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

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 Infra-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)-interconformers are stepwise judged from the time lag between the first and second proton transfers. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The theoretical investigation on the effect of polar solvents on 2-aryl-3-hydroxyquinolone (3HQ) revealed different emission peaks related to different conformations, with intramolecular PT processes possible for Intra-HB conformers and intermolecular double PT processes possible for Inter-HB conformers. The mechanisms of excited-state intermolecular double PT processes for 3HQ(CH3OH)-inter and 3HQ(H2O)-inter conformers were judged to be stepwise based on the time lag between the first and second proton transfers.