Synthesis and physical properties of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran moiety

Four series of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran (THP) moiety have been synthesised via multistep reactions based on 4-alkylcyclohexanecarboxylic acids and 4-bromo-2,3-difluorophenol. Their properties were measured by differential scanning calorimetry, polarising optical microscopy, Abbe refractometer and an electrical constants instrument. The results show that the THP-based liquid crystals nT reveal a relatively high value of the birefringence, negative dielectric anisotropy, good solubility and a broad nematic mesophase. The effects of the terminal alkyl chain, the lateral fluoro substituents and the THP terminal group on the mesomorphic and physical properties are discussed. Meanwhile, density functional theory calculations of molecular conformation and polarisability were conducted to correlate the experimental findings.