Synthesis and photochemical stability of 1‐phenylazo‐2‐naphthol dyes containing insulated singlet oxygen quenching groups

Abstract

Abstract Although 1‐arylazo‐2‐naphthols undergo direct and sensitised photochemical fading in solution by a singlet oxygen mechanism, the introduction of singlet oxygen‐quenching substituents (N,N‐dialkylaminomethyl‐) affords no protection against fading, and in many cases accelerates photodegradation. This has been attributed to the high reactivity of the dialkylaminomethyl‐groups towards hydrogen abstraction, thus rendering free radical modes of decomposition more favourable. In the presence of peroxide‐radical scavengers the latter reactions are suppressed, and the dialkylaminomethyl‐groups then show a protecting effect against fading by singlet oxygen.