Multisite Constrained Model of trans-4-(N,N-Dimethylamino)-4鈥?nitrostilbene for Structural Elucidation of Radiative and Nonradiative Excited States
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- 作者：Cheng-Kai Lin ; Yu-Fu Wang ; Yuan-Chung Cheng ; Jye-Shane Yang
- 刊名：The Journal of Physical Chemistry A
- 出版年：2013
- 出版时间：April 18, 2013
- 年：2013
- 卷：117
- 期：15
- 页码：3158-3164
- 全文大小：350K
- 年卷期：v.117,no.15(April 18, 2013)
- ISSN：1520-5215
文摘
A constrained model compound of trans-4-(N,N-dimethylamino)-4鈥?nitrostilbene (DNS), namely, compound DNS-B3 that is limited to torsions about the phenyl-nitro C鈥揘 bond and the central C鈺怌 bond, was prepared to investigate the structural nature of the radiative and nonradiative states of electronically excited DNS. The great similarities in solvent-dependent electronic spectra, fluorescence decay times, and quantum yields for fluorescence (桅f) and trans 鈫?cis photoisomerization (桅tc) between DNS and DNS-B3 indicate that the fluorescence is from a planar charge-transfer state and torsion of the nitro group is sufficient to account for the nonradiative decay of DNS. This conclusion is supported by TDDFT calculations on DNS-B3 in dichloromethane. The structure at the conical intersection for internal conversion is associated with not only a twisting but also a pyramidalization of the nitro group. The mechanism of the NO2 torsion is discussed in terms of the effects of solvent polarity, the substituents, and the volume demand. The differences and analogies of the NO2- vs amino-twisted intramolecular charge-transfer (TICT) state of trans-aminostilbenes are also discussed.