Effects of solvents on the excited‐state intramolecular proton transfer in 3‐HTC

Abstract

AbstractIt has been demonstrated experimentally that proton transfer can occur in the excited state of 3‐hydroxy‐2‐mercapto‐4‐one (3‐HTC) molecule. However, the effect of solvent polarity on excited‐state intramolecular proton transfer of 3‐HTC has not been reported. In this paper, the molecular structures of ground and excited states in different solvents are optimized by density functional theory and time‐dependent density functional theory. Based on the optimized structure, infrared vibration frequency, electronic spectra, natural bond orbital (NBO) population, and potential energy curves were calculated and analyzed. By analyzing the bond lengths and the bond angles related to the hydrogen bond, it can be seen that the intramolecular hydrogen bond intensity of 3‐HTC molecule in the S1state is strengthened in different solvents. With the increase of the solvent polarity, the degree of hydrogen bond strength decreases. Through the analysis of the infrared vibration frequency, it could be found that intramolecular hydrogen bond of 3‐HTC is weakened as the solvent polarity increases. By analyzing the frontier molecular orbitals and the charge density difference (CDD) maps, it is proved that charge transfer occurs during photoexcitation, which promotes the excited‐state proton transfer process. Further, the analysis of potential energy curves of 3‐HTC in the ground state and S1state shows that proton transfer can be realized in the S1state of 3‐HTC in different solvents. With the increase of solvent polarity, the difficulty of intramolecular proton transfer is increasing.