乙炔桥键四环异硫氰酸酯液晶化合物的合成及性能

为了研究液晶材料结构与性能的关系,本文以含乙炔桥键的四环异硫氰酸酯化合物为研究对象,芳基硼酸和3-氟-4-溴碘苯为起始原料,经6步反应合成了12种目标化合物,LC纯度大于99%,采用核磁共振、红外光谱对其结构进行了表征。采用DSC和POM对目标化合物的介晶性进行了研究,采用外推法对其双折射率和介电各向异性值进行了测试。结果表明:目标化合物具有300℃以上高清亮点、150℃以上向列相温度区间、0.40~0.51的双折射率以及大于17的介电各向异性值。对于同一系列化合物,随着末端烷基链的增长,化合物熔点降低,但呈现近晶相的趋势增加。在Y、Z位引入侧向氟取代基,熔点和清亮点均降低;X位再引入侧向氟取代基,熔点上升、清亮点下降。用环己烷替代左边第一个苯环,化合物熔点降低、向列相温度区间变宽。引入侧向氟取代基使双折射率下降0.008~0.036。目标化合物有利于提高混合液晶配方的双折射率、清亮点和降低阈值电压。

Synthesis and properties of four-ring isothiocyanate liquid crystals with ethynyl bridge

In order to investigate the relationship between the structures and properties of LCs, twelve isothiocyanate liquid crystals composed of four-ring core and ethynyl bridge were synthesized via six steps based on arylboronic acid and 1-bromo-2-fluoro-4-iodobenzene. Their structures were confirmed by infrared spectrometry (IR) and ¹H-nuclear magnetic resonance (¹H NMR). The mesomorphic properties, birefringence and dielectric anisotropy of these compounds were investigated. The result reveals that all these compounds exhibit high clearing points (>300℃), wide nematic phase range (>150℃), high birefringence (△n=0.40~0.51) and large dielectric anisotropy (△ε>17). The melting points of these compounds decreased with increasing the carbon number of alkyl chain, while the smectic phase intervals enlarged. Lateral fluorines in the position of Y, Z result in a drop of the melting points and the clearing points, but an additional fluorine in the position of X results in an increase of the melting points and decrease of the clearing points. Replacement of the left benzene ring by cyclohexane is useful to lower the melting point and increase nematic phase range. The introduction of lateral fluorine will reduce the birefringence of 0.008~0.036. The target compounds are useful for elevating the birefringence values, clearing points and reduce the threshold voltage of liquid crystal mixtures.