The synthesis, photophysical properties, DFT study and textile applications of fluorescent azo dyes bearing coumarin-thiazole

Abstract

In this study, four novel coumarin-thiazole-based azo dyes were prepared by coupling N-methyl-N-phenylaniline and 3-methyl-1-phenyl-2-pyrazoline-5-one with coumarin-2-aminothiazole hybrid and they were characterized by 1H/13C NMR and mass spectroscopic techniques. The photophysical properties of the synthesized dyes were studied, and the absorption spectra in different solvent polarities were observed in the range of 408–513 nm. The effect of acidity on the photophysical properties was also studied. When the solvent-dependent spectral properties of the compounds were studied, they showed a positive solvatochromic shift. Despite the presence of the azo group, the azo dyes were found to be fluorescent with low emission intensity. The coumarin-thiazole-pyrazolone azo dyes exhibited prototropic tautomerism and the determination of most stable tautomeric form of dyes was used 1H NMR spectroscopy method. The stability of the compound was also studied using density functional theory calculations (DFT) by comparing the total energy of the possible tautomeric forms. The thermal study showed that these azo dyes can be used in any dyeing process where the temperature is below 269 °C without decomposition. The textile applications showed that the thiazole and coumarin structures in the molecule provided excellent color fastness properties and color variations on the fabrics.