Concerning the use of amines as probes for participation of singlet oxygen in dye-sensitised oxygenation reactions

Abstract

Amines quench the excited singlet states of Methylene Blue and Rose Bengal. Aromatic amines are particularly potent quenchers. Quenching of dye-sensitised oxygenation reactions by amines involves interaction of the amine with singlet oxygen and the excited singlet and triplet states of the dye. An equation is developed which describes the rate of oxygenation of a compound in the presence of an amine. The use of amines as probes for the participation of singlet oxygen in dye-sensitised oxygenation reactions has a number of pitfalls. These may be minimised by keeping the amine concentration below 10^–3 M. Oxygenation reactions sensitised by tris-(2,2′-′bipyridyl)ruthenium(II) chloride are also quenched by amines establishing that these reactions involve singlet oxygen. The kinetics of these reactions are simpler than those of the dye-sensitised reactions since only one excited state of the complex is involved.