone nickel (11) chelates have been found to effectively inhibit the photooxidation of c>-l,4-polybutadiene through their ability to quench singlet oxygen and trapping free radicals470 while nickel dialkyldithiocarbamates have been found to be effective in inhibiting the photofading of crystal violet lactone colour formers in paper by destroying hydroperoxide groups. 471 The mechanical processing o f polyvinylchloride has been found to markedly influence its subsequent photostability due to the formation of hydroperoxides 472 A radical trap 2-methyl-2-nitrosopropane was
.
I V : Polymer Photochemistry
485
found to be an effective photoanti-oxidant in this respect. Infrared spectroscopy has been used to monitor the changes in organotin mercaptile stabilisers during irradiation in poly(viny1 chloride). 473 The compounds, whilst exhibiting good photoantioxidant behaviour nevertheless underwent considerable yellowing. The photobehaviour of anti-oxidants in polyolefins has been shown to be concentration dependent. 4 7 4 Thus, whilst at low concentrations an anti-oxidant effect is observed at high concentrations ( 0 . 5 % w/w) there is a gradual reinforcing effect due to additive interactions. Transition metal ions, in particular, titanium (IV) and iron (111) have been shown to markedly influence the photobehaviour of butylated hydroxytoluene in polypropylene. 475 Thus, whilst the former photosensitised the decomposition of the stabiliser the latter induced the photocleavage of the tertiary butyl groups. The same group of workers476 have also studied the photostabilising action of phenolic and phosphite anti-oxidants in polyethylene made by the Phillips and Zeigler processes. In the former polymer high levels of unsaturation accelerated the photodecomposition of the additives compared with that of the latter giving rise to antagonistic effects and overall poorer stabilisation efficiency. Hindered piperidine compounds continue to be investigated in some detail as the most effective stabilisers for a variety of polymers. It has been shown that hindered piperidine molecules are oxidised by peroxy radicals under irradiation but more slowly by hydroperoxides. 477 Absorbers protect and synergise with the hindered piperidine s t a b i 1 i ~ e x - while s ~ ~ ~ grafting a hindered piperidine stabiliser through the use of an acryloyl group results in a marked improvement in photostabilisation. 479 Detailed kinetic studies in solution for a variety of tetramethylpiperidine compounds have shown variable activity in terms of hydroperoxide decomposition, excited carbonyl quenching and singlet oxygen scavenging.480 It should be borne in mind however, that all the experiments were carried out in solution and, as such, bear little relation to their mechanistic behaviour in a solid polymer. Other workers have found hindered piperidine compounds to be ineffective in inhibiting the photolysis of c u m e r ~ e ~whilst ~’ they have been found to be effective in acrylicmelamine coatings482 and as esters in a propylene-maleic anhydride copolymer. 483 Diolfunctional ultraviolet stabilisers have been
Photoch em isrry
486 Stilbene ( S , ) 4 stilbene(S,l Stilbene ( 5 , )
+
[Stilbcne; indolefl
___)
stilbcne(T1 1
oT-
indole 4 Istilbene; indole: 1
+Istilbenc
HI*
+
6 oxidation products
.
Stilbene
+ HOi Scheme 8
Stilbcne (So) 4 stilbcne (S,) Stilbenc (T,) lo,+
3
+0
, N stilbcne (So) +'02
indole 4 oxidation
where
+stilbenc (TI 1 products
So = ground state S, T,
= =
excited singlet state excited triplet
state Scheme 9
IV: Polymer Photochemistry
487
found to be effective in polyurethanes484 while mono and diborates of diphenylolpropane are effective in poly( vinyl chloride) 4 8 5 and paper from the pulp of pine and eucalyptus is more resistant to photoyellowing than that from birch.486 Other effective light stabiliser systems include s p i r o i n d o l i n o n a p h t h o d a z i n e s as photochromic stabilisers for all polymers,4 8 7 zinc and calcium salts of N-benzoyl and &-benzene-sulphonyl-6-amidocaprates for poly (vinyl chlorides)488 phenylstyrenes and phenolamine for butadienestyrene rubber,489 general anti-oxidants f o r poly( 1,1,2-trichlorobutadiene) and 2,2-bis( 4 - h y d r o x y - 3 - t e r t - b u t y l p h e n y l ) propane for polystyrene.491
6. Dyes and Pigments The photofading mechanisms of dyes in both solution and polymer media have been reviewed492-494 as well as the bleaching of textile fibres and the effects of ultraviolet radiation.495 Many objectives to date appear to be efforts toward improving dye lightfastness as well as the photostability of the polymer fibre. Basic triphenylmethane dyes have long been known to be much less photostable on wool than on acrylics but recently it has been found that comparable lightfastness with the latter may be achieved by treating The photostability of quinophthalthe wool with sulphonic acid. one in cellulose triacetate is improved through the use of nickel complexes and the mechanism associated with singlet oxygen quenching.497 It is surprising that the author does not consider the ability of these nickel complexes to decompose hydroperoxides which would appear to be more valid in a solid polymer. Several stilbene based fluorescent whitening agents have been found to sensitise the formation of singlet oxygen in wool and then attack the indole residues by one o r both Schemes 8 and 9.498 In the first mechanism the excited-state of the stilbene interacts primarily with the indole to give radicals that will subsequently react with oxygen whereas in the second scheme singlet oxygen is generated directly by the quenching of the photoexcited triplet state of the stilbene. The same workers'499 have found that thiourea dioxide enhances the whiteness of wool and its lightfastness properties. The photofading of crystal violet is inhibited by the presence of cyclodextrins due to the formation of an inclusion complex'500 whereas the photfading o f 4-(phenylazo)-l-naphthol in sodium lauryl sulphateethoxylated octadecanol is reduced by the addition o f l - o ~ t a n o l . ~ ~ ' Some fluorescent brightening agents have been found to impair the
"'
Photochemistry
488
photofading of disperse dyes in polyester fibre502 as have nickel (11) complexes of bisdithioq-diketone for solvent dyes in cellulose triacetate film.503 The photoexcited singlet state of aminoanthraquinones is concluded to be inactive in their photofading504 and the excited-state lifetimes of 2-piperidinoanthraquinone have been found to be influenced by the presence of oxygen in blocks of various polymers. 505 The incorporation of m-nitrophenol and m-nitroaniline to disperse dyes in solution media enhances their p h o t ~ s t a b i l i t ywhile ~ ~ ~ singlet oxygen has been concluded to be responsible for the photofading of polymethine dyes507 and erythrosine.5 08 The photochemical stability of nylon yarns has been found to be influenced by the nature of the acid dye as well as the denier of the fibre.509 In polyester fibres the photostability of azo dyes has been linked to the supramolecular structure of the polymer and its influence on cis-trans i s o m e r i ~ a t i o n . ~ ’In ~ the case of polyester-cotton fabrics thepresence o f indigo dyes reduces their tensile strength on irradiation5’ while reactive dyes have been found to protect silk512 and the fouling of naturally occurring dyes has been examined for museum textile applications.5 1 Reactive dyes have also been observed to photoprotect cotton but in this case there was a correlation between dye lightfastness and the degree of photopr~tection.~’~ The partial least - squares method has been applied to the modelling of dye light fastness and these authors have found that 13C-NMR could be used to predict dye lightfastneSS The photoreduction of azomethine dyes have been studied in the presence of benzophenone as a sensitiser.516 The dyes apparently form a charge-transfer complex with the benzophenone ketyl radicals. Azomethine dyes which were anilides of acylacetic acids were significantly less reactive than those dyes based on pyrazolones. Indanthrene dyes possessing polycondensed aromatic rings have been observed to form endoperoxides on photooxidation due to singlet oxygen formation.5 1 7
’
The zinc oxide, titanium dioxide and cadmium sulphide photocatalysed oxidation of an ethylene-propylene elastomer has been studied in some depth.518 With light above 300 nm the presence of the pigments induces the formation af high concentrations of ketonic and lactonic acid groups without reversion to the usual acidic ester and vinyl groups. It is suggested that many of the
IV: Polymer Photochemistry
489
ketonic photoproducts are absorbed on the pigment surface. Once again the photoactivity of titanium dioxide pigments have been predicted b y studying the photosensitised oxidation of 2-propanol to a ~ e t o n e . ~ ” Finally, the photofading of alizarin lakes520 and photocatalytic oxidation o f cationic surfactants by titanium dioxide pigments 52 have been examined.
’
490
Photochemistry
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2,
151, 151,
so,
w,
Photochemistry
502 462)
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I V: Polymer Photochemistry
503
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s.
-
Author Index
In this index the numbers in parentheses are the Part and, where applicable, Chapter numbers of the citation and are followed by the reference number or numbers of the relevant citations within that Chapter, e . g . , (3.2) 14 Z Part I11 Chapter 2 ref 14
Aari, H. (3.4) 84 Aaviksoo, J. (1) 270 Abdel-Bany, E.M. (4) 394, 470 Abdel-Latif, F.F. (3.7) 144 Abdel-Mogib, M. (3.2) 51; (3.4) 156 Abdel-Razik, E.A. ( 4 ) 394, 470 Abdou, W.M. (3.2) 50 Abdul-Ghani , A. J. (3.4) 18 Abe, K. (3.2) 136; (3.4) 106; (4) 247 Abe, M. (3.2) 60; (3.7) 150; (4) 501 Abelt, C.J. (3.7) 9 Abou-A1 Einin, S. (1) 321 Abou-Elzahab, M.M. (3.2) 51; (3.4) 156 Abou-Gamra, Z. (2.1) 24 Abrahamson, H.B. (2.2) 38, 39 Abrams, S.R. (1) 160 Absalon, M.J. (3.3) 15 Abuin, E. ( 4 ) 67, 219 Abu-Mustafa, E.A. (3.2) 51; (3.4) 156 Abu-Orabi, S.T. (2.3) 54 Abu-Zeid, E.M. ( 4 ) 401 Acholla, F.V. (2.1) 49 ACS, A. (1) 455, 456 Adachi, G. (2.1) 166, 170, 181; (4) 237, 251 Adam, G. (3.7) 133 Adam, W. (1) 363; (3.5) 71, 72; (3.7) 15-17, 20, 23, 26 Adamiak, R.W. (3.6) 142 Adam, R.D. (2.2) 103 Adamson, A.W. (2.1) 109
Adebayo, A.T.O.M. (3.7) 190 Adeniyi, J.B. (4) 472 Ades, C. (2.3) 62 Adzuma, S. ( 4 ) 214 Aeling, E.O. (3.3) 82; (3.4) 184 Afonichev, D.D. (2.1) 198 Agaev, U.Kh. (4) 165 Agarwal, H.K. (4) 323 Agmon, N. (1) 128 Agosta, W.C. (3.2) 63 Agostini, G. (1) 379 Ahmad, Y. (3.6) 49 Aido, T. (4) 69 Aime, S. (2.2) 99 Aizawa, K. (1) 530 Ajayaghosh, A. (3.6) 75 Ajima, A. (1) 467 Akabori, S. (3.6) 106 Akagi, M. (3.4) 152 Akasaka, T. (3.5) 73, 80, 117, 121-123 Akasheh, T.S. (2.1) 76 Akhmedova, Kh.R. (4) 62, 99, 101 Akhmedzade, D.A. (4) 460 Aki, L.Y. (3.3) 15 Akiya, T. (3.3) 18 Akiyama, K. (3.7) 148 Akiyama, S. ( 4 ) 245 Akutagawa, K. (3.6) 200 Albertson, A.C. (4) 444 Albini, A. (3.4) 149, 167, 168, 180; (3.5) 88; (3.6) 62, 64 Aldhen, I . S . (3.4) 113 Aleinikova, V.N. (2.2) 124 Al-Ekabi, H. (3.3) 3; (3.4) 166 Aleksandrova, T.A. (4) 505
316 Alfimov, M . V . (1) 236, 245, 350; (3.3) 9 , 10 Al-Hassan, K.A. (1) 186 Ali, H. (1) 464 Aliev, M.Kh. (4) 460 Aliev, S.M. (4) 491 Alif, A. (3.4) 72 Alina, S. (4) 402 Al-Jalal, N. (3.4) 41; (3.6) 117 Allakhverdiev, I.K. (4) 491 Allen, A.D. (3.1) 12; (3.7) 59 Allen, M.T. (1) 334 Allen, N.S. (4) 125-127, 351, 413, 471, 475, 476, 492-494 Allen, S.D. (2.3) 64 Allen, T. (1) 92; (4) 80 Al-Malaika, S. (4) 469, 472 Aloisi, G.G. (1) 189; (3.3) 11, 59; (4) 50 Alok, A.M. (1) 347 Al'perovich, M.A. (4) 516 Alpha, B. (2.1) 182, 184 Al-Takritz, E.T.B. (4) 292 Altheer, C. (2.1) 190 Alvarez, C. (2.2) 41 Alvaro, M. (3.1) 45 Aly, M.M. (3.7) 144 Amadelli, R. (2.2) 99 Amarasekara, A.S. (3.7) 73 Amari, K. (3.7) 176 Amashta, I . A . (1) 219 Amatore, C. ( 3 . 4 ) 80 Ameloot, M. (1) 52, 333 Amer, M.F. (4) 401
Photochemistry
506
Amirav, A. (1) 26 Ammon, H.L. (3.2) 123, 125; (3.4) 52; (3.6) 119 Amos, A.T. (1) 129 Amrehn, J. (1) 475 Anarieva, T.D. (4) 313 Anderson, A.B. (2.2) 64; (3.5) 61 Anderson, H.C. (4) 200 Anderson, J.E. (2.3) 46 Andersson, K. (3.3) 12; (3.4) 146, 147 Ando, M. (4) 162 Ando, R. (1) 330 Ando, T. (4) 116, 117 Ando, W. (2.3) 15, 17, 42, 47, 49; (3.5) 73, 121-123; (3.6) 178, 195, 206; (3.7) 36, 40, 41, 64, 126 Andoh, A. (3.2) 87; (3.7) 172 Andrady, A.L. (4) 468 Andre, J.-J. (1) 272 Andre, J.C. (1) 36 Andreeva, I.M. (3.4) 128 Andreeva, T.A. (3.7) 102 Andrei, C. (4) 446 Andrejewski, D. (2.2) 52 Andreo, C.S. (1) 501 Andreoni, A. (1) 155 Andres, M. (2.1) 209, 210 Andrews, M.P. (2.2) 159 Andriichik, E.G. (4) 378 Andrzejewska, E. (4) 48 Anfinrud, P.A. (1) 261, 262 Angela, T.A. (3.2) 34 Angelici, R.J. (2.2) 91 Anson, S.M. (2.1) 173 Anthony, D. (2.3) 75 Antipin, M.Yu. (2.3) 26 Anufrieva, E.V. (4) 307 Aoe, K . (3.2) 119; (3.6) 86 Aoki, T. (2.2) 123 Aono, S. (3.5) 31 Aoshima, K. (2.1) 86 Aoyama, H. (3.6) 89 Aoyama, Y. (2.1) 139 Apicella, A. (4) 120 Arad-Yellin, R. (3.3) 66 Arai, H. (3.1) 14 Arai, K. (4) 88 Arai, S. (2.3) 11; (3.4) 115 Arai, T. (1) 412; (4) 59 Araki, T. (3.2) 128; (3.6) 173; (4) 248 Arata, Y. (3.6) 89 Arbeloa, I.L. (1) 219
Arbuzov, B.A. (3.6) 204 Arct, J. (4) 425, 426 Arguello, G.A. (1) 464 Arita, H. (4) 75 Ariyama, K. (3.2) 131 Arjunan, P. (3.2) 67 Armesto, D. (3.2) 70; (3.3) 21, 22, 76; (3.6) 42-44; (3.7) 160 Arnand, R. (4) 416 Arnason, J.T. (1) 454 Arnaud, R. (4) 518 Arnaut, L.G. (1) 37 Arneberg, U. (4) 486 Arnold, D.R. (3.3) 14, 86; (3.4) 181, 182 Arnold, S. (1) 259 Arnoud, N. (1) 322 Arora, K.S. (4) 260 Arora, S.K. (3.7) 89 Artz, P.G. (1) 47 Asai, K . (3.6) 29 Asakawa, H. (4) 26 Asali, K.J. (2.2) 36 Asano, M. (1) 437 Asano, T. (4) 154 Asano, Y. (2.1) 140 Asao, K. (4) 503, 517 Asher, S.A. (1) 488 Ashikaga, K. (3.6) 93; (4) 92, 270 Ashitkova, N.S. (4) 274 Ashok, K . (3.2) 112 Askadskii, A.A. (4) 254 Askarov, M.A. (4) 61, 62 Aslanov, L.A. (2.1) 128 Aslanyan, K.V. (4) 490 Astruc, D. (2.2) 84 Atherton, S.J. (1) 471, 516; (2.1) 148, 151 Atkinson, R. (3.5) 86 Atta-ur-Rahman, (3.6) 49 Audebert, R. (4) 246 Audenaert, F. (3.2) 33 Auerbach, R.A. (2.1) 107 Auffret, J. (2.2) 149 Augustyniak, W. (3.4) 99 Autrey, T. (3.7) 105 Avaria, L. (4) 67 Avarmaa, R. (2.1) 128, 179 Avdeeva, V.I. (1) 214 Avetisyan, A.A. (3.2) 25 Avetisyan, T.V. (3.2) 25 Avila, L. (2.1) 188 Ayala, N.P. (2.1) 90 Aymonino, P.J. (2.1) 59 Ayscough, P.B. (3.7) 29 Ayyangar, N.R. (3.2) 56 Azumi, T. (1) 186, 376, 378
Babbitt, R.J. (1) 139 Babin, J.E. (2.2) 103 Babneva, S.G. (4) 460 Babu, B.S. (4) 98 Baceirdo, A. (3.6) 203 Baciocchi, E. (3.5) 63 Badamkhanov, G.O. (4) 63 Badovskaya, L.A. (3.6) 50, 51 Badr, M.Z.A. (3.7) 144 Bassler, H. (1) 354 Baeza, J. (4) 411 Bagchi, B. (1) 21, 27, 29, 226 Bagdasar'yan, E.I. (4) 490 Bagdasar'yan, Kh.S. (3.1) 5 Bagdasar'yan, R.V. (4) 490 Baglioni, P. (1) 318 Bahnemann, D.W. (2.1) 112, 113; (3.5) 120 Bahners, T. (4) 385, 433, 434 Bai, F. (1) 281 Baik, W. (3.7) 182 Bailie, C. (4) 520 Bain, A.J. (3.3) 36 Baines, K.M. (2.3) 33 Bakac, A. (2.1) 194; (2.2) 111 Bakeev, K.N. (1) 297; (4) 262, 319 Baker, A.D. (2.1) 79 Baker, M.V. (2.2) 92 Bakobza, L. (4) 208 Balard, H. (3.5) 67 Balashev, K.P. (2.1) 153-157 Balch, A.L. (2.1) 152; (2.2) 134, 135 Baldenius, K.U. (2.1) 55 Baldovi, V. (3.1) 45 Baldwin, S. (2.2) 64 Ballardini, R. (2.1) 74, 89 Balli, H. (3.7) 103 Balzani, V. (2.1) 74, 77, 89, 144, 182, 183 Bambal, R. (3.7) 30 Bamji, S.S. (4) 331 Ban, Y. (3.4) 151 Banciu, A. (3.7) 62 Banciu, M. (3.7) 62 Bandermann, F. (4) 97 Bandopadhyay, A.R. (4) 183 Bandopadhyay, J. (1) 393 Banduin, G. (4) 171 Banerjee, M.K. (4) 445 Banert, K. (3.7) 78, 79
Author Index
Bansal, W.R. (3.4) 91; (3.5) 36 Baracchi, A. (3.3) 64 Barachevskii, V . A . (3.2) 145; (3.4) 33 Baraldi, I . (1) 243 Baranetskaya, N . K . (2.2) 51 Baranowska, I . (3.4) 58 Barashkov, N . N . (4) 185 Barbara, P.F. (1) 163, 208, 227 Barbe, J . M . (2.3) 46 Barboriak, K.D. (3.3) 6 Barclay, L.R.C. (3.5) 70 Bard, A . J . (2.1) 207 Barigelletti, F. (1) 218; (2.1) 77; (4) 65 Barker, P. (4) 21 Barlas, H. (3.4) 93, 94; (3.6) 134 Barnickel, B. (3.4) 86 Baronovskii, V . I . (2.1) 117 Baros, F. (1) 36 Barqawi, K . R . (2.1) 76 Barri, E. (4) 515 Barriola, A.M. (2.3) 1 Barsegova, M.N. (2.2) 51 Barthou, C . (1) 272 Bartocci, G . (1) 242, 243; (3.3) 11 Bartolus, P. (1) 244; (4) 429 Barton, D.H.R. (3.7) 109, 111-114, 116, 117 Barton, J . K . (2.1) 66 Bartoszek, R. (4) 173 Bartoszewicz, J . (3.6) 142 Barzoukas, M. (3.4) 80 Basche, T. (1) 445 Bashi, N . O . T . (3.4) 18 Baskin, K.A. (3.5) 70 Bassi, L.G. (4) 50 Basson, S.S. (2.2) 36 Basu, A . (2.2) 156 Basu, S. (1) 179 Bates, R.B. (3.2) 1; (3.4) 134; (3.6) 28 Battersby, A.R. (3.6) 25 Baudry, D. (2.2) 60 Bauer, D.R. (4) 216, 482 Baum, G. (3.6) 66 Baumann, F. (1) 479 Baumann, W. (1) 115, 166, 171, 176, 193 Baumgartner, M.T. (3.4) 79; (3.7) 185 Baumgartner, R. (1) 531 Baysal, B. (4) 104 Bazhin, N.M. (1) 420;
507
(3.7) 82 Bazhutin, Yu.V. (2.1) 46 Beach, D.B. (2.3) 23; (3.6) 181 Beaman, R . A . (2.3) 60 Beanland, J. (3.1) 33 Beaumont, P . C . (1) 516; (2.1) 76 Beck, M.T. (2.1) 40 Becker, E. (1) 267 Becker, €I.-D. (1) 247, 249; (3.3) 12; (3.4) 146, 147 Becker, R . S . (1) 429, 438; (4) 505 Beckwith, A.L.J. (3.7) 201 Beentjes, P . C . J . (2.2) 90 Begum, T. (3.6) 49 Behrens, U. (2.2) 89 Bekturov, E.A. (4) 250, 268 Belayev, V.L. (4) 488 Bel'gibaeva, Z . K . (4) 250, 268 Belichenko, A . S . (4) 377 Bellobono, I.R. (4) 60 Bellstedt, K. (4) 105 Belmore, K.A. (2.2) 29 Belomoina, N.M. (4) 138 Belotti, D. (3.1) 50, 51; (3.6) 85 Belousov, V.M. (2.1) 12; (3.5) 75 Belser, P. (2.1) 77 Belton, P.S. (2.1) 173 Beltrame, P . L . (4) 510 Belyaev, A.B. (3.2) 132 Benezuitskii, G.K. (4) 81 Benoist d'Azy, 0. (1) 367 Bensasson, R . (1) 433, 446, 459 Bentrude, W.G. (3.6) 200 Bentsen, J . G . (2.2) 98 Bera, S.C. (1) 393 BCrces, T. (1) 132 Berci Filho, P. (1) 97 Berendsen, N . (3.3) 32 Berezin, B.D. (3.5) 57, 58 Bergelson, L.D. (1) 130 Berger, R.M. (2.1) 160 Bergman, R.G. (2.2) 42 Berkovic, G. (1) 118 Bernat, J . (3.4) 135, 136; (3.7) 170, 171 Berns, D.S. (1) 275 Berthod, A . (1) 294 Bertolotti, S . G . (1) 320 Bertran, J. (3.5) 41 Bertrand, G. (3.6) 203 Best, L . (1) 332
Beswick, R.B. (1) 439 Beugelmans, R. (3.7) 187, 188, 193, 195 Bezdadea, M. (4) 79, 374 Bhakuni, D.S. (3.5) 111 Bhardwaj, C. (2.1) 92 Bhardwaj, R . C . (2.1) 92 Bhat, A. (1) 39 Bhattacharjee, G. (3.7) 61 Bhattacharya, J . (1) 393 Bhattacharya, P . K . (1) 373 Bhattacharyya, K. (1) 111, 430 Bhattacharyya, P. (3.5) 115 Bhushan, K. (1) 223 Bianchi, A . S . (4) 512 Bianchini, C . (2.1) 137; (2.2) 128 Biczok, L. (1) 132 Bigger, S.W. (1) 146; (4) 344, 465 Biggin, 1.s. (4) 369 Bilba, N . (4) 79 Billing, R. (2.1) 3 Billups, W.E. (2.2) 137 Bilmes, G.M. (1) 257 Binana-Limbele, W. (4) 243 Bini, R. (1) 144 Binkert, T. (1) 70 Birch, D.J.S. (1) 50, 51 Birkofer, L. (2.3) 18 Birks, J.W. (1) 453 Birmachu, W. (1) 83, 84 Bisagni, E. (1) 520 Bischof, €I. (1) 115 Bisht, P.B. (1) 168 Bismuto, E. (1) 494 Bitit, N . (1) 113 Bittl, R . (1) 361 Blacker, A.J. (3.5) 35 Blades, M.W. (1) 57 Blaha, J.P. (2.2) 83 Blakely, R . L . (2.1) 68 Blanchard, G . J . (1) 203 Blanco, C . C . (1) 48, 104 Blankenship, R.E. (1) 537 Blanzat, B. (1) 272 Blasse, G. (2.1) 174, 185, 200 Blatt, E. (1) 197, 305-307, 343, 511; (4) 278 Blau, W. (1) 71, 515 Blednova, Q.V. (4) 143 Bleier, H. (1) 286 Blinov, 1.1. (2.1) 155-157 Blok, P . M . L . (2.1) 70
Photochemistry
508
Blonski, S. ( 4 ) 290 Bloomgarden, D.C. ( 1 ) 442 Blough, N.V. ( 1 ) 181 Blount, J.R. ( 3 . 4 ) 25 Blumen, A. ( 1 ) 20 Bobbitt, K.L. ( 2 . 3 ) 1 9 ; ( 3 . 6 ) 193
Boboev, T.B. ( 4 ) 405 Bochu, C. ( 3 . 2 ) 7 1 , 7 2 ; ( 3 . 6 ) 35
Boenisch, J. ( 4 ) 368 Boens, N. ( 1 ) 5 2 , 5 3 , 301 Bottcher, H. ( 1 ) 344; ( 4 ) 508
Bogdanov, V.S. ( 3 . 2 ) 26 Bohm, R. ( 1 ) 32 Bohorquez, M. ( 1 ) 320, 327, 331
Bois-Choussy, M. ( 3 . 7 ) 1 8 7 , 193, 195
Bojarski, J. ( 3 . 2 ) 9 1 ; ( 3 . 6 ) 170
Bokobza, L. ( 4 ) 280, 286, 287
Boldyreva, E.V. ( 2 . 1 ) 116 Boledovicovo, J. ( 1 ) 315 Bol'shakov, G.F. ( 4 ) 356 Bolte, M. ( 2 . 1 ) 3 5 ; ( A ) 33
Bolton, J.R. ( 1 ) 328 Bondell, G.M.A. ( 3 . 1 ) 1 1 Bondevska, H. ( 4 ) 374 Bong, P.H. ( 1 ) 145 Bonneau, R. ( 3 . 4 ) 1 4 0 , 141
Bonneviot, L. ( 2 . 2 ) 141 Bonterin, B. ( 4 ) 1 6 1 , 171 Boothe, R. ( 3 . 7 ) 25 Born, L. ( 3 . 2 ) 50 Borowiak-Resterna, A. ( 4 ) 448
Borst, H.-U. (1) 415 Borst, W.L. ( 1 ) 264 Bortolus, P. ( 1 ) 255; ( 4 ) 6 5 , 353
Bossmann, A. ( 4 ) 385 Bott, D.C. ( 4 ) 223 Bottiroli, G. ( 1 ) 466 Bottom, R.A. ( 4 ) 21 Bottorff, K.J. ( 2 . 3 ) 1 6 ; ( 3 . 2 ) 8 1 ; ( 3 . 6 ) 196
Bouas-Laurent, H. ( 1 ) 1 1 3 ; ( 4 ) 409, 410
Boudjouk, P. ( 3 . 6 ) 190 Boule, P. ( 3 . 4 ) 7 2 Bourdelande, J.L. ( 3 . 7 ) 5 8 ; ( 4 ) 221
Bourkba, A. ( 1 ) 377 Bourson, J. ( 2 . 3 ) 61 Boussand, J. ( 4 ) 518 Boussquet, J.A. ( 4 ) 349, 395, 396, 397
Bouwstra, J. ( 1 ) 313 Bovey, A.F. ( 4 ) 363 Bowe, M.D. ( 4 ) 84 Bowley, H.J. ( 4 ) 369 Bowman, W.R. ( 3 . 7 ) 190 Boyd, D.C. ( 2 . 2 ) 113 Boyer, J.H. ( 3 . 6 ) 8 1 Brackemann, H. ( 4 ) 7 1 Bradley, D.C. ( 4 ) 223, 318
Brauchle, C. ( 1 ) 1 5 , 173, 445; ( 3 . 7 ) 154
