Anaerobic photodecomposition of an acridan drug through energy transfer

Anaerobic irradiation of 2-chloro-9-(3-dimethylaminopropyl)acridan phosphate (1:1) (IIIa) with filtered visible light (300-400 nm) resulted in its quantitative conversion to its acridine derivative IV. Photoproduct IV exerted significant product catalysis on the reaction rate at concentrations of 5 x 10(-6) M. The anaerobic photodecomposition of IIIa to IV was catalyzed by the monosodium salt of riboflavin 5-phosphate (Ia). Loss of Ia was insignificant relative to that of IIIa, and reagents known to serve as quenchers of the triplet state of Ia retarded the reaction. Fluorescence spectra of Ia in the presence of IIIa and 1 x 10(-4) M KI indicated no quenching of the Ia singlet excited state. No deuterium isotope effect was noticed when IIIa and its deuterated derivative IIIb were subjected to anaerobic photodecomposition in the presence of Ia. It is suggested that the anaerobic photodecomposition of IIIa by visible light in the presence of Ia proceeds via a triplet-triplet energy transfer from Ia to IIIa.