【作者】 孙贵祥；

【导师】 石高全； 唐洪；

【作者基本信息】 清华大学 ， 化学， 2004， 博士

【摘要】 由于在垂直排列薄膜晶体管和铁电等液晶显示模式中的特殊应用,近年来侧向含氟负介电各向异性液晶成为研究的热点。此外,这类液晶也用来调节液晶混合物的参数,以提高显示器件的性能。为满足液晶显示的需要,我们设计、合成了13系列、共100多种侧向氟取代的液晶化合物。用气相色谱、液相色谱等方法分析了化合物的纯度,并用元素分析、红外光谱、核磁共振和质谱等分析手段对化合物的结构进行了鉴定。用偏光显微镜和DSC研究了这些化合物的相变性质,对其中部分目标化合物的介电各向异性和光学各向异性也作了研究。系统地讨论了末端基团、环体系、连接基团、侧向基团对液晶性质的影响。此外,对中间体2,3-二氟-4-烷氧基苯甲醛和2-(4-烷基苯基)-1,3-丙二醇的合成路线作了改进。主要结果如下:合成了三个系列分子中含2,3-二氟苯和1,3-二氧六环的三环液晶化合物。大部分化合物具有近晶A相和(或)向列相,并具有负的介电各向异性和较小的光学各向异性。合成了两个系列分子中含2,3-二氟苯、环己烷环和1,3-二氧六环的四环液晶化合物。所有化合物具有宽的介晶相温度范围,且大部分化合物具有宽的近晶C相温度范围和Cr?SmC?SmA?N?Iso的相序。合成了六个系列分子中含侧向氟取代苯、环己烷环和1,3,2-二氧硼杂环的液晶化合物。所有三环化合物和绝大部分四环化合物只具有向列相,而部分四环化合物具有向列相、近晶A和(或)近晶B相。部分化合物具有负的介电各向异性。合成了两个系列分子中含2,3-二氟苯、环己烷环和1,3-二氧六环的化合物。其性质与具有类似结构的1,3,2-二氧硼杂环类化合物作了比较,发现1,3,2-二氧硼杂环类化合物具有较低的。更多还原

【Abstract】 Laterally fluoro-substituted liquid crystal materials with negative dielectric anisotropy have been studied extensively due to their unique applications in some display modes, such as MVA-TFT-LCD (multi-domain vertical alignment thin film transistor liquid crystal display) and FLCD (ferroelectric liquid crystal display). In addition, such materials also can be used to reduce Δε/ε⊥, which can increase the steepness of the electrooptic contrast curve of supertwisted nematic display.Thirteen series with more than one hundred laterally fluoro-substituted liquid crystalline compounds were designed and synthesized. The purities of all these compounds were tested by GC and HPLC, and their structures were identified by element analysis,IR, H-NMR and MS. The mesmorphic properties of all the target compounds were observed and measured by polarizing optical microscopy and differential scanning calorimetry, respectively. The dielectric anisotropy and birefringence properties of part of the target compounds were determined. The influences of terminal groups, ring systems, linking groups and lateral substituents on properties of liquid crystals were investigated as well. Furthermore, we successfully modified the synthesizing routes of some intermediates, including 2-(4-alkylphenyl)-1,3-propanediol and 2,3-difluoro-4-alkoxybenzaldehyde.The main results are as follows:Three series three-ring liquid crystals containing 2,5-substituted 1,3-dioxane and 1,4-substituted 2,3-difluorophenyl units were synthesized. Most of these compounds exhibit a smectic A phase and/or a nematic phase with negative dielectric anisotropy and low birefringence.We introduced trans-1,4-substituted cyclohexane, 2,5-substituted 1,3-dioxane and 1,4-substituted 2,3-difluorophenyl units into the liquid crystalline molecules and synthesized two new series four-ring compounds. All these compounds exhibit broad mesomorphic phase, and most of them show a wide smectic C phase and a phase sequence of Cr?SmC?SmA?N?Iso. <WP=5>Six series liquid crystals containing 2,5-substituted 1,3,2-dioxaborinane, trans-1,4-substituted cyclohexane and 1,4-substituted laterally fluorinated phenyl units were synthesized. All these compounds are thermotropic liquid crystalline materials. All three-ring compounds and most four-ring compounds exhibit only a nematic phase, while some four-ring compounds show a nematic phase, a smectic A phase and even a smectic B phase. Some of the target compounds show negative dielectric anisotropy. In addition, two series liquids containing 1,3-dioxane, cyclohexane and 2,3-difluorophenyl units were prepared, and their properties were compared with that of their 1,3,2-dioxaborinane analogues, and the 1,3,2-dioxaborinane analogues have lower .更多还原