Photoreaction of 2-nitrophenazine 10-oxide with amines

Abstract

The photodeoxygenation and the photosubstitution of the nitro-group of 2-nitrophenazine 10-oxide has been investigated by kinetics methods supplemented by quenching measurements. Photodeoxygenation by triethylamine occurs quite efficiently (Φ_rca. 0, 2) in acetonitrile and methanol and is little affected by triethylamine concentration. The other amines employed are much less efficient; their efficiency strongly depends on the amine concentrations. Examination of the fluorescence quenching data with the quantum yields of reduction allows the conclusion that in the case of triethylamine, the main pathway of reduction involves an exciplex derived from the singlet state. The same pathway is also proposed for the reduction by concentrated solutions of other amines in acetonitrile. In different conditions a pathway from a triplet state seems to be more important. Both the pathways lead to the same intermediate. Quenching of the reduction by oxygen and by tetramethyldiazetine dioxide supports this point. The mechanism of photosubstitution of the nitro group is also discussed.