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

Abstract

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 λ–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.

Acknowledgement

This work was supported by the Aomori Prefecture Collaboration of Regional Entities for the Advancement of Technological Excellence, JST.

Notes

†. In equation (1), F denotes the reaction field factor [F = 1/(1−fα); f = (ε−1)/2πεa ³(2ε+1)], and h the cavity factor [h = 3ε/(2ε+1)]. The macroscopic dielectric constant is used for ε.