The influence of an alkenyl terminal group on the mesomorphic behaviour and electro-optic properties of fluorinated terphenyl liquid crystals
作者:Julita S. Gasowska、Stephen J. Cowling、Martin C. R. Cockett、Michael Hird、Robert A. Lewis、E. Peter Raynes、John W. Goodby
DOI:10.1039/b914260f
日期:——
Novel liquid crystal terphenyls with two, three and four lateral fluoro substituents and an alkene unit at the end of a terminal chain are presented in terms of synthesis, mesomorphic behaviour and electro-optic properties. The difluoro analogues were found to exhibit the smectic C phase over a wide temperature range, with short temperature ranges of the smectic A and the nematic phase above. Very low melting points were recorded for the trifluoro analogues, and the shorter chain homologues of these materials exhibit the nematic phase over a wide temperatures with a monotropic smectic C phase and the higher homologues exhibit the smectic C phase over a wide temperature range with the nematic phase above. The tetrafluoroterphenyls exhibit the nematic phase over a wide temperature range with the complete absence of smectic phases. As appropriate, the materials were evaluated for dielectric anisotropy and threshold voltage in nematic phase, and mixed with a chiral dopant to evaluate the spontaneous polarisation, tilt angle and switching times in the chiral smectic C phase. The results show that these compounds are strong potential candidates for application in both vertically aligned nematic (VAN) and ferroelectric liquid crystal (FLC) devices.
介绍了一种新型液晶三苯基化合物,具有两个、三个和四个侧位氟取代基,以及一个末端链上的烯烃单元,涵盖了合成、相态行为和电光性质。研究发现,二氟类似物在较宽的温度范围内表现出胆甾相C,且其上方存在少量温度范围的胆甾相A和向列相。三氟类似物记录到非常低的熔点,而这些材料的短链同系物在较宽的温度范围内显示向列相,并具有单向胆甾相C,而长链同系物在较宽温度范围内展现胆甾相C,且上方有向列相。四氟三苯基化合物在较宽的温度范围内表现出向列相,完全没有胆甾相。根据需要,对这些材料的介电各向异性和向列相的阈值电压进行了评估,并与手性掺杂剂混合,以评估手性胆甾相C阶段的自发极化、倾斜角和开关时间。结果显示,这些化合物是垂直对齐向列液晶(VAN)和铁电液晶(FLC)设备潜在应用的强有力候选者。