Photochemical Reaction between Acridine and Acridan in the Presence and in the Absence of Oxygen. I. Studies by the Steady Light Illumination

Photochemical reactions between acridine and acridan in benzene solution have been studied. The product is diacridan in the absence of oxygen, while in the presence of oxygen, it is acridine. The reactive excited state in both cases is, most likely, the lowest π-π* triplet state. Contrary to the expectation, the kinetics in the degassed solution is difficult to interpret. The rate of acridine production in the presence of oxygen, gives a sharp maximum near ∼10−4 m of oxygen at fixed acridan concentrations. Its quantum yield is reproduced by Φ=0.25×β[AH2]/(α[O2]+β[AH2]) with α/β=3.3 (1). Two schemes consistent with (1) have been tentatively presented in which one involves the mere deactivation of the triplet acridine by oxygen, and the other assumes the formation of an excited oxygen (or the like), which oxidizes acridan but is partially deactivated by a certain substance.