NDLI: Intramolecular charge transfer processes in donor-acceptor substituted vinyltetrahydropyrenes

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Intramolecular charge transfer processes in donor-acceptor substituted vinyltetrahydropyrenes

Content Provider	CSIR - National Institute for Interdisciplinary Science and Technology (NIIScT)
Author	Sumalekshmy, S. Gopidas, K. R.
Abstract	Two novel donor-acceptor-substituted vinyltetrahydropyrene derivatives, 2-N,N-dimethylamino-7(1-carbethoxyvinyl)-4,5,9,10-tetrahydropyrene,1, and 2-N,N-dimethylamino-7-(1,1-dicyanovinyl)-4,5,9,10-tetrahydropyrene, 2, were synthesized and their photophysical properties investigated in solvents of different polarities. Our studies revealed the existence of intramolecular charge transfer excited states in these molecules. For both compounds the fluorescence maxima exhibited solvent polarity-dependent red shifts. These were quantitatively analysed by the Lippert-Mataga and Liptay equations to obtain the excited state dipole moments. Our results indicated that in the case of 1, emission takes place from a planar (CT)-C-1 state in all non-protic solvents. In the case of 2, the nature of the excited state depends on the solvent. A fast relaxation to a triplet state is proposed in cyclohexane. The emitting state in medium polar solvents is a planar 1CT state. In highly polar solvents a twisted 1CT state is invoked to explain the low fluorescence quantum yield. For both compounds CT nature of the emitting states were further confirmed by studies in acidic medium. The ground and excited state pK(a) values for 1 and 2 were determined using absorption and emission spectral changes observed in the presence of protic acids.
Starting Page	539
Ending Page	546
Page Count	7
ISSN	1474905X
Journal	Photochemical & Photobiological Sciences
Volume Number	4
Issue Number	7
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2005-01-01
Access Restriction	Authorized
Subject Keyword	Vinyltetrahydropyrenes Intramolecular charge transfer Photophysical properties Protic acids
Content Type	Text
Resource Type	Article
Subject	Physical and Theoretical Chemistry

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