The effect of substituents on the photochemistry of phenazine N-oxides

Abstract

Disappearance quantum yields of a set of substituted phenazine N-oxides were determined; from these values and on the basis of the composition of 10% conversion mixtures, the formation quantum yields of the major reaction products [the lactams (4) and the oxepinoquinoxalines (5)] were estimated. By correlating quantum yields and spectroscopic properties of the N-oxides, it was confirmed that there are two different pathways for the formation of quinoxalines and lactams, the latter being formed only when the excited state has internal charge transfer character. This had already been suggested on the basis of solvent effects on the photoisomerization of phenazine N-oxide.