| Since its inception,LCD has experienced three times:TN,STN and TFT.As a new type of display,FFS liquid crystal display has the characteristics of high transmittance and low power consumption compared with traditional TFT display,and can be widely used in various sizes of displays.Benzofuran and benzopyran derivatives,as typical representatives of a class of oxygen-containing heterocyclic compounds,are widely used in various fields such as medicine.The structure of these compounds is stable.The introduction of benzofuran or benzopyran unit in the structure design of conventional liquid crystal compounds can reduce the melting point and clear point of liquid crystal monomer.Its low-temperature miscibility is good,which can provide a wide range of operating environment temperature.The performance of liquid crystal materials can be significantly improved by using them in the mixed crystal formula.In this paper,a kind of liquid crystal intermediate based on fluorobenzofuran and fluorobenzopyran was designed and synthesized.The main contents are as follows:1)Using 2-fluoro-4-bromophenol as starting material,target benzofuran liquid crystal intermediates were synthesized by iodization and Sonogashira coupling reaction.In this process,the influencing factors on the Sonogashira reaction were studied,and the optimal reaction conditions were obtained:In triethylamine and THF mixed solvent,Pd（PPh3）4with 1‰eq and Cu I with 5‰eq as cocatalyst.The reaction was reacted at 40℃for 4h.TLC was used to track the reaction until the reaction was complete.The total yield was 77.5%and the purity of GC was 97.7%.The liquid crystal compound synthesized from the benzofuran liquid crystal intermediate has the expected low melting point,high resistivity and transmittance,and the dielectric anisotropyΔεis positive and between3.5 and 4.5.2)Starting from 2,3,4-trifluorobromobenzene,the target benzopyran liquid crystal intermediate was synthesized by Sonogashira coupling,hydrogenation and Williamson etherification.In this process,the influencing factors of Williamson etherification reaction were studied,and the optimal reaction conditions were obtained:in DMF solvent,potassium tert butyl alcohol was used as the base source and acid binding agent of the system,and samples were taken at 80～90℃for 7h.TLC was used to track the reaction until the reaction was complete.The total yield of the product obtained by vacuum distillation was 79.2%,and the purity of GC was 96.6%.The target compounds were obtained through the study of their properties.The dielectric anisotropyΔεof the three liquid crystal compounds were negative and ranged from-8 to-11.Finally,the above two kinds of liquid crystal compounds can be used in the mixed crystal formula of new FFS liquid crystal display materials. |
