Rodlike mesogenic molecules consisting of two diacetylenic groups: mesomorphic behavior and photoimaging

A series of mesogenic compounds with two diacetylenic groups were synthesized. The diacetylene groups were connected to a benzene ring via ester linkages, becoming a part of a rigid rod. The thermal behavior of the compounds and their polymerization were investigated. Compounds 7, 8, 9 and 10 having long alkyl tails showed nematic mesophases. They were thermally polymerized in the isotropic state above 200degreesC. Partial polymerization occurred by annealing in the liquid crystalline state. When the compounds were exposed to UV light in the liquid crystalline state, the polymerization was completed within 30 min to give amorphous polydiacetylenes. In the UV-Vis spectra, absorption of the polymers occurred up to about 600 nm, attributable to the short conjugated polydiacetylene backbones. Compound 9 with an octyl tail was fabricated into a thin film and the photopolymerization was carried out through a photomask in the liquid crystalline state resulting in a patterned image.