Synthesis and mesomorphic properties of fluorinated Schiff base liquid crystals

A series of fluorinated Schiff base ester liquid crystals, 4-(4-alkyl-trans-cyclohexyl)-bensoic acid 4-[(2, 3, 4-trifluorophenylimino)-methyl]-phenyl ester, were synthesized. Their chemical structures were identified by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance (¹H NMR); their mesomorphic properties were studied by polarized optical microscopy (POM) and differential scanning calorimeter (DSC). It was found that all the four compounds showed nematic and smectic properties and possessed high clearing point over 300℃. And with the increase of the length of alkyl chain, the thermal range of nemarie phase and clearing point temperatures decreased, while the smectic-nematic transition temperature and thermal range of smectic phase increased, but their melting point temperatures showed no distinct regularity.