A series of new heterocyclic disperse azo dyes based on 8-hydroxyquinoline have been prepared. The structures of these dyes were confirmed by UV-vis, FT-IR, 1H NMR and LC-MS spectroscopic techniques. Their solvatochromic properties in different solvents were investigated; the dyes are strongly solvent dependent and exhibited azo-common anion equilibrium in DMSO and DMF. The acid and base effects on this equilibrium are also examined. The colour of dyes is discussed with respect to nature of the heterocyclic ring and substituent therein. Absorption maxima of the dyes showed large bathochromic effects in comparison with analogous dyes containing carbocyclic amine residues and also the thiadiazolylazo dyes absorb bathochromically compared with their triazolyl analogues. © 2006 Elsevier Ltd. All rights reserved.