D- -A azo dyes bearing thiazole-diphenylamine units: Synthesis, photophysical and molecular structure properties, and use for dyeing of polyester fabrics

Herein, six new thiazole-dipehenylamine-based azo dyes containing azo and thiazole bridges and diphenylamine donor with different donor/acceptor groups were synthesized. All the synthesized dyes were characterized by FTIR, NMR and HRMS analyses. The structure of (E)-N-methyl-4-((thiazol-2-yl)diazenyl)-N-phenylaniline (4) was conclusively confirmed by single crystal X-ray diffraction analysis. Photophysical studies were performed in different solvents with various polarity. Although the three synthesized compounds can be represented as potential azo-hydrazone tautomers only the azo form was observed in all solvents used. UV/vis spectroscopic studies showed that the color changed dramatically when the dyes contain a strong electron accepting nitro substituent. Moreover, after protonation of azo dyes, with the exception of the azo dyes with nitro group, a bathochromic shift was observed. The effects of protonation on the geometry and electronic structure of the compounds were studied, and the NLO properties were also investigated using DFT calculations. In addition, the thermal stability of the azo dyes was investigated using thermal gravimetry (TGA). Dyeing performance was evaluated with these dyes on polyester fabric in an aqueous medium. All dyes except dyes 3 and 6 showed good color fastness properties. Therefore, these compounds can be used as textile dyes for polyester fabrics.