Braitbart, 0.. ( 1 ) 9 1 Braiia, M.F. ( 1 ) 100 Brand, J.R. ( 4 ) 519 Brandas, E.J. ( 1 ) 40 Braron, B. ( 4 ) 381 Braslavsky, S.E. ( 1 ) 44 Bratschkov, Ch. ( 4 ) 374 Brauer, H.-D. ( 1 ) 449, 451, 455, 456; ( 3 . 5 ) 51 Brault, D. ( 1 ) 433 Brauman, J.I. ( 2 . 1 ) 52 Braun, C.L. ( 1 ) 81 Braun, D. ( 2 . 1 ) 6 5 ; ( 4 ) 374 Braverman, S . ( 3 . 7 ) 143 Brazdil, J.F. ( 3 . 5 ) 61 Brearley, A.M. ( 1 ) 185 Bredereck, K. ( 1 ) 415 Brefman, 0 . ( 4 ) 226 Bren, V.A. ( 3 . 6 ) 4 0 , 41 Brennan, P.J. ( 4 ) 345 Breslin, D.T. ( 3 . 4 ) 157 Bridon, D. ( 3 . 7 ) 1 0 9 , 114 Bridoux, M. ( 1 ) 377 Bright, F.V. ( 1 ) 8 Brinke, U.H. ( 3 . 7 ) 68 Brisimatzakis, A.C. ( 3 . 2 ) 95 Brittain, H.G. ( 1 ) 1 1 ; ( 2 . 1 ) 1 7 2 ; ( 2 . 2 ) 158 Brittinger, C. ( 1 ) 166 Brivio, G.P. ( 4 ) 224 Brnicevic, N. ( 2 . 1 ) 26 Brocklehurst, B. (1) 8 8 , 89 Broka, C.A. ( 3 . 2 ) 96 Brook, A.G. ( 2 . 3 ) 3 3 , 3 4 ; ( 3 . 6 ) 192 Brooke, G.M. ( 3 . 2 ) 14 Brosig, S. ( 1 ) 415 Broult, D. ( 1 ) 327 Brouty, C. ( 4 ) 45 Brown, E.S. ( 3 . 7 ) 39 Brown, G.R. ( 1 ) 235 Brown, R.D. ( 1 ) 502 Brown, S.H. ( 3 . 5 ) 60 Brown, T.L. ( 2 . 2 ) 46 Brubaker, G.R. ( 2 . 1 ) 1 Bruce, D.W. ( 2 . 2 ) 147 Brucker, G.A. ( 1 ) 149
Brune, D.C. ( 1 ) 537 Brune, H.A. ( 2 . 2 ) 1 5 1 , 152
Bruno, J.W. ( 2 . 2 ) 158 Brunschwig, B.S. ( 1 ) 30 Brusilovsky, D. ( 1 ) 285 Bryan, S.A. ( 2 . 1 ) 150 Bryukhanov, V.V. ( 3 . 5 ) 52 Buback, M. ( 4 ) 7 1 , 103 Bubnov, N.N. ( 2 . 2 ) 31 Buchardt, 0 . ( 3 . 6 ) 8 0 Buchberger, E.M. ( 1 ) 137 Bucher, S.E. ( 1 ) 106 Buchhammer, H. ( 4 ) 508 Buck, H.M. ( 1 ) 232 Buckland, S.J. ( 3 . 5 ) 125 Budde, F. ( 2 . 1 ) 75 Buenzli, J.C.G. ( 2 . 1 ) 175 Bukivskaya, G.A. ( 2 . 1 ) 178
Bulavin, A.V. ( 4 ) 94 Bulgakov, R.G. ( 2 . 2 ) 10 Bulinski, A.T. ( 4 ) 331 Bulkin, B.J. ( 4 ) 383 Bullock, W.H. ( 3 . 3 ) 1 6 ; ( 3 . 6 ) 149
Buloichik, Zh.1. ( 4 ) 175 Bulska, H. ( 1 ) 4 2 , 199 Bunce, N.J. ( 3 . 4 ) 7 0 , 9 8 , 169
Buntinx, G. ( 1 ) 377 Buono-Core , G.E. ( 2 . 2 ) 153, 154; ( 3 . 2 ) 3 7 ; ( 3 . 4 ) 47 Burbaum, B.W. ( 3 . 2 ) 2 Burditt, N.A. ( 4 ) 456 Buresova, M. ( 4 ) 311 Burgess, L.W. ( 1 ) 62 Burk, M.J. ( 2 . 2 ) 127 Burke, L.D. ( 3 . 3 ) 2 4 , 2 5 ; ( 3 . 6 ) 45 Burke, S.D. ( 3 . 7 ) 212 Burkhard, 0 . ( 1 ) 31 Burkhardt, E.R. ( 2 . 2 ) 42 Burkhart, R.D. ( 4 ) 299, 309 Burlakov, V.M. ( 4 ) 326 Burnett, M.N. ( 3 . 7 ) 25 Burrell, G.J. ( 1 ) 349 Burrows, H.D. ( 2 . 1 ) 189 Burrows, J.A.J. ( 4 ) 299 Buscemi, S . ( 3 . 4 ) 21 Bushby, R.J. ( 3 . 7 ) 29 Butera, R.J. ( 4 ) 169 Butler, R.J. ( 4 ) 173 Butrimovich, O.V. ( 3 . 5 ) 4 3 ; ( 4 ) 507 Buttafava, A. ( 4 ) 353 Bykova, I.N. ( 4 ) 502 Byrne, H. ( 1 ) 7 1 Byteva, I.M. ( 1 ) 4 5 0 ; ( 3 . 5 ) 48
Author Index
Cabrera, I. ( 3 . 6 ) 2 0 ; ( 4 ) 249
Cadona, L. ( 4 ) 50 Caetano, C.A. ( 1 ) 422 Cagne, M.R. ( 2 . 2 ) 97 Cai, F.X. ( 2 . 2 ) 141 Cai, S . ( 2 . 2 ) 62 Caigui, J. ( 1 ) 345 Caldwell, C. ( 3 . 7 ) 65 Callomon, J.H. ( 1 ) 78 Calvin, M. ( 2 . 1 ) 143 Camacho, J.J. ( 1 ) 100 Cameron, B.A. ( 4 ) 496 Caminade, A.M. ( 2 . 3 ) 62 Campagna, S. ( 2 . 2 ) 145 Campbell, A.L. ( 3 . 6 ) 26 Campen, A.K. ( 2 . 1 ) 55 Carnpion, A. ( 2 . 1 ) 207 Camyshan, S.V. ( 1 ) 420 Canceres, P. ( 4 ) 302, 303 Cannon, J.R. ( 3 . 4 ) 30 Cano-Yelo, H. ( 2 . 1 ) 87 Cantos, A. ( 3 . 4 ) 6 5 , 66 Cao, J.R. ( 2 . 3 ) 73 Cao, W. ( 4 ) 9 6 , 108 Cao, Y. ( 3 . 5 ) 2 9 , 7 8 , 7 9 Capocci, G. ( 4 ) 455 Capponi, M. ( 3 . 5 ) 26 Carassiti, V. ( 2 . 2 ) 99 Cardona, R. ( 2 . 1 ) 45 Carless, H.A.J. ( 3 . 1 ) 3 3 ; ( 3 . 2 ) 52
Carlini, C. ( 4 ) 2 7 , 65 Carlson, C.W. ( 3 . 6 ) 177 Carmichael, I. ( 1 ) 17 Caronna, T. ( 3 . 4 ) 21 Carpignano, R. ( 4 ) 315 Carr, C.M. ( 4 ) 466 Carre, C. ( 1 ) 432 Carroll, P.J. ( 3 . 6 ) 161 Carson, P.A. ( 3 . 3 ) 29 Carter, S.P. ( 3 . 7 ) 60 Carter, T.P. ( 1 ) 173 Carter, W.P.L. ( 3 . 5 ) 86 Cartwright, P.S. ( 2 . 1 ) 70 Casamayor, P.M. ( 1 ) 371 Casarotto, M.G. ( 3 . 5 ) 69 Casey, M. ( 3 . 7 ) 35 Castel, A. ( 2 . 3 ) 4 8 ; ( 3 . 6 ) 198
Castel, N. ( 1 ) 413 Castellan, A. ( 1 ) 1 1 3 ; ( 4 ) 4 0 9 , 410
Castellani, M.P. ( 2 . 2 ) 28 Castellano, J.M. ( 1 ) 100 Castello, A . ( 3 . 4 ) 66 Castellucci, E. ( 1 ) 144 Castillo, F. ( 4 ) 366, 367 Castle, R.N. ( 3 . 4 ) 1 3 7 , 1 3 8 ; ( 3 . 6 ) 147, 148
Castner, E.W. ( 1 ) 2 7 , 29 Catalani, L.H. ( 1 ) 383
509
Catalina, F. ( 4 ) 125-127, 233, 493, 494 Cater, R. ( 3 . 4 ) 70 Caulton, K.G. ( 2 . 1 ) 53 Cavazza, M. ( 3 . 2 ) 24 Cavicchio, G. ( 3 . 3 ) 59 Sebe, P. ( 4 ) 328 Cekovic, Z. ( 3 . 6 ) 138 Celewicz, L. ( 3 . 2 ) 8 3 ; ( 3 . 6 ) 112 Celli, F.G. ( 2 . 2 ) 7 0 , 71 Cerfontain, H. ( 3 . 1 ) 53 Cerny, M. ( 3 . 2 ) 118 Cervantes, H. ( 3 . 2 ) 36 Cha, Y.S. ( 4 ) 131 Chabal, Y.J. ( 2 . 2 ) 7 2 Chac, M.H. ( 4 ) 439 Chacon, J.N. ( 1 ) 461 Chae, K.H. ( 3 . 5 ) 44 Chae, W.K. ( 3 . 7 ) 2 Chaiko, A.K. ( 4 ) 36 Chak, B. ( 3 . 4 ) 171 Chambers, R.D. ( 3 . 7 ) 38 Chan, K.C. ( 4 ) 264 Chan, L. ( 2 . 2 ) 21 Chan, M.K. ( 2 . 2 ) 113 Chan, S.C. ( 4 ) 166 Chan, T.H. ( 2 . 3 ) 2 8 ; ( 3 . 6 ) 179 Chan, Y. ( 3 . 5 ) 82 Chandar, P. ( 1 ) 298, 336 Chandra, A.K. ( 1 ) 365; ( 3 . 6 ) 174 Chandrasekhar, J. ( 3 . 1 ) 1 8 ; ( 3 . 6 ) 1 5 6 , 175 Chang, C.H. ( 4 ) 283 Chang, H.T. ( 3 . 2 ) 141 Chang, M.C. ( 1 ) 496 Chang, S.C. ( 2 . 2 ) 137 Chang, Z. ( 4 ) 55 Changfu, X. ( 3 . 6 ) 49 Chapman, O.L. ( 3 . 7 ) 48 Chappuis, P.P. (1) 541 Char, K. ( 4 ) 289 Charbonnel, Y. ( 3 . 6 ) 200 Charlesby, A . ( 4 ) 419 Chassot, L. ( 2 . 1 ) 1 4 4 ; ( 2 . 2 ) 150 Chateauneuf, J.E. (1) 369; ( 3 . 7 ) 4 3 , 1 2 4 , 125 Chatterton, W.J. ( 2 . 3 ) 3 4 ; ( 3 . 6 ) 192 Chattopadhyaya, S. ( 4 ) 275
ChatzidimitriouDreismann, C.A. ( 1 ) 40 Chavez, E. ( 4 ) 351 Chawla, H.M. ( 3 . 5 ) 109 Che, C.M. ( 2 . 1 ) 1 1 0 , 146 Che, M. ( 2 . 2 ) 141 Chemyakovskii, F.P. ( 4 ) 274
Chen, C.-C. ( 3 . 4 ) 129 Chen, C.H. ( 1 ) 80 Chen, J. ( 3 . 5 ) 2 9 , 7 8 , 79 Chen, L. ( 4 ) 292, 293 Chen, L.X-Q. ( 1 ) 493 Chen, Q. ( 3 . 6 ) 6 0 ; ( 3 . 7 ) 181
Chen, S. ( 1 ) 337; ( 2 . 2 ) 1 5 , 1 6 ; ( 4 ) 83
Chen, X. ( 2 . 1 ) 58 Chen, Y. ( 3 . 5 ) 3 0 ; ( 2 . 2 ) 7 9 ; ( 4 ) 480
Chen, Z. ( 2 . 1 ) 7 2 , 7 3 ; ( 4 ) 361, 362
Cheng, E.X. ( 2 . 2 ) 1 5 3 , 154
Cheng, X. ( 3 . 4 ) 62 Cherek, H. ( 1 ) 5 9 , 188 Cherepanova, E.G. ( 3 . 2 ) 26
Cherezov, A.A. ( 4 ) 420 Cherkasskaya, O.V. ( 4 ) 307
Chernyakovski, F.P. ( 1 ) 20 1
Chesnoy, J. ( 1 ) 206 Chetcuti, P.A. ( 2 . 2 ) 129 Cheung, F. (1) 523 Chhaya, P.N. ( 3 . 7 ) 155 Chiang, W.Y. ( 4 ) 166 Chiang, Y. ( 3 . 5 ) 26 Chiba, T. ( 3 . 2 ) 1 7 ; ( 3 . 6 ) 111
Chien, J.C.W. ( 4 ) 480 Chien, Y.Y. ( 4 ) 373 Chikishev, A.Y. ( 1 ) 436 Chilbert, M.A. ( 1 ) 514 Chimichi, S . ( 3 . 2 ) 4 7 ; ( 3 . 3 ) 6 4 , 6 5 ; ( 3 . 6 ) 91
Chinnasamy, P. ( 3 . 2 ) 5 8 ; ( 3 . 4 ) 1 3 0 ; ( 3 . 6 ) 32
Chiorboli, C. ( 2 . 1 ) 94 Chiou, J.H. ( 3 . 3 ) 54 Chirinos-Padron, A.J. ( 4 ) 351, 474, 476
Cho, H.S. ( 3 . 3 ) 6 Cho, 1.4. ( 3 . 4 ) 1 1 7 ; ( 3 . 6 ) 123
Cho, I.H. ( 3 . 2 ) 108 Cho, K.C. ( 2 . 1 ) 110, 1 4 6 ; ( 4 ) 264
Cho, T.H. ( 3 . 6 ) 133 Chohan, Z.H. ( 2 . 2 ) 96 Choi, J.H. ( 2 . 3 ) 5 Choi, K.-J. ( 1 ) 314 Choi, L.S. ( 4 ) 325 Chojnacki, H. ( 1 ) 112 Chopra, P. ( 1 ) 289 Chou, C.H. ( 3 . 4 ) 1 1 Chou, T.C. ( 3 . 3 ) 54 Choudhary, V. ( 4 ) 459 Choudhry, G.G. ( 3 . 4 ) 9 6 ,
Photochemistry
510 107; ( 3 . 7 ) 177
Chow, Y. ( 3 . 3 ) 8 4 ; ( 1 ) 523
Chow, Y.L. ( 2 . 2 ) 153, 154; ( 3 . 2 ) 3 7 ; ( 3 . 4 ) 47, 92; (3.5) 9 ; (3.6) 126, 139 Chowdhury, B.K. ( 3 . 5 ) 115 Chowdhury, M. ( 1 ) 111, 179 Choy, C.C. ( 4 ) 264 Christensen, D. ( 1 ) 256 Christian, G.D. ( 1 ) 62 Christl, M. ( 3 . 7 ) 28 Christope, D.R. ( 1 ) 469; ( 3 . 7 ) 80 Christophorou, L.G. ( 1 ) 107 Chronister, E.L. ( 2 . 2 ) 17 Chu, D. ( 4 ) 314 Chu, J.O. ( 2 . 3 ) 2 3 ; ( 3 . 6 ) 181 Chu, N.Y.C. ( 4 ) 487 Chu, Y.D. ( 4 ) 279 Chuklanova, E.B. ( 2 . 1 ) 124 Chupka, E . I . ( 4 ) 326 Chuvashev, D.D. ( 4 ) 326 Chvatal, Z. ( 1 ) 93 Ci, X. ( 3 . 3 ) 74 Ciardelli, F. ( 4 ) 27, 186 Cicero, M.G. ( 3 . 4 ) 21 Ciciani, G. ( 3 . 3 ) 6 5 ; ( 3 . 6 ) 91 Cioransecu, E. ( 3 . 7 ) 62 Ciriano, M.A. ( 2 . 2 ) 133 Clardy, J. ( 3 . 6 ) 49 Clark, D.T. ( 4 ) 414 Clark, E. ( 3 . 7 ) 25 Clark, K.B. ( 3 . 3 ) 19 Clark, M.D. ( 4 ) 310 Clarson, S.J. ( 4 ) 286 Clawson, P. ( 3 . 7 ) 149 Clemente, D.A. ( 1 ) 379 Clementi, S . ( 4 ) 515 Clements, M.T.M. ( 3 . 2 ) 9 ; ( 3 . 4 ) 50 Clennan, E.L. ( 3 . 5 ) 55 Clifton, M.S. ( 2 . 2 ) 146 Closs, G.L. ( 1 ) 356 Clough, R.L. ( 1 ) 458 Codher, A. ( 1 ) 540 Coe, P.L. ( 3 . 7 ) 45 Coghlan, M.J. ( 3 . 2 ) 31 Cohen, D.M. ( 3 . 3 ) 66 Cohen, Y. ( 1 ) 217 Cole-Hamilton, D.J. ( 2 . 2 ) 147 Collart, P. ( 4 ) 195, 288 Colmenares, M.A. ( 4 ) 474 Combellas, C. ( 3 . 4 ) 80 Cominciolli, V. ( 4 ) 353
Condorelli, G. ( 2 . 2 ) 67 Conlin, R.T. ( 2 . 3 ) 1 9 ; ( 3 . 6 ) 193
Conlou, D.A. ( 4 ) 156 Connelly, J.S. ( 1 ) 196 Contineanu, M. ( 2 . 1 ) 114 Cook, B.R. ( 2 . 1 ) 49 Cook, M.I. ( 3 . 7 ) 45 Cook, S . ( 3 . 4 ) 86 Cooper, C.B. ( 3 . 7 ) 33 Cooper, G. ( 3 . 7 ) 91 Cooper, J.C. ( 2 . 2 ) 12 Coppini, G. ( 3 . 2 ) 47 Coquereb, X. ( 4 ) 122 Cordonnier, M. ( 4 ) 350 Corin, A.F. ( 1 ) 511 Cormier, J.M. ( 2 . 2 ) 60 Cornelisse, J. ( 3 . 4 ) 35-37; 71
(3.5) 10; (3.6)
Corvaja, C. ( 1 ) 379, 400 Cosa, J.J. ( 1 ) 320 Cosstick, K.B. ( 3 . 4 ) 42 Cossy, J. ( 3 . 1 ) 5 0 , 51; ( 3 . 6 ) 85
Costanzo, L.L. ( 2 . 2 ) 67 Costello, S.A. ( 2 . 3 ) 71 Cotsaris, E. ( 1 ) 266 Cottier, L. ( 3 . 5 ) 103 Coughlin, E.B. ( 3 . 4 ) 7 4 , 75
Coulon, D.A. ( 4 ) 441 Coulter, D.R. ( 4 ) 300 Courbon, H. ( 3 . 5 ) 77 Courtot, P. ( 2 . 2 ) 1 3 , 149 Couture, A. ( 3 . 2 ) 7 1 , 7 2 ; ( 3 . 4 ) 131; ( 3 . 6 ) 35
Couture, Y. ( 3 . 7 ) 198 Cox, D.M. ( 2 . 1 ) 21 Coxon, J.M. ( 3 . 1 ) 4 ; (3.2) 115; (3.4) 9
Crabtree, R.H. ( 2 . 2 ) 127; ( 3 . 5 ) 60
Craig, B.B. ( 1 ) 471; ( 3 . 7 ) 107
Craig, R.H. ( 3 . 7 ) 90 Creary, X. ( 3 . 7 ) 53 Cresente, 0. ( 4 ) 235 Creus, P.C. ( 4 ) 513 Creutz, C. ( 2 . 1 ) 5 6 , 80 Crich, D. ( 3 . 7 ) 115 Crimmins, M.T. ( 3 . 2 ) 10 Cristensen, J.E. ( 4 ) 146 Cristol, S.J. ( 3 . 3 ) 82; ( 3 . 4 ) 184
Crivello, J.V. ( 4 ) 1 , 8 9 , 156, 441
Crocco, G. ( 3 . 6 ) 203 Croke, D.T. ( 1 ) 515 Crosby, G.A. ( 2 . 1 ) 127 Crossan, D. ( 4 ) 123 Croucher, M.D. ( 4 ) 291,
293
Crozet, M.P. ( 3 . 7 ) 186 Cruciana, G. ( 3 . 2 ) 79 Csatorday, K. ( 1 ) 275 Csomorova, K. ( 4 ) 454 Cubeddu, R. ( 1 ) 155 Cummings, R.T. ( 1 ) 486; ( 3 . 4 ) 29
Cundall, R.B. ( 1 ) 190; ( 4 ) 30
Curatola, G. ( 1 ) 521 Curley, R.W. ( 1 ) 233 Cusumano, M. ( 2 . 2 ) 145 Cutrone, L. ( 4 ) 347 Cyr, D.R. ( 3 . 2 ) 7 7 , 112 Czanderna, A.W. ( 4 ) 423 Dabler, J. ( 1 ) 508 Dachre, S . ( 1 ) 273 Dadomatov, Kh.D. ( 4 ) 405 Da Graca, M. ( 2 . 1 ) 189 Dahl, L.F. ( 2 . 2 ) 81 Dai, G. ( 3 . 2 ) 109; ( 4 ) 467
Dallinger, R.F. ( 2 . 1 ) 160 Dal Piaz, V. ( 3 . 3 ) 6 5 ; ( 3 . 6 ) 91
Daltrozzo, E. ( 1 ) 222 Daluge, S.M. ( 3 . 7 ) 90 Damayanthi, W.P. ( 2 . 3 ) 58 Damiani, A. ( 2 . 1 ) 31 Damodaran, N.P. ( 3 . 3 ) 8 1 ; ( 3 . 4 ) 185; ( 3 . 7 ) 178
Daniel, C. ( 2 . 2 ) 2 7 , 43 Daniker, Y.M. ( 4 ) 30 Danno, M. ( 2 . 1 ) 125 Dantos, M. ( 1 ) 18 Daran, J.C. ( 2 . 2 ) 41 Darmanyan, A.P. ( 3 . 5 ) 4 7 ; ( 4 ) 327
Darsillo, M.S. ( 2 . 2 ) 73 Das, P.K. ( 1 ) 8 2 , 374, 430, 434; ( 2 . 2 ) 143; ( 3 . 2 ) 7 6 , 7 7 , 112; ( 3 . 4 ) 118 Das, S. ( 1 ) 438 Das, T.K. ( 3 . 4 ) 153; ( 3 . 6 ) 27 da Silva, E. ( 3 . 7 ) 111 Datta, D.B. ( 3 . 4 ) 153; ( 3 . 6 ) 27 Dauben, W.G. ( 3 . 3 ) 4 1 , 46 D'Auria, M. ( 3 . 4 ) 8 2 , 8 3 ; ( 3 . 7 ) 173, 174 David, R.M. ( 4 ) 292 Davidenko, N.K. ( 2 . 1 ) 178 Davidova, D. ( 3 . 6 ) 127 Davidson, A.G. ( 1 ) 46 Davidson, R.S. ( 4 ) 498, 499 Davidson, S.R. ( 3 . 5 ) 125
Author Index
51 1
Davies, A.K. (4) 30 Davies, J.W. (3.7) 115 Davis, D.D. (2.1) 23 Davis, J.E. (4) 80 Dawidar, A.M. (3.2) 51; (3.4)
156
DeAmicis, C.V. (3.1) 20 Dean, M.J. (4) 482 DeArmond, M.K. (2.1) 68 Debe, M.K. (1) 324 De Cardenas, L. (3.1) 49 Decker, C. (4) 31, 118, 119, 451
Decl&my, A. (1) 25, 60 De Cola, L. (2.1) 185 de Costa, M.D.P. (1) 158 Dedek, P. (1) 93 Deeb, T.M. (3.7) 118 Degen, J. (1) 140 DeGraff, B.A. (2.1) 90 De Gregori, A. (3.6) 153 De Guidi, G. (2.2) 67 De Keukeleire, D. (3.1) 11; (3.2)
33
Dekkers, H.P.J.M. (2.1) 70
Dektar, J.L. (3.4)
158, 132 Delaney, J.K. (1) 528 Delatycki, 0. (4) 344 Delduc, P. (3.7) 127 DeLearie, L.A. (2.2) 50 Del Giacco, T. (3.5) 63 Dell'Erba, C. (3.4) 77; (3.7) 191, 194 Dellonte, S. (2.1) 183 Delmer, D. (3.7) 91 Del Rossi, K.J. (2.2) 136 De Maeyer, A. (3.3) 30 Demas, D.J. (1) 49 Demas, J.N. (1) 49; (2.1) 90 de Mayo, P. (3.3) 3, 29; (3.4) 166 Demchuk, M.I. (1) 214 De Meijere, A. (3.5) 74 De Mico, A. (3.4) 82, 83; (3.7) 173, 174 Demmig, S. (1) 200 Demuth, M. (3.2) 21, 74 Deng, F. (3.6) 22 Denning, R.G. (2.1) 191 Dennis, W.M. (1) 71 Densley, R.J. (4) 331 Deota, P.T. (3.2) 75, 113, 114; (3.4) 46 De Paoli, M.A. (1) 422 Depireux, T. (4) 271 De Poortere, M. (4) 351, 476 Deranleau, D.A. (1) 67 Dernbinskii, I.K. (4) 488 159; (3.7)
Deronzier, A. (2.1) 87 De Ryck, P.H. (2.3) 51 Desai, J. (3.5) 68 De Schryver, F.C. (1) 52, 53, 172, 194, 301, 345; (4) 195, 280, 286-288 Descotes, G. (3.5) 103 Desilets, D.J. (1) 56 de Silva, A.P. (1) 158 De Silvestri, S. (1) 120 De Sio, F. (3.3) 64, 65; (3.6) 91 desolms, S.J. (3.6) 103 Deson, J. (2.3) 59 DesprGs, A. (1) 367 Desvergne, J.P. (1) 113 Detzer, N. (1) 31, 32, 176, 193 Dev, S. (3.3) 81; (3.4) 185; (3.7) 178 de Vaal, P. (3.4) 37 Devakumar, C. (3.5) 9 1 Deval, P. (1) 231 Devanathan, S. (3.1) 37; (3.6) 159 Devoe, R.J. (2.3) 76; (3.4) 160 De Young, D.J. (3.6) 177 Dhanya, S. (1) 373 Dianova, E.N. (3.6) 204 Diaz, R.R. (3.5) 101 Dick, B. (1) 151, 152 Dick, H.A. (1) 328 Dickinson, L.C. (4) 480 Dicks, P.F. (3.7) 199 Dickson, M.K. (2.1) 150 Dickson, R.S. (2.2) 125 Dieckmann, G.H. (2.1) 201 Dieter, T. (2.1) 79 Diffey, B.L. (1) 41 Diffontaine, A. (1) 377 Dilung, 1.1. (1) 539; (4) 56 Dirksen, G.J. (2.1) 174 Disanayaka, B.W. (3.2) 38, 39 D'Ischia, M. (3.5) 112, 113 Disovski, N. (4) 489 Divelle, R. (1) 68 Dixon, A.J. (1) 469; (3.7) 80 DiZio, J.P. (3.4) 29 Djafari, H. (3.3) 48; (3.6) 143 Djoufac-Noumf0, E. ( 1) 322 Dmitriev, F.M. (3.4) 27, 28; (3.7) 84 Do, C.H. (4) 383 Dobson, C.B. (2.2) 36, 37 Dobson, G.R. (2.2) 36, 37
Dopp, D. (3.6) 79 Doerr, G. (2.1) 101 Dorr, M. (3.7) 15 Dogra, S.K. (1) 96, 98, 133-135
Dohmaru, T. (2.3) 24 Doi, E. (3.6) 33 Do Khac, D. (3.2) 36 Dolson, D.A. (2.3) 70 Domen, K. (2.1) 10 Domenech, J. (2.1) 39, 209, 210
Donati, D. (3.3) 64 Doncean, G. (4) 495 Doney, J.J. (2.2) 42 D'Onofrio, F. (3.4) 82, 83; (3.7)
173, 174
Donvianyan, P. (4) 176 Dopp, D. (3.4) 51 Dorhout, P.K. (2.1) 202 Dormans, G.J.M. (1) 232 Dorofeev, Yu.1. (4) 391 Dorsch, J.L. (4) 473 Dorscheln, W. (3.4) 24 Dote, T. (1) 246 Dougherty, D.A. (3.7) 19 Drabent, R. (4) 244 Draghici, C. (3.7) 62 Dreeskamp, H. (1) 124; (2.3)
53
Drew, M.G.B. (3.4) 42 Drexhage, K.H. (1) 207, 209, 210, 451
Druger, S.D. (1) 259 Druzhinin, S.I. (1) 157 Duan, Y. (2.1) 205 Dubini-Paglia, E. (4) 510 Dubonosov, A.D. (3.6) 40 Durr, H. (2.1) 101; (3.6) 57
Dugan, C.H. (2.3) 75 Duggan, M.E. (3.6) 161 Duguid, R. (1) 82 Duhaime, R.M. (3.5) 23, 24
Dumitru, P. (4) 402 Dumont, F. (4) 271 Duncan, J.A. (3.3) 15 Dunkin, I.R. (3.4) 20; (3.7)
121
Dupuis, G. (3.7) 87 Dupuis, P. (1) 505 Dupuy, F. (1) 396 Duran, N. (4) 411 Dureja, P. (3.3) 83; (3.5)
42, 91
Dusi, A. (3.6) 55 Dusi, R. (3.6) 55 Dvornikov, A.S. (3.6) 199 Dyatlova, N.M. (2.1) 122 Dyszlewski, A.D. (3.3) 16; (3.6)
149
Photochemistry
512
Dyumnaev, K.M. ( 4 ) 377 Dzevitskii, B.E. ( 2 . 1 ) 43 Dzhagarov, B.M. ( 3 . 5 ) 46 Earl, C.Q. ( 3 . 7 ) 9 0 Ebbesen, T.W. ( 3 . 5 ) 1 4 , 2 8 , 8 9 ; ( 3 . 7 ) 63
Eberlein, T.H. ( 3 . 7 ) 137 Ebersole, M.H. ( 2 . 1 ) 206 Edmunds, A.J.F. ( 3 . 7 ) 27 Edwards, M. ( 3 . 2 ) 123 Edwards, P.N. ( 3 . 7 ) 45 Eftink, M.R. ( 1 ) 487 Egan, L.S. ( 4 ) 273, 291 Egawa, H. ( 3 . 3 ) 1 3 ; ( 3 . 6 ) 37
Ege, D. ( 3 . 4 ) 4 Eggert, L. ( 3 . 4 ) 103 Eggleston, D.S. ( 3 . 3 ) 4 3 ; ( 3 . 7 ) 142
Egholm, M. ( 3 . 6 ) 80 Egorov, M.P. ( 2 . 3 ) 2 6 ; ( 3 . 6 ) 199
Eguchi, S. ( 3 . 6 ) 29 Ehrenfreund, E. ( 4 ) 226 Ehrenson, S. ( 1 ) 30 Eichenberger, H. ( 3 . 2 ) 59 Eichstaedt, D. ( 2 . 3 ) 18 Einaga, H. ( 2 . 1 ) 119 Einterz, C.M. ( 1 ) 6 6 Eisch, J.J. ( 2 . 3 ) 6 , 7 El-Aasser, M.S. ( 4 ) 54 Elbanowski, M. ( 2 . 1 ) 1 7 6 , 177
El'darov, E.G. ( 4 ) 355 Elev, I.V. ( 2 . 2 ) 30 Elfinger, G. ( 1 ) 478 Elian, M. ( 3 . 7 ) 62 Elisei, F. ( 1 ) 1 8 9 , 251 El Khatib, F. ( 2 . 3 ) 62 Elliott, J.D. ( 3 . 3 ) 4 3 ; ( 3 . 7 ) 142
Ellis, A.B. ( 2 . 1 ) 1 7 1 , 201, 202; ( 2 . 2 ) 59
Ellis-Davies, G.C. R. (3.4) 49; (3.6) 76
Elrod, L.F. ( 3 . 7 ) 1 4 Elsaesser, T. ( 1 ) 142 El-Sayed, L. ( 2 . 1 ) 109 El-Sayed, M.A. ( 1 ) 342; ( 2 . 2 ) 17
Elsner, H. ( 4 ) 236 El'tsov, A.V. ( 3 . 4 ) 2 7 , 28; ( 3 . 6 ) 7 7 ; (3.7) 84 Endicott, J.F. ( 2 . 1 ) 1 , 3 2 , 192 Eng, K.K. ( 3 . 7 ) 34 Engel, P.S. ( 3 . 7 ) 1 Englert, G. ( 3 . 2 ) 66 Ennis, P.M. ( 4 ) 86 Ephritikhine, M. ( 2 . 2 ) 60
Erabi, T. ( 2 . 2 ) 142 Erden, I. ( 3 . 5 ) 7 4 Erdle, W. ( 3 . 7 ) 68 Eremenko, A.M. ( 3 . 5 ) 75 Eriyama, Y. ( 2 . 3 ) 4 1 ; ( 3 . 6 ) 191
Erman, B. ( 4 ) 321 Ernsting, N.P. ( 1 ) 152, 207
Eroshkin, V.I. ( 3 . 6 ) 5 9 ; ( 3 . 7 ) 102
Espenson, J.H. ( 2 . 1 ) 1 9 4 ; ( 2 . 2 ) 111
Eyal, M. ( 1 ) 217 Factor, A. ( 4 ) 421, 422 Fadiran, E.O. (1) 46 Fageol, P. ( 4 ) 33 Fahie, B.J. ( 3 . 3 ) 8 6 ; ( 3 . 4 ) 182
Fahmy, A.M. ( 3 . 7 ) 144 Faidas, H. ( 1 ) 107 Falanga, L.A. ( 4 ) 134 Fallon, G.D. ( 2 . 2 ) 125 Falvey, D.E. ( 3 . 7 ) 47 Fan, H. ( 3 . 7 ) 8 Fan, M. ( 3 . 2 ) 8 2 ; ( 3 . 6 ) 110
Fang, S.W. ( 4 ) 167 Fang, T.S. ( 3 . 2 ) 141 Fang, W. ( 2 . 3 ) 73 Farid, S. ( 3 . 4 ) 4 Fasani, E. ( 3 . 4 ) 167, 168; ( 3 . 6 ) 6 2 , 64
Fassler, D. ( 1 ) 202 Fatinikun, K.O. ( 4 ) 1 2 6 , 475
Faucitano, A. ( 4 ) 353 Favaro, G. ( 3 . 3 ) 59 Fayer, M.D. ( 1 ) 271 Febvay-Garot, N. ( 1 ) 520 Fedorikova, I. ( 3 . 7 ) 171 Fedoseev, A.M. ( 2 . 1 ) 180 Feigelman, V.M. ( 1 ) 157 Feis, A. ( 1 ) 117 Felkin, H. ( 2 . 2 ) 60 Feller, K.-H. ( 1 ) 202 Feller, R.L. ( 4 ) 520 Fellion, E. ( 3 . 7 ) 92 Feng, X. ( 4 ) 5 5 , 9 6 , 108 Ferguson, J. ( 2 . 1 ) 6 7 , 69 Feringa, B.L. ( 3 . 5 ) 4 Ferles, M. ( 3 . 6 ) 127 Fernandez, I. ( 3 . 3 ) 31 Fernandez-Picot, I. ( 3 . 7 ) 109
Fernando, C.A.N. ( 2 . 3 ) 58 Ferradini, C. ( 1 ) 446 Ferraudi, G. ( 1 ) 464; (2.1) 97; (2.2) 1
Ferreira, L.F.V. ( 1 ) 338
Ferrer, I. ( 4 ) 411 Ferrero, F. ( 4 ) 140 Ferrick, M.R. ( 4 ) 87 Ferrigno, K. ( 4 ) 123 Fery-Forgues, S. ( 3 . 4 ) 102
Fessenden, R.W. ( 1 ) 434, 536
Fessner, W.-D. ( 3 . 3 ) 51-53
Fetizon, M. ( 3 . 2 ) 36 Fibiger, R. ( 3 . 7 ) 73 Fiedler, E. ( 3 . 5 ) 56 Field, L.D. ( 2 . 2 ) 92 Figueroa, A. ( 1 ) 504 Filimushkin, A.G. ( 4 ) 356 Filipov, P.G. ( 1 ) 236; (3.3) 9
Filippov, Yu.V. ( 2 . 3 ) 2 Finckh, P. ( 1 ) 164 Findsen, E.W. ( 1 ) 529; ( 2 . 1 ) 142
Fini, L. ( 1 ) 206 Fink, M.J. ( 2 . 3 ) 2 9 , 30; ( 3 . 6 ) 1 7 7 , 184, 185
Finnie, A.A. ( 3 . 4 ) 112 Fiorini, R.M. ( 1 ) 521 Firey, P.A. ( 1 ) 526 Firth, S. ( 2 . 2 ) 49 Fischer, C.H. ( 3 . 5 ) 120 Fischer, E. ( 1 ) 413 Fischer, H. ( 1 ) 384 Fiscus, D. ( 3 . 7 ) 56 Fisera, L. ( 3 . 3 ) 7 5 ; ( 3 . 4 ) 1 4 8 ; ( 3 . 6 ) 50-56
Fissi, A. ( 4 ) 186 Fisslinger, H. ( 1 ) 531 Fitjer, L. ( 3 . 1 ) 40 Flamigni, L. (1) 7 4 ; ( 4 ) 6 5 , 429
Flammersheim, H.J. ( 4 ) 77 Flechtner, T.W. ( 3 . 6 ) 74 Fleming, G.R. ( 1 ) 2 7 , 29, 239, 356, 493, 496
Fleming, P. ( 3 . 6 ) 122 Fleming, R.J. ( 4 ) 330 Flerova, A.N. ( 4 ) 47 Fletcher, T.R. ( 2 . 2 ) 1 Flintjer, B. ( 3 . 6 ) 186 Floeel, M. ( 2 . 2 ) 58 Floser, G. ( 1 ) 519 Fofano, M. ( 4 ) 281 Foggi, P. ( 1 ) 1 1 6 , 117, 144
Fok, N.V. ( 4 ) 376 Folan, L.M. ( 1 ) 259 Fomier de Violet, P. ( 4 ) 410
Font, J. ( 4 ) 221 Fookes, C.J.R. ( 3 . 6 ) 25 Foote, C.S. ( 1 ) 4 6 0 ; (3.5) 93
Author lridex Ford; P.C. ( 2 . 1 ) 1 2 9 ; ( 2 . 2 ) 7 , 126 Ford, R.R. ( 2 . 3 ) 3 4 ; ( 3 . 6 ) 192 Ford, T.M. ( 3 . 7 ) 44 Ford, W.E. ( 1 ) 225 Formoshino, S.J. ( 2 . 1 ) 189 Formosinho, S.G. ( 1 ) 37 Forster, L . S . ( 2 . 1 ) 29 Foster, B. ( 3 . 4 ) 1 7 2 ; ( 3 . 7 ) 152 Foster, G.P. ( 2 . 2 ) 66 Foster, R.W.G. ( 3 . 1 ) 16 Fouassier, J.P. ( 4 ) 5 1 , 5 3 , 5 7 , 349, 395-397 Fourie, L. ( 3 . 2 ) 140; ( 3 . 6 ) 136 Fourmann, B. ( 1 ) 367 Fowble, J.W. ( 1 ) 233 Fox, L.S. ( 2 . 2 ) 131 Fox, M.A. ( 1 ) 340; ( 2 . 1 ) 1 6 , 4 5 , 207; ( 3 . 4 ) 129 Frackowiak, D. ( 1 ) 220 Francisco, C.G. ( 3 . 7 ) 209 Franck-Neumann, M. ( 3 . 7 ) 22, 31 Frank, C.W. ( 4 ) 200, 201, 209, 289, 312 Frank, F.J. ( 3 . 4 ) 86 Franke, L.A. ( 3 . 4 ) 164 Franzreb, K.H. ( 2 . 2 ) 48 Frasani, E. ( 3 . 4 ) 149 Fraser, I.F. ( 2 . 1 ) 54 Frattini, V. ( 3 . 4 ) 1 6 8 ; ( 3 . 6 ) 62 Fredrickson, G.H. ( 1 ) 3 4 ; ( 4 ) 200 Freeman, P.K. ( 3 . 4 ) 104 Frei, B. ( 2 . 3 ) 3 2 ; ( 3 . 2 ) 59 Freiberg, A. ( 1 ) 270 Freire, R. ( 3 . 7 ) 209 Freiser, B.S. ( 2 . 2 ) 65 Freund, M. ( 3 . 7 ) 143 Freund, S . ( 3 . 7 ) 28 Friberg, S.E. ( 4 ) 73 Friderichs, A. ( 3 . 6 ) 66 Friedman, A.E. ( 2 . 2 ) 7 , 126 Friedman, J.M. ( 2 . 1 ) 142 Friend, C.M. ( 2 . 2 ) 72 Friend, R.H. ( 4 ) 223, 318 Friesen, D.A. ( 2 . 1 ) 30 Frimmer, M. ( 3 . 7 ) 88 Frinault, T. ( 3 . 7 ) 188 Frink, M.E. ( 2 . 1 ) 129 Fritsche, K. ( 4 ) 133 Fritz, H. ( 3 . 3 ) 5 1 , 52, 6 2 ; ( 3 . 7 ) 30, 76 Fritzen, W. ( 3 . 2 ) 135 Frohling, J.-C. ( 1 ) 166
513 Frolov, B.I. ( 4 ) 408 Fromageot, P. ( 3 . 7 ) 92 Fu, H. ( 3 . 2 ) 8 2 ; ( 3 . 6 ) 110
Fucaloro, A.F. ( 2 . 1 ) 29 Fuchs, B. ( 3 . 2 ) 73 Fuchs, Y. ( 1 ) 79 Fueki, K. ( 4 ) 352 Fuh, M.-R.S. ( 1 ) 62 Fujii, A. ( 3 . 7 ) 9 5 , 97 Fujii, M. ( 3 . 7 ) 141 Fujikawa, H. ( 2 . 1 ) 166 Fujimoto, M. ( 2 . 1 ) 51 Fujisawa, M. ( 3 . 2 ) 8 6 ; ( 3 . 6 ) 167 S . ( 4 ) 6 4 , 112 ( 1 ) 517 ( 4 ) 386 (3.5) 11; ( 3 . 6 ) 178 Fujita, Y. ( 4 ) 521 Fujiwara, H . ( 4 ) 14 Fujiwara, K. ( 1 ) 63 Fujiwara, Y. ( 1 ) 401 Fukami, A. ( 4 ) 116, 117 Fukaya, T. ( 2 . 1 ) 100 Fukuchi, Y. ( 4 ) 38 Fukuda, K. ( 1 ) 182; ( 3 . 6 ) 8 Fukuda, M. ( 1 ) 309 Fukumura, K. ( 1 ) 409 Fukunaga, T. ( 3 . 7 ) 164 Fukushi, S. ( 3 . 5 ) 87 Fukushima, M.J. ( 3 . 5 ) 6 Fukushima, Y. ( 2 . 1 ) 50 Fukuyama, K. ( 3 . 2 ) 102; ( 3 . 5 ) 17 Fukuzumi, S. ( 2 . 3 ) 5 5 ; ( 3 . 5 ) 95 Funasaki, Y. ( 1 ) 390 Funke, U. ( 3 . 6 ) 4 Furlong, D.N. ( 1 ) 343 Furuhata, K. ( 3 . 6 ) 97 Furui, T. ( 4 ) 258 Furukawa, J. ( 4 ) 42 Furukawa, K. ( 3 . 6 ) 68 Furusaki, A. ( 3 . 2 ) 138 Furuta, K. ( 3 . 7 ) 211 Futakami, M. ( 1 ) 165, 174
Fujishige, Fujita, H. Fujita, K. Fujita, M.
