A novel mechanism of intramolecular proton transfer in the excited state of 3-hydroxy-4H-benzochromone derivatives: A new explanation at the theoretical level

Abstract

The excited-state intramolecular proton transfer (ESIPT) mechanism and photophysical properties of a series of 2-(1H-1,3-benzodiazol-2-yl)-3-hydroxy-4H-benzo[h]chromen-4-one (HBC4H) derivatives are explored theoretically. From these, a new explanation of ESIPT mechanism of 3-hydroxy-4H-benzochromone derivatives has been proposed. Firstly, three isomers are optimized in toluene solvent. Through the analysis of the hydrogen bond parameters and infrared vibration spectrum, it is found that the hydrogen bonds of HBC4H should be strengthened in the S1 state. In order to explain the mechanism of ESIPT, the Boltzmann distribution and torsion forces of the three isomers are deliberated, and the searched transition state (TS) structures are depicted. It is discovered that the potential barriers are all lower than 5.00 kcal/mol in the S1 state, and HBC4H-Ia and HBC4H-Ic may coexist in the S0 state, and more significantly, among the three isomers, HBC4H-Ia may be the most favorable form of ESIPT.