Photostability of a range of azobenzene dyes and their benzothiazolyl analogues in the presence of air

Irradiation of a range of azobenzene dyes and their benzothiazolyl analogues with visible light in the presence of air has been shown to give rise to the conversion of a triplet oxygen to the singlet state. As proof of the presence of a singlet oxygen, its reaction with tetraphenylcyclopentadienone was studied. The formation of the oxidation product cis-α,α'-dibenzoylstilbene by a singlet oxygen has been confirmed by chemical ionisation mass spectrometry, both in ethyl benzoate solution and on polyester fabric. Inhibition of photodegradation of the dyes by a singlet oxygen quencher (DABCO) has also been demonstrated.