DYE-SENSITIZED OXYGENATION AND DIMERIZATION OF 4-METHOXYSTYRENE THROUGH ELECTRON-TRANSFER

Photoreactions of 4-methoxystyrene (1) sensitized with dyes such as Acriflavine, Rhodamine 6G, and Methylene Blue in methanol under oxygen afforded 4-methoxybenzaldehyde, its dimethyl acetal, and 2-methoxy-2-(4-methoxyphenyl)ethanol as oxidation products together with the corresponding dimers, cis- and trans-cyclobutanes in a ratio of cis/trans ca. 5/95. On the basis of quenching studies of fluorescence and T-T absorption of the dyes, the oxygenation and dimerization are proposed to proceed through an electron transfer from 1 to excited singlet dyes but not to involve generation of singlet oxygen.