Two series of new heterocyclic and carbocyclic disperse azo dyes based on 8-hydroxyquinoline were prepared and characterized by FT-IR, H-1 NMR, mass spectroscopic techniques and elemental analysis. Their solvatochromic properties in different solvents were investigated and their absorption spectra were strongly solvent dependent The acid and base effects on this equilibrium were also examined. In addition, the colors of dyes were discussed with respect to the nature of the carbocyclic and heterocyclic rings and substituent therein. To determine the tautomeric forms of the prepared dyes in solid state, X-ray data for 5-(5-methylthiazol-2-yldiazenyl)-8-hydroxyquinoline were recorded. The X-ray results showed that the dye exists as an azo tautomer in the solid state. (C) 2014 Elsevier B.V. All rights reserved.