Abstract: The photochemistry of 1, 1, 4-triphenyl-3, 3-dimethy1-1, 4-pentadiene was investigated. This triphenyldiene was found to rearrange on direct irradiation to give 1-a- styryl-2, 2-diphenyl-3, 3-dimethylcyclopropane as the major product. The alternative di-n- methane rearrangement product, 1-(2, 2-diphenylvinyl)-l-phenyl-2, 2-di-methylcyclopropane, was not produced. The rearrangement was shown to involve reaction of the singlet excited ...