Regulating excited‐state intramolecular proton transfer behavior and fluorescent property of 3‐thiolflavone by electron‐donating ability: A time‐dependent density functional theory study

Abstract

BackgroundSince the excited‐state intramolecular proton transfer (ESIPT) process involving sulfur is extremely fast, its mechanism is still unclear, and its derivatives are rarely studied, we have performed a theoretical study the ESIPT process of 3‐thiolflavone (3TF) and its derivatives.ObjectiveThe ESIPT mechanism and photophysicalproperties of 3‐thiolflavone (3TF) and its derivatives 3NTF, 3ATF and 3OTF modified by ‐N(C2H5)2, ‐NH2 and ‐OCH3 groups were studied theoretically.MethodsDensity functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) with PBE0 functional and 6‐31G(d, p) basis set.ResultsFor 3TF, 3NTF, 3ATF and 3OTF, the ESIPT processes are barrier‐less, and the barrier of ground‐state intramolecular proton transfer (GSIPT) reduces in the order of 3TF > 3OTF > 3ATF > 3NTF, as the electron‐donating ability of the substituent increases. When the electron‐donating groups are introduced, the absorption and fluorescence wavelengths of 3TF red‐shift and blue‐shift, respectively.ConclusionSubstituents with electron‐donating ability can regulate the ground‐state intramolecular proton transfer process and photophysical properties of 3TF.