The light stability of azo dyes and azo dyeings IV. Kinetic studies on the role of dissolved oxygen in the photofading of two heterobifunctional azo reactive dyes in aqueous solution

Heterobifunctional reactive derivatives of two previously studied azo chromophores were exposed to light in aqueous solution. In the presence of artificial perspiration, the initial and final rate of photofading depended on the oxygen level of the dye solution. An initial low rate of light-induced dye decomposition was followed by a much higher rate in the final stages of exposure. The lower the initial oxygen concentration the shorter the initial period low dye degradation and the higher the rate of photodegradation in the final stages. Light-induced dye decomposition follows first order kinetics. A reductive mechanism for perspiration assisted, light-induced degradation was supported by results from the photofading of the dyes in the presence of reductive compounds.