Ferrielectric and antiferroelectric chiral twin liquid crystals showing a stable chiral nematic phase
Ferrielectric and antiferroelectric chiral twin liquid crystals showing a stable chiral nematic phase
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亚铁电和反铁电手性孪生液晶表现出稳定的手性向列相
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
H. Yokoyama
中科院分区：
文献类型：
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作者：
I. Nishiyama;J. Yamamoto;J. Goodby;H. Yokoyama
合成了一系列具有相同手性基团的手性孪晶-bis{4-[(4′-(1-methylheptyloxycarbonyl)-4-biphenylyl)oxycarbony]phenoxy}alkanes，，即光学活性α，ω液晶，并研究了它们的液晶性质。同系物更倾向于显示铁电和/或反铁电相，而不是铁电相。随着中心间隔基长度的增加，铁电相的温度范围变窄，最终对于十二烷基同系物消失，这表明每个孪生分子的两个介晶部分之间的运动和/或方向上的耦合对铁电相的稳定有重要的影响。辛基和十二烷基同系物显示出宽温度范围的手性向列相(约10°C或更高)，因此这些化合物是第一个显示反铁电相和/或铁电相的例子，手性向列相的温度范围很宽。X-射线衍射研究表明，同系物倾向于形成单层结构。结果还表明，在反铁电相和铁电相中形成了相对清晰的层状结构，这对反斜相有序的形成具有重要意义。观察到偶元同系物的各向同性-各向同性转变，其特征是出现一个宽广的弥散DSC峰。
A homologous series of chiral twin liquid crystals possessing identical chiral moieties at both peripheral ends, i.e. optically active α,ω -bis{4-[(4′-(1-methylheptyloxycarbonyl)-4-biphenylyl)oxycarbony]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°C 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 mono-layered 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.