A theoretical study of excited state intramolecular proton transfer (ESIPT) and the photophysical mechanism of UV absorbers of 2-phenylbenzotriazole derivatives with different proton donor: 2-(2-hydroxyphenyl)benzotriazole (H-TIN), 2-(2-aminophenyl)benzotriazole (APyBT) and 2-(2-Mercaptophenyl)benzotriazole (MPyBT) have been performed by density functional theory (DFT) and second order Møller-Plesset perturbation theory (MP2). The results show that the most stable tautomer is normal configuration N which has intramolecular hydrogen bond for different tautomers of three compounds in ground state, while the tautomer T and twisted configuration T_twisted are unstable in ground state. The potential energy curves for ESIPT of three compounds show that H-TIN and APyBT can occurs ESIPT that overcome the energy barrier of ca. 7.06 and 20.7 kJ/mol, respectively, however the ESIPT of MPyBT can occur without a barrier|meanwhile combined the results of molecular orbital and charge difference density three-dimensional cube for the three compounds, it indicates that H-TIN, APyBT and MPyBT can occur the fast ESIPT and twisted intramolecular charge transfer, these reasons show that they all have good UV stabilization.

Key words: density functional theory (DFT), Møller-Plesset perturbation theory (MP2), benzotrizole, excited state intramolecular proton transfer (ESIPT), charge transfer, ultraviolet stabilizers