Tautomerism, solvatochromism, preferential solvation, and density functional study of some heteroarylazo dyes

Abstract

Photophysical characteristics of four synthesized heteroarylazo quinoline dyes were studied in various media with different solvatochromic parameters. Preferential solvation of the compounds was investigated in some mixed binary solvents. It was established that in the media with basic nature, only one tautomeric form and corresponding anion exist, which the latter is the main species. In the polar protic solvent, both the azo and hydrazone forms are present. The linear solvation energy relationships (ISER) were used to correlate the absorption spectral data. Using the absorption and emission spectra, the ground and the excited states dipole moments of the compounds were evaluated. The dyes were observed to show halochromism, dichromism, and anion affinity as well. The acid-base equilibria between neutral and anionic forms of the compounds were studied in buffer solutions of varying pH and ionization constants for these dyes were determined. The dyes exhibit positive linear dichroic behavior in the anisotropic medium, which indicate that all the absorption bands are due to the pi - pi* transitions. In order to analysis of the spectral behavior, time-dependent density functional theory (TD-DFT) calculations were performed. (C) 2018 Elsevier B.V. All tights reserved.