Synthesis, spectroscopic, DFT, TD-DFT, and dyeing studies of 2-amino-3--cyano thiophene-based azo dyes on wool and nylon

This study presents the design, synthesis, and application of eight novel thiophene-based acid azo dyes featuring benzoic and salicylic acid acceptors. The synthesized dyes demonstrate versatile light absorption properties, spanning the near UV, visible, and deep red regions. Notably, the thiophene acid azo dyes containing benzoic acid acceptor unit (AB series dyes) exhibited red-shifted absorption, while their salicylic acid counterparts (SR series dyes) displayed blue-shifted absorption. The influence of increased donor strength at position 4 of the thiophene ring on absorption properties is systematically explored. Theoretical findings from Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) substantiate the experimental results. Moreover, the dyes are applied to wool and nylon fabrics, displaying excellent dyeability with % exhaustion properties above 70%. The dyed fabrics manifest rich shades, ranging from blue-black to deep orange. Enhanced K/S values are observed for wool-dyed fabrics in the case of SR series dyed fabrics, whereas the AB series dyes show superior results for nylon-dyed fabrics. The dyed fabrics exhibit remarkable light, wash, and rubbing fastness. Notably, nylon-dyed fabrics outperformed wool-dyed fabrics in light and wash fastness. UV protection studies reveal the fabrics' potential to block harmful UV-A and UV-B radiation with excellent UPF ratings.