Ferrielectric and antiferroelectric chiral twin liquid crystals showing a stable chiral nematic phase

A homologous series of chiral twin liquid crystals possessing identical chiral moieties at both peripheral ends, i.e. optically active alpha,omega-bis{4-[(4-(1-methylheptyloxycarbonyl)-4-biphenylyl)oxycarbonyl] phenoxy} alkanes, has been prepared and their liquid crystalline properties investigated. The homologues preferred to show the ferrielectric and/or antiferroelectric phase rather than the ferroelectric phase. With ascending central spacer length, the temperature range of the ferrielectric phase became narrow and eventually disappeared for the dodecyl homologue, suggesting that the coupling in motion and/or direction between two mesogenic parts of each twin molecule has an important effect on the stabilization of the ferrielectric phase. The octyl and dodecyl homologues showed a wide temperature range chiral nematic phase (ca. 10 degreesC or more), so that these compounds were found to be the first examples showing antiferroelectric and/or ferrielectric phases with a broad temperature range of the chiral nematic phase. X-ray diffraction studies showed that the homologues tend to form a monolayered structure. The formation of a relatively well defined layered structure was also indicated, which is considered to be important for generating anticlinic ordering in the antiferroelectric and ferrielectric phases. An isotropic-isotropic transition characterized by the emergence of a broad diffuse DSC peak was observed for the even-membered homologues.