Condensation pigments for pigment printing of cotton - synthesis, photophysical properties, TD-DFT studies

Three novel mono azo condensation pigments were prepared by reacting two moles each of 1- aminoanthraquinone, 2-aminoanthraquinone, and 1-amino-5-benzimidoanthraquinone with the acid chloride of monoazo dye obtained by diazotizing 5-aminoisopthalic acid and coupling on to 2-napthol. The structures of the dyes were confirmed using FT-IR, UV-Visible, elemental, and thermogravimetric analysis techniques. The geometries of the azo and hydrazone tautomeric forms of the pigments were optimized and their electronic excitation properties were evaluated using density functional theory. The computed absorption spectral data of the azo pigments were in good agreement with the experiment, thus allowing an assignment of the UV-Vis spectra. The pigments displayed a broad absorption maximum in the visible region between 460 and 523 nm. The synthesized pigments were applied on cotton for printing application and they showed very good light fastness and washing fastness properties.