2-(3-巯基-2-吡啶基)苯并咪唑分子内质子转移及溶剂化效应

Intramolecular Proton Transfer Reaction and Solvent Effects in 2-(3-Mercapto-2-pyridyl)benzimidazole

在B3LYP/6-31G(d,p)和TD B3LYP/6-31++G(d,p)//CIS/6-31G(d,p)水平上,研究了2-(3-巯基-2-吡啶基)苯并咪唑(MPyBI)在气相和七种溶剂(环己烷、苯、三氯甲烷、乙醇、乙腈、二甲亚砜和水)中基态和激发态的分子内质子转移(GSIPT和ESIPT)过程.在基态势能面的研究中发现,该化合物存在分子内双质子转移,其中分步的双质子转移在动力学上具有优势.同时对激发态质子转移势能面及激发态转移过程中的光物理现象进行了研究,结果表明该化合物存在快速的无能垒的激发态分子内质子转移,随着溶剂极性的增强,可以降低基态过渡态的能垒,改变硫醇式与硫酮式互变异构体的比例,从而灵敏地控制荧光的强度.

The ground-and excited-state intramolecular proton transfer（GSIPT and ESIPT） reactions of 2-（3-mercapto-2-pyridyl）benzimidazole（MPyBI） were studied at the B3LYP/6-31G（d,p） and TD B3LYP/6-31＋＋G（d,p）// CIS/6-31G（d,p） levels.The effect of solvents（cyclohexane,benzene,chloroform,ethanol,acetonitrile,dimethylsulfoxide,and water） was investigated.We studied the ground-state potential energy surface and discovered a double proton transfer mechanism while a stepwise mechanism was observed to dominate the reaction kinetics.The excited state proton transfer potential energy surface and the photophysical behavior of MPyBI were also studied.Results show that a barrierless ESIPT for MPyBI probably exists and that as the polarity of the solvent increases,the barrier in the GSIPT decreases.When the tautomer ratio is changed,the fluorescence intensity can be easily controlled.