Phototransformations of 6-X-5-Nitroquinoxalines

Photophysical properties and photochemical activity of 6-X-5-nitroquinoxalines with electron-donor substituents (X = H, CH₃, Cl, OC₂H₅, NH₂) ortho to the nitro group were studied. The quantum yield of the formation of 5-hydroxyquinoxaline from the corresponding nitro derivative depends on the nature of the substituent and irradiation conditions. Phototransformations can go through nitro-nitrite rearrangement with the participation of two alternative T(n*) levels, depending on the size and electronic effects of the substituent. The latter factor is largely determined by the population on excitation of different charge-transfer states involving the nitro group.