Insights into the excited state hydrogen bond and proton transfer behaviors associated with solvent polarity for NHBQ fluorophore: a theoretical study

Inspired by the excellent photochemical properties of hydroxybenzo[h]quinoline and its derivatives, in this work, the novel electron withdrawing nitro substituted HBQ (i.e., NHBQ) fluorophore is explored about its photo-induced behaviors. By investigating the photoexcitation characteristics in different solvents, the solvent-polarity-related photo-induced hydrogen bond of NHBQ indicates polar aprotic solvents largely enhance S-1-state hydrogen bond interactions. Charge reorganization stemming from photoexcitation, strengthening excited state hydrogen bond effects, and the polarity-dependent energy gap of frontier molecular orbitals further reveals the excited state intramolecular proton transfer (ESIPT) tendency. Insights into potential energy curves along ESIPT paths in solvents with different polarities, we present that solvent polarity could harness the ESIPT behavior for NHBQ compound.