Abstract: The ¹³C NMR spectra of seven azo dyes derived from pyridones were measured. The assignment of the peaks was carried out with the aid of Selective Insensitive Nuclear Enhanced by Polarization Transfer technique (SELINEPT). It has been pointed out that the phenomenon of colour-change caused by acid-base is due to the shift of equilibrium in hydrazone-azo tautomerism according to the influence of pH values upon ¹³C chemical shifts, ¹H NMR spectra and UV-VIS absorption spectra. The enhancement of acidity and basicity is in favour of hydrazone and azo forms respectively. The different structures of the pyridone dyes change their colour at quite different pH values.

Key words: NMR spectrum, pyridone azo dyes, Tautomerism of hydrazonc-azo forms, Selective Insensitive Nuclear Enhanced by Polarization Transfer (SELINEPT)