Synthesis and mesomorphic properties of semi-perfluorinated chain liquid crystals

Three homologous series of 4-(n-polyfluoroalkoxycarbonyl)phenyl 4-[(4-n-alk oxyphenyl)ethynyl]benzoates have been synthesized from 1,1,3-trihydroperflu oropropanol, 1,1,5-trihydro-perfluoropentanol and 1,1,7-trihydroperfluorohe ptanol. Polarizing microscopic textural observations and DSC measurements o f the phase transitions of these compounds show that most of them are therm otropic liquid crystals with smectic A and very broad smectic C phases; fur thermore, several show very narrow monotropic SmB phases. The effect of the terminal polyfluoroalkoxy and alkoxy groups on the mesomorphic behaviour i s also discussed.