Theoretical insights of solvent effect on excited-state proton transfers of 2-aryl-3-hydroxyquinolone

Abstract

© 2020 Elsevier B.V. The effect of polar solvents (DMSO, CH3OH, and H2O) on possible conformations, photophysical properties, and excited-state proton transfer (ESPT) processes of 2-aryl-3-hydroxyquinolone (3HQ) has been theoretically investigated using time-dependent density functional theory at B3LYP/TZVP level both static and dynamic calculations. From exploration of potential energy surfaces, two stable conformers with the lowest energy of 3HQ complexing with solvent molecules are found namely Intra-HB and Inter-HB conformers. Both Intra-HB and Inter-HB conformers are attributed to their enol and keto emission peaks depending on type of solvent used. Based on the results of potential energy curve along PT coordinates, reaction energy of PT, and on-the-fly dynamic simulations, excited-state intramolecular PT processes are possible for all Intra-HB conformers while excited-state intermolecular double PT processes are only plausible for 3HQ(CH3OH)-inter and 3HQ(H2O)-inter but not for 3HQ(DMSO)-inter. Moreover, excited-state intermolecular double PT mechanisms of 3HQ(CH3OH)-inter and 3HQ(H2O)-inter conformers are stepwise judged from the time lag between the first and second proton transfers.