Synthesis, Solvatochromism, Electronic Structure and Nonlinear Optic Properties of Quinolin-8 2-Hydroxybenzoate

Abstract

Quinolin-8-yl 2-hydroxybenzoate (QHB) was synthesized and its physical and electronic properties were investigated both experimentally and theoretically. The electronic structure and spectral behavior were determined by using UV-vis absorption and fluorescence spectra in 11 different polarity solvent media. The absorption band observed at 306-308 nm is attributed to pi-pi* and n-pi* electronic transitions due to its geometric structure in the solution phase. Solvatochromism of QHB was investigated by using Kamlet-Taft and Catalan methods based on the linear solvation energy relationships (LSER). The 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. The solvatochromic model of Catalan states 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 a greater effect on fluorescence spectra compared to absorption spectra. Computational calculations were performed by the application of the B3LYP/6-311+(d,p) level of theory. Conformational analysis performed for QHB showed five staggered conformers on torsional potential energy surfaces. Accordingly, the most stable conformer was found to be the one involving infra-molecular hydrogen bonding. The geometry of the other conformers indicated that the absence of hydrogen bonding gave rise to relatively higher energy. Frontier molecular orbitals (HOMO, LUMO) and non-linear optical (NLO) parameters were calculated by B3LYP/6-311+(d,p) level of theory. Theoretical UV spectra both in gas and solution phases were also investigated by TDDFT-CAM-B3LYP/6-311+(d,p) level of theory.