AMMONIUM-AZONIUM TAUTOMERISM IN SOME N,N-DIALKYLAMINOAZO DYES .1. GENERAL-CONSIDERATIONS

The UV-Vis properties in neutral and acid media of some N,N-dialkylami noazobenzenes containing electron donor substituents in the unsubstitu ted benzene ring are discussed. A redistribution of the individual vib ronic band intensities within the long wavelength absorption pi-pi ba nd due to specific solvation of the molecules in neutral media is obse rved and the corresponding vibrational sub-bands are assigned, In acid media, the increased positive halochromism is explained within the ch arge transfer (CT) models of the corresponding chromogenic systems. Th e tautomeric equilibrium constants, K-T and pK(a) values of the ammoni um and azonium tautomeric forms are evaluated. Copyright (C) 1996 Else vier Science Ltd.