Behavior of a Twisted Intramolecular Charge-Transfer Compound

Chapter 12

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Behavior of a Twisted Intramolecular Charge-Transfer Compound Bonded to Poly(methyl methacrylate) 1

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Ryuichi Hayashi , Shigeo Tazuke , and Curtis W. Frank

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Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama, Japan Department of Chemical Engineering, Stanford University, Stanford, CA 94305 2

A twisted intramolecular charge transfer (TICT) compound, a 4-(N,N-dimethylamino) benzoate group,was bonded to poly(methyl methacrylate) (PMMA) (the content of the TICT compound, Mn = 3 χ 10 ) ( l ) and e t h y l N,N-dimethylaminobenzoate ( I I ) a r e compared i n F i g u r e 2. Except f o r a s m a l l r e d s h i f t ( ^ 3 nm) i n I , the a b s o r p t i o n s p e c t r a are almost i d e n t i c a l . A l t h o u g h the presence of a ground s t a t e dimer o r s o l u t e - s o l v e n t complex i s known f o r Ν,Ν-dimethylaminobenzonitrile, the b e s t s t u d i e d TICT compound, t h e r e seems t o be no such c o m p l i c a t i o n s f o r the p r e s e n t s t u d i e s . T h i s i s a f a v o r a b l e c o n d i t i o n t o s t u d y the TICT chromophore i n polymers s i n c e polymers tend t o enhance c o m p l i c a t e d m o l e c u l a r a s s o c i a t i o n even i n e x t r e m e l y d i l u t e s o l u t i o n [12] which overshadows the aimed photo­ p h y s i c a l phenomenon. C o n t r a r y t o a b s o r p t i o n s p e c t r a , f l u o r e s c e n c e s p e c t r a o f I and I I are l a r g e l y d i f f e r e n t . W h i l e both I and I I e x h i b i t d u a l f l u o r e s c e n c e a t 350 nm and 450 nm, t h e i n t e n s i t y r a t i o o f a* band t o b* band (R) of I I i s much h i g h e r than t h a t o f I . Assignment o f the a* and b*

Hoyle and Torkelson; Photophysics of Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Fig.

PHOTOPHYSICS OF POLYMERS

1 Grabowski's k i n e t i c model The i n i t i a l l y formed e x c i t e d s t a t e ( b * s t a t e ) i s c o n v e r t e d t o the charge s e p a r a t e d s t a t e ( a * s t a t e ) by c r o s s i n g over an energy b a r r i e r (E^) . D e f i n i t i o n s o f r a t e c o n s t a n t s a r e as f o l l o w s : k^ : f o r w a r d r a t e c o n s t a n t o f b*-^a*. k£ : backward r a t e c o n s t a n t o f b*