Synthesis and physical properties of novel liquid crystal oligomers possessing polar terminal groups

A homologous series of novel liquid crystal oligomers possessing 4-fluorobiphenyl and 4-trifluoromethoxyphenyl benzoate moieties was prepared and the physical properties investigated. The dimesogenic compounds, 4- trifluoromethoxyphenyl 4-{6-[4-(4-fluorophenyl)phenyloxy]alkoxy} benzoates, exhibited nematic (N) and smectic A (SmA) phases. Pronounced odd-even effects were seen, not only for the phase transition but also for the induced dielectric anisotropy in the N phase of the mixture with a host material, on varying the spacer length of the dimeric compounds. The lambda-shaped trimesogenic compound, 4-trifluoromethoxyphenyl 3,4-bis{6-[4-(4-fluorophenyl)phenyloxy]hexyloxy}benzoate, was found to show monotropic N and SmA phases. We discuss oligomeric effects of the mesogenic moieties on the phase transition behaviour, and on the induced dielectric anisotropy.