2-(2-巯苯基)苯并噁唑分子内质子转移取代基电子效应的密度泛函理论研究

在B3LYP/6-31G(d,p)和TDB3LYP/6-31++G(d,p)//CIS/6-31G(d,p)水平上研究了2-(2-巯苯基)苯并噁唑及其衍生物基态和激发态分子内质子转移现象,并探讨取代基电子效应对分子内质子转移的影响,研究结果表明,在基态时,硫醇式异构体为优势构象,供电子取代基使基态分子内正向质子转移能垒(烯醇式→酮式)升高;而吸电子取代基则可降低能垒,有利于基态分子内质子转移并有助于硫酮式异构体的稳定.在激发态时,硫酮式结构为优势构象,所研究的2-(2-巯苯基)苯并噁唑化合物及衍生物均可以发生无能垒或低能垒(≤1.5kJ/mol)的激发态分子内质子转移.巯苯基部分是激发态失活的主要活性部分,供电子基团有利于激发态的质子转移,吸电子基团使激发态跃迁困难,不利于激发态的质子转移.

A Density Functional Theory Study on the Substituent Electronic Effects in Intramolecular Proton Transfer of 2-(2-Mercaptophenyl)benzoxazole

The ground- and excited-state intramolecular proton transfer (GSIPT and ESIPT) reactions of 2-(2-mercaptophenyl)benzoxazole compounds have been studied at B3LYP/6-31G(d,p) and TD B3LYP/6-31++G(d,p)//CIS/6-31G(d,p) level, respectively, and the effects of substituent electronic effects in the intramolecular proton transfer reactions have been explored. The calculated results show that the enol form was the normal form in the ground state. The GSIPT (enol form→keto form) barrier increases when the substituent is electron donating and the barrier decreases when the substituent is electron withdrawing which is conducive to the GSIPT and keto form stable. In the excited state, the keto form is the normal form and there may be no barrier or a low-barrier (≤1.5 kJ/mol) ESIPT curves for these 2-(2-mercaptophenyl)-benzoxazole compounds. The mercaptophenyl is the main moiety which bears the excited-state radiation deactivation. The electron donating substituent in favor of ESIPT and the electron withdrawing substituentmake against of it.