A combined experimental and TD-DFT investigation of three disperse azo dyes having the nitroterephthalate skeleton

•Synthesized three derivatives of dimethyl 5-nitroterephthalate mono disperse azo dyes.•Correlation between experimental photo-physical properties and computed values (DFT).•Dyeing and fastness properties were studied.•Computational approach is used for azo-hydrazone tautomerism study.

Three disperse azo dyes were synthesized using diazotized dimethyl 2-amino-5-nitroterephthalate (5) followed by the diazo coupling with different N-substituted aromatic amines. The structures of the dyes were confirmed using FT-IR, 1H NMR, 13C NMR, MS and HRMS spectral analysis. The geometries of the azo and hydrazone tautomeric forms of the dyes were optimized at B3LYP/6-31G(d) level of theory, and their electronic excitation properties were evaluated using density functional theory. The computed absorption spectral data of the azo derivatives are in good agreement with the experiment, thus allowing an assignment of the UV–vis spectra. The dyes displayed a broad absorption maximum in the visible region between 498 and 561 nm. The synthesized azo disperse dyes were applied on polyester and nylon fiber and they show very good light fastness and washing fastness properties.