The effect of a single atom in the terminal position of a fluorocarbon chain on liquid crystalline properties

Eight series of chiral compounds with semi-fluorocarbon chains have been synthesized. The compounds were characterized by IR, ¹H NMR, ¹⁹F NMR and mass spectroscopies and elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry and polarizing optical microscopy. Their clearing points increase with an increase of the length of fluorocarbon chain. For a certain compound, when the terminal hydrogen atom in the semi-fluoroalkyl chain was substituted by a chlorine atom, both the clearing point and melting point were increased, and the thermal stability of the chiral smectic C (SmC*) phase was enhanced. However, the clearing point decreased and the melting point increased with the introduction of a triple bond into the core.