HAL Id: jpa-00225110
https://hal.archives-ouvertes.fr/jpa-00225110
Submitted on 1 Jan 1985
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
TIME-RESOLVED AND POLARIZED EMISSION
SPECTROSCOPY OF SINGLE-CRYSTAL
[Ru(bpy)3](PF6)
H. Yersin, E. Gallhuber, G. Hensler
To cite this version:
TIME-RESOLVED AND POLARIZED EMISSION SPECTROSCOPY O F SINGLE-CRYSTAL
C R ~ ~ P Y )
3 1 ( ~ ~ 6 )
H. Yersin, E. Gallhuber and G. Hensler
Universitat Regensburg, I n s t i t u t fiir PhysikaZische und l'heoretische Chemie,
8400 Regensburg, F . R. G. A b s t r a c t . The l o w e s t e x c i t e d s t a t e s o f [ R ~ ( b p y ) ~ l ( P F ~ ) ~ s i n g l e c r y s t a l s a r e i n v e s t i g a t e d b y a d e t a i l e d a n a l y s i s o f t h e t e m p e - r a t u r e d e p e n d e n c e o f t h e p o l a r i z e d e m i s s i o n ( d o w n t o 1 . 6 K ) . I t i s p o s s i b l e t o r e s o l v e a f i n e s t r u c t u r e a n d t o a s s i g n t w o d i f f e - r e n t z e r o - p h o n o n t r a n s i t i o n s . F u r t h e r , we r e p o r t o n p o l a r i z e d a n d t i m e - r e s o l v e d m e a s u r e m e n t s w h i c h show a t 10 K a d e l a y e d + + + + e m i s s i o n f o r t h e E l l c - p o l a r i z a t i o n b u t a p r o m p t o n e f o r E l c . T h i s p o i n t s t o t h e e x i s t e n c e o f an e n e r g y b a r r i e r b e t w e e n t h e c o r r e s p o n d i n g s t a t e s . [ ~ u ( b ~ y ) ~ l ~ + compounds ( w i t h b p y = 2 , 2 ' - b i p y r i d i n e ) h a v e b e e n i n - v e s t i g a t e d i n t e n s i v e l y d u r i n g t h e p a s t d e c a d e due t o t h e i r i n t e r e s t i n g p h o t o c h e m i c a l p r o p e r t i e s , w h i c h m i g h t b e u t i l i z e d t o e x p l o i t t h e s o l a r e n e r g y i n a c y c l i c s y s t e m b y a p r o c e s s o f s t o r a g e i n c h e m i c a l e n e r g y .
[ l l
T h i s i s a c h i e v e d b y l i g h t - i n d u c e d r e d o x r e a c t i o n s w h i c h p r o c e e d f r o m t h e l o w e s t e x c i t e d ( a n d b r i g h t l y e m i t t i n g ) s t a t e s o f t h e [ ~ u ( b ~ y ) ~ l ~ + c o m p l e x e s . I t has b e e n shown t h a t s e v e r a l c l o s e - l y i n g s t a t e s a r e i m p o r t a n t a n d h a v e t o b e t a k e n i n t o a c c o u n t . Many i n v e s t i - g a t i o n s w e r e c a r r i e d o u t t o c h a r a c t e r i z e t h e s e s t a t e s , m a i n l y b y m e a s u r e m e n t s o n c o m p l e x e s e i t h e r d i s s o l v e d o r d o p e d i n t o m a t r i c e s . H o w e v e r , n o a g r e e m e n t i n t h e a s s i g n m e n t h a s b e e n f o u n d . [ 2 , 3 ] C o n s e - q u e n t l y , i t i s n e a r a t h a n d t o i n v e s t i g a t e n e a t s i n g l e - c r y s t a l compounds.t h e b r o a d bands ( i n F i g . 1 : band I a t 17200 cm-' and band I 1 a t 17550 c m c l ) . F u r t h e r i t was c o n c l u d e d t h a t t h e o s c i l l a t o r s t r e n g t h o f t h e t r a n s i t i o n from 2E' t o t h e ground s t a t e i s s u b s t a n t i a l l y h i g h e r t h a n from 1 E ' . ( S e e a l s o [ 2 ] . )
The d i s c o v e r y o f t h e f i n e s t r u c t u r e ( F i g .
1 ,
l e f t p a r t ) l e a d s t o a more d e f i n i t e d e s c r i p t i o n o f t h e p r o p e r t i e s o f t h e l o w e s t e x c i t e d+ +
s t a t e s . Two s h a r p , E l c - p o l a r i z e d l i n e s ( l i n e I a t 17809 cm-I and l i n e I 1 a t 17816 c m - I ) , o c c u r on t h e v e r y b l u e s i d e o f t h e b r o a d - b a n d e m i s - s i o n . The e n e r g y d i f f e r e n c e i s A E = 7 c m - l . T h e s e l i n e s a r e a s s i g n e d t o two d i f f e r e n t z e r o - p h o n o n t r a n s i t i o n s , c o r r e s p o n d i n g t o t h e b r o a d b a n d s I and 11. T h i s i s c o r r o b o r a t e d by t h e f a c t t h a t t h e t e m p e r a t u r e d e p e n d e n c e o f l i n e s I and I 1 i s e x a c t l y d i s p l a y e d by t h a t of b a n d s I and I I . [ 8 1 ( H e n c e t h e c o r r e s p o n d i n g a c t i v a t i o n e n e r g y c o u l d a l r e a d y be d e t e r m i n e d from t h e t e m p e r a t u r e d e v e l o p m e n t of t h e b r o a d b a n d s . ) + Moreover, t h e i n t e n s i t y r a t i o I(;L;)/I(;I l c )
i s
a t l e a s t a s h i g h a s t w e n t y f o r e i t h e r o f t h e two s h a r p l i n e s and no a d d i t i o n a l l i n e s a r e + + found i n t h e E l l c - s p e c t r a . T h u s , a p p l y i n g t h e s e l e c t i o n r u l e s , i t f o l l o w s t h a t t h e two e x c i 2 e d s t a t e s have b o t h t o be a s s i g n e d t o E' r e p r e s e n t a t i o n s ( l E 1 and 2 E ' ) . T h i s r e s u l t r e p r e s e n t s an e x c e l l e n t c o n f i r m a t i o n o f t h e c l a s s i f i c a t i o n g i v e n i n r e f . [ 4 1 ( s e e F i g . 3 ) . Moreover, t h e i n t e n s i t y r a t i o o f l i n e I 1 t o l i n e I i s g o v e r n e d by a Boltzmann f a c t o r w i t h an a c t i v a t i o n e n e r g y which e q u a l s t h e v a l u e d i r e c t l y t a k e n fromt h e
s p e c t r u m . T h i s b e h a v i o r i s e x p e c t e d u n d e r con- d i t i o n of a t h e r m a l e q u i l i b r i u m between l E 1 and 2E't o t h e o c c u r r e n c e o f s u c h a b a r r i e r .
G r a t z e l , M., A c c . Chem. R e s .
