Chemically generated singlet oxygen reacts with adanantylideneadamantane () in acetone solution to give mainly the corresponding 1,2-dioxetane () together with traces of the epoxide . When rose bengal (RB) is added to the reaction mixture, epoxide , becomes the chief product at the expense of the dioxetane , even in the dark. Charge transfer conplexes (CTCs) formed between N-ethylcarbazole and fluorene with 2,4,7-trinitrofluoren-9- one and pyromellitic dianhydride, as well as quinhydrone, behave like RB in that their addition to the reaction mixture favors epoxide formation. Their epoxidizing power is related to the energies of their CT bands. Free energies (ΔG) calculated for the interaction of the CTC with singlet oxygen ranged from -2.07 to 0.45 kcal/mol. CTCs having a ΔG greater than 0.5 kcal/mol are inefficient for the production of . The results are explained in terms of two different processes. The normal course is the reaction of singlet oxygen with to give dioxetane. Addends such as CTCs and dimeric RB compete for singlet oxygen and convert it to superoxide radical ion, which in a secondary process is indirectly responsible for epoxidation.