Photooxygenation of Polycyclic Aromatic Hydrocarbons by Pyrimido[5,4-g]pteridine N-Oxide.

Photooxygenation of naphthalene (4), phenanthrene (5), pyrene (6), and benzo [a] pyrene (7) by pyrimido [5,4-g] pteridine N-oxide (1) was examined in comparison with that of benzene. These polycyclic aromatic hydrocarbons (PAHs) consumed 1 more smoothly than did benzene under irradiation with ultraviolet-visible light, as expected from the fact that their oxidation potentials for conversion to the corresponding phenols and/or further oxidized products are lower. The photooxygenation of the PAHs occurred predominantly at the most reactive position of the corresponding cation-radicals. These and other experimental results led us to conclude that the PAHs are oxygenated via photo-induced single-electron transfer (SET) from the PAHs to 1 followed by oxygen-atom transfer between the resulting radical-ion pairs. The occurrence of the SET in an excited charge-transfer complex formed between the PAHs and 1 is at variance with the case of benzene