The title compounds, both disazo dyes, were found to undergo photoisomerism in dimethylphthalate solution and in films cast from a mixture of dye and cellulose acetate. Light-induced isomerism did not occur, however, in PET film that had been extruded, oriented, and dyed with the same two colorants. The prolonged irradiation of disperse yellow 23 in either solution or a polymer matrix produced azobenzene and some mono-substituted azobenzenes. Disperse orange 29 underwent photodegradation to produce a mixture of disubstituted monoazobenzenes, a partially reduced disazo- benzene, and para-nitroaniline.
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