170; ( 3 . 6 ) 70
Galiazzo, G. ( 1 ) 244, 251; ( 3 . 3 ) 11
Gallego, M. ( 3 . 2 ) 7 0 ; ( 3 . 6 ) 42
Gallhuber, E. ( 2 . 1 ) 65 Gal'minas, A.M. ( 2 . 3 ) 26 Galvez, C. ( 3 . 3 ) 31 Gamba, A. ( 3 . 4 ) 149 Gamble, E.B. ( 1 ) 120 Gandolfi, M.T. ( 2 . 1 ) 89 Gandolfi, R. ( 2 . 1 ) 74 Gangopadhyay, S. ( 1 ) 264 Gano, J.E. ( 3 . 3 ) 20 Ganzha, V.A. ( 3 . 5 ) 46 Garbarino, G. ( 3 . 4 ) 7 7 ; (3.7) 191, 194
Garcia, H. ( 3 . 1 ) 45 Garcia, N.A. ( 1 ) 320 Garcia Alvarez-Coque, M.C. ( 1 ) 294, 348 Garcia-Garibay, M. ( 3 . 3 ) 27
Garcia Segura, R. ( 3 . 2 ) 121; ( 3 . 6 ) 121
Garg, H.S. ( 3 . 5 ) 111 Gargallo, L. ( 4 ) 219, 220, 304
Gariboldi, P. ( 3 . 2 ) 8 ; ( 3 . 6 ) 153
Garnett, J.L. ( 4 ) 176 Gartstein, Y.N. ( 1 ) 175 Gase, R. ( 3 . 6 ) 1 4 Gashgari, M.A. ( 4 ) 201 Gaspar, V. ( 2 . 1 ) 40 Gaspard, S . ( 2 . 1 ) 18 Gassman, P.G. ( 2 . 3 ) 1 6 ; ( 3 . 2 ) 8 1 ; ( 3 . 6 ) 196
Gast, A.P. ( 4 ) 289 Gatilov, Yu.V. ( 3 . 2 ) 19 Gaumet, S. ( 4 ) 365 Gautier, H. ( 3 . 4 ) 80 Gautron, R. ( 1 ) 457 Gauvin, P. ( 4 ) 384 Gavrilova, 1.1. ( 4 ) 313 Gaziev, S.A. ( 2 . 1 ) 196 Gdaniec, 2. ( 3 . 6 ) 142 Geacintov, N.E. ( 1 ) 513 Geenevassen, J.A.J. ( 3 . 1 ) 53
Gaber, D.J. ( 4 ) 145 Gabert, K. ( 4 ) 13 Gacel, G. ( 3 . 7 ) 92 Gafney, H.D. ( 2 . 1 ) 7 9 ; ( 2 . 2 ) 73
Gai, Y. ( 3 . 4 ) 62 Gaillard, B. ( 3 . 4 ) 172; ( 3 . 7 ) 152
Gaillard, E. ( 2 . 1 ) 4 5 ; ( 3 . 4 ) 129
Gainsford, G.J. ( 3 . 4 )
Geetha, R. ( 4 ) 352 Gehetz, M. ( 3 . 7 ) 154 Geier, D. ( 3 . 4 ) 86 Geigel, H. ( 3 . 2 ) 110 Gelas-Mialhe., Y. ( 3 . 2 ) 6 2 ; ( 3 . 6 ) 36
Geletii, Yu.V. ( 2 . 1 ) 158 Gelles, R. ( 4 ) 209 Gendin, D.V. ( 2 . 3 ) 4 5 ; ( 3 . 6 ) 197
Genet, R. ( 3 . 7 ) 92 Genizi, E. ( 3 . 3 ) 78
Photochemistry
514 Gennari, G. (1) 244 Geoffroy, G.L. (2.2) 40 George, M.V. ( 1 ) 374; (3.2) 76, 77, 112; (3.4) 118 Georges, J. (1) 322 Geraghty, N.W.A. (3.2) 13 Gerasimenko , Yu. E. (3.2) 145; (3.4) 33 Gerasimov, G.N. ( 4 ) 47 Gerasimov, O.V. (2.1) 108 Gerasimov, S.F. (2.1) 25 Gerasimova, T.N. (3.6) 59 Gerhartz, W. (2.2) 82 Gerlock, J.L. ( 4 ) 482 Gero, S.D. (3.7) 112 Gerrard, D.C. ( 4 ) 369 Getmanchuk, Yu.P. ( 4 ) 40 Geuskens, G. ( 4 ) 358, 477 Ghatak, U.R. (3.7) 61 Ghiggino, K.P. (1) 146; ( 4 ) 465 Ghosh, P. (4) 183 Ghosh, S. ( 1 ) 397, 425, 503; (3.4) 153; (3.6) 27 Ghosh, U. ( 4 ) 275 Giacometti, G. ( 1 ) 379 G i a n n o t t i , C. (2.1) 1 8 ; (3.5) 34 Gibson, C.P. (2.2) 81 G i l , M.H. ( 4 ) 21 G i l a b e r t , E. (1) 60, 191 G i l b e r t , A. (3.1) 3 ; (3.4) 40-42, 49, 9 5 ; (3.6) 117 G i l b e r t , S.R. (4) 297 G i l l a r d , R.D. (2.1) 70 Giniger, R . ( 1 ) 268, 269 Ginley, D.S. ( 4 ) 225 Giordano, C. ( 4 ) 280, 287 G i r i , B.P. (3.1) 27 G i s i n , M. (3.7) 25 G i u f f r i d a , A. (2.2) 67, 145 G i u l i e t t i , G. ( 4 ) 515 Giumanini, A.G. (3.6) 131 Glasbeek, M. ( 1 ) 399 G l a s e r , M. ( 1 ) 521 Gleiter, R. (3.1) 34; (3.3) 37; (3.7) 6 9 Glenzen, M.M. (2.2) 54 Gleria, M. ( 4 ) 429 Glikman, J.F. ( 4 ) 416 Glinka, J. (3.7) 56 Glover, S.A. (3.7) 199, 201 Gloyna, D. ( 1 ) 188 Glubish, P.A. (4) 511 Go-An, Y. (3.7) 164 Godwin, F.G. (2.3) 72 Goedewuck, R. (4) 195
Goel, V.K. (3.5) 97 G o e l l e r , G. (1) 222 Gorner, H. (1) 248, 250, 251 Gogol, A. (3.1) 29, 30 Golankiewicz, K. (3.2) 83 Golankiewicz, L. (3.6) 112 G o l d b l a t t , R.D. (4) 181 Goldschmidt, Z. (3.3) 78 Goleneva, L.M. (4) 254 Gomez, P. ( 3 . l ) 35; (4) 463 Gomez, R.P. (3.4) 23; (3.6) 46 Gomez-Anton, M.R. ( 4 ) 242 G o n e l l i , M. (1) 498, 499 Gong, S.S. ( 1 ) 256 Gonzalez, D.H. ( 1 ) 501 Good, L. (1) 435 Goodchild, N.J. (3.7) 45 Gooden, R. ( 4 ) 363 Goodman, J.L. (3.7) 18 Goodwin, H.A. (2.1) 129 Goosen, A. (3.7) 199 Gopidas, K.R. (3.2) 76, 77; (3.4) 118 Gorbacheva, S.V. (3.7) 156 Gorbunova, O.P. ( 4 ) 313 Gorman, A.A. (3.5) 7 Gornostaev, L.M. (3.4) 27, 28; (3.7) 84 Gorry, P.A. (2.3) 72 Gorshkov, N.G. (2.1) 196 Gosh, B. (4) 9 5 Goswami, K. (2.1) 143 Goth, H. (3.4) 24 Goto, J. (3.4) 151 Goto, M. (2.3) 38 Goto, T. (3.4) 126; ( 4 ) 284 Goto, Y. (4) 59 Gould, I . R . (1) 362; (2.1) 66; (3.4) 4 ; (3.7) 7 Gould, L.D. (3.2) 10 Gouzalez-Lafont, A. (3.5) 41 Gozdz, A.S. (4) 84 Gozzelino, G. (4) 140 Grabowska, A. ( 1 ) 199 Grabowski, S. (3.7) 26 G r a e t z e l , M. (2.1) 9 , 13, 17; (2.2) 122 G r a f f , A. (3.6) 155 Graham, N . J . (3.4) 107; (3.7) 177 Graham, W.A.G. (2.2) 130 Granchak, V.M. (4) 56 Grandclaudon, P. (3.2) 72; (3.4) 131
Grant, E.R. (2.2) 75 Grant, J.L. (2.1) 143 Grasso, R.P. ( 4 ) 169 Gratton, ,E. (1) 58, 494, 521 G r a v e l l e , L. (3.4) 162; (3.7) 151 Graves, H.M. (1) 462 G r a y , H.B. ( 2 ) 131; (2.1) 110, 147, 149; (2.2) 144 Gray, P. ( 4 ) 18 Grayeski, M.L. (1) 477 Greathead, J.M. (3.3) 39 Grebenik, P.D. (2.2) 33 Green, D.M. (1) 514 Green, G.E. (4) 159 Green, M. ( 1 ) 160; (2.2) 63, 33 Green, P. ( 1 ) 389; ( 4 ) 51, 125-127 Green, S.B. (3.3) 66 Green, W.A. ( 1 ) 389; (4) 125 Greenberg, F.H. (4) 422 Greene, B . I . ( 1 ) 290 Gregoire, V. (3.5) 103 Gregorcic, A. (3.3) 17 Greiser, F. (1) 325, 326 Grelbig, T. (2.3) 68 Grellmann, K.H. ( 1 ) 417; (3.4) 24 Grenges, J. (4) 221 Greulich, K.O. (1) 518 Grevels, F.W. (2.2) 20, 82, 102 Griesbeck, A. (3.1) 2; (3.5) 71 Griesser, H.J. (1) 108 G r i f f i n , G.W. (3.1) 42; (3.7) 50 Grigoreva, G.A. ( 4 ) 70 Griller, D. (2.3) 25; (3.7) 49 Grimaldi, P. (4) 120 Grishenko, V.K. (4) 174 G r i t s a n , N.P. (1) 420; (3.4) 27; (3.7) 82 Groenen, J. (2.2) 53 Groenenboom, G.C. ( 1 ) 232 Gron, L.U. (2.2) 59 Grubbs, R.H. (2.2) 14 Gruda, I. (1) 220 Griitzmacher, H.-F. (3.6) 4 Grund, C. (3.3) 51 Grund, I. (1) 308 Grupp, A. (4) 228 Gryczynski, I. (1) 38, 188, 489 Gu, H.B. (4) 211 Gu, 2. (2.1) 199 '
~
Author lndex Guard-Friar, D. ( 1 ) 275 Guarini, A. ( 3 . 5 ) 53 Guckert, J.A. ( 2 . 1 ) 37 Gudzera, S.S. ( 4 ) 58 Gunther, E. ( 3 . 7 ) 17 Giisten, H. ( 1 ) 143 Guglielmo, G. ( 2 . 2 ) 145 Guilard, R. ( 2 . 3 ) 46 Guillet, J.E. ( 4 ) 32, 197 Guillony, W.A. ( 1 ) 408 Gunasekara, M.U. ( 2 . 3 ) 77 Gunder, O.A. ( 4 ) 185 Guo, C. ( 1 ) 51 Guo, S. ( 4 ) 24 Gupta, A. ( 4 ) 300 Gupta, S.N. ( 4 ) 238 Gurinovich, G.P. ( 1 ) 450; ( 3 . 5 ) 4 6 , 48
Guseinova, A.D. ( 2 . 1 ) 46 Gusev, O.V. ( 2 . 2 ) 74 Gusev, Yu.K. ( 2 . 1 ) 197 Gusten, H. ( 3 . 4 ) 17 Gutensohn, K.U. ( 2 . 2 ) 88 Guthrie, J.T. ( 4 ) 21 Guyot, D. ( 2 . 3 ) 48 Gyor, M. ( 2 . 2 ) 18 Haarer, D. ( 1 ) 519 Habata, Y. ( 3 . 6 ) 106 Haberfield, P. ( 1 ) 9 4 , 9 5 ; ( 3 . 6 ) 13 Hacker, N.P. ( 3 . 4 ) 158, 159; ( 3 . 7 ) 132 Haddaway, K. ( 3 . 6 ) 122 Haddleton, D.M. ( 2 . 2 ) 119-121, 132 Hadel, L.M. ( 3 . 7 ) 7 , 8 , 10 Hadjirapoglou, L.P. ( 3 . 7 ) 180 Hagedorn, A.A. ( 3 . 1 ) 35; ( 3 . 4 ) 23; ( 3 . 6 ) 46 Hagedorn, L. ( 3 . 4 ) 167; ( 3 . 6 ) 64 Haggquist, G.W. ( 4 ) 309 Hagiwara, H. ( 3 . 5 ) 6 Hagiwara, K. ( 2 . 3 ) 42; ( 3 . 6 ) 195 Halary, J.L. ( 4 ) 198, 246 Hale, P.D. ( 3 . 2 ) 48 Haley, B.E. ( 3 . 7 ) 86 Hall, R.A. ( 3 . 4 ) 112 Haller, K . J . ( 2 . 2 ) 59 Halton, B. ( 3 . 1 ) 4 ; ( 3 . 4 ) 9 Ham, H.S. ( 3 . 5 ) 44 Hama, Y. ( 2 . 3 ) 11 Hamaguchi, H. ( 1 ) 385 Hamai, S . ( 1 ) 177 Hamanoue, K. ( 1 ) 390 Hamblett, I. ( 3 . 5 ) 7
515
Hambright, P. ( 2 . 1 ) 24 Hamid, S.M. ( 4 ) 90 Hampl, P. ( 4 ) 348 Han, C.H. ( 3 . 3 ) 36 Hanaoka, M. ( 3 . 6 ) 67 Hanaya, K. ( 3 . 7 ) 146, 147 Hancock, M.P. ( 2 . 1 ) 134 Handa, T. ( 4 ) 285, 286 Haney, W.A. ( 3 . 2 ) 134 Hanley, N.M. ( 3 . 2 ) 13 Hannemann, K. ( 3 . 1 ) 25, 26; ( 3 . 4 ) 145; ( 3 . 5 ) 22; ( 3 . 7 ) 1 6 , 26, 52 Hannon, F.J. ( 3 . 2 ) 12 Hanson, L.K. ( 1 ) 533 Hara, K. ( 1 ) 121, 309; ( 4 ) 386 Haradu, M. ( 4 ) 78 Hargis, P.J. ( 4 ) 253 Haroutounian, S.A. ( 1 ) 138 Harrah, L.A. (4) 239, 241 Harriman, A. ( 1 ) 274, 389; ( 2 . 1 ) 24 Harrison, P.J. ( 3 . 6 ) 25 Harrit, N. ( 3 . 4 ) 2 0 ; ( 3 . 7 ) 121 Harrsch, P.B. ( 3 . 7 ) 13 Hartl, H. ( 2 . 2 ) 34 Hartman, R.F. ( 3 . 7 ) 166 Harvey, E.L. ( 2 . 1 ) 147 Harvey, P.D. ( 2 . 2 ) 144 Hasebe, M. ( 3 . 6 ) 1 6 4 ; ( 3 . 7 ) 108 Hasegawa, E. ( 2 . 3 ) 1 3 ; ( 3 . 6 ) 125 Hasegawa, M. ( 3 . 3 ) 6 3 ; ( 3 . 7 ) 161; ( 4 ) 8 , 9 Hasegawa, S. ( 4 ) 379 Hasegawa, T. ( 3 . 1 ) 14 Haseltine, J . N . ( 3 . 3 ) 36 Hasenbein, N. ( 4 ) 97 Hashimoto, C. ( 3 . 4 ) 132, 133; ( 3 . 6 ) 31 Hashimoto, H. ( 1 ) 364 Hashimoto, K. ( 2 . 1 ) 88 Hashimoto, S. ( 1 ) 524; ( 2 . 1 ) 162; ( 3 . 5 ) 39 Hassaneen, H.M. ( 3 . 7 ) 25 Hasse, H. ( 1 ) 125 Hassner, A. ( 3 . 5 ) 109; ( 3 . 7 ) 73 Hata, N. ( 3 . 4 ) 8 8 ; (3.6) 128 Hatanaka, Y. ( 3 . 2 ) 1 ; ( 3 . 4 ) 134; ( 3 . 6 ) 28 Hattori, T. ( 1 ) 24 Hauck, J. ( 3 . 7 ) 28 Hauck, M. ( 3 . 7 ) 69 Hauge, R.H. ( 2 . 2 ) 137, 138 Haupt, A. ( 3 . 7 ) 88
Hauser, M. ( 1 ) 308, 415 Havinga, E. ( 3 . 4 ) 64 Hawari, J.A. ( 2 . 3 ) 25 Hawecker, J. ( 2 . 1 ) 93 Hawthorne, F.M. ( 2 . 2 ) 129 Hayakawa, K. ( 1 ) 109, 311 Hayashi, H. ( 1 ) 323; ( 2 . 3 ) 50
Hayashi, K. ( 1 ) 509; ( 4 ) 41, 114, 187
Hayashi, N. ( 4 ) 261 Hayashi, S . ( 4 ) 211 Hayashi, T. ( 2 . 1 ) 5 2 ; ( 2 . 2 ) 117
Hayashida, R. ( 3 . 5 ) 87 Hayden, G.W. ( 4 ) 324 ' Hayes, R. ( 3 . 7 ) 98 Hayes, W. ( 4 ) 318 Hazin, P.N. ( 2 . 2 ) 158 He, Y. ( 4 ) 428 He, 2. (2.3) 67 Heath, P. ( 3 . 4 ) 4 0 , 4 1 , 4 9 ; ( 3 . 6 ) 117
Heathcock, C.H. ( 2 . 2 ) 42 Heckendorn, R. ( 3 . 4 ) 3 9 ; ( 3 . 6 ) 116
Hees, U. ( 3 . 6 ) 58 Heicklen, J. ( 3 . 5 ) 68 Heihoff, H. ( 1 ) 44 Heimgartner, H. ( 2 . 2 ) 105; ( 3 . 6 ) 160
Heineman, W.R. ( 3 . 1 ) 26 Heinze, J. ( 1 ) 143 Heisel, F. ( 1 ) 195 Heitele, H. ( 1 ) 164 Heller, H.G. ( 4 ) 235 Helman, W.P. ( 1 ) 17 Helms, C.A. ( 2 . 1 ) 127 Hemetsberger, H. ( 3 . 3 ) 26 Hendricks, R.T. ( 3 . 3 ) 15 Henglein, A. ( 1 ) 341; ( 3 . 5 ) 120
Henin, F. ( 3 . 1 ) 2 2 ; ( 3 . 2 ) 5 3 ; ( 3 . 5 ) 19-21
Henman, T.J. ( 4 ) 475 Hennan, A. ( 4 ) 290 Henneberger, H. ( 3 . 7 ) 28 Hennig, D. ( 3 . 2 ) 28; ( 3 . 4 ) 174
Hennig, H. (2.1) 3 Henning, H.G. ( 3 . 1 ) 21 Henry, E.R. ( 1 ) 495 Hensler, G. ( 2 . 1 ) 65 Hentschel, C. ( 3 . 1 ) 21 Herbert, B. ( 2 . 1 ) 34 Herdtweck, E. ( 2 . 2 ) 5 2 , 58 Herman, M.S. ( 3 . 7 ) 18 Hermann, C.K.F. ( 3 . 4 ) 7 8 ; ( 3 . 7 ) 196
Hernandez, P.H. ( 4 ) 351, 476
Photochemistry
5 16 Hernandez-Fuentes, I. ( 4 ) 242 H e r r i c k , R.S. (2.2) 4 Herrmann, W.A. (2.2) 52, 58 H e r t z , 0. ( 1 ) 344 Herve, Y. (3.7) 113 Herz, J.M. (1) 502 Herzog, H. (3.2) 30 Hesse, M. (2.3) 34; (3.6) 192 Hester, R.E. (1) 382 Hevey, R.C. (1) 47 Hey, J.P. (3.2) 12 H i b i , S. ( 4 ) 272, 315 Hida, M. (2.3) 63; (3.4) 115, 116 Hidaka, H. ( 4 ) 521 Hidaka, J. (2.1) 119 Hienuki, Y. (3.2) 137 Higaki, Y. (3.5) 1 3 Higuchi, J. ( 1 ) 405 Higuchi, M. (3.6) 1 0 ; ( 4 ) 230 Hikida, T. ( 1 ) 148 Hiller, W. (2.2) 88 Hino, A. ( 4 ) 248 Hinokuma, S. (2.1) 162 Hirabe, T. ( 4 ) 407 Hirai, H. ( 4 ) 68 Hirai, N. (2.3) 40 Hirai, T. (2.3) 10 Hirai, Y. (3.3) 13; (3.6) 37 H i r a k i , K. (2.2) 107 Hiramatsu, Y. ( 1 ) 156 Hiramoto, M. (2.1) 88 H i r a n i , S.K. (3.5) 115 Hirao, K. (3.3) 60 Hirasa, 0. ( 4 ) 382 Hirata, Y. (1) 234 Hiratsuka, H. ( 1 ) 148, 472; (3.5) 11 H i r a t s u k a , M. (2.2) 109 Hirayama, S. (1) 54, 114 Hirokami, S. (3.6) 16 Hirornitsu, I. ( 1 ) 538 H i r o t a , K. (3.5) 114; (3.7) 139 H i r o t a , M. (3.4) 106; (3.5) 87; ( 4 ) 100 H i r o t a , N . (1) 375, 381 Hiroyoshi, H. ( 4 ) 8 2 H i r s c h f e l d , T. (1) 62 Hisamune, T. (4) 284 Hitchman, M.A. (2.1) 164 Hixson, S.S. (3.4) 164 Ho, C.-J. (1) 139 Ho, T.-I. (1) 240; (3.6) 126 Hobbs, D.W. (3.4) 76; (3.7) 184
Hobel, K. (3.1) 15 H o c h s t r a s s e r , R.M. (1) 23, 141, 292, 495; (3.3) 36 Hochweber, M. (3.2) 110 Hodgkin, J. ( 1 ) 197 Hoehnk, H.D. (2.1) 55 Hossel, P. (1) 363; (3.7) 17, 20 Hoesterey, B. ( 1 ) 408 Hoffman, D.M. (2.2) 62 Hoffman, M.Z. (2.1) 35 Hoffmann, M.R. (2.1) 112, 113 Hoffmann, V.T. (3.3) 67 Hofmann, H. (3.3) 48; (3.6) 143 Hohenadel, R. (2.2) 151 Holden, D.A. ( 4 ) 182, 257 H o l f t e r , U. ( 4 ) 77 Holm, A . (3.4) 20; (3.7) 121 Holmes, A.S. ( 1 ) 50 H o l t , E.M. (3.7) 1 4 Holton, D. (1) 184, 525; (2.1) 81, 159 Holzwarth, A.R. ( 1 ) 55 Homer, R.B. (2.1) 173 Honda, K. (2.1) 165; (2.3) 15 Hong, A.P. (2.1) 1 1 2 , 113 Hong, Y. (3.5) 96 Honnen, W. (1) 346 Hoo, K.H. (3.6) 1 Hopkins, J . B . (1) 105 Hori, M. (3.6) 205 Horigome, T. (1) 109 Horiguchi, R. ( 1 ) 110 Horiguchi, Y. (3.2) 27; (3.6) 97, 98 Horn, K.A. (1) 369; (3.7) 43, 50 ( 1 ) 337 Horng, M.-J. Horng, P. ( 4 ) 457 Horspool, W.M. (3.2) 20, 70; (3.3) 21, 22, 76; (3.6) 42-44; (3.7) 160 Horta, A. ( 4 ) 242, 302, 303 Hosangadi, B.D. (3.7) 155 Hoshi, M. (3.5) 5 Hoshi, T. (3.4) 59; (3.6) 39, 130 Hoshina, 0. (3.7) 169 Hoshino, M. (1) 391, 392; (2.1) 138; (2.3) 10, 11 Hou, H. (2.3) 67 Hou, X. ( 4 ) 320 Howes, K.R. (2.1) 194 Hoyano, J . K . (2.2) 130 Hoyle, C.E. ( 4 ) 151, 152, 282, 310, 392, 403
Hrabal, R. ( 1 ) 9 3 Hrdina, R. ( 1 ) 93 Hrdlovic, P. ( 4 ) 427 Hritzova. 0. (3.4) . . 136; (3.7) i70 HSU, J.-L. ( 1 ) 284; ( 4 ) 269 Hsu, W.L. (1) 342 Hu, J. ( 2 . 1 ) 205 Hu, M. ( 3 . 5 ) 33 Huab, V. ( 4 ) 359 Huang, D.-B. (3.6) 46 Huang, H.Y. ( 4 ) 389 Huang, J. ( 4 ) 135, 36 Huang, S.J. ( 4 ) 181 Huang, Y. (2.2) 65; (2.3) 73 Hubig, S.M. ( 1 ) 317 Hubmann, M.R. ( 1 ) 542 Huckestein, B. ( 4 ) 103 Hummer, W. (1) 363; (3.7) 20 Huffman, J . C . (2.2) 62 Hug, G.L. (1) 1 7 , 82 Hughes, A.N. (3.6) 202 Hughes, N . ( 4 ) 471 Huguchi, H . (3.6) 207 Hui, Y. ( 3 . 4 ) 62 Huizer, A.H. ( 1 ) 402 Hulpke, H. (3.2) 50 Hummel, K. (4) 147 Hunig, S. ( 3 . 6 ) 113 Hunkler, D. (3.3) 51 Hunt, J . L . (3.4) 169 Huppert, D. ( 1 ) 128, 335 Hurley, J . K . ( 1 ) 196 Hurtubise, R.J. ( 1 ) 349 Hush, N.S. (1) 266 Hussein, F.H. (3.5) 65 Huth, V. (1) 207 Huys-Francotte, M. (3.7) 103 Hwang, C.-K. (3.6) 161 Hwang, T.C. (1) 240 Ichikawa, K. (3.1) 14 Ichikawa, S. (2.1) 8 Ichimura, K. (3.6) 21; ( 4 ) 64, 91, 109-115 Ichimura, T. (3.4) 73 I g a , R. ( 4 ) 232, 252 I g n a t o v , V.N. (3.2) 26 I h a r a , K. ( 4 ) 521 Ihaya, Y.J. (1) 416; (2.3) 50 Iijima, T. (4) 153 I i n o , Y. (1) 182 I i t a k a , Y. (3.7) 100 I i z u k a , H. (3.4) 97 Ikawa, K. (4) 438 Ikeda, H. (3.3) 72; (4)
517
Author Index Ishikawa, M. (1) 472;
227
Ikeda, M. (3.2) 55; (3.6) 88
Ikeda, N. (1) 386; (4) 329
Ikeda, T. (3.6) 7 Ikeda, Y. (3.2) 88; (3.5) 105, 106; (3.6)
15, 163
Ikegami, A. (1) 500 Ikegami, Y. (3.2) 131; (3.7)
146-148
Ikejiri, F. (1) 280 Ikeyama, T. (1) 378 Ilge, H.-D. (3.4) 127 Ilijev, D. (3.6) 138 Iliopoulos, I. (4) 246 Illeperuma, O.A. (2.3) 58 Il'yuchin, A.B. (2.1) 122 Imagi, K. (1) 386; (4) 329
Imam, S.Y. (3.1) 16 Imamura, T. (2.1) 51 Imanaga, H. (2.1) 50 Imanishi, M. (3.7) 100 Imazu, S. (2.3) 20 Imhof, R.E. (1) 50, 51 Imrich, J. (3.4) 135, 136; (3.7) 170, 171 Inada, Y. (1) 467 Indelli, M.T. (2.1) 94 Ingold, K.U. (3.7) 110, 124, 125 Inomata, K. (3.6) 39 Inoue, H. (2.3) 63; (3.4) 59; (3.6) 39, 130 Inaue, M. (3.6) 67 Inoue, S. (4) 69 Inoue, T. (3.4) 126; (4) 124 Ionescu, S.G. (2.1) 114 Ippen, E.P. (1) 120 Irace, G. (1) 494 Irie, M. (3.2) 102; (3.3) 40; (3.4) 123; (3.6) 38; (4) 187, 189, 192, 196, 232, 234, 252, 276 Irie, T. (3.3) 24; (3.6) 45 Irion, M.P. (2.3) 4 Irngartinger, H. (3.4) 13; (3.7) 28 Isaka, H. (1) 480 Isakovich, V.N. (4) 485 Ishchenko, A.A. (1) 214 Ishhakov, N.I. (4) 63 Ishibashi, H. (3.2) 55; (3.6) 88 Ishida, H. (2.1) 102 Ishii, K. (3.2) 60; (3.7) 150 Ishii, T. (2.2) 19; (3.5) 87; (4) 285
(2.1) 119; (2.3) 35; (3.4) 115; (4) 124, 387, 388 Ishikawa, T. (3.6) 39 Ishimoto, H. (4) 500 Ishitani, 0. (2.2) 56, 57; (3.5) 37, 108 Ishiwata, I. (1) 500 Iskhakov, N.I. (4) 99, 101 Ismail, G.M. (4) 498, 499 Ismail, K.Z. (2.1) 126 Ismailov, E.G. (2.1) 46 Ismailov, 1.1. (4) 61 Isogawa, M. (4) 329 Isomura, K. (3.7) 77 Itaya, A. (1) 277, 278 Ito, H. (3.6) 5 Ito, R.D. (3.3) 82; (3.4) 184 Ito, S. (3.6) 93; (4) 92, 30 1 Ito, Y. (1) 246; (3.1) 55; (3.2) 102, 103; (3.3) 8 ; (3.4) 16, 61, 90; (3.5) 17; (3.6) 5, 135; (4) 247 Itoh, K. (3.2) 37; (3.4) 47; (4) 315 Itoh, M. (1) 85, 401; (3.2) 133; (3.3) 79, 80; (3.4) 48; (3.7) 203, 205, 206 Itoh, T. (1) 403 Itokawa, H. (3.1) 32 Iu, K.-K. (1) 458 Ivanchenko, A.G. (3.3) 10 Ivanchenko, G. (1) 245 Ivanov, M. (4) 489 Ivanov, V.B. (4) 368, 375 Ivanov, V.L. (3.4) 81, 103; (3.7) 197 Ivanova, N.V. (2.1) 117 Iwai, M. (3.4) 73 Iwamoto, H. (2.3) 56; (3.1) 54 Iwamoto, N. (3.4) 176; (3.6) 201 Iwamura, H. (2.1) 86; (3.1) 46 Iwamura, M. (3.1) 46 Iwasa, E. (3.2) 29; (3.6) 94 Iwasa, K. (3.2) 58; (3.4) 130; (3.6) 32 Iwasaki, G. (2.3) 32 Iwasaki, N. (1) 110 Iwata, K. (3.3) 38; (3.6) 18 Iyoda, T. (2.1) 165 Izquierdo, A. (2.2) 33
Izumi, H. (4) 76 Izumrudov, V.A. (1) 297; (4) 262, 319
Jacke, J. (2.2) 20 Jackson, S.A. (2.2) 119 Jacob, P.W. (3.2) 5 Jacques, P. (1) 388 Jaeger, W. (4) 268 Jaegerman, P. (1) 474 Jahnig, F. (1) 332 Jain, R. (3.7) 19 James, D.R. (1) 492 Jameson, D.M. (1) 527 Janata, E. (3.5) 120 Janda, K.C. (2.2) 70, 71 Jardon, P. (1) 457 Jarecki, C. (3.7) 29 Jarzeba, W. (1) 187 Jasinski, J.M. (2.3) 23; (3.6)
181
Jaswal, S.K. (3.4) 91 Jaun, B. (3.3) 45 Jaworska-Augustyniak, A. (2.2)
94, 95
Jayasree, B. (3.1) (3.5)
24;
15
Jayaweira, R. (1) 59 Jazwinski, J. (3.5) 35 Jeganathan, A. (3.7) 86 Jeger, 0. (3.2) 59 Jemmis, E.D. (3.3) 57 Jenkins, A.D. (4) 292 Jenkins, S.M. (2.2) 125 Jensen, F. (1) 460 Jensen, H.P. (1) 10 Jent, F. (1) 384 Jentzer, 0. (3.7) 186 Jett, J.H. (1) 512 Jha, S.K. (2.2) 80 Jhoun, C.S. (4) 432 Ji, H. (2.2) 15, 16 Jiang, C. (4) 362 Jiang, 2. (3.2) 107; (3.5)
90
Jin, L. (2.1) 175 Jitsumatsu, T. (4) 121 Joacham, D. (1) 531 Joerg, H. (2.2) 3, 139 Johari, G.P. (4) 281 John, E. (1) 332 Johnson, D.A. (1) 502 Johnson, I.D. (1) 190 Johnson, J.F. (4) 181 Johnson, J.W. (3.7) 48 Johnson, L.B.A. (1) 130 Johnson, L.K. (2.2) 9 1 Johnson, M.L. (1) 38, 39 Johnson, M.P. (2.3) 30; (3.6)
185
Johnston, L.G.
