Inhibition of the biacetyl‐sensitised photo‐oxidation of azo dyes

The photo‐oxidation of azo dyes in the presence of oxygen and biacetyl is inhibited by phenol, sodium 1‐naphthol‐4‐sulphonate, the sodium salt of naphthionic acid and the azo dyes themselves. Phosphorescence quenching of biacetyl by these compounds revealed that inhibition is mainly caused by quenching of its first triplet state. Kinetic behaviour was investigated by phosphorescence measurements and inhibition experiments on the system. The results indicate that there is a possibility that the light fastness properties of dyed substrates containing carbonyl groups might be improved by adding efficient quenchers for the excited triplet states of these groups.