Photochemical Degradation of Aminoazobenzene Disperse Dyes in Ethanolic Solution: Part II : Effect of pH and of Dye Structure

Aminoazobenzene disperse dyes exhibit diverse fading rates in ethanolic solution with changes in pH; ten-fold differences in rates of fading are observed between acidic and alkaline media. Good correlations are observed between the electronegativity of the β-azo nitrogen atom (assessed in terms of the pK. value of the dyes) and their fading rates. This latter relationship is particularly valid in dyes of closely related structure, but may be disrupted by the presence in the dyes of photodegradable substituents, e.g., nitro.