Photoreaction of olefinic compounds in the organized system

Photoreaction of di- and tetraolefinic compounds has been investigated in the organized system such as crystals and Langmuir-Blodgett (LB) films. Olefinic compounds studied include the following series: p-phenylenedi- acrylic acid (p-PDA) monoesters, p-PDA diesters and 5, 5′-(1, 4-phenylene)- bis(2-cyano-2, 4-pentadienoic acid) (PCPA) diesters. In the crystalline state, p-PDA monoesters with shorter alkyl chains, are photoreactive yielding oligomers, while both p-PDA and PCPA diesters gave crystalline polymers on irradiation. The photoreaction in these crystals proceeded by cycloaddition of double bonds forming cyclobutane rings. Crystal structure analysis of these compounds revealed that reaction of p-PDA and PCPA diesters took place topochemically, but that of p-PDA monoesters did not. Regarding LB films, p-PDA monoesters with long-chains gave Z-type LB films and p-PDA and PCPA diesters with long-chains formed Y-type films when mixed with arachidic acid. On irradiation, these films yielded oligomers or p lymers. The spectral data and the molecular area of these compounds indicate that molecular arrangement in each LB films is different from that of crystals. The reaction mechanism was discussed with reference to the molecular alignment.