The effect of lateral fluorination on the properties of phenyl-tolane liquid crystals

Multifluorinated phenyl-tolane liquid crystals were synthesised by two steps cross-coupling reactions, and their structures were confirmed by nuclear magnetic resonance (NMR), mass spectra (MS) and infrared spectrometry (IR). All of these compounds show only nematic phase, and their melting points decrease dramatically with the introduction of lateral fluorine atom. The physical properties of the compounds were also evaluated. The extrapolated birefringence of the compounds are at the range of 0.32–0.37 at 589 nm, and the dielectric anisotropies exist between 3.1 and 20.6, and the rotational viscosities are as low as 63.7–130.7 mPa·s. With the increase of lateral fluorine substituents in the benzene ring, the Δε value increases tremendously while the clearing points, birefringence and rotational viscosity decrease. These compounds show good solubilities and are favourable to form eutectic mixtures. The effect of lateral fluorine atoms at different region of the core on the dielectric anisotropy and mesophase is also discussed.