Photochemical Synthesis of a Main-Chain LC Oligomer from an α,ω-Dicinnamoyl-Functionalized LC Monomer: Photoirradiation in the Crystalline State

Abstract

An LC compound 1,4-bis[4-(6-cinnamoyloxyhexyloxy)benzoyloxy]benzene, 1, was synthesized, having cinnamoyl groups at the each end of the molecule, and was found to show polymorphism in the crystalline state. A rapid cooling from the isotropic melt of 1 to room temperature gave a K1 crystal, while annealing the mesophase of 1 at 95°C afforded a K2 crystal. UV irradiation (>300 nm) of both the K1 and K2 crystals at room temperature resulted in the formation of linear LC oligomers with cyclobutane rings in the main chain. 1H NMR spectroscopy revealed that the cyclobutane units of the oligomer obtained from K1 assumed anti and syn head-to-head configurations, whereas those from K2 predominantly formed an anti head-to-tail structure.