Yang Jye-Shane, Liau Kang-Ling, Hwang Chung-Yu, Wang Chin-Min
Department of Chemistry, National Taiwan University, Taipei, Taiwan 10617.
J Phys Chem A. 2006 Jul 6;110(26):8003-10. doi: 10.1021/jp060296g.
The electronic absorption and fluorescence spectra, quantum yields for fluorescence (Phi(f)) and trans --> cis photoisomerization (Phi(tc)), and fluorescence lifetimes of trans-4-(N-arylamino)-4'-cyanostilbenes (2H, 2Me, 2OM, 2CN, and 2Xy with aryl = phenyl, 4-methylphenyl, 4-methoxyphenyl, 4-cyanophenyl, and 2,5-dimethylphenyl, respectively), trans-4-(N-methyl-N-phenylamino)-4'-cyanostilbene (2MP), trans-4-(N,N-diphenylamino)-4'-cyanostilbene (2PP), trans-4-(N-methyl-N-phenylamino)-4'-nitrostilbene (3MP), and three ring-bridged analogues 2OMB, 2MPB, and 3MPB are reported. Whereas fluorescence and torsion of the central double bond account for the excited decay of the majority of these donor-acceptor substituted stilbenes in both nonpolar and polar solvents (i.e., Phi(f) + 2Phi(tc) approximately 1), exceptions are observed for 2OM, 3MP, and 3MPB in solvents more polar than THF and for 2Me and 2MP in acetonitrile as a result of the formation of a weakly fluorescent and isomerization-free twisted intramolecular charge transfer (TICT) state (i.e., Phi(f) + 2Phi(tc) << 1). The TICT state for 2OM, 2Me, and 2MP results from the torsion of the stilbenyl-anilino C-N single bond, but the torsion of the styryl-anilino C-C bond is more likely to be responsible for the TICT state formation of 3MP and 3MPB. In conjunction with the behavior of aminostilbenes 1, a guideline based on the values of Phi(f) and Phi(tc) for judging the importance of a TICT state for trans-stilbenes is provided. Accordingly, the TICT state formation is unimportant for the excited decay of trans-4-(N,N-dimethylamino)-4'-cyanostilbene (DCS). In contrast, our results support the previously proposed TICT state for trans-4-(N,N-dimethylamino)-4'-nitrostilbene (DNS).
报道了反式-4-(N-芳基氨基)-4'-氰基芪（2H、2Me、2OM、2CN和2Xy，其中芳基分别为苯基、4-甲基苯基、4-甲氧基苯基、4-氰基苯基和2,5-二甲基苯基）、反式-4-(N-甲基-N-苯基氨基)-4'-氰基芪（2MP）、反式-4-(N,N-二苯基氨基)-4'-氰基芪（2PP）、反式-4-(N-甲基-N-苯基氨基)-4'-硝基芪（3MP）以及三种环桥类似物2OMB、2MPB和3MPB的电子吸收光谱和荧光光谱、荧光量子产率（Phi(f)）和反式→顺式光异构化量子产率（Phi(tc)）以及荧光寿命。在非极性和极性溶剂中，大多数这些供体-受体取代芪的激发态衰变是由荧光和中心双键的扭转引起的（即Phi(f)+2Phi(tc)≈1），但在比四氢呋喃极性更大的溶剂中，2OM、3MP和3MPB以及在乙腈中的2Me和2MP是例外，这是由于形成了弱荧光且无异构化的扭曲分子内电荷转移（TICT）态（即Phi(f)+2Phi(tc)<<1）。2OM、2Me和2MP的TICT态是由芪基-苯胺基C-N单键的扭转引起的，但苯乙烯基-苯胺基C-C键的扭转更有可能是3MP和3MPB的TICT态形成的原因。结合氨基芪1的行为，提供了一个基于Phi(f)和Phi(tc)值来判断TICT态对反式芪重要性的指导原则。因此，TICT态的形成对反式-4-(N,N-二甲基氨基)-4'-氰基芪（DCS）的激发态衰变不重要。相比之下，我们的结果支持先前提出的反式-4-(N,N-二甲基氨基)-4'-硝基芪（DNS）的TICT态。
