Synthesis and Application of Benzidine‐Based Bisazo Metal Complexes as High‐Performance Disperse Dyes for Polyester Fabrics

ABSTRACT A new series of benzidine‐based bisazo metal complexes were synthesized, characterized, and applied for polyester fabric dyeing. The parent bisazo dye was prepared by diazotizing benzidine and coupling it with acetylacetone. This dye was then complexed with Fe (III), Cr (III), Cu (II), Mn (II), and Ni (II) ions to produce five metal complexes. The structures of the synthesized compounds were confirmed using spectroscopic techniques, including FT‐IR, NMR, TGA, and elemental analysis. Enhanced thermal stability of the metal complexes relative to the parent dye was demonstrated by thermal analysis. Moreover, when applied to polyester fabrics, superior performance was observed through colorimetric analysis and fastness testing. The highest color strength ( K / S  = 12.5) was exhibited by the iron complex. Excellent fastness properties (ratings of 4–5 or 5) were achieved for washing, perspiration, and light fastness. Significant variations in color characteristics between complexes and the parent dye were revealed by CIE Lab analysis. The electronic properties and reactivity of the parent dye were investigated using DFT calculations.