Solvatochromism and azo–hydrazo tautomerism of novel arylazo pyridone dyes: Experimental and quantum chemical study

Abstract

The state of the tautomeric equilibria of eleven arylazo pyridone dyes was evaluated from UV–Vis absorption spectra with the aid of the quantum mechanical modeling. NMR analysis and theoretical calculations, by using PCM/ωB97X-D/6-311G(d,p) method, confirmed that prepared compounds exist mainly in Hydrazo form. Internal hydrogen bonding in Hydrazo tautomer, analyzed by AIM topological analysis and total electron density at the bond critical point (BCP), confirmed a presence of strong hydrogen bond which contributes to higher stability of Hydrazo form. Linear solvation energy relationships (LSERs) rationalized solvent influence on solvatochromism of all compounds in Hydrazo form and KT by using Kamlet–Taft model. Linear free energy relationships (LFERs) were applied to the substituent-induced NMR chemical shifts (SCS) using SSP (single substituent parameter) and DSP (dual substituent parameter) model. Density plots over the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO) energy surface provide information on the charge transfer during excitation. The molecular electrostatic potential (MEP) surface map was plotted over the optimized geometry of the molecules in order to visualize electron density distribution and explain origin of solvent/solute interactions. Keywords: Arylazo pyridone dye, UV–Vis spectra, Solvatochromism, Azo–Hydrazo tautomerism