Lenoble C, Becker R S
Department of Chemistry, University of Houston-University Park, TX 77204.
Photochem Photobiol. 1990 Dec;52(6):1063-9. doi: 10.1111/j.1751-1097.1990.tb08446.x.
The photophysics and photochemistry of the 4'-diethylamino derivative of both 2-phenyl-benzothiazole and 2-(2'-hydroxyphenyl)benzothiazole have been studied by nanosecond and microsecond laser flash photolysis and picosecond emission spectroscopy. For the non-hydroxy substituted molecule, the singlet excited state was shown to relax primarily via fluorescence emission, and a very weak triplet transient was observed after laser flash excitation. The 2-(2'-hydroxy-4'-diethylaminophenyl)benzothiazole (AHBT) was shown to undergo excited state intramolecular proton transfer (ESIPT) in the picosecond timescale (k greater than 3 x 10(10) s-1) to form a colored zwitter-ion/keto form in solution at room temperature while the ground state back proton transfer was slower by a factor of approximately 10(5). However, in marked contrast with other derivatives of 2-(2'-hydroxyphenyl)benzothiazole and related molecules, the ESIPT was not the only deactivation process of the lowest singlet excited state of the enol form. Under steady-state excitation at room temperature (and low temperature), the fluorescence emission of the enol form was observed. The T-T absorption of the enol form was also observed and furthermore, the ESIPT was shown to have an activation energy which was estimated to be approximately 4 kJ. None of the foregoing, fluorescence and T-T absorption of the enol nor activation energy for proton transfer have been observed for the parent or derivatives of 2-(2'-hydroxyphenyl)benzothiazoles. The striking new features for the ESIPT photochemistry and photophysics for the 4'-diethylamino derivative of 2-(2'-hydroxyphenyl)benzothiazole are discussed and MO calculations are used to aid in the interpretation of some of the experimental results.
通过纳秒和微秒激光闪光光解以及皮秒发射光谱研究了2-苯基苯并噻唑和2-(2'-羟基苯基)苯并噻唑的4'-二乙氨基衍生物的光物理和光化学性质。对于非羟基取代的分子，单重激发态主要通过荧光发射弛豫，激光闪光激发后观察到非常微弱的三重态瞬态。2-(2'-羟基-4'-二乙氨基苯基)苯并噻唑(AHBT)在皮秒时间尺度(k大于3×10(10)s-1)内发生激发态分子内质子转移(ESIPT)，在室温下在溶液中形成有色两性离子/酮式结构，而基态反向质子转移则慢约10(5)倍。然而，与2-(2'-羟基苯基)苯并噻唑的其他衍生物及相关分子形成显著对比的是，ESIPT并非烯醇式最低单重激发态的唯一失活过程。在室温(和低温)下稳态激发时，观察到了烯醇式的荧光发射。还观察到了烯醇式的T-T吸收，此外，ESIPT显示具有约4 kJ的活化能。对于2-(2'-羟基苯基)苯并噻唑的母体或衍生物，未观察到上述烯醇式的荧光和T-T吸收以及质子转移的活化能。讨论了2-(2'-羟基苯基)苯并噻唑的4'-二乙氨基衍生物ESIPT光化学和光物理的显著新特征，并使用MO计算辅助解释一些实验结果。
