Some heterocyclic azo dyes derived from thiazolyl derivatives; synthesis; substituent effects and solvatochromic studies

A series of azo disperse dyes were synthesized by coupling reaction of N,N-diethylaniline, 2-anilinoethanol and N-phenyl-2,2′-iminodiethanol with diazotized aminothiazolyl derivatives as diazo components. These dyes have been prepared in good yields, and were characterized by UV–Vis, FT-IR and 1H NMR spectroscopic techniques. The effects of solvent polarity and various pH on dyes in the visible absorption spectra were evaluated. All dyes exhibit an excellent correlation coefficient (r > 0.92) for the linear solvation energy relationship with π* values calculated by Kamlet et al. The influence of the pH on the dyes with electron-donating group implied that these dyes exist in acid–base equilibrium in acidic environment. The effect of substituents of both coupler and diazo component on the color of dyes was investigated as well.