(1) 462
518
Photochemistry
Johnston, L.J. (1) 16, 43, 102, 103; (3.1) 8; (3.4) 70, 125 Johnston, R.F. (2.2) 12 Johnston-Feller, R.M. (4) 520 Jommi, G. (3.2) 8, 22; (3.6) 153 Jones, B.J. (1) 64 Jones, G., I1 (3.2) 134 Jones, M. (3.7) 44 Jones, W.D. (2.2) 61, 66 Jones, W.M. (2.2) 93 Jongeward, K.A. (1) 510 Jordan, K. (1) 90 Jorgensen, C.K. (2.1) 190 Joins, M.S. (3.7) 165 Jortner, J. (1) 26 Jorzeba, W. (1) 227 Joseph-Nathan, P. (3.4) 109 Joshi, G.C. (1) 168 Joshi, H.C. (1) 263 Josse, D. (3.4) 80 Joussot-Dubien, J. (3.4) 87 Jovanovic, D. (4) 400 Jovin, T.M. (1) 511 Jung, J.C. (4) 20 Jureak, J.G. (3.6) 96 Juris, A. (2.1) 77
Kabachnik, M . I . (2.2) 3 1 Kabamba, M.S. (4) 358 Kabanov, V.A. (1) 297; (4) 256, 319
Kabir, S.E. (2.2) 76 Kabuto, C. (3.2) 65 Kachan, A.A. (4) 364 Kachanova, Zh.P. (3.5) 98 Kadish, K.M. (2.3) 46 Kadota, S. (3.4) 165; (3.7)
162
Kafafi, Z.H. (2.2) 137, 138
Kagan, J. (3.6) 146 Kagawa, K. (1) 65 Kagiya, T. (2.1) 11, 15; (3.5)
32, 107; (4) 214
Kahlow, M . A . (1) 163, 208 Kai, T. (4) 12 Kaim, W. (2.1) 57 Kaito, A. (4) 212 Kaizu, Y. (1) 437, 437 Kaji, M. (3.6) 69 Kaji, N. (3.5) 31 Kaj'ic, Y. (1) 148 Kajii, Y. (1) 437; (3.5) 11
Kajimoto, 0. (1) 165, 174 Kajitani, M. (2.1) 140
Kakiuchi, H. (4) 153 Kako, M. (3.5) 123 Kaldor, A. (2.1) 21 Kalechits, 1.1. (4) 256 Kallfass, D. (3.4) 13 Kallir, A.J. (1) 406 Kallmayer, H.J. (3.2) 135; (3.7)
153
Kalontarov, I.Ya. (4) 417 Kalyanasundaram, K. ( 1) 293; (2.1)
17
Kamachi, M. (1) 323; (4) 248
Kamalov, V.F. (1) 436 Kamat, P.V. (1) 225; (4) 265
Kamata, M. (3.3) 28; (3.5)
99
Kamath, A.P. (3.3) 23 Kamei, H. (1) 253 Kamernitskii, A.V. (3.2) 26
Kameta, K. (1) 490; (3.4) 110
Kameyama, A. (4) 114, 115 Kampmann, K.-H. (3.7) 71 Kamyshnyi, A.L. (2.1) 128 Kaname, M. (3.7) 96 Kanaoka, Y. (3.2) 1, 88, 119, 126, 127; (3.4) 134; (3.5) 105, 106; (3.6) 15, 28, 86, 162-165, 176 Kanazawa, J. (3.4) 97 Kane, V.V. (3.2) 1; (3.4) 134; (3.6) 28 Kaneko, C . (3.2) 16, 17, 40, 42; (3.6) 100, 105, 108, 111 Kaneko, M. (4) 259, 320
Kane-Maguire, N.A.P. (2.1)
37
Kaneto, K. (4) 211 Kanetsunn, H. (4) 212 Kang, H.K. (3.2) 44, 45 Kano, K. (1) 524; (3.5) 39; (4) 188
Kano, Y. (4) 245 Kanofsky, J.R. (1) 448 Kapinus, E.I. (1) 539 Kaplan, J.H. (3.6) 76 Karatsui, T. (1) 412 Karavaev, B.I. (3.5) 57 Karger, B.L. (1) 504 Karolczak, J. (2.2) 94 Karpinski, K. (4) 3, 6 Karup, G. (3.6) 80. Kasai, K. (3.2) 17, 42, 43; (3.6)
108, 109, 111
Kasai, T. (4) 153 Kaschke, M. (1) 207; (3.4)
127
Kasha, M. (1) 150 Kashima. C. (3.2) 89: (3.6)-137, '169; (317) 158 Kashimura, T. (2.2) 104
Kashoulis-Koupparis, A. (3.4)
49
Kashuba, E.V. (2.1) 12 Kaszas, G. (4) 170 Katagiri, N. (3.2) 17, 42, 43; (3.6) 104, 108, 109, 111 Kataoka, T. (3.6) 205 Kato, H. (3.4) 19; (3.5) 124; (3.6) 145 Kato, M. (2.3) 40; (4) 64, 112 Kato, S. (1) 79; (3.3) 63 Katoh, A. (3.2) 89; (3.6) 137 Katsen, J. (J.)152 Katsumo, T. (4) 272 Katsurao, T. (2.2) 118 Kattelman, E.J. (3.7) 89
Katzenellenbogen, J.A. (1) 138
Katzka, P. (1) 68 Kaub, J. (2.2) 24 Kauer, W. (1) 508 Kauffmann, H.F. (1) 137 Kaufmann, D. (3.5) 74 Kaupp, G. (3.3) 69; (3.4) 53, 55; (3.6) 101 (4) 78 (3.6) 8 (4) 137 (3.2) 40; (3.6) 100 Kawamura, S. (1) 482; (3.6) 12 Kawamura, Y. (3.4) 120 Kawano, C. (3.2) 84; (3.6) 92 Kawasaki, M. (4) 26, 131 Kawase, T. (2.3) 41; (3.6) 191 Kawski, A. (1) 188 Kazakov, V.P. (2.1) 198; (2.2) 10; (3.5) 2 Kazama, S. (3.4) 89 Kazanskii, V.B. (2.2) 30 Keeffe, J.R. (3.5) 8 Keel, M. (4) 152 Kelemen, J. (1) 415 Keller, R.A. (1) 512 Kelley, C.K. (2.1) 97 Kelley, D.F. (1) 149 Kellmann, A. (1) 481 Kellogg, M.S. (3.3) 46 Kelly, J.M. (1) 71, 515; (4) 86 Kemp, T.J. (1) 431
Kawabata, M. Kawabata, Y. Kawakami, I. Kawakami, K.
519
Author Index
Kempf, H. ( 3 . 7 ) 31 Keneko, C. ( 3 . 2 ) 4 3 ;
105
282, 392
( 3 . 6 ) 104, 109
Kennedy, J.C. ( 1 ) 523 Kennedy, J.P. ( 4 ) 170 Kercha, S.F. ( 4 ) 81 Kerkemeyer, M. ( 3 . 4 ) 86 Kermarec, M. ( 2 . 2 ) 141 Kern, J.M. ( 2 . 1 ) 163 Kerzhner, B.K. ( 3 . 6 ) 3 Kessar, S.V. ( 3 . 2 ) 120; ( 3 . 6 ) 87
Kesselmeyer, M.A. ( 3 . 1 ) 19
Kessler, H. (3.7) 88 Ketsle, G.A. ( 3 . 5 ) 52 Kettley, J.C. ( 1 ) 129 Kevan, L. ( 1 ) 318, 538 Khabashesku, V.N. ( 3 . 7 ) 145
Khalil, Z. ( 4 ) 371 Khamidova, L.G. ( 4 ) 380 Khamidullina, L.A. ( 2 . 1 ) 198
Khamzamulina, R.E. ( 4 ) 250, 268
Khan, A.U. ( 3 . 5 ) 49 Khan, M.A. ( 2 . 2 ) 29 Khannanov, N.K. ( 2 . 1 ) 9 5 , 103
Kharchenko, V.I. ( 4 ) 36 Khasawneh, I.M. ( 1 ) 348 Khechinashvili, D. ( 3 . 4 ) 127
Khemiss, A. ( 3 . 7 ) 22 Khire, U.R. ( 3 . 2 ) 56 Khodorkovskii, V.Yu. ( 3 . 6 ) 152
Khodosevich, A.O. ( 4 ) 378 Khodyrev, V.I. ( 4 ) 408 Kholodenko, Yu.V. ( 2 . 1 ) 19
Khranovskii, V.A.
102, 125
Kim, K.J. ( 4 ) 151, 152, Kim, O.K. ( 4 ) 325 Kim, S.K. ( 1 ) 239 Kim, S.S. ( 3 . 2 ) 108; ( 3 . 3 ) 2 ; ( 4 ) 328 Kim, Y.R. ( 1 ) 292 Kimura, H. ( 4 ) 137 Kimura, M. ( 2 . 1 ) 8 3 , 115 Kina, K. ( 1 ) 482; ( 3 . 6 ) 12 Kinoshita, T. ( 3 . 6 ) 1 0 ; ( 4 ) 230 Kinosita, K. ( 1 ) 500 Kira, M. ( 3 . 6 ) 187, 189 Kirchhoff, J.R. ( 3 . 1 ) 26 Kirk, A.D. ( 2 . 1 ) 36 Kirmaier, C. ( 2 . 1 ) 159 Kirmse, W. ( 3 . 7 ) 70-72
Kirsch de Mesmaeker, A. ( 2 . 1 ) 106
Kirsh, Yu.E. ( 4 ) 313 Kirski, T. ( 1 ) 260 Kiryukhin, Yu.1. ( 3 . 1 ) 5 Kiselev, M.Yu. ( 3 . 3 ) 30 Kishikawa, K. ( 3 . 6 ) 7 2 , 73
Kishimoto, T. ( 3 . 6 ) 2 Kissinger, P.T. ( 1 ) 56 Kissler, B. ( 3 . 1 ) 34 Kitaguchi, K. ( 2 . 1 ) 208 Kitahara, Y. ( 3 . 2 ) 65 Kitai, M.S. ( 4 ) 370 Kitamura, N. ( 2 . 1 ) 6 4 , 7 8 , 8 2 , 8 4 ; ( 3 . 4 ) 89
Kitanishi, T. ( 1 ) 156 Kitayama, M. ( 3 . 6 ) 73 Kitayama, T. ( 2 . 1 ) 140 Kitazaki, Y. ( 4 ) 245 Kiuchi, F. ( 3 . 2 ) 2 9 ; ( 3 . 6 ) 94
( 4 ) 81,
174
Khudyakov, I.V. ( 3 . 5 ) 12 Ki, S. ( 3 . 4 ) 57 Kido, M. ( 3 . 2 ) 55; ( 3 . 6 ) 88
Kiel, Yu.G. ( 2 . 2 ) 102 Kiesewetter, R. ( 3 . 6 ) 155 Kiffer, D. ( 3 . 7 ) 188 Kiguchi, T. ( 3 . 2 ) 57; ( 3 . 4 ) 132, 133; ( 3 . 6 ) 3 0 , 31 Kikuchi, K. ( 1 ) 409; ( 3 . 3 ) 18 Kikuchi, T. ( 3 . 4 ) 1 6 5 ; ( 3 . 7 ) 162 Kim, B.H. ( 3 . 6 ) 115 Kim, Ha-B. ( 2 . 1 ) 64, 7 8 , 84 Kim, J.H. (3.2) 8 5 ; ( 3 . 6 )
Kiwi, J. ( 2 . 1 ) 13 Klafter, J. ( 1 ) 20 Klasnic, L. ( 3 . 4 ) 17 Klein-Bolting, P. ( 1 ) 55 Kleinschmidt, J. ( 1 ) 207 Klemm, E. ( 4 ) 3 7 , 7 7 , 105 Kliger, D.S. ( 1 ) 66 Kline, E.S. ( 2 . 2 ) 138 Klingler, 0. ( 3 . 7 ) 75 Klopffer, W. ( 1 ) 137 Kloosterboer, J.G. ( 4 ) 163
Klotzbuecher, W.E.
(2.2)
4 9 , 82
Kluter, U. ( 1 ) 479 Klyuchinskii, S.A. ( 2 . 3 ) 52
Kmiecik-Lawrynowicz, G. ( 3 . 7 ) 10
Knerel'man, E.I. ( 2 . 1 )
Knight, R.E. ( 4 ) 28 Knobler, C.B. ( 2 . 2 ) 129 Knox, C.N. ( 1 ) 155, 419 Knyazhanski , M. I. ( 1 ) 157; ( 3 . 4 ) 128; ( 3 . 6 ) 41 Kobayashi, A. ( 2 . 2 ) 123 Kobayashi, E. ( 4 ) 42 Kobayashi, H. ( 1 ) 437, 490; ( 3 . 4 ) 110 Kobayashi, J. ( 2 . 1 ) 208 Kobayashi, K. ( 3 . 3 ) 7 9 , 8 0 ; ( 3 . 4 ) 48; ( 3 . 7 ) 203, 205, 206 Kobayashi, M. ( 2 . 3 ) 4 3 , 44 Kobayashi, N. ( 3 . 6 ) 67 Kobayashi, S . ( 1 ) 8 6 , 253, 530 Kobayashi, T. ( 1 ) 24, 165, 174; ( 4 ) 227, 258 Koch, H. ( 3 . 2 ) 30 Koch, T.H. ( 1 ) 213 Kochany, J. ( 3 . 4 ) 154 Kocher, M. ( 1 ) 434 Kochi, J.K. ( 3 . 3 ) 7 3 ; ( 3 . 4 ) 6 3 , 183 Kodaka, M. ( 2 . 1 ) 100 Kodera, Y. ( 1 ) 467 Koegler, J. ( 2 . 2 ) 32 Kohler, G. ( 1 ) 183 Koelle, U. ( 2 . 2 ) 122 Koenig, M. ( 2 . 3 ) 62 Koenig, P. ( 3 . 3 ) 77 Kofanov, V.I. ( 3 . 6 ) 3 Koga, G. ( 2 . 1 ) 162 Koga, N. ( 3 . 1 ) 46 Koglov, P.V. ( 4 ) 256 Kogure, M. ( 1 ) 392 Kohara, M. ( 2 . 1 ) 140 Kohler, G. ( 1 ) 76 Koike, K. ( 1 ) 409 Kojima, H. ( 3 . 5 ) 118 Kokkes, M.W. ( 2 . 2 ) 90 Kokubu, T. ( 4 ) 91 Kokubun, H. ( 1 ) 409 Koleske, J.V. ( 4 ) 157 Kolesnikov, S. P. ( 2 . 3 ) 26; ( 3 . 6 ) 199 Kolesnikova, V.V. ( 2 . 1 ) 141 Kolninov, O.V. ( 2 . 1 ) 141 Koloczek, H. ( 1 ) 442, 497 Kolomytsin, V.P. ( 4 ) 458 Komada, Y. ( 1 ) 375 Komatsu, T. ( 4 ) 109, 111 Komeno, M. ( 4 ) 17 Komiyama, M. ( 4 ) 68 Komizu, H. ( 4 ) 26 Kompa, K . I . ( 2 . 3 ) 4 Komura, A. ( 1 ) 405
Photochemistry
520 Komura, T. ( 2 . 1 ) 5 0 ; ( 3 . 7 ) 77 Konak, C. ( 4 ) 311 Konarski, J. ( 2 . 1 ) 176, 177
Konderska-Olexinska , D. ( 2 . 1 ) 169
Kondratenko, N.V.
(3.7)
101
Kondratenko, P.A.
(3.7) 101; ( 4 ) 435 Koneda, N. ( 1 ) 509 Kong, H . ( 3 . 4 ) 62 Kong, T.J. ( 1 ) 163, 208 Konopikova, M. ( 3 . 6 ) 52 Kontos, E.G. ( 4 ) 287 Kopecky, J. ( 3 . 2 ) 118 Kopelman, R . (1) 355 Kopyl, O.N. ( 4 ) 378 Kordonskii, L.E. ( 4 ) 354 Kornblum, N. ( 3 . 4 ) 179 Korolev, V.V. ( 1 ) 420 Koroteev, N.I. ( 1 ) 436 Korshak, V.V. ( 4 ) 138 Korvatovsky, B.N. ( 1 ) 535 Korzhak, A.V. ( 2 . 1 ) 1 9 , 20 Koseki, K. ( 4 ) 139, 164 Koshioka, M. ( 3 . 4 ) 97 Kosower, E.M. ( 1 ) 268, 269; ( 3 . 7 ) 147 Kossanyi, J. ( 3 . 1 ) 48 Kossanyi, S. ( 1 ) 159 Kostikov, R.R. ( 3 . 3 ) 30 Kostomarov, V.B. ( 4 ) 378 Kostyanovskii, R.G. ( 3 . 7 ) 200 Kotov, S. ( 4 ) 21 Kotulak, L. ( 4 ) 359 Kotzian, M. ( 2 . 2 ) 139 Koviak, C. ( 2 . 2 ) 157 Kowalczik, U. ( 3 . 7 ) 24 Koyama, K. ( 3 . 7 ) 104 Koyama, Y. ( 1 ) 234, 364 Kozhina, N.D. ( 3 . 6 ) 5 0 , 51 Koziol, A.E. ( 2 . 2 ) 93 Kozlov, Yu.N. ( 3 . 5 ) 98 Koz'menko, M.V. (I) 252 Krabichler, G. ( 1 ) 346 Krafft, G . A . ( 1 ) 486; ( 3 . 4 ) 29 Kraft, A. ( 3 . 7 ) 28 Krakovyak, M.G. ( 4 ) 313 Kralzic, I. ( 3 . 4 ) 17 Kramer, H.E.A. ( 1 ) 222, 415 Kramer, W. ( 3 . 7 ) 81 Kranganz, V. ( 4 ) 249 Kraus, G.A. ( 3 . 7 ) 214 Krause, R.A. ( 2 . 1 ) 2 Krausz, E. ( 2 . 1 ) 6 7 , 69
Krausz, P. ( 2 . 1 ) 18 Kreiter, C.G. ( 2 . 2 ) 8 , 24, 32, 47, 48 (3.1) 12; ( 3 . 5 ) 8 , 26; ( 3 . 7 ) 59 Kresin, V.Z. ( 1 ) 366 Krestonosich, S . ( 3 . 4 ) 95 Krijnen, E.S. ( 3 . 4 ) 37 Krishna, A. ( 3 . 2 ) 6 1 ; ( 3 . 4 ) 142; ( 3 . 5 ) 110 Krishnamurthy, M. ( 1 ) 98 Krishnan, A.M. ( 3 . 6 ) 81 Krishnan, V. ( 2 . 1 ) 17 Kristian, P. ( 3 . 4 ) 135, 136; ( 3 . 7 ) 170, 171 Krivopalov, V.P. ( 3 . 7 ) 102 Krivykh, V.V. ( 2 . 2 ) 23, 74 Krogh, E. ( 3 . 4 ) 177; ( 3 . 7 ) 106 Krogh-Jespersen, K. ( 3 . 7 ) 8 , 10 Kron, J. ( 3 . 7 ) 15 Kronfeld, K.P. ( 4 ) 51 Kronganz, E.S. ( 4 ) 138 Krongauz, V. ( 1 ) 413; ( 3 . 6 ) 20 Kropp, M. ( 3 . 4 ) 105 Kriiger, C. ( 3 . 6 ) 57 Krueger, G. ( 2 . 1 ) 130 Kruegerke, T. ( 2 . 3 ) 68 Kruepfer, L. ( 4 ) 508 Kruse, L . I . ( 3 . 7 ) 13 Kryukov, A . I . ( 2 . 1 ) 1 9 , 20, 42 Krzeczek, J. ( 3 . 4 ) 1 4 ; ( 3 . 6 ) 17 Krzyminiewoski, R. ( 4 ) 48 Ksenofontova, N.M. ( 3 . 5 ) 4 3 ; ( 4 ) 507 Kubo, M. ( 3 . 7 ) 161 Kubo, Y. (3.2) 1 2 8 ; ( 3 . 6 ) 173; ( 4 ) 248 Kubota, M. ( 2 . 2 ) 113, 146 Kubota, S. ( 4 ) 116, 117 Kubota, T. ( 3 . 2 ) 105 Kucherova, I.Y. ( 1 ) 539 Kuchmii, S.Ya. ( 2 . 1 ) 1 9 , 2 0 , 42 Kudo, A. ( 2 . 1 ) 10 Kudo, K. ( 2 . 2 ) 104 Kiimmell, A. ( 3 . 6 ) 66 Kuestermann, E. ( 4 ) 13 Kuesthardt, U. ( 2 . 2 ) 58 Kuhn, D. ( 1 ) 415 Kuhnle, W. ( 1 ) 124 Kulikova, V.A. ( 4 ) 356 Kulpe, J. ( 2 . 2 ) 58 Kum, J.U. ( 2 . 3 ) 13 Kumagai, T. ( 3 . 6 ) 106 Kumamoto, Y. ( 2 . 3 ) 6 9 ;
Kresge, A . J .
( 3 . 6 ) 206; ( 3 . 7 ) 3 6 , 126 Kumar, C.V. ( 2 . 1 ) 66 Kumaraswamy, G. ( 3 . 2 ) 6 1 ; ( 3 . 5 ) 110 Kumari, S. ( 3 . 5 ) 97 Kumazoe, M. ( 2 . 2 ) 142 Kumitskaya, L . R . ( 4 ) 40 Kundu, L. ( 1 ) 179 Kunieda, T. ( 3 . 2 ) 8 4 ; ( 3 . 6 ) 92 Kunitake, T. ( 1 ) 330; (3.6) 6 Kunkely, H . ( 2 . 1 ) 4 1 , 131 Kuo, L. ( 2 . 2 ) 146 KUO, P.-L. ( 1 ) 302; ( 4 ) 54, 277 Kuo, Y.H. ( 3 . 5 ) 100 Kurahashi, N. ( 3 . 7 ) 139 Kuramada, T. ( 4 ) 478 Kuramoto, N. ( 4 ) 497, 503, 517 Kurihara, S. ( 3 . 6 ) 7 Kurimoto, H. ( 4 ) 78 Kurimoto, I. ( 2 . 1 ) 98 Kurita, J. ( 3 . 3 ) 3 8 ; ( 3 . 5 ) 1 1 8 ; ( 3 . 6 ) 18 Kurita, Y. ( 3 . 4 ) 126; ( 3 . 5 ) 104 Kurkina, L.G. ( 4 ) 516 Kuroda, S. ( 2 . 3 ) 5 5 ; ( 3 . 5 ) 95 Kurokawa, K. ( 1 ) 24 Kurokawa, M. ( 2 . 2 ) 1 9 ; ( 3 . 6 ) 132 Kuroki, M. ( 4 ) 69 Kurtz, I. (1) 68 Kurumisawa, H. ( 3 . 5 ) 124 Kurz, M.E. ( 3 . 4 ) 86 Kusba, J. ( 1 ) 258 Kushner, A.S. ( 3 . 4 ) 45 Kutal, C. ( 2 . 1 ) 97 Kutschabsky, L. ( 3 . 7 ) 133 Kutschy, P. ( 3 . 4 ) 135, 136; ( 3 . 7 ) 170, 171 Kuwabara, H. ( 2 . 3 ) 40 Kuzmic, P. ( 3 . 1 ) 4 4 ; ( 3 . 4 ) 6 7 , 6 8 , 6 9 , 71 Kuzmin, G.M. ( 4 ) 256 Kuzmin, M.F. ( 1 ) 539 Kuzmin, M.G. ( 1 ) 297, 321; ( 3 . 4 ) 8 1 ; ( 3 . 7 ) 197 Kuz'min, V.A. ( 1 ) 358, 360; ( 2 . 1 ) 103; ( 3 . 2 ) 130, 132; ( 3 . 5 ) 1 2 ; ( 3 . 6 ) 199; ( 4 ) 516 Kvach, V.V. ( 1 ) 436 Kwei, T.K. ( 4 ) 373 Kwiatkowski, E. ( 2 . 1 ) 169 Kwok, J.C.T. ( 1 ) 311 Kwong, K.S. ( 3 . 3 ) 15
Author Index
Laarhoven, W. ( 1 ) 125; ( 3 . 3 ) 3 2 ; ( 3 . 4 ) 6 , 119 Lablache-Combier, A. ( 1 ) 520; ( 3 . 2 ) 7 1 , 7 2 ; ( 3 . 6 ) 3 5 ; ( 4 ) 122 Labsky, J. ( 4 ) 311 Lacher, B. ( 3 . 7 ) 112, 116, 117 Lacoste, J. ( 4 ) 518 Ladd, D.L. ( 3 . 7 ) 13 Lakowicz, J.R. ( 1 ) 38, 3 9 , 59, 489 Laliberte', S. ( 1 ) 220 Lalley, J.M. ( 3 . 4 ) 3 4 ; ( 3 . 6 ) 151 Lalo, C. ( 2 . 3 ) 59 Lalsky, J. ( 4 ) 306 La Mantia, F.P. ( 4 ) 357 Lambert, C. ( 3 . 5 ) 7 Lammel, U. ( 3 . 4 ) 148 Lamont, L.J. ( 3 . 3 ) 8 6 ; ( 3 . 4 ) 182 Lamotte, M. ( 3 . 4 ) 87 Lampeda, Ya.D. ( 2 . 1 ) 120, 121 Lan, J.Y. ( 3 . 5 ) 94 Land, E.J. ( 1 ) 419, 459 Landers, J.P. ( 3 . 4 ) 98 Lando, J.B. ( 4 ) 169 Langa, F. ( 3 . 3 ) 21, 2 2 ; ( 3 . 6 ) 4 3 , 44 Langford, C.H. ( 2 . 1 ) 118 Langhals, H. ( 1 ) 200 Langhorst, M.A. ( 4 ) 317 Langshaw, J.A. ( 3 . 4 ) 98 Lan-Hargest, H.-Y. ( 3 . 3 ) 4 3 ; ( 3 . 7 ) 142 Lapa, L. ( 4 ) 21 Lapin, S.C. ( 3 . 7 ) 47 Laplante, J.P. ( 1 ) 483 Lapouyade, R. ( 1 ) 191; ( 3 . 4 ) 8 7 , 140 Lappas, D. ( 2 . 2 ) 62 Lattanzi, G. ( 2 . 1 ) 183 Lattes, A. ( 1 ) 295 Launay, J.P. ( 2 . 1 ) 71 Launikonis, A. ( 1 ) 305; ( 4 ) 278 Laurinas, V.Ch. ( 3 . 5 ) 52 Lavabre, D. ( 1 ) 483; ( 3 . 4 ) 102 Lavieri, F.P. ( 3 . 2 ) 93 Lawrynowicz, W. ( 3 . 7 ) 7 Lazara, S. ( 3 . 4 ) 140 Lazarenko, E.T. ( 4 ) 378 Lazarev, G.G. ( 3 . 5 ) 1 6 ; ( 3 . 7 ) 200 Lazortchak, N. ( 1 ) 457 Leaver, I.H. ( 1 ) 1 4 6 ; ( 4 ) 465, 466 Lebedev, V.B. ( 2 . 3 ) 52 Lebedev, Ya.S. ( 3 . 5 ) 1 6 ;
521 ( 3 . 7 ) 200
Leblanc, R.M. ( 1 ) 328 Le Breton, G.C. ( 3 . 7 ) 89 Lechevallier, A. ( 3 . 7 ) 188
Leckta, T.C. ( 3 . 2 ) 5 Lederev, P. ( 2 . 1 ) 38, 62 Ledermann, M. ( 3 . 6 ) 58 Ledoux, I. ( 3 . 4 ) 80 Ledwith, A. ( 4 ) 35 Lee, C.Y. ( 2 . 2 ) 25, 77-79 Lee, D.G. ( 2 . 1 ) 52 Lee, D.H. ( 2 . 2 ) 100 Lee, H.C. ( 3 . 6 ) 126 Lee, J. ( 1 ) 228-230; ( 4 ) 8 9 , 441
Lee, K.T. ( 1 ) 145 Lee, K.W. ( 2 . 2 ) 46 Lee, L.C. ( 2 . 3 ) 66 Lee, M. ( 1 ) 141, 292; ( 3 . 3 ) 3 6 ; ( 3 . 7 ) 192
Lee, S.G. ( 3 . 6 ) 200 Lee, S.H. ( 1 ) 468; ( 2 . 1 ) 3 0 ; ( 4 ) 346 (3.3) 2 ( 1 ) 173 (3.7) 1 ( 4 ) 213 (3.2) 85; (3.6) 102 Leeds, A. ( 3 . 4 ) 86 Leela, G. ( 3 . 3 ) 57 Lees, A.J. ( 2 . 2 ) 21, 22, 54 Lega, M. ( 2 . 1 ) 114 Legendre, 0. ( 2 . 2 ) 141 Lehn, J.M. ( 2 . 1 ) 9 3 , 182, 184; ( 3 . 5 ) 35 Leibnitz, P. ( 3 . 7 ) 133 Leigh, W.J. ( 3 . 3 ) 19 Leiner, M.J.P. ( 1 ) 5 , 542 Leinhos, U. ( 4 ) 103 Lejeune, V. ( 1 ) 367 Lemaire, J. ( 3 . 4 ) 7 2 ; ( 4 ) 33, 365, 371, 384, 416 Lemaistre, J.-P. ( 1 ) 351 Lemaitre, E. ( 4 ) 122 Lendzion, F. ( 1 ) 474 Lenka, S . ( 4 ) 107, 179 Lenoble, C. ( 1 ) 429, 438 Lenz, G.R. ( 3 . 6 ) 26 Lenz, H. (1) 531 Leone, S.R. ( 2 . 3 ) 70 Lepetit, C. ( 2 . 2 ) 141 Lerkeu, M.L. ( 4 ) 29 Lerner, D. ( 2 . 1 ) 75 Lesage, M. ( 2 . 3 ) 25 Leshina, T.V. ( 2 . 3 ) 4 5 ; ( 3 . 6 ) 197 L'Esperance, R.P. ( 3 . 7 ) 44 Lessard, J. ( 3 . 7 ) 198
Lee, T.S. Lee, V.Y. Lee, W.K. Lee, Y.D. Lee, Y.S.
