Synthesis, Performance And Application Of Novel Lateral Fluorine-substituted Olefinic Liquid Crystal Compounds

Because of the excellent properties,superior picture quality,low energy consumption,portability,the AM-TFT-LCD was widely used for display.On the other hand,the increasing performances of the LCDs lead to extremely stringent demands on the liquid crystals.The fluoro substituted liquid crystals with high stability,low viscosity and high resistivity could meet the extremely stringent demands and become the essential materials,so new liquid crystals have been of great interest of chemists.To further improve the response speed of the liquid crystal display,three series of more than 20 novel laterally fluoronited liquid crystals with terminal unsaturated chains were designed and synthesized.The GC and HPLC were used to analysis the purities of the intermediates and the final products,and their structures were confirmed by a variety of spectral methods:infrared spectrometry(IR),nuclear magnetic resonance(1H NMR and 13C NMR),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).The dielectric and optical anisotropies were measured.Additionally,the applications of part compounds were preliminary investigated.Finally,the effects of terminal group and the lateral fluoro substituents on the mesomorphic properties were discussed.The main obtained results are as follows:(1):Synthesis of fluoro-terphenyl liquid crystals with n-propyl and but-3-enyl terminal chains was established,and three isomers with fluoro substituent at different sites were synthesized.The effect of fluoro substituent at different sites was discussed.A new and facile method to synthesis the intermediate of 4-bromo-4'-propyl-1,1'-biphenyl was applicated,in which the Friedel-Crafts and Bromination reaction catalysed by aluminium chloride were successfully completed in one pot.The final products were obtained in high yield.This method could be widely used to prepare 4-bromo-4'-alkyl-1,1'-biphenyl.These compounds exhibited high clearing points,large optical anisotropy and broad nematic phase.The site of fluoro substituent affected the mesophase range greatly,when it was lccated at the same benzene ring with but-3-enyl group,it was most useful to decrease the melting points and inhance the stability of the nematic phase.(2):Two kinds of three-ring type fluoro-biphenyl liquid crystals were designed and synthesized with trans-cyclohexane,ethylene linking group,alkyl and but-3-enyl terminal chains.The effect of but-3-enyl group,the sites and number of fluoro substituents on the mesomorphic properties was studied.The intermediate of 1-(cis-4-propylcyclohexyl)-2-(3-fluorophenyl)ethanone was converted to 1-(trans-4-propylcyclohexyl)-2-(3-fluorophenyl)ethanone,and the mechanic of transition reaction was discussed.The synthesis of arylboronic acid from aryl iodide was optimized with high y'ield,short reaction time and low cast.These compounds exhibited very low melting points,high clearing points,relatively large optical anisotropy and wide nematic phase.The introduction of the but-3-enyl group was helpful to increase the clearing points,decrease the melting points and inhance the stability of the mesophase,the most important is that could inhance the stability of the nematic phase,which was discussed;the introduction of the fluoro substituent could decrease the melting points,compress the smectic phase,enhance the stability of the nematic phase,and decrease the transition temperature of SmA-N;when introducing two fluoro substituents,the melting points could be further decreased,but the clearing point was decreased drastically,and the mesophase range was compressed.(3):Two kinds of allyloxy-based liquid crystals were designed and synthesized with trans-cyclohexane,2,3-difluoro-1,4-phenylene moiety,ethylene linking group,alkyl and allyloxy terminal chains.The effect of the allyloxy and fluoro substituents on the mesomorphic properties and the dielectric anisotropy was studied.A new and facile method to synthesis liquid crystals containing 2,3-difuorophenyl was established,in which the Suzuki coupling reaction was applied with excess base and the Williamson reaction was successfully completed in one pot with Suzuki coupling reaction.The final products were obtained in high yield.This method could be widely used to prepare 2,3-difluorophenyl derivatives with alkenoxy as terminal chains.These compounds exhibited negative dielectric anisotropy and broad nematic mesophases with relatively low melting points and high clearing points.The introduction of the allyl was helpful to increasing the clearing point,decreasing the melting point,enhance the stability of the mesophae,and lead to a formation of smectic phase;the introduction of the 2,3-difluoro substituents could decrease the melting points,compress the smectic phase,enlarge the range of nematic phase,decrease the transition temperature of Sm-N,but lead to a decrease in clearing point;the combined action of the oxygen in the ether chain and the fluoro substituent could inhance the negative dielectric anisotropy and clearing point;the introduction of the third fluoro substituent could further decrease the melting points,but not inhance the negative dielectric and the mechanic was discussed.(4):A nematic base liquid crystal mixture with large optical anisotropy,low melting and high clearing points,was obtained and suitable for use in many LCDs mixed with materials which have special properties.The measured and calculated values of the clearing points were compared,and the result showed those values agreed well.Preliminary studies on liquid crystal mixtures used in TN and VA display inspectively showed that TN exhibited low melting,suitable optical anisotropy,but low clearing point,which need to be improved;VA liquid crystal mixtures exhibited low melting,high clearing point,relatively fast response speed,low activation voltages and have potential for use in large screen TV-LCD.During the process of the study of liquid crystal mixtures,the results showed that compounds nC2BFB2V and nC2BBF2V showed different effect on the optical-electric properties:nC2BFB2V was helpful to increase the clearing point,and the most important is to decrease the activation voltage and improve the response speed.nC2BBF2V was helpful to decrease the melting point,increase the negative dielectric anisotropy and decrease the activation voltage.Additionally,the calculated values of the dielectric anisotropy agreed well with the measured,which was helpful to evaluate the dielectric anisotropy of new liquid crystal mixtures.