Synthesis and mesomorphic properties of 4,4”-dialkynyl-2’,3’-difluoro-p-terphenyls – the influence of C≡C acetylene linking bridge

Abstract

ABSTRACTDielectrically negative liquid crystals (LC) based on the terphenyl molecular core are widely used class of rod-like mesogenes. One of the most important parameters from applications point of view is optical anisotropy at nematic phase. Hence some applications require high values of birefringence (optical anisotropy in the case of nematic medium), which can be ensured by mesomorphic molecules having high anisotropy of electronic polarisabilities Δα. The molecular design of presented terphenyls is based on the idea of elongation of conjugated π electronic system by terminal acetylene bridge (C ≡ C), as a linking element to terminal alkyl chains. In this work, we developed synthesis of 4,4’’-dialkynyl-2’,3’-difluoroterphenyls with different length of terminal alkyl chains. All synthesised compounds have wide nematic phase ranges. Synthetic problems of this work will be presented. The purity and structures of the final products and intermediates were confirmed by spectral methods: gas chromatography GC-MS, GC-FID, IR spectroscopy and nuclear magnetic resonance NMR. The phase transition temperatures, phase situation and enthalpy data were determined by polarising optical microscopy (POM) and differential scanning calorimetry.