Synthesis And Properties Of Fluorinated Benzene Liquid Crystal Compounds Bridging Side Cyclohexyl Ethylene

Because of the superior picture quality, low energy consumption and portability, the active matrix thin film trasistor liquid crystal display (AM-TFT-LCD) has become the mainstream in the field of display devices. It needs liquid crystal materials with low viscosity, wide phase interval and negative dielectric anisotropy. The fluoro substituted liquid cryctals exhibited negative dielectric anisotropy and lower viscosity. Therefore, in recent years, this kind of liquid crystal compounds have become the focus of scientific research.To further explore liquid crystals with low melting point, broad liquid crystal phase and negative dielectric anisotropy, three series of28laterally fluoronited biphenyl liquid crystals were designed and synthesized by changing the sides and introducing ethylene linking group. The total yield was4.2～8.7%. The purities of the compounds was more than99.0%, and their structures were confirmed by a variety of spectral methods, including nuclear magnetic resonance (1H NMR and13C NMR), infrared spectrometry (IR), mass spectra (MS). The phase transition temperatures and the textures of the mesophase of the final products were measured by differential scanning calorimeter (DSC) and polarizing optical microscopy (POM). Additionally, the effects of terminal group on the mesomorphic properties were discussed.The main contents are as follows:(1) Three kinds of alkoxy-based liquid crystals with2,3-difluoro-1,4-phenylene moiety,trans-cyclohexane and ethylene linking group were synthesized. The conditions of iodination reaction were optimized. These compounds exhibited relatively low melting point (56.8℃), high clearing point (148.7℃) and broad nematic phase (87.4℃) as well as smectic phase. An increasing length of alkoxy chain can improve the clearing point; the increasing length of alkyl chain can reduce the melting point, but lead to the formation of smectic phase; the introduction of ethylene linking group can reduce the melting point.(2) Two kinds of three-ring type fluoro-biphenyl liquid crystals with trans-cyclohexane, ethylene linking group and allyloxy were synthesized. Successfully transformed2-(3-fluorinated phenyl)-1-(ci-4-propyl cyclohexyl) ethyl ketone to 2-(3-fluorinated phenyI)-1-(anti-4-propyl cyclohexyl) ethyl ketone, and its transformation mechanism was discussed. These compounds exhibited low melting point (42.7℃) and wide nematic phase (75.7℃). The introduction of the third fluorine can further reduce the melting point; an introduction of the allyloxy could help to decrease the melting point and broaden the nematic phase meanwhile leading to the formation of smectic phase.(3) Two kinds of ester-based bifluoro-biphenyl liquid crystals with trans-cyclohexane and ethylene linking group were synthesized. The conditions of the esterification reaction were optimized. These compounds exhibited high clearing point (162.5℃) and wide nematic phase (82.6℃). Terminal olefins can reduce the melting point (about3.7℃) and improve the clearing point (about24.8℃), broaden the nematic phase interval (from54.1℃to82.6℃).By comparing of series3with series1and series2compounds, we can find that the introduction of ester group can increase the clearing points, and help to eliminate smectic phase.In brief, these series of compounds exhibited lower melting point (the lowest is42.7℃), wider phase transition range (the widest is87.4℃) and have potential for use in the vertical alignment (VA) and in plan switch (IPS) display mode.