Abstract
Photolysis of α,β-diacetoxystilbene ( 1) adsorbed onto a Fe 3+-doped sepiolite (Fe-Sp) leads to benzoic acid ( 3), 9,10-diacetoxyphenanthrene ( 5), diphenic anhydride ( 6), and benzil ( 7). While compounds 3, 5 and 6 are also observed in the direct irradiation of 1 in hexane solution, diketone 7 is formed under electron transfer conditions using 2,4,6-triphenylpyrylium tetrafluoroborate as photosensitizer. These results strongly suggest that formation of benzil ( 7) in the photolysis of 1 on Fe-Sp involves the intermediacy of 1 +, generated by single electron transfer from excited 1 to the iron active sites of the clay. In contrast to the unsubstituted stilbene, reactivity of 1 + with ground state molecular oxygen has been established by cyclic voltammetry through the current intensity decrease of the oxidation peak of 1 in the presence of oxygen. Finally, the thermodynamic feasibility of a direct electron transfer pathway between excited 1* and oxygen leading to the formation of a dioxetane intermediate is discussed.
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