Analysis of the catalytic fading of pyridone-azo disperse dyes on polyester using the semi-empirical, molecular orbital PM5 method

The catalytic fading of combination dyeings on polyester fabric of six pyridone-azo and one quinolone-azo yellow disperse dyes imparted by C.I. Disperse Blue 165 as a result of exposure to a carbon arc in air was analyzed in terms of reactivity (k0) towards singlet oxygen and the photosensitivity (f) of the dyes. Based on the assumption that the rate of photo-fading of single dyeings is proportional to the product of k0 and f, the fading behavior of both single and mixture dyeings was explained. The k0 values for the seven azo dyes could be correlated to the sum of electrophilic frontier densities determined using the PM5 method. The nitro groups in the pyridone-azo dyes decreased the reactivity of the electron density in parts of the diazo component. Disperse dyes with excellent light fastness on polyester exhibit low values of both f and k0. The f values observed for the combination dyeings did not show simple additivity.