Abstract:

Sixteen liquid crystals with 3,3,3-trifluoropropynyl terminal group were reported. The target compounds were synthesized via a series of reactions including the zinc reagent's reaction, Suzuki cross-coupling, and the elimination reaction of HCl. The total yields are more than 67%, and the gas chromatograph(GC) purities are more than 99.5%. The structures of the target compounds were characterized by infrared spectroscopy(IR), nuclear magnetic resonance(NMR) and mass spectrometry(MS). Moreover, their thermal properties were investigated by differential scanning calorimetry(DSC) and polarizing microscope(POM). The results show that the biphenyl type of compounds exists no liquid crystal phase while the terphenyl compounds have a smectic A phase. The melting points drop with the increase in the number of alkyl chain carbon. In terms of physical properties, these compounds have large Δε value(12.61~21.94), and the value of Δε is increased by trifluoromethyl and lateral fluorine substitution. The Δn value is about 0.19~0.29 with the increase of the number of benzene rings. The γ₁ value is in the range from 49.9 to 468.0 mPa·s, which goes up with the increase of the number of benzene rings. Compounds 4n have high Δε(>19.2), high ε_⊥(>10.3), and low Δε/ε_⊥(<2). The influence of the position of the acetylenic bond on the properties of this kind of liquid crystal was discussed by simulation. All of the above properties of these liquid crystals have been proved to be useful for tuning the birefringence and the dielectric anisotropy of the liquid crystal mixtures, and these liquid crystals also have good value for FFS(fringe-field switching) display mode by the improvement of molecular structure.

Key words: liquid crystal, liquid crystal mode of fringe-field switching, trifluoropropynyl, dielectric anisotropy, birefringence, rotational viscosity