Lessard, R.B. ( 2 . 1 ) 1 Lester, W.A. (1) 366 Leung, H. ( 3 . 5 ) 82 Leupacher, W. ( 1 ) 198, 215
Levanon, H. ( 1 ) 434, 536 Lever, A.B.P. ( 2 . 1 ) 88 Levin, P.P. ( 1 ) 358, 360; ( 2 . 1 ) 103; ( 3 . 2 ) 130, 132; ( 3 . 5 ) 12 Levina, I.S. ( 3 . 2 ) 26 Levine, L.M.A. ( 1 ) 525; ( 2 . 1 ) 81 Levine, S.G. ( 3 . 3 ) 6 Levine, Y.K. ( 1 ) 333 Levshin, L.V. ( 3 . 5 ) 52 Levy, G. ( 1 ) 483 Lewis, D.M. ( 4 ) 498, 499 Lewis, F.D. ( 3 . 2 ) 48 Lewis, J.W. ( 1 ) 66 Leyendecker, M. ( 2 . 2 ) 47 Li, E. ( 2 . 2 ) 155 Li, M. ( 4 ) 5 5 , 229 Li, S . ( 2 . 2 ) 155 Li, T. ( 4 ) 96 Li, W. ( 2 . 1 ) 170, 181; ( 4 ) 229, 251, 428 Li, X.J. ( 2 . 1 ) 186, 187 Li, Y. ( 2 . 1 ) 1 6 8 ; ( 3 . 7 ) 5 4 , 55 Liang, R.C. ( 4 ) 46 Liang, T.-Y. ( 1 ) 470; ( 3 . 7 ) / 85 Liang, X. ( 3 . 5 ) 30, 33 Liang, 2. ( 4 ) 229, 428 Lianos, P. ( 1 ) 303 Ligan, W.V. ( 4 ) 421 Lijten, G.F.C.M. ( 4 ) 163 Lilie, J. ( 2 . 1 ) 30 Lim, C.T. ( 3 . 7 ) 89 Lim, E.C. ( 1 ) 7 2 , 73 Lin, C.H. ( 2 . 2 ) 2 5 , 77-79 Lin, C.T. ( 1 ) 342 Lin, H.-S. ( 3 . 2 ) 31 Lin, S. ( 2 . 1 ) 205; ( 3 . 4 ) 1 0 ; ( 3 . 6 ) 65 Lin, W.H. ( 4 ) 336 Lin, 2. ( 3 . 6 ) 180 Linden, J. ( 3 . 7 ) 90 Linden, S.M. ( 1 ) 221, 224, 463; ( 4 ) 238 Lindenberger, H. ( 4 ) 318 Lindner, T. ( 1 ) 415 Lindsay, J.S. ( 1 ) 528
Lindstrom, M.J. (3.7) 135, 136
Link, P.A.J. ( 3 . 5 ) 38 Linschitz, H. ( 1 ) 528 Lipatov, Yu.S. ( 4 ) 8 1 , 174
Lipczynska-Kochany, E. ( 1 ) 101; ( 3 . 4 ) 154
522 Lippert, E. ( 1 ) 22 Lippitsch, M.E. ( 1 ) 5 Lippmas, J. ( 1 ) 270 Lipsky, S. ( 1 ) 77 Liptay, W. ( 1 ) 3 1 , 3 2 , 115
Lis, S. ( 2 . 1 ) 176, 177 Lissi, E. ( 4 ) 6 7 , 219 Little, R.D. ( 3 . 7 ) 21 Liu, C.S. ( 2 . 2 ) 2 5 , 77-79 Liu, F. ( 4 ) 362 Liu, J.X. ( 1 ) 178 Liu, L. ( 3 . 6 ) 1 1 8 ; ( 4 ) 467
Liu, M.T.H. ( 3 . 7 ) 5 , 6 Liu, R. ( 3 . 6 ) 2 2 ; ( 3 . 2 ) 6 7 ; ( 3 . 3 ) 44 Liu, W. ( 2 . 1 ) 199; ( 4 ) 2 29 Liu, X. ( 3 . 2 ) 8 2 ; ( 3 . 6 ) 1 1 0 ; ( 3 . 2 ) 37 Liu, X.Y. ( 3 . 4 ) 47 Liu, Y. ( 2 . 2 ) 1 5 , 16 Liu, Z. ( 2 . 3 ) 3 1 , 7 1 ; ( 3 . 5 ) 96 Liver, N. ( 1 ) 26 Lluch, J.M. ( 3 . 5 ) 41 Locke, R.J. ( 1 ) 7 2 , 73 Locke, S.J. ( 3 . 5 ) 70 Lockwood, F.E. ( 4 ) 7 3 Lodder, G . ( 3 . 4 ) 3 7 , 64 Loder, J. ( 1 ) 197 Lofters, S . ( 2 . 1 ) 7 9 Lohray, B.B. ( 3 . 2 ) 7 6 ; ( 3 . 4 ) 118 Lohse, C. ( 3 . 4 ) 1 6 7 ; ( 3 . 6 ) 64 Loim, N.M. ( 2 . 2 ) 51 Lombardo, D.A. ( 3 . 5 ) 25 Lomolder, R. ( 3 . 7 ) 123 Long, T.D. ( 4 ) 325
Lopes-Espinosa, M.T.P. ( 3 . 5 ) 101
Lopez, A.F.J. ( 3 . 5 ) 101 Lopez-Arbeloa, F. ( 1 ) 194 Lorenz, I.P. ( 2 . 2 ) 8 8 Losev, A.P. ( 1 ) 4 5 0 ; ( 3 . 5 ) 48
Loucheux, C. ( 4 ) 122 Loughnot, D.G. ( 1 ) 432 Lougnot, D.J. ( 4 ) 5 1 , 5 3 , 57
Loutfy, R.O. ( 4 ) 207 Loutz, J.M. ( 4 ) 29 Lovgren, T. ( 1 ) 9 L o n , E.M. ( 3 . 4 ) 7 Loye, B.A. ( 4 ) 19 Loza, R. ( 1 ) 314 Lu, T.J. ( 3 . 5 ) 119 Lu, X.-M. ( 1 ) 504 Luc-Gardette, J. ( 4 ) 1 2 6 , 365, 393
Photochemistry
Ludman, C.J. ( 3 . 7 ) 38 Ludmer, Z. ( 1 ) 118 Ludwig, M. ( 1 ) 488 Lueck, H. ( 1 ) 90 Lugovskii, A.P. ( 3 . 5 ) 43 Lugtenburg, J. ( 3 . 5 ) 10; (3.6) 71
Lukac, I. ( 4 ) 427 Lunak, S. ( 1 ) 9 3 Luneva, N.P. (2.1) 104 Luo, H. ( 1 ) 5 3 , 301 Lushchik, V.B. ( 4 ) 307, 313
Luston, J. ( 4 ) 454 Lusztyk, J. ( 3 . 7 ) 1 1 0 , 1 2 4 , 125
Luttrull, D.K. ( 1 ) 221 Lyashenko, L.V. ( 2 . 1 ) 1 2 ; ( 3 . 5 ) 75
Lyashik, O.T. ( 3 . 4 ) 128 Lynch, J.C. ( 4 ) 422 Lytle, F.T. ( 1 ) 56 Lyubarskaya, A.E. ( 3 . 6 ) 4 0 , 41
1 6 2 , 165, 176
Maciejewski, A. ( 1 ) -427, 428; ( 2 . 2 ) 94
Macielag, M. ( 3 . 2 ) 9 3 , 99 MacInnis, J.M. ( 1 ) 356 McIntosh, A.R. ( 1 ) 196 McKeithan, D.N. ( 1 ) 35 McKenney, J.D. ( 3 . 4 ) 1 3 8 ; ( 3 . 6 ) 148
McLauchlan, K.A. ( 1 ) 473 McLearie, J. ( 1 ) 461 McLendon, G. ( 1 ) 485 MacLeod, H. ( 3 . 5 ) 86 McMahon, R.J. ( 3 . 7 ) 48 McMaster, A.D. ( 2 . 2 ) 130 McMillin, D.R. ( 2 . 1 ) 159-161
McMurry, T.B.H. ( 3 . 2 ) 9 ; ( 3 . 4 ) 50
Macova, E. ( 2 . 1 ) 3 8 , 62 McWhorter, W.W. ( 3 . 3 ) 45 Madge, D. ( 1 ) 510; ( 2 . 1 ) 1 3 4 , 135
Maeda, K. ( 2 . 1 ) 4 4 ; ( 3 . 5 ) 85
Ma, H. ( 2 . 1 ) 199 Ma, J. ( 3 . 6 ) 144 Ma, S . ( 3 . 1 ) 4 1 ; ( 3 . 7 ) 120
Ma, X.H. ( 4 ) 41 Ma, Z. ( 4 ) 483 Maas, G. ( 3 . 7 ) 3 7 , 6 4 Mabiala, G. ( 3 . 2 ) 6 2 ; ( 3 . 6 ) 36
Mac, M. ( 1 ) 187 McAuley, I. ( 3 . 4 ) 1 7 7 ; ( 3 . 7 ) 106
McCalla, D.R. ( 3 . 6 ) 1 McCamley, A. ( 2 . 2 ) 121 McCann, M.P. ( 1 ) 8 0 McCarry, B.E. ( 3 . 6 ) 1 McCarthy, P.J. ( 3 . 3 ) 36 McCleland, C.W. ( 3 . 7 ) 199 MacColl, R. ( 1 ) 275 McConnell, D.J. ( 1 ) 515 McCormick, C.L. ( 4 ) 310 McCubbin, I. ( 1 ) 382 McCullough, J.J. ( 3 . 4 ) 1 ; ( 3 . 6 ) 90
McDonald, D.B. ( 1 ) 185 MacEachern, A. ( 1 ) 454 McElwee-White, L. ( 3 . 7 ) 19
McEwen, J. ( 3 . 3 ) 1 McGarvey, D.J. ( 3 . 2 ) 5 , 6 McGimpsey, W.G. ( 1 ) 1 6 , 387; ( 3 . 7 ) 4 9 McGown, L.B. ( 1 ) 3 , 8 , 299, 300 Machida, M. ( 3 . 2 ) 1 1 9 , 126, 1 2 7 ; ( 3 . 6 ) 8 6 ,
Maeda, M. ( 4 ) 272, 315 Maeda, T. ( 1 ) 311 Maekawa, Y. ( 1) 1 4 8 ; ( 3 . 3 ) 63
Miirkl, G. ( 3 . 7 ) 42 Maertin, R. ( 4 ) 168 Maestri, M. ( 2 . 1 ) 144 Magaryan, A.Kh. ( 3 . 2 ) 25 Magde, D. ( 2 . 1 ) 28 Magdinets, V.V. ( 4 ) 36 Magnier, J. ( 2 . 1 ) 7 1 Maguire, J.A. ( 2 . 2 ) 61 Mahaffy, P.G. ( 3 . 7 ) 58 Mahon, P. ( 4 ) 471 Mahran, R.M. ( 3 . 2 ) 50 Maidan, R. ( 2 . 1 ) 101 Maier, A. ( 1 ) 222 Mafer, G. ( 3 . 7 ) 24 Mafer, V.E. ( 2 . 1 ) 9 5 , 1 0 4 , 132
Maillard, B. ( 3 . 7 ) 110 Maillard, P. ( 2 . 1 ) 18 Mafllos, Ph. ( 3 . 7 ) 188 Majeed, N.N. ( 3 . 6 ) 140 Majewski, M. ( 3 . 7 ) 49 Majima, T. ( 2 . 2 ) 19 Majumdar, R.B. ( 3 . 2 ) 1 ; ( 3 . 6 ) 28
Makarova, N.I. ( 3 . 6 ) 41 Makedonov, Yu.V. ( 4 ) 354 Maki, A.H. ( 1 ) 397, 425, 503
Maki, Y. ( 3 . 5 ) 1 1 4 ; ( 3 . 7 ) 139
Makino, K. ( 3 . 4 ) 1 6 5 ; ( 3 . 7 ) 162
Makita, Y. ( 3 . 4 ) 8 4 ;
Author Index (3.7) 176 Makowska, B. (2.1) 176, 177 Malati, M.A. (2.1) 14 Malkhasian, A.Y.S. (2.1) 118 Malkin, Ya.N. (3.7) 157 Malliaris, A. (1) 53, 296, 301, 304 Mallory, C.W. (3.4) 8 Mallory, F.C. (3.4) 8 Mallouk, T.E. (2.1) 207 Maloney, C. (1) 71 Mal'tsev, A.K. (3.7) 4, 145 Mamaev, V.P. (3.7) 102 Mamedova, R.A. (4) 491 Mamedova, S.G. (4) 165 Mamykin, A.V. (2.1) 198 Manabe, 0. (3.6) 11 Manavi, M. (1) 173 Mandler, D. (2.1) 99, 101 Manenkov, A.A. (4) 377 Mang, J. (3.4) 61 Mani, R.S. (3.7) 86 Maniara, G. (1) 442 Maniero, A.L. (1) 400 Manmade, A. (3.1) 42 Mann, K.R. (2.2) 113 Manoharan, R. (1) 96, 133-135 Manojlovic-Muir, L. (2.2) 85 Mansanet, I.S.M. (1) 371 Mansilla, H. (4) 411 Mansour, A. (3.5) 67 Mansour, E.M.K. (2.1) 18 Manzarbeitia, J .A. (4) 222 Mapelli, C. (3.7) 14 Marais, P.C. (3.7) 134 Marcandalli, B. (4) 510 Marcantonatos, M.D. (2.1) 190 Marchaj, A. (2.1) 26 Marchetti, V. (3.3) 59 Marciniak, B. (3.5) 9 Marcondes, M.E.R. (4) 415 Maree, S.N. (3.4) 18 Margaretha, P. (3.1) 13, 15: (3.2) 79: (3.6) 155 Margolin, A.L. (4) 354, 408 Margrave, J.L. (2.2) 137, 138 Mari, S. (2.2) 104 Mariano, P.S. (2.3) 13; (3.3) 4; (3.4) 5, 117: (3.6) 122-125 Marinas, J.M. (3.5) 76 Markiewicz, A. (4) 330 Marko, J. (1) 520
523
Markov, V.I. (4) 488 Marogi, A. (4) 469 Maroncelli, M. (1) 27 Maroshina, M.Yu. (2.3) 65 Marples, B.A. (3.1) 16 Marquet, J. (3.4) 65, 66; (3.5) 41 Marschke, G.E. (3.7) 1 Marshalkovich, A.S. (4) 254 Marshall, G.P. (4) 476 Marshall, J.L. (2.2) 131 Marterer, W. (3.7) 76 Martin, A.R. (3.2) 1; (3.4) 134; (3.6) 28 Martin, E. (1) 100 Martin, J.C. (1) 512 Martin, N. (3.3) 76; (3.7) 160 Martinez, C. (3.4) 95 Martinez, G. (4) 366, 367 Martinez-Utrilla, R. (4) 222, 233 Martinotti, F. (4) 353 Martins, F.J.C. (3.2) 140: (3.6) 136 Martins, L.J.A. (1) 431 Martirosyan, G.T. (4) 490 Martl, M.G. (4) 147 Maruyama, K. (2.1) 10; (2.3) 56; (3.1) 28, 54; (3.2) 80, 133; (3.3) 58: (3.4) 85: (3.6) 132: (3.7) 175 Maruyama, Y. (1) 110 Maryasova, V.I. (2.3) 45: (3.6) 197 Marzin, C. (2.1) 75 Marzocchi, M.P. (1) 117 Masamune, S. (2.3) 41; (3.6) 191 Masanet, J. (2.3) 59 Mascal, M. (3.4) 143, 144; (3.7) 167, 168 Masetti, F. (1) 242, 243 Mashirov, L.G. (2.1) 196 Maslyuk, A.F. (4) 81, 174 Maslyukov, A.P. (4) 377 Massa, W. (3.6) 66 Massafra, M.R. (4) 512 Massara, R. (2.1) 175 Masschelein, A. (2.1) 106 Masuhara, H. (1) 277, 278, 386; (4) 193, 329 Masui, Y. (3.2) 49 Masuko, F. (4) 439 Mataga, N. (1) 166, 171, 172, 176, 193, 234, 280, 359, 509 Mateo, J.L. (4) 127, 222 Mathews. C.K. (2.1) 204 Mathis,-G. ( 2 . i ) 184
Mathur, N. (3.4) 172; (3.7) 152 Mathur, P. (2.2) 80 Matienzo, L.J. (4) 181 Matlin, A.R. (3.2) 5, 6 Matoba, K. (3.2) 78, 94; (3.6) 24 Matsubara, H. (4) 121 Matsubayashi, G. (2.2) 55 Matsuda, A. (3.7) 129, 130 Matsuda, M. (4) 308 Matsuhiro, Y. (2.2) 142 Matsumoto, H. (2.3) 37: (3.1) 32 Matsumoto, M. (2.2) 110 Matsumoto, T. (4) 14, 76 Matsumura, N. (3.6) 171 Matsuo, K. (3.4) 15 Matsushima, A. (1) 467 Matsushima, R. (1) 156 Matsuura, T. (1) 246, 490, 491; (3.1) 55; (3.2) 101-103; (3.3) 8; (3.4) 16, 61, 90, 108, 110, 111; (3.5) 17, 100, 116; (3.6) 5, 135 Matsuzaki, Y. (3.4) 60 Mattay, J. (3.4) 3, 38, 39; (3.6) 116 Mattes, S.L. (3.4) 4 Matthews, R.S. (3.2) 14 Mattice, W.L. (4) 305 Matveev, M.Yu. (4) 327 Matyushin, G.A. (4) 377 Mau, A.W.H. (1) 197, 305, 343; (4) 278 Maurer, R. (1) 506, 507 Mauzerall, D.C. (1) 528 Maverick, A.W. (2.1) 22 Maxfield, P.L. (2.1) 188 Maxka, J. (2.3) 3 Maxwell, B.D. (1) 82; (3.1) 49 May, R.J. (4) 421 Mayes, R.T. (2.3) 22 Mayr, U. (2.2) 152 Mazuronok, L.A. (4) 175 Mazzocchi, P.H. (3.2) 123-25: (3.4) 52; (3.6) 118-20 Mazzucato, V. (1) 189, 242, 243, 251 Meahcov, L. (2.1) 114 Mechin, R. (1) 452 Medina, P. (1) 424, 540 Medvedenko, L.I. (3.7) 101 Medyantseva, E.A. (3.4) 128 Meesen, A.W. (4) 263 Mehandru, S.P. (3.5) 61
5 24 Mehring, M. ( 4 ) 228 Mehrsheikh-Mohammadi, M.E. ( 3 . 7 ) 53 Mehta, G. ( 3 . 2 ) 7 , 116; ( 3 . 3 ) 55-57
Mehta, S. ( 3 . 4 ) 153; ( 3 . 6 ) 27
Meichsner, G. ( 3 . 7 ) 32 Meier, H. ( 3 . 3 ) 77 Meier, K. ( 2 . 2 ) 1 1 ; ( 4 ) 160
Meister, E.C. ( 1 ) 55 Mekera, H. ( 3 . 7 ) 141 Mele, E.J. ( 4 ) 324 Meli, A. ( 2 . 1 ) 137 Meling, H. ( 1 ) 411 Mel'nikov, M.J. ( 4 ) 376 Melzig, M. ( 1 ) 478, 479 Memarian, R. ( 3 . 4 ) 51 Mendenhall, G.D. (1) 468; ( 4 ) 323
Mendicuti, F. ( 4 ) 305 Meng, J. ( 3 . 2 ) 102, 103; (3.4) 16; (3.5) 17, 116; ( 3 . 6 ) 135 Meno, M. ( 4 ) 16 Menzel, R. ( 1 ) 1 4 , 8 7 , 9 0 , 204, 205 Merati, F. ( 3 . 6 ) 153 Mercier, G. ( 1 ) 505 Mercier, R. ( 4 ) 122 Messelhaeuser , J. ( 2 . 2 ) 88 Metcalf, B.W. ( 3 . 3 ) 4 3 ; ( 3 . 7 ) 142 Metelitsa, A.V. ( 3 . 4 ) 128 Metev, S. ( 2 . 2 ) 3 Meth, J.S. ( 1 ) 271 Meth-Kohn, 0. ( 3 . 7 ) 134 Metwally, M . A . ( 3 . 2 ) 5 1 ; ( 3 . 4 ) 156 Meyer, F.K. ( 4 ) 453 Mi, X. ( 1 ) 289 Mialocq, J . C . ( 1 ) 167 Mibu, K. ( 1 ) 375 Michaille, S. ( 4 ) 371 Michalczyk, M . J . ( 3 . 6 ) 177 Micheau, J.C. ( 1 ) 483
Michel-Beyerle, M.E. (1) 164
Michels, E. ( 2 . 2 ) 24 Michels, G . ( 3 . 6 ) 58 Michl, J. ( 2 . 3 ) 1 4 ; ( 3 . 6 ) 177, 194; ( 4 ) 240
Midorikawa, K. ( 2 . 1 ) 139 Miehg, J . A . ( 1 ) 195 Miejer, E.W. ( 4 ) 255 Mieloszyk, J. ( 4 ) 244 Miesch, M. ( 3 . 7 ) 31 Migirdicyan, E. ( 1 ) 367 Mihaila, G. ( 4 ) 79
Photochemistry Mihashi, S . ( 3 . 1 ) 32 Mikhailishin, P.D. ( 4 ) 141
Mikhailov, V.P. ( 1 ) 214 Miki, S. ( 3 . 4 ) 15 Mikulova, M. ( 4 ) 427 Milinchuk, V.K. ( 2 . 1 ) 141; ( 4 ) 380
Millan, J . L . (4) 366, 367 Millard, R.R. ( 1 ) 290 Miller, M.E. ( 2 . 2 ) 75 Miller, R.D. ( 4 ) 11 Milligan, B. ( 4 ) 404 Milone, L. ( 2 . 2 ) 99 Milosavljevic, B.H. ( 1 ) 127
Minami, M. ( 1 ) 416 Mindl, A. ( 1 ) 478 Minemura, N. ( 4 ) 431 Mines, S.A. ( 3 . 3 ) 14 Ming, Y. ( 3 . 2 ) 9 2 ; (3.5) 7 8 , 7 9 ; ( 3 . 6 ) 48
Mingbo, H. ( 4 ) 479 Minkin, V . I . ( 3 . 4 ) 128; ( 3 . 6 ) 4 0 , 41
Mintas, M. ( 3 . 2 ) 4 6 ; ( 3 . 4 ) 17
Miola, L. ( 1 ) 9 2 , 334 Miranda, M.A. ( 3 . 1 ) 4 5 ; ( 3 . 7 ) 23
Mirbach, M.J. ( 2 . 1 ) 4 Miroshnichenko, B.D. ( 3 . 5 ) 59
Mirto, F. ( 4 ) 429 Misawa, H. ( 1 ) 412, 443; ( 3 . 5 ) 27; ( 3 . 7 ) 122
Mishima, T. (2.1) 170, 181; ( 4 ) 237, 251
Mishra, H. ( 4 ) 179 Miskowski, V.M. ( 4 ) 300 Misra, T.N. ( 4 ) 275 Misterkiewicz, B. ( 3 . 7 ) 116
Mistral, J.P. ( 4 ) 171 Misumi, S. ( 3 . 6 ) 207 Mita, K. ( 2 . 1 ) 111 Mitani, M. ( 3 . 7 ) 104 Mitani, T. ( 1 ) 109 Mitchell, M.B. ( 1 ) 408 Mitchenko, S.A. ( 3 . 5 ) 59 Mitra, P. ( 4 ) 183 Mitra, S . ( 4 ) 484 Mitra, S.B. ( 4 ) 484 Mittal, J.P. ( 1 ) 404 Miura, C. ( 3 . 5 ) 87 Miura, Y. ( 3 . 4 ) 106 Miwa, M. ( 2 . 1 ) 4 4 ; ( 3 . 5 ) 85
Miyadzu, H. ( 3 . 5 ) 32 Miyagi, Y. ( 3 . 6 ) 9, 132; ( 4 ) 217
Miyake, M. ( 3 . 2 ) 137, 138
Miyamoto, R. ( 3 . 2 ) 65 Miyano, K. ( 4 ) 106 Miyasaka, H. ( 1 ) 280 Miyasaka, T. ( 3 . 2 ) 8 7 ; ( 3 . 7 ) 100, 172
Miyashi, T. ( 3 . 2 ) 144; ( 3 . 3 ) 1 8 , 28; ( 3 . 5 ) 99
Miyata, 0. ( 3 . 2 ) 57; ( 3 . 6 ) 30, 33, 34
Miyazaki, K. ( 3 . 6 ) 11 Miyazaki, T. ( 2 . 1 ) 44; ( 3 . 5 ) 6 4 , 85
Miyazawa, A. ( 3 . 4 ) 124 Miyoshi, N. ( 1 ) 309 Mizuno, K. ( 2 . 3 ) 57 Mladenov, I. ( 4 ) 489 Mochida, K. ( 2 . 3 ) 50 Modes, S . ( 1 ) 303 Modiano, S.H. ( 1 ) 73 Mobius, K. ( 1 ) 474 Moeller, K.D. ( 3 . 7 ) 21 Moensted, L. (2.1) 33 Moensted, 0. ( 2 . 1 ) 33 Moerner, W.E. ( 1 ) 173 Mogilnyi, V.V. ( 4 ) 175 Mogoto, J . K . ( 3 . 1 ) 48 Mohapatra, G.K.D. ( 1 ) 393 Mohler, C.E. ( 1 ) 131 Mohlmann, G.R. ( 4 ) 263 Mohri, M. ( 3 . 3 ) 4 0 ; ( 3 . 4 ) 123
Mokhtari, A. ( 1 ) 206 Molchanov, A.P. ( 3 . 3 ) 30 Molla, M.E. ( 2 . 2 ) 76 Molloy, B. ( 1 ) 137 Molotkovsky, J . G . (1) 130 Momicchioli, F. ( 1 ) 243 Momose, Y. ( 4 ) 438 Monaghan, M.J. ( 3 . 2 ) 13 Monnerie, L. ( 4 ) 198, 202, 203, 208, 280, 281, 286, 287, 321 Monnier, A. ( 2 . 1 ) 17 Monso, S . ( 1 ) 540 Monssa, K. ( 4 ) 118, 119 Montgomery, C.R. ( 3 . 4 ) 169 Monti, S. ( 1 ) 255 Moody, C . J . ( 3 . 4 ) 143, 144; ( 3 . 7 ) 35, 167, 168 Moore, D.E. ( 1 ) 541; ( 3 . 4 ) 170; ( 3 . 6 ) 70 Moore, J.N. ( 1 ) 414 Moquin, R.V. ( 3 . 1 ) 35; ( 3 . 4 ) 23; ( 3 . 6 ) 46 Morales, P. ( 2 . 1 ) 203 Morales-Rios , M. S ( 3 . 4 ) 109 Morand, P. ( 1 ) 454 Morawetz, H. ( 1 ) 276; ( 4 ) 191, 199, 306 Mordzinski, A. ( 1 ) 417
.
Author lridex
Moreno-Manas , M. ( 3 . 4 ) 6 5 , 6 6 ; ( 3 . 5 ) 41 Morgan, R. ( 2 . 1 ) 79 Morgan, T. ( 3 . 2 ) 123 Morgat, J.L. ( 3 . 7 ) 92 Mori, A. ( 3 . 2 ) 64, 105; ( 3 . 5 ) 84 Mori, K. ( 4 ) 74 Mori, M. ( 3 . 2 ) 101 Mori, 0. ( 3 . 6 ) 171 Mori, S. ( 1 ) 426, 426; ( 4 ) 215 Mori, Y. ( 1 ) 148; ( 3 . 4 ) 73; (3.5) 1 Morikawa, A. ( 3 . 5 ) 66 Morimoto, H. ( 4 ) 406 Morisaki, K. ( 3 . 4 ) 106 Morishima, Y ( 4 ) 258 Morishita, N ( 4 ) 43 Morita, H. ( 1 426; ( 4 ) 129 Moriwaki. T. ( 4 ) 116, 117 Moriya, T. ( 1 ) 154, 310 Moriyama, H. ( 2 . 2 ) 9 ; ( 3 . 7 ) 83 Moron, J. ( 1 ) 520 Moro-oka, Y. ( 2 . 2 ) 100 Morozova, S.S. ( 4 ) 143 Morris, D.G. ( 3 . 7 ) 183 Morris, T.H. ( 3 . 1 ) 31; ( 3 . 6 ) 172 Morrison, H. ( 1 ) 8 2 ; ( 2 . 2 ) 157; ( 3 . 1 ) 4 9 ; ( 3 . 4 ) 2 , 179 Morrison, I.D. ( 2 . 1 ) 191 Morsters, J.C. ( 1 ) 510 Mortezaei, R. ( 3 . 1 ) 2 2 ; ( 3 . 5 ) 1 9 , 20 Mosetti, F. ( 1 ) 189 Moss, R.A. ( 3 . 7 ) 7 , 8 , 1 0 , 11 Motol'ko, G.R. ( 4 ) 485 Moulton, D.V. ( 4 ) 347 Moussa, K. ( 4 ) 451 Moylan, C.R. ( 2 . 1 ) 52 Mozzanega, M.N. ( 3 . 5 ) 77 Mrotzeck, U. ( 3 . 7 ) 72 Mtetwa, V.S.B. ( 2 . 2 ) 33 Mudler, U. ( 4 ) 10 Mueller, F. ( 3 . 5 ) 38 Muller, W. ( 3 . 7 ) 24 Muir, K.W. ( 2 . 2 ) 85 Mujumdar, R.B. ( 3 . 4 ) 134 Mukai, T. ( 3 . 2 ) 6 5 , 144; ( 3 . 3 ) 1 8 , 7 2 ; ( 3 . 5 ) 99 Mukai, Y. ( 1 ) 234 Mukamel, S. ( 1 ) 75 Mukerjee, S.K. ( 3 . 3 ) 8 3 ; ( 3 . 5 ) 42, 91 Mukerji, I. ( 2 . 1 ) 172 Mukherjee, S. ( 1 ) 169; ( 4 ) 95
525 Mukherjee, T. ( 1 ) 404 Mukhopadhyay, G. ( 4 ) 445 Mulazzi, E. ( 4 ) 224 Muldakhmetov, Z.M. ( 3 . 5 ) 52
Mulder, J.J. ( 3 . 4 ) 35 Muller, F.W. ( 4 ) 508 Muller, U. ( 4 ) 51 Mundy, S.J. ( 4 ) 322 Munger, G. ( 1 ) 328 Munoz, J. ( 2 . 1 ) 39 Munoz de la Pena, A. ( 3 . 2 ) 143
Munoz-Sola, Y. ( 1 ) 82 Munro, H.S. ( 4 ) 8 5 , 414 Munzel, N. ( 3 . 3 ) 49 Muradov, N.Z. ( 2 . 1 ) 46 Murai, H. ( 1 ) 395, 416; ( 2 . 3 ) 50; ( 3 . 7 ) 57
Murai, T. ( 3 . 4 ) 97 Murakami, S. ( 3 . 4 ) 124 Muralidharan, S. ( 3 . 4 ) 178
Muramatsu, S. ( 3 . 4 ) 108 Muramatsu, T. ( 3 . 7 ) 146, 147
Murao, Y. ( 1 ) 482; ( 3 . 6 ) 12
Muras, J. ( 4 ) 355 Murata, K. ( 1 ) 472 Murayama, K. ( 4 ) 412 Murillo, J.A. ( 3 . 2 ) 143 Muroi, A. ( 4 ) 74 Murtagh, J. (1) 357; ( 4 ) 87
Murthy, A . N . ( 3 . 2 ) 116 Murty, B.A.R.C. ( 3 . 3 ) 5 1 , 52
Musaeva, F.M. ( 4 ) 491 MUSSO, H. ( 3 . 3 ) 67 Mustafaeva, S.K. ( 4 ) 460, 49 1
Mustapha, A. ( 3 . 5 ) 115 Mutai, K. ( 3 . 6 ) 83 Muthuramu, K. ( 1 ) 8 2 ; ( 3 . 3 ) 44
Mutoh, Y. ( 3 . 4 ) 1 9 ; (3.6) 145
Muzart, J. ( 3 . 1 ) 2 2 ; ( 3 . 2 ) 53; ( 3 . 5 ) 19-21
Mwesigye-Kilbende, S. ( 3 . 1 ) 33
Myong, S.O. ( 3 . 2 ) 98 Myrick, M.L. ( 2 . 1 ) 68 Myshko, R.R. ( 4 ) 141 Nadolski, B.Z. ( 1 ) 50 Nagai, Y. ( 2 . 3 ) 37, 38, 40
Nagakura, M. ( 3 . 5 ) 3 Nagamatsu, T. ( 3 . 2 ) 8 4 ;
( 3 . 6 ) 92
Nagamura, T. ( 1 ) 170; (2.3) 9
Nagasaki, H. ( 3 . 5 ) 107 Nagata, M. ( 3 . 6 ) 16 Nagata, T. ( 3 . 7 ) 211 Nagata, Y. ( 2 . 3 ) 24 Nagaya, S. ( 4 ) 352 Nagle, J.K. ( 2 . 1 ) 152; ( 2 . 2 ) 134, 135
Nagraba, K. ( 3 . 5 ) 55 Naguchi, H. ( 4 ) 38 N a b , K. ( 3 . 2 ) 6 8 , 6 9 ; ( 3 . 4 ) 4 3 , 44
Naik, S.N. ( 3 . 2 ) 56 Naito, T. ( 3 . 2 ) 1 6 , 57; ( 3 . 4 ) 132, 133; ( 3 . 6 ) 30, 3 1 , 33, 34, 105 Najbar, J. (1) 33, 187 Nakada, M. ( 3 . 4 ) 106; ( 3 . 5 ) 87 Nakadaira, Y. ( 2 . 3 ) 27 Nakagaki, R. ( 3 . 6 ) 83 Nakagawa, K. ( 3 . 2 ) 80 Nakagawa, M. ( 3 . 5 ) 117 Nakahara, H. ( 3 . 6 ) 8 Nakahara, N. (1) 182 Nakai, J.S. ( 3 . 4 ) 98 Nakajima, T. (1) 524 Nakamura, H. ( 4 ) 259, 320 Nakamura, K. ( 3 . 2 ) 104; ( 3 . 7 ) 141 Nakamura, T. ( 2 . 2 ) 110 Nakamura, Y. ( 4 ) 7 4 Nakanishi, E. ( 4 ) 4 3 , 44, 272, 315 Nakanishi, H. ( 4 ) 44 Nakanishi, K. ( 3 . 7 ) 65 Nakanishi, S. ( 4 ) 439 Nakano, N. ( 4 ) 379 Nakao, R. ( 2 . 3 ) 24 Nakasato, I. ( 1 ) 517 Nakashima, N. ( 1 ) 330, 386, 414 Nakata, H. ( 3 . 2 ) 54 Nakatani, K. (1) 172 Nakayama, K. ( 4 ) 212 Nakayama, M. ( 4 ) 59 Nakayama, N. ( 3 . 7 ) 147 Nakayama, T. ( 1 ) 390 Nakazawa, H. ( 4 ) 16 Nakos, S . ( 4 ) 123 Nalbandyan, G.K. ( 3 . 1 ) 52; ( 3 . 2 ) 25 Naman, S.A. ( 1 ) 441 Namasivayam, C. ( 2 . 1 ) 36 Namura, I. ( 2 . 2 ) 56 Narasimhan, N. S. ( 3 . 4 ) 113 Narayanaswamy, R. ( 1 ) 61
Nasielski-Hinkens, R. ( 2 . 1 ) 106
Photochemistry
526 Natake, M. (3.2) 136 Natarajan, L.V. (1) 429; ( 4 ) 505 Natarajan, P. (2.1) 6 Nate, K. (4) 124, 387 Natsukawa, K. ( 4 ) 517 Naum, N. ( 4 ) 79 Naumova, I.A. (4) 506 Naumova, S.F. (4) 485 Nayak, P.L. ( 4 ) 107, 179 Nayak, S.K. (2.1) 204 Nazarov, A.A. ( 4 ) 458 Nazran, A.S. (3.7) 49 N e c h i t a i l l o , V.S. (4) 377 Neckers, D.C. ( 1 ) 216, 221, 224, 463; (3.4) 25, 26; (4) 238 Nedelkos, G. ( 4 ) 477 Nefedov, O.M. (2.3) 26; (3.6) 199; (3.7) 4 , 145 Neidlein, R. (3.7) 81 Neidlinger, H.H. ( 4 ) 463 Neiland, 0. (3.6) 152 Nekrasova, T.N. ( 4 ) 307 Nelson, G. ( 1 ) 7 , 126; ( 4 ) 403 Nelson, K . A . ( 1 ) 119, 120 Nelson, T. (2.3) 60 Nenkov, G. ( 4 ) 372 Nepras, M. ( 1 ) 93 Neshushtai, R. (1) 536 Neshvad, G. (2.1) 35 Nesi, R. (3.3) 64 Neta, P. ( 1 ) 389; (2.1) 24 Netzel, T.L. (2.1) 80 N e u r e i t e r , M. (1) 222 Newcomb, M. (3.7) 118 Newcornbe, P.J. (3.7) 192 Newell, V.J. (1) 271 Newhouse, E.I. ( 1 ) 355 Ng, H.C. ( 4 ) 264 Nguyen, C. (1) 283 Nguyen, D.C. (1) 512 Nguyen, H.T.L. (4) 437 N i , H. ( 4 ) 387 N i c h o l a i s , L. ( 4 ) 120 Nicholas, K.M. (2.2) 29 Nickel, B. (1) 398, 417, 418 Nicola, G. (2.2) 99 Nicolaou, K.C. (3.6) 161 Niedbalska, M. (1) 220 Nielsen, P.E. (3.6) 80 Nigay, H. (3.5) 103 Niino, H. (3.6) 8 Nikiforov, G.A. (3.7) 67 Nimbalkar, M.M. (3.7) 155 N i m e s g e r n , H. (3.7) 60 Ninomiya, A. (4) 149 Ninomiya, I. (3.2) 57; (3.4) 132, 133; (3.6)
