Syntheses And Properties Of Novel Laterally Fluoro-substituted Liquid Crystals With Negative Dielectric Anisotropy

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. 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 .