Synthesis and microwave properties of fluorinated terphenyl isothiocyanate liquid crystals

In recent years, the research of liquid crystal in microwave communication devices has developed rapidly, and the dielectric loss of liquid crystal materials has become the main factor restricting its development. The isothiocyanate terphenyl compound is a low-viscosity, high-birefringence liquid crystal compound with stable structure, which is suitable as a component of liquid crystal material for microwave. In this paper, four fluorine-containing terphenyl isothiocyanate liquid crystal compounds nPGUS (n=2 similar to 5) were synthesized by coupling method, and the structure of the compounds was confirmed to be correct by IR, H-1 NMR, C-13 NMR, and F-19 NMR. Differential thermal analysis (DSC) results show that they all have a wide-temperature nematic liquid crystal state and a relatively low melting point. The nematic temperature range of 5PGUS reaches 101.8 degrees C, and the melting point is only 57.4 degrees C. Their dielectric properties of LC in the microwave K bands were tested by the vector network analyzer, and they are mixed with the matrix liquid crystal, the dielectric constant value at 18 GHz (Delta epsilon(r)) is 0.95, the dielectric loss (tan delta epsilon(r-max)) 0.007 63, dieletric tunability coefficient (tau) 0.265, which can satisfy the performance requirements of nematic liquid crystal materials for microwave use.