30, 31, 33, 34 N i s h i b a t a , Y. (3.2) 119; (3.6) 8 6 Nishida, A. (3.6) 9 ; (4) 217 Nishida, S . (2.1) 83, 115; (3.2) 137, 138; (3.3) 33, 34; (3.4) 1 2 Nishigaki, M. (4) 329 Nishiguchi, Y. (3.2) 57; (3.6) 30 Nishihara, A. (4) 23 Nishijima, Y. (3.6) 93, 95; (4) 92, 301 Nishikubo, T. (4) 49, 75, 132, 150, 155 Nishimoto, S . (2.1) 11, 15; (3.5) 32, 107; ( 4 ) 214 Nishimura, Y. (3.5) 28, 89 Nishio, T. (3.1) 36; (3.2) 41, 54, 86, 89, 90; (3.5) 45; (3.6) 107, 129, 137, 166-169 Nishio, Y. ( 4 ) 113 Nishisaka, T. (3.5) 31 Nishiwaki, T. ( 4 ) 149 Nishiyama, T. (3.5) 45 N i s t , K. (2.2) 32 Nithipatikom, K. (1) 299, 300
Nitsche, C. (3.7) 91 Nitzan, A. ( 1 ) 26 N i w a , M. (4) 76 Nizova, G.V. (2.1) 158 No, Y.G. ( 4 ) 403 Nobbe, M. (3.3) 26 Noda, H. (3.2) 78, 94 Nogue, Y. (4) 284 Noh, I. ( 4 ) 462 Nomiya, K. (2.1) 44; (3.5) 85 Nomura, S. ( 4 ) 272 Nomura, Y. (3.5) 117 Noreuil, T. (3.4) 8 6 N o r r i s , R.K. (3.7) 192 Nosaka, Y. (1) 340 Novi, M. (3.4) 77; (3.7) 191, 194 Novichenkov, V.E. (3.5) 46 Nowicki, W. (2.1) 169 Noyeri, R. (2.1) 9 8 Nozakura, S . (4) 258 Nunez, A. (3.1) 23 Nunez, I.M. (4) 134 Nunn, D.S. (3.2) 100 Obata, R. (2.1) 78, 84 Obi, K. ( 1 ) 437; (3.5) 11
Ochoa, J.R. (1) 219 O'Connell, C.M. (4) 8 6 O'Connell, M.J. (3.2) 115 O'Conner, D.B. (4) 300 Oda, K. (3.2) 126, 127; (3.6) 162, 165, 176 Oda, M. (3.2) 15, 106; (3.4) 56 Oda, R. (4) 5 Odszanowski, A. (4) 448 Oduwolet, D. (3.7) 29 Oelkrug, D. ( 1 ) 346 O e s t e r h e l t , D. (1) 508 Oevering, H. (1) 266 O f i r , H. ( 1 ) 434 Ogasawara, H. (3.7) 169 Ogasawara, Y. (1) 437 Ogawa, K. (3.5) 87 Ogawa, T. (3.2) 49; (3.5) 32 Ogilby, P.R. (1) 458 Ogino, H. (2.2) 87 Ogino, K. (4) 501 Ogiwara, Y. ( 4 ) 88 Ogoshi, H. (2.1) 139 Ogura, H. (3.6) 97 Ogura, K . (3.2) 101 Ogurtsov, N.A. (3.2) 142 Oh, S.C. ( 4 ) 102 Oh, S.W. (3.2) 85; (3.6) 102 O'Hara, P.B. (1) 484 Oharu, K. (2.3) 27 Ohashi, M. (3.4) 100, 101 Ohashi, T. ( 4 ) 42 Ohashi, Y. (2.1) 125 Ohba, Y. ( 1 ) 410 Ohkawa, K. ( 4 ) 4 O h l l i g i n , C. ( 1 ) 515 Ohno, A. (3.7) 141 Ohno, 0. ( 1 ) 437 Ohno, T. ( 1 ) 359 Ohsaku, M. (3.3) 35 Ohsawa, H. (4) 478 Ohshita, J. (1) 472 Ohta, J. (1) 311 Ohtani, B. (2.1) 11, 15; (3.5) 32; (4) 214 Ohtani, 0. (3.5) 107 Ohzeki, T. ( 1 ) 480 O i s h i , S. (2.1) 91; (2.2) 107, .lo8 O i s h i , T. (3.4) 151 Ojeda, P.R. ( 1 ) 219 O j i m a , S.'(3.2) 49 Ok, H. (3.7) 6 5 Oka, K. (2.3) 24 Oka, S . (3.7) 141 Okada, K . (3.2) 15; (3.4) 56 Okada, M. (3.4) 122; (3.7) 131
Author Index
Okada, S. ( 3 . 5 ) 17 Okada, T. ( 1 ) 166, 171, 172, 176, 193; ( 4 ) 2 , 154 Okajima, H. ( 3 . 2 ) 8 8 ; ( 3 . 6 ) 15 Okamoto, A. ( 3 . 4 ) 181 Okamoto, K. ( 2 . 1 ) 119 Okamoto, M. ( 3 . 7 ) 7 Okamoto, N. ( 4 ) 277 Okamoto, Y. ( 3 . 4 ) 175, 176; ( 3 . 6 ) 201; ( 4 ) 123 Okasaki, S. ( 4 ) 438 Okazaki, K. ( 2 . 3 ) 35 Okubo, J. ( 3 . 4 ) 59; ( 3 . 6 ) 3 9 , 130 Okubo, K. ( 2 . 1 ) 162 Okuda, N. ( 3 . 6 ) 169 Okugawa, Y. ( 2 . 1 ) 11 Okura, I. ( 3 . 5 ) 31 Okusako, K. ( 3 . 2 ) 128; ( 3 . 6 ) 173 Olba, A. ( 1 ) 424, 540 Oleinik, A.V. ( 4 ) 138 Olesker, A.G. ( 3 . 7 ) 112 Oliveros, L. ( 2 . 3 ) 6 1 Olivier, D. (2.2) 141 Olken, M.M. ( 2 . 1 ) 171 Ol'khovskii, V.V. ( 3 . 6 ) 77 Ollis, W.D. ( 4 ) 401 Ollmann, R.R., jun. ( 3 . 3 ) 41 Olmstead, M.M. ( 2 . 1 ) 152; ( 2 . 2 ) 135 Olson, D.R. ( 4 ) 156 Olszowski, 0. ( 1 ) 106 Olteanu, M. ( 2 . 1 ) 114 Omelanczuk, J. ( 3 . 6 ) 200 Omote, Y. ( 3 . 2 ) 4 1 , 5 4 , 8 6 , 9 0 ; ( 3 . 5 ) 45; ( 3 . 6 ) 8 9 , 107, 129, 167, 169; ( 3 . 7 ) 158 Ondrias, M.R. ( 1 ) 529; ( 2 . 1 ) 142 O'Neill, P.J. ( 2 . 1 ) 37 Onescu, T. ( 2 . 1 ) 114 Onishi, M. ( 2 . 2 ) 107 Onishi, T. ( 2 . 1 ) 10 Ono, H. ( 4 ) 261 Ono, I. ( 3 . 4 ) 8 8 ; ( 3 . 6 ) 128 Ono, M. ( 3 . 5 ) 64 Onodera, S. ( 3 . 7 ) 146, 147 Oozu, Y. ( 3 . 1 ) 55 Opfermann, J. (1) 344 Orakhovata, A. ( 2 . 2 ) 105 Oram, D.E. ( 2 . 2 ) 134 Oram, J.W. ( 1 ) 129 Oravec, P. ( 3 . 6 ) 50 Orchard, W.S. ( 3 . 3 ) 39
527
Ordukhanyan, K.A. ( 4 ) 490 O'Reilly, A.M. ( 1 ) 348 Oremus, V. ( 3 . 3 ) 7 5 ;
Paik, N. ( 3 . 7 ) 6 Paillous, N. ( 1 ) 444;
( 3 . 6 ) 54-56 Oren, J. ( 3 . 2 ) 73 Orenstein, J. ( 1 ) 290 Orita, Y. ( 3 . 2 ) 8 4 ; (3.6) 92 Orito, K. ( 3 . 6 ) 68 Orlandi, G. ( 1 ) 7 4 , 242 Oro, L.A. ( 2 . 2 ) 133 Orpen, A.G. ( 2 . 2 ) 63 Ors, J.A. ( 4 ) 134 Ortega, R. ( 3 . 2 ) 1 ; ( 3 . 4 ) 134; ( 3 . 6 ) 28 Osaki, H. ( 2 . 1 ) 15 Osawa, Z. ( 4 ) 333 Osella, D. ( 2 . 2 ) 99 Oshima, N. ( 2 . 2 ) 100 Oshima, T. ( 3 . 1 ) 32 Oshio, M. ( 3 . 4 ) 5 9 ; ( 3 . 6 ) 130 Oskam, A. ( 2 . 1 ) 136; ( 2 . 2 ) 90 Osselton, E.M. ( 3 . 4 ) 36, 37 Osuka, A. ( 3 . 1 ) 28 Osvach, R.G. ( 4 ) 420 Oszajca, J. ( 2 . 1 ) 27 Otsubo, T. ( 3 . 6 ) 207 Otsuji, Y. ( 2 . 3 ) 57 Ottewill, R.H. ( 4 ) 273 Otvos, J . W . ( 2 . 1 ) 143 Ouchabane, R. ( 3 . 5 ) 54 Ouchi, A. ( 3 . 6 ) 8 ; ( 3 . 7 ) 83 Ovchinnikov, V.N. ( 4 ) 375 Owen, S.M. ( 4 ) 273 Oxman, J.D. ( 3 . 2 ) 48 Oyama, H.T. ( 4 ) 289 Ozaki, K. ( 3 . 4 ) 152 Ozaki, T. ( 1 ) 85 Ozer, Z. ( 2 . 2 ) 26 Ozkar, S . ( 2 . 2 ) 20, 26
Pailthorpe, M.T. ( 4 ) 496 Pakhomova, I.K. ( 4 ) 488 Pakray, S. ( 3 . 4 ) 137;
Pabon, R. ( 3 . 1 ) 27 Pac, C. ( 2 . 2 ) 5 6 , 57; (3.3) 70; (3.4) 60; ( 3 . 5 ) 37, 108; ( 3 . 7 ) 163, 164 Pace, M.D. ( 3 . 7 ) 107 Pacreau, A. ( 2 . 2 ) 41 Paczkowski, J. ( 1 ) 221 Paddon-Row, M.N. (1) 266 Padma, S . ( 3 . 3 ) 55-57 Padmanabhan, K. ( 3 . 6 ) 79 Padwa, A. ( 3 . 3 ) 1 6 ; ( 3 . 6 ) 149; ( 3 . 7 ) 60 Pagan, P. ( 4 ) 334, 335, 418 Pagni, R.M. ( 3 . 7 ) 25
( 2 . 3 ) 6 2 ; ( 3 . 4 ) 102
( 3 . 6 ) 147
Pal, H. ( 1 ) 404 Palenik, G.J. ( 2 . 2 ) 93 Paleta, 0. ( 4 ) 66 Palewska, K. ( 1 ) 112 Palmer, C.E.A. ( 2 . 1 ) 159, 161
Palmer, T.F. ( 1 ) 129 Paluchowska, M. ( 3 . 2 ) 9 1 ; ( 3 . 6 ) 170
Pan, J. ( 4 ) 483 Pan, X. ( 2 . 2 ) 28 Panarin, E.F. ( 4 ) 313 Pancoska, P. (1) 535 Pandey, G. ( 3 . 2 ) 56, 6 1 ; ( 3 . 4 ) 142; ( 3 . 5 ) 110
Pandit, A. ( 4 ) 449 Pandya, S. ( 4 ) 449 Pankova, T.A. ( 4 ) 458 Pankratov, A.N. ( 4 ) 47 Pannell, K.H. ( 2 . 2 ) 101; ( 4 ) 390
Pant, D.D. ( 1 ) 168 Pant, T.C. ( 1 ) 263 Pantov, V.D. ( 4 ) 307, 313 Papirer, E. ( 3 . 5 ) 67 Papp, S. ( 2 . 1 ) 6 0 , 61 Pappas, S.P. ( 4 ) 7 Paprotskaya, 0.1. ( 4 ) 141 Paquette, L.A. ( 3 . 2 ) 3 1 , 32; ( 3 . 3 ) 24, 25, 6 1 ; ( 3 . 6 ) 45 Paquette, M.S. ( 2 . 2 ) 73 Pariente, R. ( 1 ) 459 Parisi, J.P. ( 4 ) 161, 171 Park, J.M. ( 4 ) 181 Park, S. ( 3 . 4 ) 5 7 ; ( 3 . 6 ) 99 Park, Y.K. ( 4 ) 432 Parlar, H. ( 3 . 4 ) 9 3 ; ( 3 . 6 ) 134 Parlier, A. ( 2 . 2 ) 41 Parmar, J.S. ( 4 ) 464 Parmar, S.S. ( 1 ) 8 8 , 89 Parmon, V.N. ( 2 . 1 ) 108 Parron, J.C. ( 3 . 5 ) 103 Parsons, R.J. ( 2 . 1 ) 76 Parthenopoulos, D.A. ( 1 ) 150 Paschenko, V.Z. ( 1 ) 535 Pascual, P. ( 4 ) 303 Pasimeni, L. ( 1 ) 379, 400 Paski, E.F. ( 1 ) 57 Pasquato, L. ( 3 . 5 ) 72 Pastakhov, A.V. ( 4 ) 254 Pasternak, E.E. ( 3 . 7 ) 3
Paszyc, S. ( 1 ) 1 5 3 ; ( 3 . 6 ) 142
Patel, A. ( 3 . 7 ) 90 Patel, B.P. ( 3 . 6 ) 103 Patel, M. ( 4 ) 464, 464 Patel, N.R. ( 3 . 7 ) 1 5 5 ; ( 4 ) 464
Patel, R.C. (1) 185 Patel, V.F. ( 2 . 2 ) 112 Paterson, C. ( 2 . 3 ) 72 Patharakorn, S. ( 4 ) 235 Pathirana, S.T. ( 1 ) 158 Patonay, G. ( 1 ) 7 , 126 Patrick, V.A. ( 3 . 4 ) 30 Pattenden, G. ( 2 . 2 ) 1 1 2 ; ( 3 . 2 ) 11
Patterson, L.K. ( 1 ) 3 2 6 , 327, 331, 536
Patyk, A. ( 3 . 5 ) 83 Paul, H. ( 1 ) 384 Pautmeier, L. ( 1 ) 354 Pavlickova, L. ( 3 . 1 ) 4 4 ; ( 3 . 4 ) 6 7 , 69
Pavlovskii, V.I. ( 2 . 1 ) 12 2- 124
Peacock, R.D. ( 2 . 1 ) 54 Peak, J . G . ( 1 ) 514 Peak, M.J. ( 1 ) 514 Pearce, E.M. ( 4 ) 373, 383 Pedrazzetti, E. ( 4 ) 453 Peinado, C. ( 4 ) 127 Pekcan, 0 . ( 4 ) 293 Pelgrims, J. ( 4 ) 22 Pelizzetti, E. ( 4 ) 521 Pellin, J. ( 1 ) 514 Penzkofer, A. ( 1 ) 198, 215
Perathoner, S. ( 2 . 1 ) 182, 183
Perez-Ossorio, R. ( 3 . 3 ) 2 2 ; ( 3 . 6 ) 43
Perfilev, V.A. ( 3 . 5 ) 5 7 , 58
Perghem, F. ( 3 . 2 ) 47 Perico, A. ( 1 ) 493 Perrine, D.M. ( 3 . 6 ) 146 Perrone, C. ( 4 ) 337 Persaud, L. ( 2 . 1 ) 207 Persy, G. ( 3 . 7 ) 25 Perutz, R.N. ( 2 . 2 ) 1 1 9 , 121, 132
Peruzzini, M. ( 2 . 2 ) 128 Pessine, F.B.T. ( 1 ) 422 Pete, B. ( 3 . 6 ) 202 Pete, J.-P. ( 3 . 1 ) 2 2 , 5 0 , 51; ( 3 . 2 ) 53; (3.5) 19-21; ( 3 . 6 ) 85 Peters, E.-M. ( 3 . 1 ) 2 5 ; ( 3 . 4 ) 145; ( 3 . 5 ) 22; ( 3 . 7 ) 16 Peters, K. ( 1 ) 6 ; ( 2 . 3 ) 36; ( 3 . 1 ) 25; ( 3 . 4 )
145; ( 3 . 5 ) 22; ( 3 . 6 ) 182; ( 3 . 7 ) 16 Petersen, J.L. ( 3 . 7 ) 21 Petillon, F.Y. ( 2 . 2 ) 85 Petkov, I. ( 1 ) 147 Petrenko, N.I. ( 3 . 6 ) 59 Petrich, J.W. ( 1 ) 493 Petrillo, G. ( 3 . 4 ) 7 7 ; ( 3 . 7 ) 1 9 1 , 194 Petrin, M. (1) 397, 425 Petrov, A.A. ( 2 . 3 ) 52 Petrovskii, P.V. ( 2 . 2 ) 74 Peyser, J . R . ( 3 . 6 ) 7 4 Pfoertner, K.-H. ( 3 . 1 ) 1 ; ( 3 . 2 ) 66 Pham-van-Cang, C. ( 4 ) 280, 286, 287 Phan, X.T. ( 3 . 2 ) 134 Philbin, C.E. ( 2 . 2 ) 28 Phillips, D. ( 1 ) 382, 4 1 4 ; ( 4 ) 194, 206 Phillips, G.O. ( 2 . 1 ) 76 Philpot, S.R. ( 1 ) 291 Piancatelli, G. ( 3 . 4 ) 8 2 , 8 3 ; ( 3 . 7 ) 1 7 3 , 174 Picard, G. ( 1 ) 328 Pichat, P. ( 3 . 5 ) 77 Pichon, R. ( 2 . 2 ) 1 3 , 149 Picken, H.A. ( 3 . 2 ) 5 Pielichowski, J. ( 4 ) 184 Pierini, A.B. ( 3 . 4 ) 7 9 ; ( 3 . 7 ) 185 Pierola, I.F. ( 4 ) 220, 242, 302-304 Pieroni, 0. ( 4 ) 186 Pierpoint, C.G. ( 2 . 2 ) 50 Pietrasanta, Y. ( 4 ) 1 6 1 , 171 Pietrzak, J. ( 4 ) 48 Pillai, V.N.R. ( 3 . 6 ) 75 Pincock, A.L. ( 3 . 4 ) 1 7 2 ; ( 3 . 7 ) 152 Pincock, J. ( 3 . 4 ) 1 7 2 ; ( 3 . 7 ) 152 Pinder, A.R. ( 3 . 2 ) 34 Pines, D. ( 1 ) 335 Pines, E. ( 1 ) 128 Pingl, J. ( 3 . 7 ) 154 Pinkos, R. ( 3 . 3 ) 51 Piotrowiak, P. ( 1 ) 356 Pirrung, M.C. ( 3 . 1 ) 20; ( 3 . 2 ) 3 , 4 , 1 8 , 100 Pitt, C.W. ( 1 ) 439 Pitt, I.G. ( 3 . 2 ) 1 2 2 ; ( 3 . 7 ) 159 Piva, 0. ( 3 . 1 ) 2 2 ; ( 3 . 2 ) 5 3 ; ( 3 . 5 ) 19-21 Plaas, D. ( 3 . 3 ) 7 1 Plancherel, D. ( 2 . 1 ) 8 5 , 175 Platsch, H. ( 1 ) 363; ( 3 . 7 ) 1 7 , 20
Platz, M.S. ( 3 . 3 ) 8 5 ; ( 3 . 4 ) 173
Pleier, J . M . ( 3 . 7 ) 9 Pleil, M.W. ( 1 ) 264 Plummer, B.F. ( 1 ) 1 3 6 ; ( 3 . 3 ) 68
Plummer, M. ( 3 . 2 ) 9 3 , 99 Pluzhnikov, P.F. ( 1 ) 358 Pochinok, A.V. ( 3 . 7 ) 101 Pochinok, V.Ya. ( 3 . 7 ) 101 Podesta, F.E. ( 1 ) 501 Poggi, G. ( 1 ) 242 Pogorzelec, P. ( 2 . 2 ) 147 Pohl, K. ( 2 . 1 ) 57 Pohl, S. ( 3 . 6 ) 183 Poiana, M. ( 3 . 6 ) 131 Poizart, 0 . ( 1 ) 377; ( 3 . 5 ) 34
Polewski, K. ( 3 . 5 ) 50 Poliakoff, M. ( 1 ) 4 6 9 ; ( 2 . 2 ) 4 9 , 6 8 , 119; (2.3) 64; (3.4) 20; ( 3 . 7 ) 8 0 , 121 Poliquen, J. ( 1 ) 161 Polit, D.K. ( 1 ) 404 Politi, M . J . ( 1 ) 97 Polyakov, Yu.N. ( 4 ) 417 Polynova, T.N. ( 2 . 1 ) 124 Ponyaev, A.I. ( 3 . 6 ) 77 Pope, K.R. ( 2 . 2 ) 35 Popov, V.I. ( 3 . 7 ) 101 Popova, Z.G. ( 4 ) 458 Popovich, M.P. ( 2 . 3 ) 2 Porai-Koshits, M.A. ( 2 . 1 ) 124 Pordo, A. ( 1 ) 100 Port, H. ( 1 ) 222 Porte, A.L. ( 3 . 6 ) 140 Pospisil, J. ( 4 ) 359 Potapov, V.K. ( 3 . 7 ) 6 7 ; ( 4 ) 70 Potier, P. ( 3 . 7 ) 113 Pottel, H. ( 1 ) 333 Potter, R.C. ( 3 . 5 ) 7 Pottier, R.H. ( 1 ) 523 Pouget, J. ( 2 . 1 ) 7 1 Pourreau, D.B. ( 2 . 2 ) 40 Poyato, J.M.L. ( 1 ) 100 Pozdynakov, O.F. ( 4 ) 436 Poznyak, A.L. ( 2 . 1 ) 122- 124 Pramat, K. ( 1 ) 434 Prasad, P.N. ( 1 ) 289 Pratapan, S. ( 3 . 2 ) 112 Preston, D.M. ( 2 . 2 ) 140 Previtali, C.M. ( 1 ) 320, 370 Prignano, A.L. ( 2 . 2 ) 148 Primo, J. ( 3 . 1 ) 45 Prinslow, D.A. ( 2 . 2 ) 44 Prinzbach, H. ( 3 . 3 ) 5 1 , 52, 62; (3.7) 75, 76
Author Index Priola, A. ( 4 ) 140, 158 Pritchina, E.A. ( 3 . 7 ) 82 Prokhorov, A.M. ( 4 ) 377 Prokofev, A . I . ( 3 . 7 ) 200 Prokof'ev, A.Z. ( 3 . 5 ) 16 Prot, T. ( 4 ) 3 , 6 Prota, G. ( 3 . 5 ) 112, 113 Prout, K. ( 2 . 2 ) 33 Prud'homme, R.K. ( 4 ) 317 Prusty, B.C. ( 4 ) 179 Ptyagina, L.M. ( 1 ) 252 Puig, S. ( 3 . 2 ) 98 Punchihewa, S. ( 2 . 3 ) 58 Puranik, D.B. ( 2 . 3 ) 29, 30; ( 3 . 6 ) 184, 185
Puskas, J. ( 4 ) 170 Pusterhofer, J. ( 1 ) 5 Putinas, J.M. ( 2 . 2 ) 66 Qian, P. ( 3 . 2 ) 3 7 ; ( 3 . 4 ) 47
Qin, Q. ( 2 . 3 ) 67 Qin, X. ( 3 . 2 ) 109 Qiu, Z.-M. ( 3 . 7 ) 181 Quabeck, U. ( 3 . 1 ) 40 Quast, H. ( 3 . 7 ) 32 Questel, J.P. ( 4 ) 321 Quillen, S.L. ( 3 . 2 ) 48 Quilliam, M.A. ( 3 . 6 ) 1 Quin, L.D. ( 3 . 6 ) 202 Quisenberry, J.G. ( 4 ) 473 Quitevis, E.L. ( 1 ) 337 Qureshi, I.H. ( 3 . 6 ) 49 Raab, M. ( 4 ) 359 Raabe, E. ( 3 . 6 ) 57 Rabek, J.F. ( 4 ) 332 Rabinovitch, E.B. ( 4 ) 473 Racherla, U.S. ( 3 . 3 ) 61 Rachinskii, A.G. ( 1 ) 236, 245; ( 3 . 3 ) 9 , 10
Racymackers, L. ( 4 ) 430 Radic, D. ( 4 ) 219, 220, 304
Radu, D.C. ( 4 ) 495 Rager, B. ( 2 . 2 ) 3 Rainbird, M. ( 2 . 3 ) 12 Rajadurai, S. ( 1 ) 374; ( 2 . 2 ) 143; ( 3 . 2 ) 7 6 ; ( 3 . 4 ) 118 Rajagopal, S. ( 2 . 1 ) 82 Raju, B.N.S. ( 3 . 2 ) 7 5 , 113, 114; ( 3 . 4 ) 46 Rak, S.F. ( 3 . 7 ) 47 Rakhimov, R.R. ( 3 . 5 ) 16 Raldugin, V.A. ( 3 . 2 ) 19 Ram, R.S. (2.3) 66 Ramaiah, D. ( 1 ) 374 Ramakrishnan, T. ( 2 . 1 ) 192
529 Ramamurthy, P. (2.1) 6 Ramamurthy, V. ( 1 ) 430; ( 3 . 1 ) 9 , 1 0 , 1 8 , 24, 37-39; ( 3 . 4 ) 161; ( 3 . 5 ) 1 5 ; ( 3 . 6 ) 7 9 , 156-159, 175 Ramasarni, T. ( 2 . 1 ) 1 Ramelow, U. ( 4 ) 104 Ramis Ramos, G. ( 1 ) 348 Ramnath, N. ( 3 . 4 ) 104 Ramos, A. ( 3 . 3 ) 7 6 ; ( 3 . 7 ) 160 Ramos, G.R. ( 1 ) 294 Rampi-Scandola, M.A. ( 2 . 1 ) 94 Ramponi, R. ( 1 ) 466 Ranogajec, F. ( 3 . 4 ) 17 Rao, B.N. ( 3 . 1 ) 9 , 1 8 ; ( 3 . 4 ) 161; ( 3 . 6 ) 175 Rao, C.B. ( 3 . 7 ) 56 Rao, K.N. ( 4 ) 98 Rao, K.S. ( 3 . 2 ) 7 Rao, P.V.R. ( 2 . 1 ) 204 Rao, T.N. ( 4 ) 98 Rao, V.P. ( 3 . 1 ) 3 8 , 39; ( 3 . 6 ) 156-158 Raoult, Y. ( 2 . 2 ) 13 Rapp, W. (1) 87 Rasbury, V. ( 1 ) 82 Raston, C.L. ( 3 . 4 ) 30 Rasulov, N.Sh. ( 4 ) 165 Ratovskii, G.V. ( 4 ) 326 Rau, H. ( 1 ) 254, 267; ( 4 ) 218 Rautenstrauch, V. ( 3 . 5 ) 81 Rawat, M.S.M. ( 3 . 6 ) 78 Raybone, D. ( 2 . 3 ) 74 Razumov, V.F. ( 1 ) 236, 245; ( 3 . 3 ) 9 , 10 Recca, A. ( 4 ) 414 Reddy, D.S.K. ( 3 . 2 ) 116 Reddy, G.D. ( 3 . 1 ) 1 0 , 24; ( 3 . 5 ) 15 Redkov, B.P. ( 4 ) 436 Reed, J.K. ( 1 ) 8 3 , 84 Reedy, P.E. ( 2 . 2 ) 134, 135 Reekmans, S. ( 1 ) 301 Rees, C.W. ( 3 . 7 ) 35 Reggel, A. ( 3 . 7 ) 154 Regitz, M. ( 3 . 4 ) 1 3 ; ( 3 . 6 ) 5 8 ; ( 3 . 7 ) 37 Rehak, V. ( 1 ) 180, 315, 316 Rehorek, D. ( 2 . 1 ) 3 Reich, H.J. ( 4 ) 84 Reichardt, C. ( 1 ) 432 Reiher, U. ( 3 . 6 ) 19 Reimschuessel, H.K. ( 4 ) 383 Reinecke, M.G. ( 3 . 7 ) 39
Reinhard, D. ( 2 . 1 ) 34 Reinhardt, B. ( 4 ) 486 Reinhart, G.D. ( 1 ) 527 Reinholdt, K. ( 3 . 1 ) 13 Reinisch, G. ( 4 ) 268 Reinot, T. ( 1 ) 270 Reis, A.T. ( 1 ) 36 Reisenauer, H.P. ( 3 . 7 ) 24 Reiser, A. ( 1 ) 462; ( 4 ) 46
Reisfeld, R. (I) 217, 285; ( 2 . 1 ) 190
Reisman, D. ( 3 . 7 ) 143 Reitinger, W. ( 1 ) 31 Renamayor, C.S. ( 4 ) 304 Rendall, W.A. ( 3 . 4 ) 7 Renson, C. ( 4 ) 29 Rentsch, S. ( 1 ) 344 Rentzepis, P.M. ( 1 ) 105 Renzi, G. ( 3 . 2 ) 47 Rereyre, J. ( 3 . 4 ) 87 Resch, P. ( 1 ) 475 Rest, A.J. ( 2 . 1 ) 136; ( 2 . 2 ) 130
Rettig, W. ( 1 ) 209-211 Reynders, P. ( 1 ) 124 Reynolds, T.A. ( 2 . 1 ) 127 Rheingold, A.L. ( 2 . 2 ) 40; (2.3) 6
Rhodes, L.F. ( 2 . 1 ) 53 Riccieri, P. ( 2 . 1 ) 31 Rice, M.J. ( 1 ) 291 Ricevuto, V. ( 2 . 2 ) 145 Rich, J.D. ( 3 . 6 ) 194 Richards, D.S. ( 2 . 3 ) 60 Richardson, S.K. ( 3 . 7 ) 86 Richert, R. ( 1 ) 354 Richoux, M.-C. ( 1 ) 389; ( 2 . 1 ) 24
Ricka, J. ( 1 ) 70 Rickerl, P.G. ( 4 ) 440 Ridley, A.B. ( 3 . 6 ) 63 Ried, W. ( 3 . 6 ) 19 Riediker, M. ( 2 . 2 ) 11 Rieker, R. ( 1 ) 222 Ries, B. ( 1 ) 354 Riesenberg, E. ( 4 ) 168 Riesenberg, R. ( 4 ) 168 Rihs, G. ( 3 . 3 ) 53; ( 3 . 7 ) 30
Riley, M.J. ( 2 . 1 ) 164 Ringer, E. ( 3 . 3 ) 6 9 ; ( 3 . 4 ) 53; ( 3 . 6 ) 101
Ringsdorf, H. ( 3 . 6 ) 20; ( 4 ) 249
Rinke, M. ( 1 ) 143 Rist, G. ( 1 ) 474 Ritter, H. ( 4 ) 236 Ritter, J. ( 1 ) 415 Rivara-Minten, E. ( 1 ) 318 Rivas, C. ( 3 . 4 ) 95 Riviere, P. ( 2 . 3 ) 4 8 ;
530 ( 3 . 6 ) 198 Rix, T. ( 3 . 1 ) 43; ( 3 . 7 ) 119 Rob, A.S. ( 4 ) 141 Robinson, G.W. ( 1 ) 228-230 Robinson, P.J. ( 4 ) 413 Robl, T. ( 1 ) 212 Robson, N.S. ( 3 . 2 ) 14 Roch, F.H. ( 4 ) 133 Rockenbauer, A. ( 2 . 2 ) 18 Rockley, M.G. ( 1 ) 45 Rodgers, M.A.J. ( 1 ) 283, 317, 447, 526; ( 3 . 5 ) 1 Rodriguez, J. ( 4 ) 411 Rodriguez-Prieto, M.F. ( 1 ) 398, 417, 418 Rodriquez, M.S. ( 3 . 7 ) 209 Roesch, N. ( 2 . 2 ) 3 , 139 R o e s l e r , H . ( 4 ) 10 Roffey, C.G. ( 4 ) 15 Rogers, C.E. ( 4 ) 437 Rojas, A.M.P. ( 3 . 5 ) 101 Rojas, G.E. ( 2 . 1 ) 28 Rojas, J. ( 1 ) 440 R o l l a , A.P. ( 4 ) 27, 65 R o l o f f , A. ( 2 . 2 ) 11 Roman, E. ( 2 . 2 ) 84 Romanov, A. ( 4 ) 454 Romashov, L.V. ( 3 . 1 ) 5 Ron, E. ( 3 . 2 ) 2 Ronby, B. ( 4 ) 167 Ronco, S.E. ( 2 . 1 ) 59 Roop, B. ( 2 . 3 ) 71 Rophael, M.W. ( 2 . 1 ) 14 Rogues, B.P. ( 3 . 7 ) 92 Rose, S . D . ( 3 . 7 ) 166 Rose, T.S. ( 1 ) 271 Rosenfeld, R.N. ( 2 . 2 ) 2 Rosenthal, G.L. ( 2 . 1 ) 202 Rosenthal, R . J . ( 3 . 7 ) 15 Rosker, M.J. ( 1 ) 18 Rosokha, S.V. (2.1) 120, 121 Ross, A.B. ( 1 ) 17 R o s s i , R.A. ( 3 . 4 ) 7 9 ; ( 3 . 7 ) 183, 185, 189 Roth, H.K. ( 4 ) 72 Roth, S. ( 1 ) 286; ( 4 ) 318 Roth, W. ( 3 . 3 ) 51; ( 3 . 7 ) 24 Rotkiewiez, K. ( 1 ) 183 Rouge'e, M. ( 1 ) 433, 459 Roundhill, D.M. ( 2 . 1 ) 148, 150, 151 Rowan, S.E. ( 3 . 3 ) 20 Roy, R. ( 1 ) 169 R o z e l l , J.M. ( 2 . 2 ) 101; ( 4 ) 390 Rtishchev, N . I . ( 3 . 4 ) 2 8 ; ( 3 . 7 ) 8 4 ; ( 4 ) 504 Rubin, M.B. ( 3 . 2 ) 111;
Photochemistry ( 3 . 4 ) 31 Rubinztain, 2. ( 4 ) 474 Ruckenstein, E. ( 4 ) 346 Rudakov, E.S. ( 3 . 5 ) 59 Rudham, R. ( 3 . 5 ) 65 Rudko, A.R. ( 4 ) 36 Rudler, H. ( 2 . 2 ) 41 Ruggiero, A.J. ( 1 ) 27 Ruiz, J. ( 2 . 2 ) 84 R u l l i e r e , C. ( 1 ) 1 9 , 25, 6 0 , 191 Rumin, R. ( 2 . 2 ) 85 Runsink, J. ( 3 . 2 ) 3 0 ; ( 3 . 4 ) 38, 39; ( 3 . 6 ) 114, 116 Ruprecht, L. ( 1 ) 531 R u s s e l l , D.H. ( 2 . 2 ) 45 R u s s e l l , F.N. ( 2 . 2 ) 106 R u s s e l l , R.A. ( 3 . 2 ) 122; ( 3 . 7 ) 159, 182 Rustamov, M . I . ( 2 . 1 ) 46 R u t t e n s , F. ( 1 ) 194 Ruziewicz, Z. ( 1 ) 112 Ryan, J.F. ( 4 ) 318 Rybak, W. ( 2 . 1 ) 53 Rybalkin, V.P. ( 3 . 6 ) 41 Rybin, L.I. ( 2 . 3 ) 4 5 ; ( 3 . 6 ) 197 Rybinskaya, M . I . ( 2 . 2 ) 23, 74 Rybova, Y. ( 1 ) 316 Rychly, J. ( 4 ) 454 Ryga, T.P. ( 4 ) 182 Rykov, S.V. ( 3 . 7 ) 6 7 , 157 Ryu, C.K. ( 2 . 1 ) 1 , 32 Rzaev, Z.M. ( 4 ) 165
Saak, W. ( 3 . 6 ) 183 S a b b a t i n i , N. ( 2 . 1 ) 182, 183, 185 Sabirov, Z.S. ( 4 ) 6 2 , 6 3 , 9 9 , 101 Sabol, J.E. ( 1 ) 45 S a b u r i , M. ( 4 ) 38 Sachdeva, Y.P. ( 3 . 4 ) 7 8 ; ( 3 . 7 ) 196 S a c k e t t , D.D. ( 2 . 1 ) 16 Sadocco, S. ( 4 ) 510 S a d o v s k i i , N.A. ( 1 ) 297; ( 4 ) 262 Saeva, F . D . ( 3 . 4 ) 157 S a f a r i k , I. ( 1 ) 395; ( 3 . 7 ) 57 Safarzadeh-Amiri, A. ( 1 ) 192; ( 4 ) 257 Saha, B. ( 3 . 7 ) 6 1 Saha, P. ( 4 ) 348 Sahara, A. ( 4 ) 49 Saheki, Y. ( 4 ) 387 Sahyyuin, M.R.V. ( 2 . 3 ) 76 Saidov, D. ( 4 ) 398, 399
Saigo, K. ( 3 . 3 ) 6 3 ; ( 3 . 7 ) 161 S a i l o f s k y , B.M. ( 1 ) 235 S t . P i e r r e , R.J. ( 2 . 2 ) 17 S a i t o , I. ( 1 ) 490, 491; ( 3 . 4 ) 108, 110, 111; ( 3 . 5 ) 100 S a i t o , S. ( 1 ) 482; ( 3 . 4 ) 124; ( 3 . 6 ) 1 2 ; ( 4 ) 155 S a i t o , Y. ( 1 ) 467; ( 2 . 2 ) 9 , 118, 123 S a i t o h , M. ( 3 . 1 ) 14 Sakae, T. ( 3 . 7 ) 164 Sakaguchi, M. ( 2 . 2 ) 107 Sakaguchi, Y. ( 1 ) 323; ( 2 . 3 ) 50 S a k a i , H. ( 1 ) 277, 278 S a k a i , K. ( 1 ) 170; ( 2 . 3 ) 9 S a k a i , Y. ( 1 ) 5 4 ; ( 3 . 2 ) 29; ( 3 . 6 ) 94 Sakaino, Y. ( 1 ) 480 Sakaki, S. ( 2 . 1 ) 162 Sakakura, T. ( 2 . 2 ) 114-1 17 Sakamoto, A. ( 2 . 3 ) 37 Sakamoto, K. ( 3 . 6 ) 187, 189 Sakamoto, M. ( 3 . 2 ) 6 0 ; ( 3 . 7 ) 150 Sakano, K. ( 3 . 5 ) 107 S a k a t a , T. ( 2 . 1 ) 88 S a k a t a , Y. ( 3 . 6 ) 207 Sakato, T. ( 1 ) 517 Sakhnovskaya, E.B. ( 4 ) 460 Sako, M. ( 3 . 5 ) 114; ( 3 . 7 ) 139 Sakuda, M. ( 1 ) 182 Sakuragi, H. ( 1 ) 412, 443; ( 3 . 5 ) 1 4 , 27, 28, 8 9 ; ( 3 . 7 ) 122 S a k u r a i , H. ( 2 . 3 ) 27; ( 3 . 6 ) 187, 189 S a k u r a i , M. ( 3 . 7 ) 77 S a k u r a i , T. ( 3 . 4 ) 59; ( 3 . 6 ) 3 9 , 130 Salaun, J . Y . ( 2 . 2 ) 1 3 , 149 S a l e s , K.D. ( 3 . 7 ) 29 S a l i b y , M . J . ( 2 . 1 ) 34 Salim, M.S. ( 4 ) 30 S a l i n a s , F. ( 3 . 2 ) 143 Salmon, J . M . ( 1 ) 69 Salokhiddinov , K. I. ( 3 . 5 ) 46 Salom, C. ( 4 ) 242 S a l t , W.G. ( 3 . 7 ) 190 S a l t i e l , J. ( 1 ) 99 S a l t i e l , S. ( 1 ) 147 Salupsky, P. ( 3 . 3 ) 75 S a l v i , P.R. (1) 144
53 1
Author index Saman, D. ( 3 . 4 ) 71 Samanta, A. ( 1 ) 111 Samizo, F. ( 3 . 2 ) 1 5 ; ( 3 . 4 ) 56
Samtsov, M.P. ( 4 ) 507 Samuel, C . J .
