溶剂效应对苯并噁唑衍生物激发态分子内质子转移的影响

Solvent Effects on Excited State Intramolecular Proton Transfer of One Benzoxazole Derivative

运用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT),在PBE0/6-31+G(d,p)水平上,研究了一种苯并噁唑衍生物2-{4-[2-(2-甲氧基乙氧基)-乙基]-[(2-甲氧基乙基)-氨基]-苯基}-5-(5-三氟甲基-苯并噁唑)-苯并呋喃-6-醇(MMTB)在3种溶剂(甲苯、乙醇和二甲基亚砜)中的激发态分子内质子转移(ESIPT)过程,考察了溶剂极性对MMTB光谱性质及ESIPT反应机理的影响。结果表明,在所考察的溶剂中,基态(S_(0))的稳定构型是烯醇式,而在第一激发单重态(S_(1))烯醇式结构和酮式结构同时存在,表现出烯醇式和酮式的双荧光发射峰;烯醇式结构的分子内氢键在S_(1)态有所增强,有助于ESIPT过程的发生;随着溶剂极性的增强,氢键增强的程度增大,发生ESIPT需要克服的能垒减小,即在极性强的溶剂中容易发生ESIPT。

The excited state intramolecular proton transfer(ESIPT)reactions of one benzoxazole derivative,2-{4-[2-(2-methoxy ethoxy)-ethyl]-[(2-methoxy ethoxy)-amino]-phenyl}-5-(5-trifluoromethyl-benzooxazole)-benzofuran-6-ol(MMTB)were studied by density functional theory(DFT)and time-dependent density functional theory(TD-DFT)at the level of PBE0/6-31+G(d,p)in different solvents,such as toluene(PhMe),ethanol(EtOH)and dimethyl sulfoxide(DMSO).The effects of solvent polarity on ESIPT mechanism of MMTB were investigated.It is found that the enol form is stable in the ground states(S_(0))while two stable configurations(enol and keto forms)are existed in the first excited states(S_(1))and exhibit dual fluorescence in all the solvents.The calculated intramolecular hydrogen bonds for enol forms can be significantly strengthened in S_(1) states,which can facilitate the ESIPT processes.In addition,as the polarity of the solvent increases,the degree of hydrogen bond enhancement increases,and the energy barrier in the ESIPT process decreases,which proves that the ESIPT processes are more likely to take place in highly polar solvents.