Spectrophotometric Investigations of Some Thiazole-azo Dyes

A series of thiazole-azo dyes i.e. 5-(phenyldiazenyl)-4-phenylthiazol-2-amines (PDTA) have been synthesized from their analogous coupling components. The absorption data of PDTA derivatives have been recorded in a series of solvents of varying polarity. They behave quite differently owing to solvent and substituent effects. The absorption spectra of these PDTA derivatives display an interesting unique behavior in DMSO. Kamlet-Taft and Catalán parameters have been used to describe the solvent effects and the absorption spectral shifts of the PDTA derivatives. These derivatives have been also screened for their in vitro antioxidant properties using 1,1-diphenyl-2-picrylhydrazyl free radical scavenging assay via ethanolic extracts of the dyes. The antioxidant strength of PDTA derivatives have been compared with the standard ascorbic acid and showed potent antioxidant activity. The absorption spectral characteristics of PDTA derivatives have been also investigated as a function of acidity and basicity (Ho/pH/H_) in aqueous phase and have been found to show azonium-ammonium tautomerism.