Synthesis and properties of some novel fluoro-substituted liquid crystals that contain phenyl and cyclohexyl rings linked by ethynyl units

Seven homologous series of some novel fluoro-substituted liquid crystals that contain phenyl and cyclohexyl or bicyclohexyl rings linked by ethynyl units were prepared and characterized. Textural observations by polarizing microscopy and DSC measurements of the phase transitions show that most of these compounds are thermotropic liquid crystals with a nematic phase or nematic, smectic A and smectic B phases; series A, C′ and D′ exhibit only a wide temperature range (>90°C) nematic phase. The mesomorphic phase stabilities of the four series A′, B′, C′ and D′ are higher than their thermal stabilities. For these compounds, no clearing points were observed before decomposition. The dielectric anisotropy (Δϵ) and birefringence (Δn) of some target compounds were determined. These compounds exhibit moderate Δϵ and large Δn.