Synthesis, solvatochromism, electronic structure and nonlinear optic properties of quinolin-8-yl 2-hydroxybenzoate

Abstract

Quinolin-8-yl-2-hydroxybenzoate (abbreviated as QHB) was synthesized and investigated both experimentally and theoretically to obtain its physical and electronic properties. The electronic structure and spectral behavior have been determined by using UV-vis absorption and fluorescence spectra in different 11 polarity solvent medium. The absorption band observed at 306 nm-308 nm is found to having mix of π-π* and n-π* electronic transitions due to its geometrical structure in the solution phase. Solvatochromism of QHB is investigated by using Kamlet-Taft and Catalan methods based on the linear solvation energy relationships (LSER). Kamlet-Taft solvatochromic model indicates that spectral shifts of absorption and fluorescence spectra are effectively controlled by dispersion-polarization forces which describe the non-specific interactions. Solvatochromic model of Catalan designates that solute-solvent interaction is governed by solvent polarity in the absorption spectra and by solvent acidity in the fluorescence spectra. Non-specific interactions have greater effect on fluorescence spectra compared to absorption spectra. Computational calculations were performed by the application of B3LYP/6-311+(d,p) level of theory. Conformational analysis is performed for QHB and five staggered conformers are observed on torsional potential energy surfaces. Accordingly, the most stable conformer is found as involving intra-molecular hydrogen bonding. The geometry of the other conformers indicates that the absence of hydrogen bonding gives rise to relatively higher energy.  Frontier molecular orbitals (HOMO, LUMO) and non-linear optical (NLO) parameters have been calculated by B3LYP/6-311+(d,p) level of theory. Theoretical UV spectra both in gas and solution phases have also been investigated by TDDFT-CAM-B3LYP/6-311+(d,p) level of theory.