Disperse dyes are a versatile class of coloring agents with applications spanning textiles to advanced optical materials. This study details the synthesis and spectroscopic characterization of innovative bisazo disperse dyes, which are derived from benzidine-based compounds. The synthetic process involves the use of two distinct couplers, namely acetylacetone and ethyl acetoacetate. The reaction of these couplers with benzidine derivatives yields two specific bisazo dyes: diethyl 2,2′-(2,2′-([1,1′-biphenyl]-4,4′-diyl)bis(hydrazin-2-yl-1-ylidene))bis(3-oxobutanoate) 3 and 3,3′-(2,2′-([1,1′-biphenyl]-4,4′-diyl)bis(hydrazin-2-yl-1-ylidene))bis(pentane-2,4‑dione) 4. The reaction of these azo compounds with hydrazine and phenylhydrazine results in the formation of azo dyes that incorporate a pyrazole ring 5–7. All the disperse azo compounds were characterized and identified through various spectroscopic methods, including UV-visible, FT-IR, NMR (both 1H and 13C), and elemental analysis. Examining the UV–vis profiles of the disperse dyes 3–7 revealed the maximum absorbance values (λmax) were affected by the change of the coupler moieties and more significant sensitivity to changes in pH. The polyester fabric (PE-F) was dyed by disperse dyes 3–7 in presence of the dispersing agent DYEWELL-002 and the fastness data were measured according to the standard procedures. The color strength (K S-1) and exhaustion (%E) values of the dyed fabrics are calculated and discussed. The synthesised bisazo dyes were subjected to computational calculations using DFT with B3LYP method and 6–31G(d,p) basis set to examine the dyeing efficiencies and anticipate the mechanism of the dyeing process. The computational analyses assessed the dipole moment, chemical reactivity descriptors and molecular electrostatic potential. Analysis of the chemical descriptor parameters revealed that the highest dyeing strength was exhibited by dye 3, as indicated by the ELUMO, EHOMO, ∆E, S, and η parameters, while dye 6 had the highest dyeing strength based on the values of χ and µ parameters.
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