Mechanism for quenching of the luminescence of 9,10-anthraquinone vapor by oxygen

The fluorescence of 9,10-anthraquinone, 1-aminoanthraquinone, 1,4-diaminoanthraquinone, and 1,5-diaminoanthraquinone is not quenched by oxygen because the singlet-triplet energy difference in these compounds is less than the energy needed for excitation of the triplet state of oxygen to the singlet state. Luminescence of 9,10-anthraquinone is quenched because it is mainly phosphorescence, for which the singlet-triplet difference is sufficient for quenching by a mechanism involving singlet oxygen formation. The weak fluorescence of 9,10-anthraquinone is not quenched. The resistance of the fluorescence of 9,10-anthraquinone vapor to quenching by oxygen and the quenching of its phosphorescence explain the different effects of oxygen on the luminescence of α-substituted and β-substituted anthraquinones known from the literature, and indicate that their singlet excited state cannot convert triplet oxygen to singlet oxygen. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 79–4, January–February, 2008.