(3.5) 43;
( 3 . 7 ) 27 Samulski, E.T. ( 4 ) 322 San-nohe, K. ( 3 . 2 ) 1 ; ( 3 . 4 ) 134 Sanchez, F.G. ( 1 ) 4 8 , 104 Sander, W. ( 3 . 2 ) 111; (3.4) 31; (3.5) 83; ( 3 . 7 ) 6 6 , 69 Sandhu, S.S. ( 2 . 1 ) 193 Sandrini, D. ( 2 . 1 ) 144 Sandros, K. ( 1 ) 247, 249 Sang, C. ( 3 . 4 ) 57 Sanjurjo, J . A . ( 1 ) 422 Sano, R. ( 3 . 4 ) 5 9 ; ( 3 . 6 ) 130 Sano, T. ( 3 . 2 ) 27; ( 3 . 6 ) 9 7 , 98 Santamaria, J. ( 3 . 5 ) 54 Santasiero, B.D. ( 2 . 2 ) 146 Santerna, J.S. ( 1 ) 312, 313 Santiago, A.N. ( 3 . 7 ) 183, 189 Saple, A.R. ( 2 . 2 ) 156 Sapre, N.Y. ( 2 . 2 ) 156 Sarahan, A.A. ( 4 ) 394, 470 Sarita, A. ( 1 ) 223 Sarti-Fantoni, P. ( 3 . 2 ) 47; (3.3) 64, 65; (3.6) 91 Saruwatari, M. ( 3 . 7 ) 77 Sasada, Y. ( 2 . 1 ) 125 Sasaki, D.Y. ( 4 ) 267 Sasaki, M. ( 1 ) 401, 517; ( 3 . 5 ) 17 Sasaki, T. ( 3 . 6 ) 29 Sashida, H. ( 3 . 7 ) 9 5 , 9 6 , 97 Sashio, S. ( 4 ) 130 Sasse, W.H.F. ( 1 ) 197, 305, 343 Sasson, R. ( 1 ) 91 Sastre, R. ( 4 ) 127, 222, 233, 366, 367 Sata, T. ( 1 ) 86 Sata, Y. ( 3 . 2 ) 101 Satake, I. ( 1 ) 311 Satge, J. ( 2 . 3 ) 48; ( 3 . 6 ) 198 Sato, E. ( 3 . 2 ) 8 8 ; ( 3 . 5 ) 105, 106; ( 3 . 6 ) 1 5 , 162-164 Sato, M. ( 2 . 1 ) 7 8 ; ( 3 . 2 ) 1 6 , 4 0 ; ( 3 . 6 ) 100, 104,
105
Sato, R. ( 3 . 5 ) 117 Sato, S. ( 3 . 6 ) 106 Sato, T. ( 1 ) 530; ( 2 . 1 ) 9 ; (2.3) 40; (3.7) 41; ( 4 ) 438 Sato, Y. ( 3 . 2 ) 119; ( 3 . 6 ) 2 , 86 Satoh, K. ( 3 . 2 ) 8 7 ; ( 3 . 7 ) 100, 172 Sauerbrey, R. ( 3 . 5 ) 62 Sauers, R.R. ( 3 . 1 ) 3 5 ; ( 3 . 4 ) 22, 23; ( 3 . 6 ) 46, 47 Sauvage, J.P. ( 2 . 1 ) 163 Savarino, P. ( 4 ) 515 Savino, T.G. ( 1 ) 369; ( 3 . 7 ) 43 Sawabe, K. ( 3 . 7 ) 122 Sawaki, Y. ( 2 . 1 ) 86 Sawan, S.P. ( 4 ) 389 Sawanishi, H. ( 3 . 7 ) 9 3 , 94 Scaffardi, L. (1) 257 Scaiano, J . C . ( 1 ) 1 6 , 43, 102, 103, 368, 387, 454; ( 3 . 1 ) 7 , 8 ; ( 3 . 4 ) 26, 7 0 , 125; ( 3 . 7 ) 4 6 , 49 Scaini, R.D. ( 1 ) 373 Scandola, F. ( 2 . 1 ) 8 9 , 94 Scanu, A.M. (1) 496 Schach, T. ( 3 . 6 ) 58 Schafer, A. ( 2 . 3 ) 3 6 ; ( 3 . 6 ) 182, 183, 186 Schaefer, F.P. ( 3 . 3 ) 71 Schiifer, H . J . ( 3 . 1 ) 29, 3 0 ; ( 3 . 7 ) 123 Schaefer, T.D. ( 3 . 5 ) 70 Schaefer, W.P. ( 2 . 2 ) 144 Schaffner, K. ( 3 . 2 ) 74 Schaffrin, H. ( 1 ) 31 Schaller, R. ( 4 ) 147 Scharf, H.-D. (3.2) 30; ( 3 . 6 ) 114 Schaverien, C . J . ( 2 . 2 ) 63 Schechter, H. ( 3 . 7 ) 56 Scheffer, J . R . ( 3 . 3 ) 27 Scheller, M.E. ( 2 . 3 ) 32 Schellman, J. ( 1 ) 10 Schepp, N.P. ( 3 . 1 ) 1 2 ; ( 3 . 5 ) 8 ; ( 3 . 7 ) 59 Schierhorn, A. ( 3 . 7 ) 133 Schiller, C.D. ( 3 . 4 ) 114 Schilling, F.C. ( 4 ) 363 Schinca, D. ( 1 ) 257 Schirmann, P.J. ( 4 ) 443 Schleifer, L. ( 3 . 2 ) 73 Schlosser, W. ( 3 . 7 ) 42 Schmehl, R.H. ( 2 . 1 ) 107 Schmetzer, B. ( 1 ) 142 Schmid, H. ( 3 . 2 ) 110
Schmidlin, F. ( 3 . 7 ) 103 Schmidt, H. ( 3 . 4 ) 24 Schmidt, J. ( 1 ) 352, 196 Schmidt, P. ( 4 ) 359 Schmidt, R. ( 1 ) 449, 451, 455, 456; ( 3 . 5 ) 5 1 ; ( 3 . 6 ) 79 Schmidtberg, G. ( 2 . 2 ) 151, 152 Schmitt, M. ( 3 . 6 ) 113 Schnabel, W. ( 1 ) 323; ( 4 ) 3 4 , 35 Schnapp, K.A. ( 3 . 7 ) 51 Schneider, F.W. ( 1 ) 475 Schneider, H.J. ( 3 . 5 ) 62 Schneider, J. ( 1 ) 70 Schneider, K. ( 3 . 7 ) 64 Schneider, M.R. ( 3 . 4 ) 114 Schneider, S. ( 1 ) 478, 479, 506, 507 Schoemaker, G. ( 2 . 1 ) 136 Schoenholzer, P. ( 3 . 2 ) 66 Schoffmann, T. ( 3 . 4 ) 136; ( 3 . 7 ) 170 Schollmeyer, E. ( 4 ) 385, 433, 434 Schooheydt, R.A. ( 1 ) 345 Schray, K.J. ( 1 ) 47 Schriver, G.W. ( 3 . 6 ) 154 Schroeder, C. ( 3 . 2 ) 6 3 Schroeder, D.R. ( 3 . 7 ) 65 Schroeder, H. ( 2 . 2 ) 3 Schubert, U. ( 2 . 2 ) 53 Schuelert, H. ( 4 ) 13 Schuetz, H. ( 4 ) 37 Schulte-Elte, K.H. ( 3 . 5 ) 81 Schulten, K. ( 1 ) 361 Schulthesis, K.J. ( 4 ) 452 Schultz, A.G. ( 3 . 2 ) 9 3 , 9 8 , 9 9 ; (3.7) 34 Schulz, M. ( 4 ) 450 Schulze, W. ( 2 . 2 ) 34 Schuster, D.I. ( 3 . 2 ) 4 6 , 95 Schuster, G.B. ( 1 ) 469, . 470; ( 2 . 3 ) 8 ; ( 3 . 4 ) 105, 120; ( 3 . 5 ) 9 4 ; ( 3 . 6 ) 150, 208; ( 3 . 7 ) 4 7 , 5 4 , 5 5 , 8 0 , 8 5 , 105 Schwab, M. ( 3 . 7 ) 140 Schwager, B. ( 1 ) 176, 193 Schwarzchild, R. ( 1 ) 518 Schweer, J. ( 4 ) 71 Schwieg, A. ( 3 . 3 ) 49 Schwimmer, W.H.. ( 4 ) 298 Scinara,,H. ( 4 ) 416 Scott, G. ( 4 ) 469, 472, 300 Scott, T.W. ( 1 ) 81 Scully, A.D. ( 1 ) 146; ( 4 ) 465
Photochemistry
537
Sears, D . F . ( 1 ) 99 Sebastiani, G.V. ( 3 . 5 ) 63 Sedelmeier, G. ( 3 . 3 ) 53 Sedlar, J. ( 4 ) 447, 481 Sedova, 0.1. ( 4 ) 143 Seebauer, J. ( 3 . 4 ) 86 Seely, G . R . ( 1 ) 537 Segawa, H. ( 2 . 1 ) 165 Seguchi, K. ( 4 ) 500 Segura, R. ( 3 . 3 ) 31 Sehmbey, C. ( 3 . 4 ) 172; ( 3 . 7 ) 152
Seiffarth, K. ( 4 ) 450 Seilmeier, A. ( 1 ) 212 Seitz, G. ( 3 . 6 ) 66 Seki, H. ( 2 . 1 ) 138 Seki, K. ( 3 . 4 ) 100 Seki, T. ( 3 . 6 ) 21 Sekiguchi, A. ( 2 . 3 ) 1 5 , 1 7 , 42, 47; ( 3 . 6 ) 178, 195; ( 3 . 7 ) 40, 41 Sekita, A. ( 2 . 3 ) 63 Sekiya, T. ( 4 ) 382 Sekretar, S. ( 3 . 2 ) 118 Selikhov, V.V. ( 4 ) 375 Seltzer, S . ( 3 . 7 ) 12 Selva, T . J . ( 1 ) 487 Semak, B . D . ( 4 ) 511 Semenyuk, I . V . ( 4 ) 141 Semerak, S . N . ( 4 ) 201, 312 Semlyen, J.A. ( 4 ) 286 Senboku, H. ( 3 . 7 ) 210 Senoh, S . ( 4 ) 247 Sens, R. ( 1 ) 209, 210 Sensfuss, S. ( 4 ) 37, 77 Seoane, C . ( 3 . 3 ) 7 6 ; ( 3 . 7 ) 160 Sepiol, J. ( 1 ) 199; ( 3 . 4 ) 155; ( 3 . 6 ) 82 Seppelt, K. ( 2 . 2 ) 3 4 ; ( 2 . 3 ) 68 Serdyukova, T . I . ( 2 . 1 ) 42 Serebryakov, E . P . ( 3 . 1 ) 5 2 ; ( 3 . 2 ) 26 Sereda, S . V . ( 2 . 3 ) 26 Seret, A. ( 1 ) 319 Sergeev, A.M. ( 3 . 7 ) 67 Serizawa, M. ( 1 ) 490, 491; ( 3 . 4 ) 110, 111 Seropegina, E.N. ( 4 ) 376 Serpone, M. ( 2 . 1 ) 35 Serpone, N. ( 2 . 3 ) 7 6 ; ( 3 . 4 ) 160; ( 4 ) 521 Sethuran, B. ( 4 ) 98 Setkina, V.N. ( 2 . 2 ) 51 Setser, D.W. ( 2 . 3 ) 60 Seves, A. ( 4 ) 510 Sevilla, F., I11 ( 1 ) 61 Sexton, D . A . ( 2 . 1 ) 134 Sha, D . ( 2 . 1 ) 63 Sha, F. ( 4 ) 428
Shafii, B. ( 2 . 3 ) 6 Shafirovich, V . Y a . ( 2 . 1 ) 95, 9 6 , 103-105,
132
Shagisultanova, G . A . ( 2 . 1 ) 153-156; ( 2 . 2 ) 124 Shah, S.S. ( 2 . 1 ) 22 Shahyun, M.R.V. ( 3 . 4 ) 160 Shakhovskii, G . P . ( 4 ) 47 Shanmugam, P. ( 3 . 4 ) 139; ( 3 . 6 ) 23 Shapiro, A.B. ( 4 ) 316 Shapirov, G.L. ( 3 . 5 ) 2 Shaposhink, A.V. ( 4 ) 70 Shapov, A . N . ( 4 ) 274 Share, P.E. ( 3 . 3 ) 41 Sharm, V . S . ( 1 ) 510 Sharma, D.K. ( 2 . 3 ) 7 6 ; ( 3 . 4 ) 160 Sharma, K.S. ( 1 ) 223; ( 3 . 5 ) 97 Shaw McBee, S.E. ( 1 ) 476 Shchapov, A . N . ( 1 ) 201 Shea, K . J . ( 4 ) 267 Sheldrick, W.S. ( 2 . 2 ) 47, 48; ( 3 . 7 ) 42 Shelimov, B . N . ( 2 . 2 ) 30 Shelkovnikov, V.V. ( 3 . 6 ) 59 Shellun, C.L. ( 1 ) 453 Shelnutt, J.A. ( 1 ) 529; ( 2 . 1 ) 142 Shen, S. ( 3 . 7 ) 8 , 10 Shen, X. ( 4 ) 225 Shen, Z.P. ( 2 . 1 ) 148, 151 Sheng, Z.-C. ( 3 . 6 ) 25 Shepherd, T. ( 3 . 7 ) 38 Shergina, N . I . ( 2 . 3 ) 65 Sheridan, J . B . ( 2 . 2 ) 40 Sheridan, P.S. ( 2 . 1 ) 3 4 ; ( 3 . 1 ) 19 Sherrington, D.C. ( 4 ) 90
Sherstyannikova, L . V . ( 2 . 3 ) 65
Sheveleva, T.V. ( 4 ) 307 Shi, W. ( 2 . 1 ) 79 Shibanov, V . V . ( 3 . 7 ) 156 Shibata, F. ( 2 . 3 ) 20 Shibata, T. ( 2 . 2 ) 104; ( 4 ) 164
Shields, C.J. ( 1 ) 469; ( 3 . 7 ) 80
Shih-Chen, S.J. ( 3 . 2 ) 141 Shiiko, 1.1. ( 4 ) 511 Shikata, T. ( 3 . 6 ) 201 Shilov, A . E . ( 2 . 1 ) 104 Shim, C.S. ( 3 . 2 ) 3 5 ; (3.3) 2
Shim, H.K. ( 3 . 6 ) 133 Shim, S.C. ( 1 ) 145; ( 2 . 3 ) 5 ; ( 3 . 2 ) 4 4 , 45, 8 5 , 108; ( 3 . 3 ) 4 7 ; ( 3 . 5 )
1 8 ; (3.6) 9 9 , 102, 133
Shima, K. ( 3 . 4 ) 60 Shima, S. ( 3 . 6 ) 9 ; ( 4 ) 217
Shimada, K. ( 3 . 5 ) 114 Shimanovskaya-Dianich,
L.M.
( 4 ) 511
Shimidzu, T. ( 2 . 1 ) 165 Shimizu, H. ( 3 . 1 ) 28; ( 3 . 6 ) 205
Shimizu, N. ( 2 . 3 ) 20 Shimo, T. ( 1 ) 491; ( 3 . 2 ) 117; ( 3 . 4 ) 111
Shimokawa, T. ( 4 ) 4 9 , 7 5 , 132, 150
Shimomura, M. (3.6) 6 Shimoshi, H. ( 3 . 2 ) 131 Shine, H.J. ( 3 . 4 ) 150; (3.7) 1
Shinkai, S . ( 3 . 6 ) 11 Shinoda, S . ( 2 . 2 ) 118, 123
Shinohara, N. ( 2 . 1 ) 7 Shiokawa, J. ( 2 . 1 ) 166, 170, 181; ( 4 ) 237, 251 Shioyama, H. ( 1 ) 359 Shirota, Y. ( 4 ) 102 Shizuka, H. ( 1 ) 472, 490, 491; ( 2 . 1 ) 138; ( 2 . 3 ) 35; ( 3 . 4 ) 110, 111; (3.5) 5 , 6 Shizuri, Y. ( 3 . 2 ) 104 Shkol'nikova, L.M. ( 2 . 1 ) 122 Shkurinov, A. ( 1 ) 436 Shlyapintokh, V. ( 4 ) 408, 354 Shmulevich, L.A. ( 1 ) 201 Shobatake, K. ( 1 ) 114 Shoji, S. ( 4 ) 43 Shook, D . ( 3 . 6 ) 118 Shoppee, C.W. ( 3 . 5 ) 102 Shriver, G.W. ( 3 . 3 ) 50 Shul'ga, A.M. ( 3 . 5 ) 46 Shul'pin, G . B . ( 2 . 1 ) 38, 158 Shultz, A . R . ( 4 ) 39 Shutz, A . R . ( 4 ) 468 Shvetsov, S.A. ( 3 . 2 ) 19 Sicard, G. ( 3 . 6 ) 203 Sichere, M.C. ( 4 ) 45 Sidel'nikov, A . A . ( 2 . 1 ) 116 Sidhu, K.S. ( 3 . 4 ) 91; ( 3 . 5 ) 36 Sidhu, M.S. ( 2 . 1 ) 193 Sidky, M.M. ( 3 . 2 ) 50 Sidorova, G . I . ( 4 ) 254 Sieber, F. ( 1 ) 532 Sielisch, T. ( 2 . 2 ) 89 Siemiarczuk, A. ( 1 ) 122, 171
Author Index Sienicki, K. ( 1 ) 279; ( 4 ) 290, 294, 295 Sigal, P.J. ( 3 . 4 ) 163 Sikorski, M. ( 3 . 4 ) 99 Silks, L.A. ( 3 . 7 ) 212 Silva, E. ( 1 ) 440 Silva, L.H.K. ( 2 . 3 ) 58 Simeonsson, J . B . ( 1 ) 63 Simon, J. ( 1 ) 272; ( 3 . 4 ) 80 Simon, J.D. ( 1 ) 28, 162 Simons, J.P. ( 1 ) 129 Simpson, D.J. ( 1 ) 181 Sinclair, R.S. ( 1 ) 461 Sindler-Kulyk, M. ( 3 . 4 ) 2 5 , 26 Singel, D.J. ( 1 ) 352 Singh, A X . ( 1 ) 231; ( 3 . 7 ) 65 Singh, K. ( 3 . 5 ) 36 Singh, R . J . ( 2 . 1 ) 193 Singh, R.P. ( 4 ) 518 Singh, S.B. ( 3 . 1 ) 27 Singh, T. ( 3 . 2 ) 120; ( 3 . 6 ) 87 Singh, T.V. ( 1 ) 8 2 ; ( 3 . 1 ) 49 Singh, V.K. ( 3 . 2 ) 113, 114; ( 3 . 4 ) 46 Singleton, S.F. ( 3 . 3 ) 68 Sinha, H.K. ( 1 ) 98 Sinisterra, J . V . ( 3 . 5 ) 76 Sintsar, A.P. ( 4 ) 141 Siodmiak, J. ( 4 ) 244 Siram, R. ( 2 . 1 ) 35 Sisti, M. ( 3 . 2 ) 8 , 2 2 ; ( 3 . 6 ) 153 Sitkina, L.M. ( 3 . 6 ) 40 Sixl, H. ( 1 ) 288; ( 4 ) 228 Sizova, O.V. ( 2 . 1 ) 117 Skakovskii, E.V. ( 3 . 7 ) 157 Skalski, H. ( 3 . 6 ) 142 Skelton, B.W. ( 2 . 2 ) 125 sket, B. ( 3 . 1 ) 4 7 ; ( 3 . 7 ) 179 Skibsted, L.H. ( 2 . 1 ) 133-135 Sklyaronko, V . I . ( 4 ) 516 Skopenko, V.N. ( 3 . 7 ) 101 Skorobogatov, G.A. ( 2 . 1 ) 43 Skuvat, V.E. ( 4 ) 391 Skvortsov, V.I. ( 1 ) 350 Slama, H. (1) 445 Slawinska, D. ( 3 . 5 ) 50 Slota, P. ( 4 ) 440 Sluma, H.D. ( 3 . 7 ) 70 S l y , W.G. (2.2) 146 Smalley, R.K. ( 3 . 7 ) 98 Smets, G. ( 4 ) 430 Smirnov, V.A. ( 3 . 7 ) 156
533 Smith, Smith, Smith, Smith,
A.B., I11 ( 3 . 3 ) 36 B.A. ( 4 ) 204, 322 B.W. ( 1 ) 63
E.H. ( 3 . 1 ) 3 1 ;
( 3 . 6 ) 172
Smith, G . J . ( 3 . 5 ) Smith, R.J. ( 3 . 7 ) Smith, R.L. ( 3 . 1 ) Smulevich, G. ( 1 )
69 25 42 116,
117
Snider, B.B. ( 3 . 2 ) 2 Snow, M.S. ( 3 . 4 ) 181 Snyder, E.J. ( 3 . 4 ) 75 Snyder, R. ( 1 ) 372 Soda, S. ( 3 . 6 ) 84 Soga, 0. ( 2 . 3 ) 5 6 ; ( 3 . 1 ) 54; ( 3 . 2 ) 133
Soini, E. ( 1 ) 9 Sokolyuk, N.T. ( 3 . 2 ) 145; ( 3 . 4 ) 33
Solodovnikov , S.P. ( 2 . 2 ) 31
Solovskii, M.V. ( 4 ) 313 Somasundaran, P. ( 1 ) 298, 336
Somei, M. ( 3 . 4 ) 8 4 ; ( 3 . 7 ) 176
Somekawa, K. ( 3 . 2 ) 117; ( 3 . 6 ) 122 K. ( 3 . 5 ) 117 J:B.M. ( 3 . 4 ) 119 L.W. ( 1 ) 78 C. ( 3 . 2 ) 123-125; ( 3 . 4 ) 5 2 ; ( 3 . 6 ) 119, 120 Song, Y. ( 4 ) 362 Sonnewald, U. ( 3 . 7 ) 12 Sonobe, H. ( 3 . 5 ) 7 3 , 122, 123 Sopina, I.M. ( 4 ) 81 Sorin, E.L. ( 4 ) 138 Sorokin, M.S. ( 2 . 3 ) 21 Soucek, M. ( 3 . 1 ) 4 4 ; ( 3 . 4 ) 67-69, 71 Soulignac, J . C . ( 1 ) 113 Soundarajan, N. ( 3 . 4 ) 173 Soundararajan, M. ( 3 . 7 ) 6 Sourisseau, C. ( 3 . 5 ) 34 Sousa, E. ( 1 ) 36 Sousa, L.R. ( 1 ) 397 Soutar, I. ( 4 ) 194 Sowinska, M. ( 2 . 1 ) 71 Spalletti, A. ( 1 ) 242, 243; ( 3 . 3 ) 1 1 , 5 9 ; ( 4 ) 50 Spillane, W . J . ( 3 . 4 ) 3 4 ; ( 3 . 6 ) 151 Spinat, P. ( 4 ) 45 Spohr, E. ( 1 ) 115 Spreer, L.O. ( 2 . 1 ) 143 Spreti, S. ( 3 . 4 ) 180; ( 3 . 5 ) 88
Someno, Somers, Somers, Somich,
Sprouse, S.D. ( 2 . 1 ) 129 Spurr, P.R. ( 3 . 3 ) 51-53 Sputova, M. ( 3 . 6 ) 127 Srikrishna, A. ( 3 . 2 ) 129 Srinivasan, R. ( 4 ) 381 Staab, E. ( 3 . 5 ) 71 Stadlbauer, W. ( 3 . 7 ) 99 Staib, R.R. ( 3 . 7 ) 34 Stammer, C.H. ( 3 . 7 ) 14 Standt, A. ( 2 . 3 ) 53 Stang, L.D. ( 4 ) 39 Stankov, S . ( 4 ) 489 Stanley, F.W. ( 4 ) 317 Starzyk, F. ( 4 ) 184 Stasicka, 2. ( 2 . 1 ) 27 Staven'kaya, V.N. ( 4 ) 40 Steel, P.J. ( 2 . 1 ) 7 5 ; ( 3 . 2 ) 115
Steenken, S. ( 2 . 1 ) 57 Steer, R.P. ( 1 ) 160, 427 Stegemeyer, H. ( 1 ) 125 Steil, H. ( 1 ) 273 Steiner, R.F. ( 1 ) 39 Steiner, U. ( 1 ) 415; ( 3 . 6 ) 57
Steinfeld, J.I. ( 2 . 3 ) 12 Steinmetz, M.G. ( 2 . 3 ) 22 Stengrevica, E. ( 4 ) 457 Stensen, W. ( 3 . 2 ) 23 Stenstrom, Y. ( 2 . 2 ) 93 Stephanie, J.G. ( 4 ) 440 Stepp, H. ( 1 ) 531 Steuerle, U. ( 3 . 3 ) 37 Stevens, B. ( 1 ) 35 Stevens, D.G. ( 1 ) 473 Stevens, R.D.S. ( 3 . 3 ) 42 Stewart, L.C. ( 3 . 4 ) 26 Stezowski, J.J. ( 1 ) 222 Stibranyi, L. ( 3 . 3 ) 7 5 ; ( 3 . 6 ) 5 0 , 5 1 , 54-56
Stiegman, A.E. ( 2 . 1 ) 147 Still, W.C. ( 3 . 4 ) 7 6 ; ( 3 . 7 ) 184
Stiver, S. ( 3 . 1 ) 17 Stoddard, G . J . ( 4 ) 267 Stohandl, J. ( 4 ) 481 Stoichitescu, L. ( 4 ) 495 Stopa, G. ( 2 . 1 ) 27 Stowe, F.S. ( 4 ) 142 Stoyanov, A. ( 4 ) 372 Strambini, G.B. ( 1 ) 498, 499
Stramel, R.D. Strauss, U.P.
( 1 ) 283 ( 1 ) 284;
( 4 ) 269
(1) 395; ( 3 . 4 ) 7 ; ( 3 . 7 ) 5 7 , 58 Strehmel, B. ( 4 ) 133 Streith, J. ( 3 . 7 ) 30 Strekas, T.C. ( 2 . 1 ) 79 Strelkova, L.D. ( 4 ) 485 Strich, A. (2.2) 43 Strausz, O.P.
Photochemistry
534 Strickland, S.M.S. ( 3 . 7 ) 212
Strickler, S.J. ( 3 . 3 ) 8 2 ; ( 3 . 4 ) 184
Striker, G. ( 1 ) 123 Strokach, Yu.P. ( 3 . 2 ) 145; ( 3 . 4 ) 33
Stronach, C. ( 3 . 4 ) 86 Struchkov, Yu.T. ( 2 . 3 ) 26 Struve, W.S. ( 1 ) 261, 262 Strydom, S.J. ( 3 . 2 ) 140; ( 3 . 6 ) 136
Stubbings, G.W.F.
Sundavam, A. ( 4 ) 514 Sunderbabu, G. ( 3 . 2 ) 129 Sundermeyer, W. ( 3 . 7 ) 140 Suschitzky, H. ( 3 . 7 ) 8 1 Susens, D.P. ( 4 ) 74 Suslick, K.S. ( 2 . 1 ) 49 Sustic, A. ( 4 ) 444, 461 Sustmann, R. ( 3 . 7 ) 24 Sutcliffe, E. ( 4 ) 381 Suter, G.W. ( 1 ) 380, 406 Sutin, N. ( 1 ) 3 0 ; ( 2 . 1 ) 5 6 , 80
(3.1)
16
Studzinskii, O.P. ( 4 ) 504 Stufkens, D.J. ( 2 . 2 ) 90 Stull, P.D. ( 3 . 7 ) 60 Stults, J.S. ( 3 . 7 ) 138 Stussi, E. ( 1 ) 67 Stynes, D.V. ( 2 . 1 ) 58 SU, S.-G. ( 1 ) 162 SU, T.-M. ( 1 ) 240 Su6rez, E. ( 3 . 7 ) 209 Suau, R. ( 3 . 6 ) 121 Suau Suarez, R. ( 3 . 2 ) 121 Subbarao, K.V. ( 3 . 3 ) 8 1 ; ( 3 . 4 ) 185; ( 3 . 7 ) 178
Subotkowska, W. ( 3 . 4 ) 150 Subramanian, R. ( 3 . 7 ) 5 , 6
Sue, J. (1) 75 Sugahura, Y. ( 4 ) 177, 178 Sugarman, J.F. ( 4 ) 317 Sugimori, A. ( 2 . 1 ) 140 Sugimoto, A. ( 3 . 4 ) 1 2 2 ; ( 3 . 7 ) 131
Suginome, H. ( 3 . 3 ) 7 9 , 80; ( 3 . 4 ) 4 8 ; ( 3 . 6 ) 6 8 , 6 9 ; ( 3 . 7 ) 202-208, 210, 213 Sugita, J. ( 4 ) 88 Sugita, N. ( 2 . 2 ) 104 Sugiura, H. ( 1 ) 517 Sugiura, K. ( 4 ) 386 Sugiura, M. (3.6) 24 Sugiyama, H. ( 1 ) 490; (3.4) 108, 110; ( 4 ) 124 Suglobov, D.N. ( 2 . 1 ) 196, 197 Suhling, K. (1) 50 Suhnel, J. ( 3 . 4 ) 127 Suisalu, A. ( 2 . 1 ) 128 Suizi, H. ( 3 . 5 ) 8 4 Suk, T.S. ( 3 . 3 ) 47 Suka, A. ( 3 . 2 ) 8 0 Sumathi, K. ( 1 ) 365; ( 3 . 6 ) 174 Sumegi, L. ( 2 . 2 ) 18 Sumitani, M. ( 2 . 3 ) 3 5 , 63 Summers, J.W. ( 4 ) 473 Sun, Y.-P. ( 1 ) 99 Sundararajan, N. ( 3 . 3 ) 85
Suto, M. ( 2 . 3 ) 66 Sutton, W.R. ( 1 ) 486 Suzuki, F. ( 4 ) 137 Suzuki, H. ( 2 . 2 ) 100; (3.1) 28; (3.2) 49; ( 4 ) 139 Suzuki, K. ( 4 ) 521 Suzuki, M. ( 1 ) 109 Suzuki, T. ( 2 . 1 ) 5 1 ; ( 3 . 2 ) 1 6 , 144; ( 3 . 5 ) 104; ( 3 . 6 ) 105; ( 4 ) 234 Svejdova, E. ( 4 ) 481 Swales, D. ( 4 ) 413 Swanson, J.R. ( 2 . 2 ) 72 Sweany, R.L. ( 2 . 2 ) 106 Swenton, J.S. ( 3 . 6 ) 96 Swiatkiewiez, J. ( 1 ) 289 Swiatkowski, G. ( 1 ) 87 Swindell, C.S. ( 3 . 6 ) 103 Syamala, M.S. ( 3 . 1 ) 9 ; ( 3 . 4 ) 161 Sycheva, E.A. ( 4 ) 307 Sydnes, L.K. ( 3 . 2 ) 23 Szemik, A.W. ( 1 ) 195 Szewczyk, J. ( 3 . 6 ) 202 Szmacinski, H. ( 1 ) 5 9 , 489 Szurgot, T. ( 3 . 4 ) 1 4 ; ( 3 . 6 ) 17 Szymanska-Buzar , T. ( 2 . 2 )
18 Szymanski, M. ( 1 ) 160, 427
Tabankia, M.H. ( 4 ) 393 Tabarov, S.Kh. ( 4 ) 436 Tabata, K. ( 3 . 5 ) 17 Tabata, Y. ( 4 ) 26 Tabei, E. ( 2 . 3 ) 38, 40 Tabuchi, K. ( 3 . 2 ) 80 Tachdjian, C. ( 3 . 7 ) 112 Tachikawa, N. ( 3 . 2 ) 139 Tachizawa, 0. ( 3 . 7 ) 104 Tada, M. ( 2 . 2 ) 109, 110; (3.6) 2
Tada, Y. ( 3 . 2 ) 5 7 ; ( 3 . 6 ) 30
Taen, S. ( 1 ) 421 Tagaki, W. ( 3 . 6 ) 8
Tagawa, H. ( 2 . 3 ) 5 6 ; ( 3 . 1 ) 54
.
Tahara, T. ( 1 ) 385 Tailhan, C . ( 3 . 7 ) 127 Tajima, K. ( 3 . 7 ) 9 3 , 94 Takagi, K. ( 2 . 1 ) 86 Takagishi, T. ( 3 . 6 ) 9; ( 4 ) 217
Takahara, S. ( 3 . 7 ) 122 Takahashi, A. ( 3 . 7 ) 169; ( 4 ) 177, 178
Takahashi, H. (1) 480; (3.6) 8
Takahashi, K. ( 1 ) 467; ( 2 . 1 ) 50
Takahashi, T. ( 3 . 6 ) 1 6 ; ( 4 ) 38
Takahashi, Y. ( 3 . 3 ) 7 3 ; ( 3 . 4 ) 183
Takaki, I. ( 2 . 2 ) 107 Takamiya, N. ( 3 . 6 ) 2 Takamuku, S. ( 2 . 2 ) 57; ( 3 . 4 ) 175, 176; ( 3 . 5 ) 37, 108; ( 3 . 6 ) 201 Takano, T. ( 3 . 6 ) 2 Takats, J. ( 2 . 2 ) 9 7 , 102 Takayanagi, H. ( 3 . 6 ) 97 Takechi, H. ( 3 . 2 ) 119; ( 3 . 6 ) 86 Takeda, E. ( 3 . 4 ) 151 Takeda, S. ( 3 . 6 ) 38 Takei, M. ( 4 ) 82 Takeoka, S. ( 4 ) 261 Takeshita, H. ( 3 . 2 ) 6 4 , 105; ( 3 . 5 ) 84 Takeshita, K. ( 3 . 6 ) 38 Takeshita, M. ( 3 . 4 ) 165; ( 3 . 7 ) 162 Takeuchi, H. ( 3 . 6 ) 29, 141; ( 3 . 7 ) 104 Takeuchi, K. ( 4 ) 68 Takeuchi, S. ( 4 ) 78 Takeuchi, T. ( 3 . 4 ) 115 Takiguchi, T. ( 4 ) 211 Takimoto, Y. ( 4 ) 78 Takizawa, A. ( 3 . 6 ) 1 0 ; ( 4 ) 230 Takuwa, A. ( 2 . 3 ) 5 6 ; ( 3 . 1 ) 5 4 ; ( 3 . 2 ) 133 Talroze, V.L. ( 4 ) 391 Tamai, N. ( 1 ) 265, 509 Tamaki, T. ( 4 ) 91 Tamao, K. ( 2 . 3 ) 7 Tamiaki, H. ( 3 . 3 ) 5 8 ; ( 3 . 4 ) 8 5 ; ( 3 . 7 ) 175 Tamilarasan, R . ( 2 . 1 ) 1, 192 Tamir, M. ( 4 ) 359 Tamura, K. ( 3 . 5 ) 13 Tamura, M. ( 3 . 7 ) 38 Tamura, S. ( 3 . 6 ) 8 Tamura, Y. ( 3 . 5 ) 124
535
Author Index
Tan, M. (2.1) 63, 167 Tanaka, F. (1) 114, 509 Tanaka, H. (1) 472; (2.1)
Tencer, M. (4) 291 Tennakone, K. (2.3) 58,
208; (2.3) 35; (3.2) 87; (3.7) 100, 172 Tanaka, I. (3.5) 11 Tanaka, K. (2.1) 102; (3.2) 106; (3.6) 61 Tanaka, M. (2.2) 114-117; (2.3) 35; (3.6) 8; (4) 130, 131, 424 Tanaka, S. (3.6) 73 Tanaka, T. (2.1) 102; (2.3) 55; (3.5) 95 Tanaka, Y. (3.4) 101 Tang, Q. (3.7) 187, 193 Tang, W.T. (4) 289 Tani, K. (3.5) 124; (3.6) 207 Tani, T. ( 1 ) 182 Tanida, H. (3.3) 24; (3.6) 45 Tanielian, C. (1) 452 Tanigaki, K. (3.7) 6 3 Taniguchi, H. (3.7) 77 Tanimoto, Y. (1) 401 Tao, F. (2.3) 31; (3.6) 180 Tappe, C. (3.7) 153 Tappet, S. (4) 288 Taquikhan, M.M. (2.1) 92 Taraban, M.B. (2.3) 45; (3.6) 197 Tarama, K. (3.5) 64 Tardien de Maleissye, J. (2.3) 59 Tasai, J.C. (2.2) 29 Tashiro, M. (3.4) 124 Tasumi, M. (1) 385 Tateuchi, S. (3.2) 119; (3.6) 86 Tatikolov, A.S. (4) 516 Tatsumi, K. ( 4 ) 412 Taube, D.J. (1) 510; (2.2) 7 Tauer, E. (3.4) 24 Tausch, M. (3.3) 5 Taveras, A.G., jun. (3.2) 97 Taylor, J.W. (4) 182 Taylor, P. (1) 502 Taylor, W.C. (3.6) 63 Tazuke, S. (1) 282; (2.1) 64, 78, 82, 84; (3.4) 89; (3.6) 7 Teague, S.J. (3.2) 11 Tecklenburg, R.E. (2.2) 45 Tegelaar, P.M.H.L. (1) 399 Telepneva, T.V. .(4) 138 Teleshov, E.N. (4) 47
Teo, B.-K. (3.6) 146 Terada, T. (3.6) 24 Teranishi, H. (1) 390 Terazima, M. (1) 376,
77
407, 423
Tercier, N. (1) 272 Terheijden, J. (3.5) 10 Tero-Kubota, S. (3.2) 131 Tetsa, A.C. (1) 372; (3.4) 121
Teuchner , K. ( 1) 273 Tezuka, T. (3.2) 65 Thakur, M.K. ( 4 ) 169 Thambaraj, P.K. (2.1) 23 Theocharis, C.R. (4) 148 Thiebault, A. (3.4) 80 Thierry, J. (3.7) 113 Thimmappa, B.H.S. (2.2) 80
Thistlethwaite, P.J.
