Ammonium-azonium tautomerism in some N, N-dialkylaminoazodyes—II. Compounds containing more than two protonation sites

Abstract

The UV-vis properties in neutral and acidic media of some N, N-dialkylaminoazo dyes containing strong electron donor substituents or an extended conjugated system, leading to more than two protonation sites, are investigated in order to clarify the influence of these structural changes on the position of the ammonium-azonium tautomeric equilibrium. The observed absorption maxima associated with the colour changes of neutral and protonated molecules are assigned within the charge-transfer (CT) model. The tautomeric equilibrium constants K T and p K a values of the ammonium and azonium tautomeric forms of N, N-dialkylaminoazobenzenes containing strong electron donor substituents are evaluated.