A computational decode of photoinduced dual hydrogen bonding interactions and ESDPT behaviors for H2BP-(OH)2DC-NH2 fluorophore

Given the distinguished luminescent properties resulting from solvent-polarity-dependent excited state behaviors, in this work, the effects of solvent polarities on the excited-state intramolecular proton transfer (ESIPT) process of H2BP-(OH)2DC-NH2 is systematically investigated. Based on DFT and TDDFT methodologies. We mainly focus on elucidating the excited-state double proton transfer (ESDPT) mechanism in H2BP-(OH)2DC-NH2 compound. By analyzing the geometrical configurations, infrared (IR) vibrational spectra, and core-valence bifurcation (CVB) indexes, we could firstly verify the enhancement of intramolecular dual hydrogen bonding interactions in the first excited state. Meanwhile, we also pay attention to the HOMO and LUMO orbitals to check the effects of charge redistribution on facilitating ESIPT/ESDPT process. The potential energy surfaces (PESs) are also scanned to confirm the stepwise ESDPT mechanism for H2BP-(OH)2DC-NH2 system. We further propose that the increase of solvent polarity can promote the process of the step-by-step ESDPT reaction processes for H2BP-(OH)2DC-NH2 fluorophore dependent on the computational potential energy barriers for H2BP-(OH)2DC-NH2 in cyclohexane, chloroform and acetonitrile solvents.