Theoretical insights into the effects of solvent polarity on the ESDPT behaviors for 2,5-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene-1,4-diol fluorophore

In this work, we mainly focus on investigating the solvent-polarity-dependent intramolecular dual hydrogen bonding interactions and excited state behaviors for 2,5-bis(4,5-diphenyl-1 H -imidazol-2-yl)benzene-1,4-diol (BDIBD). We theoretically explore potential regulation mechanism of solvent polarity related to excited-state double proton transfer (ESDPT) behavior of BDIBD. We find nonpolar solvents can significantly enhance the intramolecular dual hydrogen bonds for BDIBD compound, Frontier molecular orbitals (MOs) analysis presents that charge distribution of BDIBD fluorophore systematically shifts with the change in solvent polarities, providing an electronic structure-level driving force for the ESDPT process. The constructed potential energy surface (PES) demonstrates the solvent-polarity-regulated stepwise ESDPT mechanism. • Photo-induced dual intramolecular hydrogen bonding strengthening promotes ESDPT tendency. • Photo-induced charge redistribution promote ESDPT reaction for BDIBD fluorophore. • We elucidate solvent-polarity-dependent step-by-step ESDPT behaviors for BDIBD fluorophore.