A homologous series of novel λ-shaped mesogenic compounds in which three mesogenic groups are connected to 3, 4-dihydroxybenzoic acid has been prepared and their physical properties investigated by means of optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. The λ-shaped compounds studied showed unusual smectic phases. 4-Cyanobiphenyl-4â²-yl 3,4-bis6-[4-(5-octylpyrimidin-2-yl)phenyloxy]hexyloxy}benzoate was found to realize an incommensurate SmA (SmAinc) phase. A âuniform planarlyâ aligned sample of 2-(4-octylphenyl)pyrimidin-5-yl 3,4-bis6-[4-(5-octylpyrimidin-2-yl)phenyloxy]hexyloxy} benzoate showed a Schlieren-like texture in the smectic phase. We discuss structural effects of the λ-shaped compounds on molecular organization in liquid-crystalline phases.
chiral alkyl group, synthesized by a palladium-catalyzed coupling reaction, provide a new series of liquid crystalline materials which form chiral smectic C (SmC*) phases exhibiting ferroelectric properties. Mesomorphic properties of the compounds composed of threearomaticrings is strongly affected by the position of an acetylenic linkage and the direction of an esterlinking unit. The effect of variations
通过钯催化偶联反应合成的具有手性烷基的二苯乙炔同系物提供了一系列新的液晶材料,其形成具有铁电性质的手性近晶 C (SmC*) 相。由三个芳环组成的化合物的介晶性质受炔键位置和酯键单元方向的强烈影响。已经系统地研究了末端链长的变化对近晶 A (SmA) 和 SmC* 两个和三个芳环系统的热稳定性的影响。
The synthesis and characterisation of a novel thiophene-based liquid crystal exhibiting ferro-, ferri- and antiferro-electric phase types
作者:David J. Byron、Lachezar Komitov、Avtar S. Matharu、Ian MCsherry、Robert C. Wilson
DOI:10.1039/jm9960601871
日期:——
The synthesis and liquid crystal properties of (R)–(–)-4-(l-methylheptyloxycarbonyl)phenyl 5-(4-decyloxyphenyl)thiophene-2-carboxylate is reported. This material exhibits the following phase types (°C): I 97.4 SA 92.2 SC* 81.4 ferri 78.8 antiferroelectric 48.6 glass state (characterised by thermal optical microscopy and differential scanning calorimetry). Results from electro-optical investigations, for example, field-induced transitions, temperature and voltage dependence and current and electro-optic response, clearly illustrate the presence of the SC* ferro-, ferri- and antiferro-electric phase types.
Fluorocarbon and hydrocarbon end groups: effects on mesomorphism and physical properties of smectic liquid crystals
作者:Stephen J. Cowling、Alan W. Hall、John W. Goodby
DOI:10.1039/c1jm11138h
日期:——
In this article we examine the effects of cyclohexane and perfluorocyclohexane being used as bulky end groups on the mesomorphism of classical smectic liquid crystal mesogens. The mesogen that is used in this work is typical of the MHPOBC family of materials. The mesophase behaviour is investigated and miscibility studies are carried out. Electro-optical evaluation of the materials is investigated to show the effect of the terminal group on physical properties such as spontaneous polarisation and tilt angle.
It was found that the synclinic interlayer interactions for materials having mesogenic cores made of repeating benzyloxycarbonyl units are stronger than for the parent MHPOBC and analogous compounds having biphenyl–phenyl mesogenic cores, as evidenced by significantly broader range of the synclinic phase and less frequent appearance of anticlinic phases in the homologous series. The biaxiality of the three-layer structure of the SmC*Fi1 phase was directly observed at the temperature where the optical pitch is spontaneously unwound. The ferrielectric phase structure is nearly Ising-like. The Ising structure is most probably enforced by strong interlayer quadrupole order, in materials in which the ferri-phase appears nearly 20 K below the SmA phase.
研究发现,与母体 MHPOBC 和具有联苯-苯基中生核的类似化合物相比,具有重复苄氧羰基单元中生核的材料的合环层间相互作用更强,这表现在同源系列中的合环相范围明显更广,反链相出现的频率更低。在光间距自发解开的温度下,可以直接观察到 SmC*Fi1 相三层结构的双轴性。铁电相结构近似于伊辛结构。在铁电相出现于比 SmA 相低近 20 K 的材料中,这种伊辛结构很可能是由强烈的层间四极秩序强制形成的。