Solvatochromic studies on 2-[(2-hydroxyphenyl)azo]-4-5-diphenylimidazole

The visible electronic spectra of the title hydroxyazo compound (abbreviated as HAI) in a number of organic solvents have been studied. It was found that in dilute solutions in basic solvents, HAI exists in an acid-base equilibrium of the type HAI reversible arrow H+ + AI(-). The proportional concentration of the conjugate base (AI(-)) in the medium is largely dependent on the HAI concentration, the basicity of the organic solvent and the tendency of stabilization of the AI(-) form through H-bond interaction with the solvent molecules. The low energy visible band of both the HAI and AI(-) forms are assigned to a transition involving the whole solute molecule associated with intramolecular CT character. The effect of time on the longer wavelength visible band of HAI has been investigated. (C) 1997 Elsevier Science Ltd.