Effect of Ground-State Twisting on the trans -> cis Photoisomerization and TICT State Formation of Aminostilbenes
Journal
Journal of Physical Chemistry A
Journal Volume
113
Journal Issue
17
Pages
4868-4877
Date Issued
2009-04
Date
2009-04
Author(s)
Lin, Cheng-Kai
Lahoti, Arland M.
Tseng, Chung-Kai
Liu, Yi-Hung
Lee, Gene-Hsiang
Abstract
The synthesis, X-ray crystal structures, and photochemical behavior of a series of methyl- and ethylene-bridge-substituted trans-4-(N-(4-cyanophenyl)amino)stilbenes (3-8) are reported and compared to those of the parent compound 1CN. Aminostilbene 1CN displays dual fluorescence in polar solvents due to planar and twisted intramolecular charge-transfer (PICT and TICT) states. Alkyl substitution on the stilbene group of 1CN significantly perturbs its photochemistry, including fluorescence, trans --> cis photoisomerization, and TICT state formation. The alkyl substituent effect can be dissected into electronic and steric influences, and both are position dependent, which is vinyl alpha-carbon > vinyl beta-carbon > phenyl o-carbon. The main outcome of the alkyl substituent effect is to lower the barrier for the singlet-state photoisomerization. As a result, the quantum yield for photoisomerization is increased, and that for fluorescence is reduced. The corresponding quantum yield for TICT state formation in polar solvents is reduced only when significant ground-state twisting (a steric influence) is present. The alkyl substitution exerts little or no effect on the rate of intersystem crossing.
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Type
journal article
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