Synthesis, characterization, and color performance of bis-azo and bis-pyrazole derivatives for dyeing of polyester.

• Novel series of bis azo dyes 3–10 were synthesized via a two-step process. • The disperse azo were synthesized and characterized by UV–visible, FT-IR and NMR. • The electronic absorption properties were investigated experimentally and computationally. • Significantly improved fastness properties of the new disperse dyes for the PET fabrics were observed. • The color strengths (K/S) and CIE Lab* color space indicate high efficiency of disperse dyes on polyester fiber. In this study, a novel series of bis-azo dyes 3–10 were synthesized via a two-step process. Initially, benzene-1,4-bis(diazonium) chloride was reacted with several active methylene compounds, such as ethyl acetoacetate, acetyl acetone, ethyl cyanoacetate, and malononitrile. yielding the corresponding bis-azo dyes 3–6. Subsequently, these dyes were cyclized through condensation with phenylhydrazine, resulting in the formation of bis-pyrazole derivatives 7–10. Comprehensive spectroscopic characterization, employing techniques like infrared (IR), nuclear magnetic resonance (NMR), and ultraviolet-visible (UV–Vis) spectroscopy, along with elemental analysis, elucidated the structural features, and electronic transitions of the synthesized dyes. The electronic absorption properties were investigated experimentally and computationally, revealing bathochromic and hypsochromic shifts influenced by substituents and tautomeric forms. The dyes showcased excellent dyeing performance on polyester fabrics, exhibiting notable color strength, perspiration fastness, light fastness, and wash fastness. Theoretical investigations of the electronic properties were conducted utilizing Density Functional Theory (DFT) methodology, employing the B3LYP functional with the 6–31G(d,p) basis set, enabling a comprehensive understanding of the structure-performance relationships governing the dyeing behavior of these dyes on polyester. [Display omitted] [ABSTRACT FROM AUTHOR]