Photocyclization and photooxidation of 3-styrylthiophene

The photocyclization, dye-sensitized photooxidation and auto-photooxidation of 3-styrylthiophene have been examined. cis-3-Styrylthiophene undergoes photochemical cis–trans isomerization and cyclization to dihydronaphtho-[1,2-b]thiophene. The quantum efficiency for photocyclization in nonpolar solvents is greater than that in polar solvents. Dye-sensitized photooxidation of 3-styrylthiophene gives benzaldehyde and 3-thiophenecarboxaldehyde. This oxidation proceeds via a superoxide radical anion pathway rather than singlet oxygen pathway. In the presence of oxygen photoirradiation of 3-styrylthiophene solution results in photocyclization, oxidation and dimerization. The mechanism of the latter two reactions was described in terms of formation of a charge transfer complex between oxygen and the substrate.