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 substituent make against of it.

Key words: 2-(2-mercaptophenyl)benzoxazole, intramolecular proton transfer, density functional theory, substituent electronic effects