Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
J Phys Chem A. 2011 Jul 7;115(26):7550-8. doi: 10.1021/jp202277t. Epub 2011 Jun 9.
In a combined study on the photophysics of 2-(2'-hydroxyphenyl)-benzothiazole (HBT) in polar acetonitrile utilizing ultrafast infrared spectroscopy and quantum chemical calculations, we show that a branching of reaction pathways occurs on femtosecond time scales. Apart from the excited-state intramolecular hydrogen transfer (ESIHT) converting electronically excited enol tautomer into the keto tautomer, known to be the dominating mechanism of HBT in nonpolar solvents such as cyclohexane and tetrachloroethene, in acetonitrile solution twisting also occurs around the central C-C bond connecting the hydroxyphenyl and benzothiazole units in both electronically excited enol and keto tautomers. The solvent-induced intramolecular twisting enables efficient internal conversion pathways to both enol and keto tautomers in the electronic ground state. Whereas relaxation to the most stable enol tautomer with twisting angle Θ = 0° implies full ground state recovery, a small fraction of HBT molecules persists as the keto twisting conformer with the twisting angle Θ = 180° for delay times extending beyond 120 ps.
在一项关于 2-(2'-羟基苯基)苯并噻唑（HBT）在极性乙腈中的光物理性质的联合研究中，我们利用超快红外光谱和量子化学计算表明，反应途径在飞秒时间尺度上发生分支。除了激发态分子内氢键转移（ESIHT）将电子激发的烯醇互变异构体转化为酮式互变异构体外，众所周知，这是 HBT 在环己烷和四氯乙烯等非极性溶剂中的主要机制，在乙腈溶液中，围绕连接羟基苯基和苯并噻唑单元的中心 C-C 键也会发生扭转，无论是在电子激发的烯醇还是酮式互变异构体中。溶剂诱导的分子内扭转使得电子基态中的烯醇和酮式互变异构体都能够有效地进行内转换途径。虽然松弛到扭转角 Θ = 0°的最稳定的烯醇互变异构体意味着完全恢复基态，但一小部分 HBT 分子作为酮式扭转构象存在，扭转角 Θ = 180°，延迟时间超过 120 ps。