(1) 108, 325, 326 Thom, K.L. (2.3) 39 Thoman, J.W. (2.3) 1 2 Thomas, E.W. (1) 190 Thomas, J.K. (1) 127, 357; (4) 87, 266, 279, 314 Thomas, L.C. (4) 25 Thomas, T.A. (3.3) 50; (3.6) 154 Thome, A. (3.6) 57 Thommen, W. (3.5) 81 Thompson, D.P. (3.6) 190 Thompson, R.B. (1) 58, 476 Thomson, S.A. (3.2) 3, 4 Thornber, J.P. (1) 536 Thorne, J.R.G. (1) 292 Thurnauer, M. (3.4) 120 Thurston, J. (3.7) 214 Tidwell, T.T. (3.1) 12; (3.7) 59 Tiefenthaler, H. (3.4) 24 Timpe, H.J. (3.3) 75; (3.4) 148; (3.6) 50, 52, 53, 55, 56; ( 4 ) 10, 13, 51, 66, 93, 133 Tintel, C. (3.5) 10; (3.6) 71 Tiripicchio, A. (2.2) 133 Tiripicchio-Camellini, M. (2.2) 133 Tissink, N.A. (4) 263 Titova, Yu.V. (3.5) 57 Tobita, H. (2.2) 87 Tocho, J.O. ( 1 ) 257 Toda, F. (3.2) 106; (3.6) 61, 84 Toda, S. (2.3) 57
Todorova, 0. (4) 374 Toi, H. (2.1) 139 Tokitoh, M. (3.6) 206 Tokitoh, N. (2.3) 69; (3.7) 36, 126
Tokuda, K. (3.1) 46 Tokumaru, K. (1) 412; (3.5) 14, 27, 28, 89; (3.7) 122; (4) 59 Tokumaru, T. (1) 443 Tokumura, K. (1) 85 Toleutaev, B.N. (1) 436 Tolstaya, M.V. (2.2) 23 Tolstikov, G.A. (2.2) 10; (3.5) 2 Tom&, F. ( 1 ) 424 Tomasik, P. (3.4) 14, 155; (3.6) 17, 82; (3.7) 3 Tombari, E. (4) 27 Tominaga, T. (2.2) 5, 69 Tomioka, H. (4) 78 Tomita, G. (1) 309 Tomiyama, K. (3.6) 130 Tomkiewcz, M. (4) 225 Tomono, T. (1) 530 Tomotake, A. (3.7) 158 Tomoyama, K. (3.4) 59 Tomura, M. (3.6) 171 Tonokura, K. (1) 472 Toporowicz, M. (1) 434 Topp, M.R. (1) 139 Torikui, A. (4) 352 Toriolo, L. (4) 65 Torizuka, K. (1) 86, 530 Torkelson, J.M. (1) 353, 394; (4) 231, 296-298 Torrent, A.O. (1) 371 Torres, M. (1) 395; (3.4) 7; (3.7) 57, 58 Torroba, T. (3.3) 64, 65; (3.6) 91 Toscano, V. (1) 159, 97; (4) 415 Tossell, J.A. (3.6) 122 Tournilhac, F. (3.4) 80 Townsend, P.D. (4) 210, 223 Trah, S. (3.3) 62 Trahanovsky, W.S. (3.4) 11 Tran, C.Q. (4) 270 Traylor, T.G. ( 1 ) 510 Treushnikov, V.M. ( 4 ) 138 Trevor, D.J. (2.1) 21 Tribel, F. (1) 481 Trifonov, L. (2.2) 105 Tripathi, H.B. (1) 168 Tripathi, S. (1) 159 Troe, J. (1) 237 Trogler, W.C. (2.2) 148 Trotter, J. (3.3) 27
Photochemistry
536 Trska, P. (3.6) 127 T r u s c o t t , T.G. ( 1 ) 155, 419 T s a i , H.B. ( 4 ) 213 T s a i , W.M. (2.2) 101 T s a i , Y.G. ( 4 ) 389 Tsay, F.D. ( 4 ) 328 Tschamber, T. (3.7) 30 Tseng, C.M. (4) 54 Tsubono, K. (3.4) 165; (3.7) 162 Tsuchida, A. (3.6) 9 5 Tsuchida, E. (4) 261 Tsuchiya, M. (3.5) 89 Tsuchiya, T. (3.3) 38; (3.5) 118; (3.6) 18; (3.7) 93-97, 108 Tsuda, Y. (3.2) 27, 29; (3.6) 94, 97, 98 Tsuge, 0. (3.2) 117 T s u i k i , H. (2.1) 208 T s u j i , T. (3.2) 137, 138; (3.3) 33, 34; (3.4) 12 Tsujimoto, K. ( 3 . 4 ) 100, 101 T s u j i t a , Y. (3.6) 10; ( 4 ) 230 Tsumuraya, T. (2.3) 47, 49 Tsuno, Y. (2.3) 20 Tsunooka, M. (4) 130, 131, 424 Tsuruta, H. (4) 284 T s u t s u i , T. (1) 482; (3.4) 124; (3.6) 12 Tsutsumi, K. (3.6) 205 Tsyupko, F.I. ( 4 ) 141 Tu, C.-L. (3.3) 4; (3.6) 124 T u a i l l o n , J. (3.7) 198 Tuazon, E.C. (3.5) 86 Tukada, H. (3.6) 83 Tumanskii, B.L. (2.2) 31 Tumas, W. (2.2) 14 Tundo, P. (3.5) 53 Tunuli, M.S. (2.1) 126 Tups, H. (4) 71 Turkevich, L.A. (1) 314 Turley, T.J. ( 1 ) 49 Turner, J.J. (1) 469; (2.2) 49; (2.3) 64; (3.7) 80, 121 Turner, J.T. (3.4) 20 Turro, N . J . ( 1 ) 298, 302, 336, 362; (2.1) 66; (3.1) 6 , 9 ; (3.4) 11, 161; (3.7) 7; (4) 54, 260, 277 Twarowski, A.J. ( 1 ) 435 Tyler, D.R. (2.2) 28 Tymyanski, Y.R. (1) 157
Uchida, A. (2.1) 125 Uchida, K. (1) 405 Uchida, Y. (4) 38 Uchino, T. (3.2) 55; (3.6) 88 Uchiyama, H. (4) 501 Uchiyama, K. (3.6) 104 Udagawa, M. ( 1 ) 85 Udayakumar, B.S. (2.3) 22 Ueda, M. ( 1 ) 65, 246 Ueda, T. (3.7) 128-130 Uenishi, S. (4) 424 Ueno, A. (2.1) 208 Ueno, K. (2.2) 8 7 Ueyama, K. (2.2) 55 U h l , H. (3.7) 81 Ullah, S.S. (2.2) 76 Ulman, A. (1) 238 U l r i c h , T. (3.6) 57 Umeda, I. ( 3 . 2 ) 29; (3.6) 94 Umehara, K. ( 4 ) 431 Umezawa, B. (3.7) 169 Uno, H. ( 1 ) 6 5 Unsold, E. (1) 531 Uozo, Y. ( 1 ) 246; (3.3) 8; (3.4) 90 Upmacis, R.K. (2.2) 119 Urabe, N. ( 4 ) 338-343 Urabe, S. (4) 509 Urban, J. (3.4) 7 1 Urbanova, M. (1) 535 Urquhart, R.S. (1) 325, 326 Uryu, T. (3.4) 101; ( 4 ) 162 Usacheva, M.N. ( 4 ) 56 U s a m i , T. (2.1) 48 Ushida, S. (4) 500 Ushiki, H. (4) 245 Usui, H. (3.7) 128 129 Usui, Y. (1) 443; 3.5) 27 Utena, Y. (4) 285, 286 Uzawa, H. (3.5) 64 Vacek, K. ( 1 ) 535 Vaculikova, D. (3.6) 127 Vaida, V. (2.2) 6 , 44 Vaidergorin, E.Y.L. (4) 415 Vaitekunas, S. (3.6) 1 Valat, P. ( 1 ) 159, 527 Valdes-Aquilera, 0. (1) 22 1 Valentino, M. (1) 521 Valenza, A. (4) 357 Valenzo, D.P. (1) 465 Valeur, B. (2.1) 71 V a l l a r i n o , L.M. (2.1) 185 V a l l r i b e r a , A. (3.5) 41
Valu, F. ( 4 ) 495 Valyocsik, E.W. (3.4) 163 Van Arnum, S.D. (3.1) 35; (3.4) 22, 23; (3.6) 46, 47 Van Camp, J . R . ( 3 . 7 ) 166 Vandenberg, D.M. (2.2) 126 Vandendriessche, J. ( 4 ) 195, 280, 286, 287 van der Auweraer, M. (1) 53, 172, 194, 301 Van d e r Braken-Van Leersum, A.M. (3.6) 71 Van d e r Hart, J.A. (3.4) 35 Vanderhoff, J . W . (4) 54 Van der Kelen, G.P. (2.3) 51 Vanderkooi, J.M. ( 1 ) 442 Van d e r P l a s , H.C. (3.5) 38 Vanderpool, R.A. (2.2) 29 van de Vorst, A. ( 1 ) 319 Vandewalle, M. (3.2) 33 van Dijk-Knepper, J.J. (3.4) 36 van Dorst, W.C.A. ( 1 ) 232 van E i j k , A.M. (1) 402 Van E l d i c k , R. (2.1) 5 , 130 Vanelle, P. (3.7) 186 Van H i j f t e , L. (3.7) 21 van Hoek, A. ( 1 ) 312, 313 Van Hooste, H. (2.3) 51 Van Houten, J. (2.1) 66 van Langen, H. (1) 333 van Lier, J.E. (1) 464 Vannuci, C. ( 4 ) 409, 410 Van Rameesdonk, H.J. (4) 263 van Riel, H.C.H.A. (3.4) 64 Van’t Zelfde, M. (3.6) 71 Van Vliet, P.M. (2.1) 174 Van Willigen, H. (2.1) 206 Van Zoeren, C.M. (2.3) 12 Vardeny, Z. (4) 226 Varlamov, S.V. (3.7) 200 Varma, C.A.G.O. (1) 402 Varma, I . K . (4) 459 Varnavsky, 0. ( 1 ) 308 Varshney, S. (4) 459 Vartanyan, S.A. (3.1) 52 V a s i l i o u , C. (4) 351, 476 V a s i l i s h i n a , N.P. (4) 511 Vass, F. (4) 454 Vasserman, A.M. (4) 316 Vassova, G. (4) 454 Vaupel, B. (1) 344 Vazquez, J. (3.3) 31
537
Author Index
Vedejs, E. ( 3 . 7 ) 137, 138 Veeramani, K. ( 3 . 4 ) 139; ( 3 . 6 ) 23
Veillard, A. ( 2 . 2 ) 27, 43 Veissier, V. ( 4 ) 281 Velek, J. ( 3 . 4 ) 67 Venediktov, E.A. ( 3 . 5 ) 5 7 , 58
Venkatesan, K. ( 3 . 6 ) 79 Venton, D.L. ( 3 . 7 ) 89 Verardo, G. ( 3 . 6 ) 131 Verdonck, K. ( 2 . 3 ) 51 Verezubova, A.A. ( 1 ) 252 Verhey, P.F.A. ( 1 ) 402 Verhoeven, C. ( 2 . 1 ) 106 Verhoeven, J.W. ( 1 ) 266; ( 4 ) 263
Vermeersch, G. ( 1 ) 520 Veronkov, M.G. ( 2 . 3 ) 21 Verpeaux, J.-N. ( 3 . 4 ) 80 Verrier, M. ( 1 ) 444; ( 2 . 3 ) 62
Verschoor, C.M. ( 2 . 1 ) 171 Vert, F.T. ( 1 ) 371 Verzele, M. ( 3 . 1 ) 11 VessiGre, R. ( 3 . 2 ) 6 2 ; ( 3 . 6 ) 36
Vever-Bizet, C. (1) 433 Veyssie, M. ( 4 ) 106 Viaene, K. ( 1 ) 345 Viallet, P. ( 1 ) 69 Victor, J.G. ( 4 ) 231 Vigo, J. ( 1 ) 69 Viguri, F. ( 2 . 2 ) 133 Viktorova, T.I. ( 4 ) 56 Viljoen, A.M. ( 3 . 2 ) 140; ( 3 . 6 ) 136
Vincze, L. ( 2 . 1 ) 6 0 , 61 Vinogradov, S.A. ( 2 . 1 ) 153, 154
Viovy, J.L. ( 4 ) 203, 281 Virgili, A. ( 3 . 5 ) 41 Virginia, 0. ( 4 ) 402 Viscardi, G. ( 4 ) 515 Visser, A.J.W.G. ( 1 ) 312, 313
Visser, D. ( 3 . 7 ) 58 Viswanathan, V.N. ( 4 ) 305 Vivona, N. ( 3 . 4 ) 21 Vlachopoulos, N. ( 2 . 1 ) 9 , 17
Vlasova, N.N. ( 2 . 3 ) 65 Vlcek, A. ( 2 . 1 ) 145, 147, 149
Vlkova, D. ( 3 . 6 ) 127 Vo-Dinh, T. ( 1 ) 347, 406 Voegele, H.P. ( 4 ) 71 Vogel, J. ( 1 ) 506, 507 Vogel, M. ( 1 ) 209-211 Vogelbacher, U.J. ( 3 . 6 ) 58
Vogl, E. ( 1 ) 434
Vogl, 0. ( 4 ) 444, 461 Vogler, A . (2.1) 4 1 , 131 Vohra, R. ( 3 . 2 ) 120;
Wakisaka, A. ( 3 . 5 ) 14 Wakui, Y. ( 3 . 3 ) 13; ( 3 . 6 ) 37
Waldeck, D.H. ( 1 ) 241;
( 3 . 6 ) 87
Voitlander, J. ( 1 ) 445 Volbushko, N.V. ( 3 . 4 ) 128 Volkotomb, M.N. ( 4 ) 458 Volkova, G.N. ( 3 . 7 ) 156 Von Angerer, S. ( 3 . 2 ) 5 8 ; ( 3 . 4 ) 130; ( 3 . 6 ) 32
von Borczyskowski, C. ( 1 ) 260
von Bunau, G. ( 1 ) 411 von Halban, H. ( 3 . 2 ) 110 Von Schnering, H.G. ( 2 . 3 ) 36; ( 3 . 6 ) 182; ( 3 . 7 ) 16
von Trebra, R.J. ( 1 ) 213 von Wartburg, B. ( 3 . 2 ) 59 von Wondruszka, R. ( 1 ) 329
Von Zelewsky, A. ( 2 . 1 ) 7 7 , 8 5 , 144; ( 2 . 2 ) 150 ( 3 . 2 ) 19 ( 4 ) 356 ( 2 . 3 ) 65 (3.5) 43; ( 4 ) 507 Vorspohl, K. ( 2 . 3 ) 34; ( 3 . 6 ) 192 Vos, J.G. ( 2 . 1 ) 85 Vos, K. ( 1 ) 312, 313 Vos, M. ( 4 ) 263 Voss, E. ( 2 . 2 ) 58 Voyakin, I.V. ( 2 . 2 ) 124 Vrachnou, E. ( 2 . 1 ) 9 Vrubel, T.L. ( 3 . 6 ) 3 Vyazankin, N.S. ( 2 . 3 ) 45; ( 3 . 6 ) 197 Vymazal, Z. ( 4 ) 442 Vysotskaya, N.A. ( 3 . 2 ) 142
Vorob'ev, A.V. Voronin, I.N. Voronkov, M.G. Voropai, E.S.
(3.3) 7
Walia, S . ( 3 . 3 ) 8 3 ; ( 3 . 5 ) 42, 91
Wallis, J.M. ( 3 . 4 ) 63 Walsh, R. ( 3 . 1 ) 31; ( 3 . 6 ) 172
Walton, J.C. ( 3 . 7 ) 110 Waltz, W.L. ( 2 . 1 ) 30
Wamhoff, H. ( 3 . 2 ) 50, 9 2 ; ( 3 . 6 ) 48, 144
Wan, P. ( 3 . 2 ) 28; ( 3 . 4 ) 171, 174, 177, 178; ( 3 . 7 ) 106 Wang, C.H. ( 1 ) 256 Wang, D. ( 2 . 3 ) 28; ( 3 . 6 ) 22, 179; ( 4 ) 108 Wang, E. ( 2 . 3 ) 4 6 ; ( 4 ) 5 2 , 55 Wang, F. ( 1 ) 62 Wang, H. ( 3 . 2 ) 8 2 ; ( 3 . 6 ) 110 Wang, J.B. (3.7) 208 Wang, K.S. ( 4 ) 318 Wang, S. ( 2 . 1 ) 199 Wang, T.4. ( 3 . 2 ) 32 Wang, X. ( 3 . 5 ) 30; ( 3 . 6 ) 60 Wang, Y. ( 4 ) 306 Ward, M.D. ( 3 . 5 ) 61 Ward, T.L. ( 4 ) 80 Ware, W.R. ( 1 ) 1 2 2 , 492 Warner, I.M. ( 1 ) 3 , 7 , 126 Warner, J. ( 1 ) 66 Warrener, R.N. ( 3 . 2 ) 122; ( 3 . 7 ) 159 Warta, R. ( 1 ) 288
Wasielewski, M.R.
(1)
196, 534
Wabnitz, H. ( 1 ) 344 Wacholtz, W.F. ( 2 . 1 ) 107 Wada, M. ( 2 . 2 ) 142 Wada, Y. ( 3 . 5 ) 66 Wade, P.A. ( 3 . 4 ) 179 Wagner, B.D. ( 1 ) 492 Wagner, K. ( 4 ) 144 Wagner, 0. ( 3 . 7 ) 37 Wagner, P.J. ( 3 . 1 ) 27; ( 3 . 2 ) 6 8 , 6 9 ; ( 3 . 4 ) 32, 43, 44; ( 3 . 7 ) 135, 136 Wagner, R. ( 1 ) 501; ( 4 ) 66 Wahiduzzaman, S M. ( 2.2) 76 Wakamatsu, K. ( 3 . 3 ) 18 Wakao, K. ( 3 . 4 ) 1 9 ; ( 3 . 6 ) 145 Wakasa, M. ( 2 . 3 ) 50
.
Wasniowska, A. (1) 497 Wasserman, H.H. ( 3 . 5 ) 119 Wasylewski, Z. ( 1 ) 487, 497
Watanabe, A. ( 4 ) 7 4 , 308 Watanabe, H. ( 2 . 3 ) 3 8 , 4 0 ; ( 3 . 2 ) 42; ( 3 . 6 ) 108; ( 4 ) 387 Watanabe, Y. ( 3 . 2 ) 5 5 ; ( 3 . 6 ) 88 Wataru, A. ( 2 . 3 ) 6 9 ; ( 3 . 5 ) 8 0 , 117 Waterman, K.C. ( 1 ) 336 Watillon, A. ( 4 ) 271 Watkinson, T.M. ( 2 . 3 ) 7 4 Watt, D.S. ( 3 . 7 ) 86 Watts, R.J. ( 2 . 1 ) 129 Watts, S.P. ( 4 ) 514 Wayda, A.L. ( 2 . 1 ) 172;
Photochemistry
538 ( 2 . 2 ) 159
Wayland, B.B. ( 2 . 2 ) 136 Wayner, D.D.M. ( 3 . 4 ) 162; ( 3 . 7 ) 151
Webb, J.D. ( 4 ) 423 Webb, K.K. ( 4 ) 156 Webb, S.P. ( 1 ) 27 Webber, S.E. ( 1 ) 281, 283; ( 2 . 1 ) 207; ( 4 ) 309
Weber, G. ( 3 . 4 ) 38 Weber, S.G. ( 2 . 1 ) 126 Weber, W.P. ( 2 . 3 ) 25 Webster, G.R.B. ( 3 . 4 ) 9 6 , 107; ( 3 . 7 ) 177
Webster, N.J.G. ( 3 . 2 ) 18 Weedon, A.C. ( 1 ) 196; ( 3 . 2 ) 38, 39; ( 3 . 5 ) 23-25 Weichman, M. ( 1 ) 222 Weidenbruch, M. ( 2 . 3 ) 36, 3 9 ; ( 3 . 6 ) 182, 183, 186 Weidmann, K. ( 3 . 3 ) 62 Weiland, R. ( 1 ) 267 Weimar, C. ( 3 . 2 ) 5 8 ; ( 3 . 4 ) 130; (3.6) 32 Weiner, A.M. ( 1 ) 120 Weinmann, D.J. ( 2 . 2 ) 3 8 , 39 Weinmann, S. ( 3 . 2 ) 73 Weinreb, A. ( 1 ) 91 Weir, D. ( 1 ) 1 6 , 103, 368, 454; ( 3 . 4 ) 2 6 ; ( 3 . 7 ) 46 Weir, N.A. ( 4 ) 425, 426 Weiss, R.G. ( 1 ) 471; ( 3 . 1 ) 23 Weitzel, K.-M. ( 1 ) 237 Weixelboumer, W.-D. ( 1 ) 137 Wells, D. (1) 343 Welsh, K.M. (3.6) 177, 194; ( 3 . 7 ) 74 Wender, P.A. ( 3 . 7 ) 33 Wendrinsky, J. ( 4 ) 172 Wenska, G. ( 1 ) 153 Wermer, P.H. ( 2 . 2 ) 37 Wessels, P.L. ( 3 . 2 ) 140; ( 3 . 6 ) 136 West, P.R. ( 3 . 7 ) 48 West, R. ( 2 . 3 ) 3 , 1 4 ; ( 3 . 6 ) 177, 188, 194; ( 3 . 7 ) 74 Weuthen, M. ( 3 . 6 ) 114 Wheeler, D.R. ( 2 . 2 ) 14 Whetten, R.L. ( 2 . 1 ) 21 White, A.H. ( 2 . 2 ) 125; ( 3 . 4 ) 30 White, C. ( 4 ) 181 White, J.M. ( 2 . 1 ) 207; ( 2 . 3 ) 71 White, N.J. ( 4 ) 413 White, R.C. ( 3 . 1 ) 4 1 , 4 3 ;
( 3 . 7 ) 119, 120
Whitehead, J.C. ( 2 . 3 ) 74 Whiting, D.A. ( 3 . 7 ) 149 Whiting, K. ( 4 ) 426 Whitman, P.J. ( 4 ) 146 Whitmore, P.M. ( 2 . 2 ) 7 0 , 71
Whitten, D.G. ( 1 ) 9 2 , 334; ( 3 . 3 ) 74
Whitwell, I. ( 2 . 2 ) 130 Whuler, A. ( 4 ) 45 Wickramanayake, S. ( 2 . 3 )
161; ( 3 . 1 ) 7 ; ( 3 . 4 ) 125
Wipf, P. (3.6) 160 Wireko, F. ( 3 . 3 ) 27 Wirth, M.J. ( 1 ) 131 Wirz, J. ( 3 . 5 ) 26; ( 3 . 7 ) 25, 26
Witherspoon, J. ( 3 . 4 ) 86 Witte, P. ( 1 ) 1 4 , 204, 205
Wlostowska, J. ( 3 . 7 ) 8 ,
58, 77
Wiczk, W. ( 1 ) 3 8 , 39 Wieghardt, K. ( 2 . 1 ) 57 Wiegrebe, W. ( 3 . 2 ) 58; ( 3 . 4 ) 130; ( 3 . 6 ) 32
Wieland, S. ( 2 . 1 ) 130 Wierzchowski, J. ( 3 . 3 ) 86; ( 3 . 4 ) 182
Wijeratne, W. ( 2 . 3 ) 58 Wilcsek, R.J. ( 2 . 3 ) 7 Wild, U.P. ( 1 ) 5 5 , 106, 380, 406
Wilde, R.G. ( 3 . 7 ) 137 Wilkey, J.D. ( 2 . 3 ) 8; ( 3 . 6 ) 208
Wilkins, B.J.
291-295, 322
Wintgen, M. ( 4 ) 228 Wintgens, V. ( 1 ) 43, 159,
( 3 . 4 ) 170;
( 3 . 6 ) 70
Wilkinson, F. ( 1 ) 338, 346; ( 4 ) 221
Willard, C.S. ( 1 ) 287 William, G.A. ( 1 ) 514 Williams, D.J. ( 1 ) 287 Williams, I.D. ( 2 . 2 ) 63 Williams, K.P.J. ( 4 ) 369 Williams, L.R. ( 1 ) 119, 120, 290
Williard, P.G. ( 3 . 2 ) 1 2 , 46
Willner, I. ( 2 . 1 ) 9 9 , 101 Willsher, C.J. ( 1 ) 346; ( 4 ) 221
Wilson, K. ( 3 . 7 ) 192 Wilson, R.M. ( 3 . 1 ) 25, 26; ( 3 . 4 ) 145; ( 3 . 5 ) 2 2 ; ( 3 . 7 ) 1 6 , 1 7 , 20, 26, 51 Wilson, T. ( 1 ) 383 Windsor, M.W. ( 1 ) 90 Winefordner, J.D. ( 1 ) 63, 64, 294, 329, 348 Wing, H. ( 3 . 4 ) 16 Wingert, H. ( 3 . 4 ) 13 Winkler, J.D. ( 3 . 2 ) 12 Winkler, J.R. ( 2 . 1 ) 56, 8 0 ; ( 2 . 2 ) 131 Winkler, T. ( 3 . 4 ) 3 9 ; ( 3 . 6 ) 116 Winnik, F.M. ( 1 ) 282 Winnik, M.A. ( 1 ) 279, 282; ( 4 ) 190, 205, 273,
1 0 , 11
Wlostowski, M. ( 3 . 7 ) 8 Wohn, C.S. ( 4 ) 73 Wojtczak, J. ( 2 . 2 ) 9 4 , 9 5 ; ( 3 . 4 ) 99
Wolf, H.R. ( 3 . 2 ) 59 Wolfbeis, O.S. ( 1 ) 5 , 542 Wolfe, J.F. ( 3 . 4 ) 7 8 ; ( 3 . 7 ) 196
Wolff, S. ( 3 . 2 ) 63 Wolff, T. ( 1 ) 411 Wolfgang, H.F. ( 4 ) 278 Won, D.J. ( 4 ) 432 Wong, E. ( 3 . 5 ) 92 Wong, K.H. ( 4 ) 264 Woo, H.G. ( 2 . 2 ) 62 Woolf, E.J. ( 1 ) 477 Wooten, W.L. ( 4 ) 146 Wortmann, R. ( 1 ) 3 1 , 32 Wrackmeyer, B. ( 2 . 3 ) 54 Wrighton, M.S. ( 2 . 2 ) 35, 8 3 , 8 6 , 98
Wrzyszczynski, A. ( 4 ) 238 Wu, G. ( 3 . 5 ) 33 Wu, S. ( 2 . 3 ) 31; ( 3 . 2 ) 107, 109; ( 3 . 5 ) 9 0 ; ( 3 . 6 ) 180; ( 4 ) 24, 5 2 , 467 wu, W.Y. ( 3 . 5 ) 102 Wu, X. ( 2 . 3 ) 73 Wu, Y. ( 4 ) 483 Wu, Z. ( 3 . 3 ) 8 4 ; ( 3 . 4 ) 9 2 ; ( 3 . 6 ) 139 Wubbels, G.G. (3.4) 7 4 , 75 Wuu, Y.M. ( 2 . 2 ) 86
Xiao, F. ( 2 . 3 ) 31; ( 3 . 6 ) 180
Xingzhon, H. ( 4 ) 479 Xu, D. ( 1 ) 216 Xu, G. ( 2 . 2 ) 1 5 , 1 6 , 155 Xu, H. ( 1 ) 1 7 8 ; ( 3 . 5 ) 40 Xu, Q.Y. ( 2 . 3 ) 46 Xu, Y. ( 3 . 5 ) 96 Xue, N. ( 3 . 5 ) 40
539
Author Index
Yabe, A. (3.5) 121; (3.6) 8; (3.7) 83; (4) 26 Yablonskaya, E.E. (2.1) 96, 103
Yagei, Y. (4) 34, 35 Yagi, M. (1) 405; (3.6) 84
Yagupol'skii, L.M. (3.7) 101 Yajima, H. (4) 285, 286 Yakoi, K. (1) 410 Yakovleva, I.V. (4) 316 Yam, V.W.W. (2.1) 110 Yamada, A. (3.4) 19; (3.6) 145; (4) 320
Yamada, E. ( 4 ) 59 Yamada, H. (4) 407 Yamada, K. (3.6) 72, 73;
(4) 44
Yamada, S. (3.6) 69: (3.7) 202, 204, 207, 208, 210, 213; (4) 521 Yamada, Y. (2.2) 5, 69 Yamaguchi, A. (4) 386 Yamaguchi, K. (3.7) 100; (4) 102 Yamaji, M. (2.3) 11 Yamakawa, T. (2.2) 118 Yamamoto, A. (3.4) 108 Yamamoto, H. (3.6) 9; (3.7) 211; (4) 217 Yamamoto, K. (4) 379 Yamamoto, M. (3.6) 72, 73, 93, 95; (4) 92, 270, 301 Yamamoto, T. (4) 100 Yamamoto, Y. (2.1) 51; (4) 41 Yamamura, S. (3.2) 104 Yamanako, T. (1) 109 Yamano, M. (3.2) 55; (3.6) 88 Yamaoka, T. (1) 426; (4) 128, 139, 164 Yamasaki, Y. (1) 165 Yamase, T. (2.1) 47, 48 Yamashita, A. (3.3) 60 Yamashita, M. (1) 86, 530 Yamashita, Y. (3.2) 144; (3.3) 72 Yamato, T. (3.4) 124 Yamauchi, S. (1) 375, 381 Yamazaki, I. (1) 52, 109, 265, 282, 509 Yamazaki, M. (3.4) 115 Yamazaki, T. (1) 148, 265; (3.2) 78, 94; (3.3) 13; (3.6) 16, 24, 37; (4) 478 Yan, W. (4) 180 Yan, X. (1) 184 Yanagida, S. (2.2) 56,
57; (3.5) 37, 108; (3.7) 164 Yanagizawa, Y. (4) 509 Yandrasits, M. (3.4) 86 Yang, C.L. (1) 342 Yang, H. (3.6) 22 Yang, N.C. (1) 496; (3.4) 54 Yang, P. (4) 180 Yang, R.D. (2.1) 186, 187 Yang, X. (3.4) 54; ( 4 ) 480 Yankelevich, A.Z. (3.7) 67 Yankov, P. (1) 147 Yano, H. (1) 121 Yano, K. (4) 130 Yano, M. (4) 406 Yao, X. (3.4) 16 Yardley, J.T. ( 1 ) 141 Yartsev, V.P. (4) 360 Yasuda, M. (3.4) 60 Yasuda, S. (3.6) 67 Yasuda, Y. (4) 248 Yasufuku, K. (2.1) 138 Yatchishin, 1.1. (4) 141 Yates, K. (3.3) 1 Yates, P. (3.1) 17 Yatsimirskii. K.B. (2.1) 120 Ye, C. (2.3) 66 Ye, L. (4) 24 Ye, W. (2.3) 73; 3.6) 200 Ye, Y. ( 4 ) 361 Yen, K. (2.1) 6 3 Yeo, H.S. (2.3) 5 (3.2) 35; (3.5) 18 Yersin, H. (2.1) 65 Yoda, K. (1) 480 Yokoyama, A. (4) 272, 315 Yokoyama, H. (1) 253 Yokoyama, I. (1) 309 Yokoyama, M. (3.4) 126 Yokoyama, Y. (3.4) 126; (3.5) 104 Yoneda, S. (3.4) 122; (3.6) 171; (3.7) 131 Yonemitsu, 0. (3.3) 60 Yonezawa, N. (3.7) 161 Yoon, T.H. (4) 325 Yoon, U.-C. (2.3) 13; (3.6) 125 Yoon, Y.J. (3.2) 108 Yoshi, A. (3.6) 132 Yoshida, E. (3.6) 165 Yoshida, H. (3.4) 175; (3.6) 178 Yoshida, K. (3.4) 151 Yoshida, M. (2.3) 44; (3.4) 15 Yoehida, T. (3.6) 11
Yoshida, Y. (1) 77; (3.2) 127
Yoshida, 2. (3.4) 15 Yoshihara, K. (1) 386, 414; (2.3) 35
,
Yoshikawa, K. (4) 382 Yoshimura, A. (1) 359 Yoshimura, H. (1) 500; (3.2) 117
Yoshino, K. (4) 211 Yoshioka, N. (3.1) 14 Yoshizawa, H. (4) 270 Younathan, J.N. (2.1) 16 Young, K.M. (3.3) 86; (3.4) 182
Young, R.N. (1) 88, 89 Yu, C. (3.5) 96 Yu, D.H.4. (1) 353, 394 Yu, L.P. (4) 322 Yu, O.H. (4) 296 Yu, S. (4) 128 Yu, T. ( 4 ) 135, 136, 462 Yuan, J. (2.1) 167 Yunusov, R.Yu. (4) 61, 63, 99, 101
Yu-Quan, S. (1) 254 Yusov, A.B. (2.1) 180 Zabala, I. (1) 424 Zabotina, E.Ya. (3.6) 204 Zachara, S. (2.1) 169 Zachariasse, K.A. ( 1 ) 123, 124
Zahradnikova, A. (4) 481 Zaitsev, A.K. (1) 321 Zaitsev, B.E. (4) 506 Zaitsev, N.K. ( 1 ) 321, 539
Zaitsev, Yu.S. (4) 94 Zaitseva, V.V. (4) 94 Zakharov, V.N. (2.1) 128 Zakhidov, A.A. (1) 175 Zakhs, E.R. (3.6) 77 Zakin, M.R. (2.1) 21 Zalupsky, P. (3.6) 53, 55, 56 Zaman, K. (3.6) 49 Zamotaev, P.V. (4) 364 Zana, R. (4) 243 Zandomeneghi, M. (3.2) 24 Zang, L.-H. (1) 503 Zanobini, F. (2.2) 128 Zard, S.Z. (3.7) 109, 111, 112, 114, 116, 117, 127 Zasada-Parzynska, A. (3.2) 83; (3.6) 112 Zavgorodnii, V. S (2.3) 52 Zawadzki, W. (3.7) 3 Zegin, A.E. (4) 262
.
Photochemistry
540 Ze l i n s k i , D.M. ( 1 ) 241; $3.3) 7 Z e i g l e r , J.M. ( 1 ) 292; ( 4 ) 239, 241, 390 Zeiri, L. ( 1 ) 118 Zellmer, V. ( 3 . 7 ) 7 1 Zeng, D . ( 3 . 2 ) 1 0 7 ; ( 3 . 5 ) 90 Zeng, K. ( 3 . 6 ) 146 Zengerle, K. ( 2 . 1 ) 101 Zeni, M. ( 4 ) 60 Zewail, A.H. (1) 1 8 , 399 Z e z i n , A . B . ( 1 ) 297; ( 4 ) 319 Zhahradinkova, A. ( 4 ) 447 Zhang, B . ( 3 . 5 ) 2 9 , 7 8 , 79 Zhang, C. ( 4 ) 461 Zhang, H. ( 4 ) 180 Zhang, J . ( 1 ) 256; ( 2 . 3 ) 73; ( 3 . 2 ) 109; ( 3 . 5 ) 9 3 ; ( 3 . 6 ) 1 5 0 ; ( 4 ) 52 Zhang, L. ( 4 ) 83 Zhang, S . ( 2 . 1 ) 1 9 5 ; ( 4 ) 80
Zhang, X. ( 2 . 1 ) 205; ( 4 ) 362 Zhang, Z. ( 3 . 1 ) 6 ; ( 3 . 4 ) 11 Zhao, F. ( 3 . 6 ) 22 Zhao, R. (4) 483 Zhdanov, G.S. ( 4 ) 380 Zhong, X. ( 2 . 3 ) 7 3 ; ( 4 ) 483 Zhou, B. ( 3 . 4 ) 3 2 ; ( 3 . 5 ) 39 Zhou, J. (2.2) 155 Zhou, Q.F. ( 1 ) 178 Zhou, Z. ( 2 . 1 ) 205 Zhu, C . ( 3 . 5 ) 82 Zhu, N. ( 3 . 2 ) 8 2 ; ( 3 . 6 ) 110 Zhu, Q. ( 2 . 3 ) 7 3 Zhu, S . - B . ( 1 ) 228, 229, 230 Z h u l i n , V.M. ( 4 ) 47 Zhuravlev, A.M. ( 4 ) 368 Z i e g l e r , K. ( 3 . 7 ) 88 Ziessel, R . ( 2 . 1 ) 9 3 Z i g l e r , S.S. ( 2 . 3 ) 1 4 ;
( 3 . 7 ) 74 Zimmerman, H.E. ( 3 . 3 ) 23 Zimmermann, H. ( 3 . 7 ) 69 Zimmt, M.B. (1) 362 Zimnyakov, A.M. ( 2 . 1 ) 157 Z i n a t o , E. ( 2 . 1 ) 31 Z i n g e r , D . ( 1 ) 513 Zink, J.I. ( 2 . 2 ) 140 Z i n t h , W. ( 1 ) 508 Ziolkowski, J.J. ( 2 . 1 ) 53 Zou, C. ( 2 . 2 ) 8 3 , 86 Zubov, V.P. ( 4 ) 256 Zuchowicz, I. ( 4 ) 51 Zuev, P.S. ( 3 . 7 ) 4 Zuk, A. ( 4 ) 48 Zulu, M.M. ( 2 . 2 ) 22 Zumofen, G . ( 1 ) 20 Zupan, M. ( 3 . 1 ) 4 7 ; ( 3 . 3 ) 1 7 ; ( 3 . 7 ) 179 Zusman, R. ( 1 ) 217 Z w e i f e l , H. ( 4 ) 160 Zwiers, R . J . M . ( 4 ) 255 Zyat'kov, I.P. ( 4 ) 175
