Synthesis of branched azo dyes based on benzene sulphonamide intermediates and their spectral properties

Benzene sulphonamide intermediates and two series of branched azo dyes (one series with H‐Acid as the coupling component, and the other, with a pyrazolone derivative as the coupling component) derived from them were synthesised. The molecular structures, spectroscopic properties and dyeing properties of the dyes obtained have been investigated. The results indicated that these dyes showed one dominant hue, despite each separate branch of chromophore, and, in the first series, four chromophoric groups led to only a threefold increase in the extinction coefficient, while the same comparison in the second series produced a fully additive effect, i.e. a fourfold increase. Compared with the mono‐branch dye of each series, the dyeing properties of the H‐Acid series were improved, whereas the pyrazolone series that were run diversely for the two series were synthesised from different coupling components. In addition, the crystallographic structure of the tri‐branch intermediate showed a non‐coplanar structure, which indicated that the derived dye would perform as the sum of three similar chromophoric units.