Solvatochromism and intramolecular hydrogen-bonding assisted dipole moment of phenyl 1-hydroxy-2-naphthoate in the ground and excited states

Abstract

Absorption and steady state fluorescence spectra of phenyl 1-hydroxy-2-naphthoate (abbreviated as PHN) have been recorded in a series of non-polar, polar protic and polar aprotic solvents at room temperature. The pH effect on the excited state intramolecular proton transfer (ESIPT) has been discussed. FT-IR spectra in solid phase, CHCl3 and CDCl3 are analyzed. The ground state (μg) dipole moment is estimated by using Bilot-Kawski method and the excited state (μe) dipole moment is calculated by using Bilot-Kawski, Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reichardt solvatochromic shift methods as a function of dielectric constant (ε) and refractive index (n) of solvents. μe is observed as higher than μg for all of the used methods which indicates the more polar PHN in the excited state. The studied compound is observed to have intramolecular hydrogen bonding assisted dipole moments in the ground and excited state. The rate of μe/μg is found as 34.857. The ground and excited state dipole moment vectors are observed to make an angle with 3.842°. Solvatochromic behavior of PHN is investigated by means of linear solvation energy relationship (LSER) by using Kamlet-Taft and Catalan parameters. Kamlet-Taft solvatochromic model indicates that non-specific solute solvent interactions are controlled by solvent dispersion-induction forces and specific interactions are directed by hydrogen-bond acceptor capacity of solvent. Catalan solvatochromic model designates that solute-solvent interactions are governed by solvent dipolarity/polarizability and solvent acidity. Theoretical μg and μe have been determined by quantum chemical calculations using DFT-B3LYP/6-31G(d) and TDDFT-B3LYP/6-31G(d) level of theory, respectively. HOMO, LUMO, molecular electrostatic potential (MEP) of PHN are calculated by the same methods in the ground and excited states.