Enhancing color brilliance and fastness of polyester dyeing with antipyrine-derived disperse dyes

Disperse azo dyes are important colorants for dyeing polyester fabrics, but developing optimized disperse azo dyes remains a challenge. This work details the synthesis of seven new disperse azo dyes 3a-g derived from the coupling reaction of 4-aminoantipyrine diazonium salt with various phenolic precursors including phenol (3a), salicylic acid (3b), salicylaldehyde (3c), cresols (3d-f), and resorcinol (3g). The dyes were characterized by spectroscopic techniques. Their UV-visible absorption spectra were studied, revealing bathochromic shifts for 3d-g containing electron-donating methyl and hydroxyl substituents compared to parent dye 3a while dyes 3b-c showed hypsochromic shifts. The impact of acid and base on the absorption spectra indicates azo-hydrazone tautomerism for 3f-g but predominant azo form for 3a-e. The dyes showed excellent dyeing on polyester fabrics with up to 97.86 % dye exhaustion. High wash, light and perspiration fastness was exhibited while fastness to respiration varied. The strongest color yield on polyester was achieved with 3g derived from resorcinol coupler. Density functional theory calculations were performed to elucidate relationships between substituent effects and spectral attributes. Lower energy gaps were computed for 3f-g, consistent with enhanced reactivity. This work expands disperse azo dye precursors while offering fundamental structure-performance insight to guide future design. The potent polyester coloration and good fastness properties warrant ongoing investigation of these dyes.