Photochemical reactions of amines on nitrophenazines. Part 2. Photoreduction versus photosubstitution

Abstract

The (n–π*) singlet excited state of 2-nitrophenazine reacts efficiently with amines. With tertiary amines extraction of a hydrogen atom from the α-carbon of the amine takes place to yield the 2-nitrophenazinyl radical (limiting quantum yield 0.64). The reaction occurs through the intermediate formation of a non-emitting exciplex, while a ground state complex formed only at high amine concentration is unreactive. The triplet excited state is similarly reduced by triethylamine. On the other hand, primary amines do not reduce but add to the triplet excited state of 2-nitrophenazine yielding addition products which are then dehydrogenated by oxygen and/or other ground state molecules of 2-nitrophenazine to give alkylaminonitrophenazines.