Thermodynamic study of solvent and substituent effects on 4-substituted aminoazobenzenes

Proton dissociation equilibria of various 4-substituted aminoazobenzenes have heen studied as a function of temperature. The corresponding thermodynamic functions ΔGo, ΔHo, and ΔSo have been calculated. Azonium-ammonium tautomeric equilibria of the monoprotonated dyes have also been investigated. The experimental data have been interpreted in terms of linear free energy relationships. Analysis of the solvatochromism of these dyes has led to the determination of some specific interactions with solvents, which, together with electronic factors, can well rationalize many aspects of the behaviour of these molecules.