Theoretical study on the relationship between ESIPT process and solvent of 9,10-dihydroxybenzo[h]quinolone

To elucidate the relationship between the excited-state intramolecular proton transfer (ESIPT) mechanism of 9,10-dihydroxybenzo[h]quinoline (9-10-HBQ) and the influence of solvents, for better application. This paper focuses on the investigation of hydrogen bond geometric changes, the ESIPT mechanism, and its behavior modulated by solvent polarity. The structural parameters of the ground-state (S₀) and excited-state (S₁) related to the hydrogen bond (O₁H₂⋯O₃), along with the infrared vibrational spectra, core-valence bifurcation (CVB) index, hydrogen bond bond-critical point (BCP) parameters, RDG function isosurfaces, and scatter plots, reveal that the enhanced hydrogen bond strength in the S₁ state promotes the ESIPT behavior of 9-10-HBQ-PT1. Further frontier molecular orbital and natural Population Analysis (NPA) charge analyses indicate that intramolecular charge redistribution facilitates the ESIPT process. Based on the analysis of potential energy curves, transition states (TS), and intrinsic reaction coordinate (IRC) pathways, we found that the reaction energy barriers can be tuned by the solvent. For example, in cyclohexane (Cy), toluene (Tol), chloroform (TCM), and acetonitrile (ACN), the reaction energy barriers were 7.12 kcal/mol, 7.25 kcal/mol, 7.65 kcal/mol, and 8.15 kcal/mol, respectively.