Synthesis and mesomorphic properties of a novel series of cholesterol-based liquid crystalline tetramers

A new series of symmetric liquid crystal tetramers involving cholesteryl-based mesogenic units and Schiff's base moiety were designed and synthesised. The target compounds were obtained by the reaction of 4-(-cholesteryloxycarbonylalkonoyloxy) benzaldehyde with compound 1,4-bis (aminophenyl-1-oxy) butane. The length of the outer two spacers is varied from 2 to 8 even-numbered methylene units, while the central spacer is held at 4 methylene units. The molecular structures of the intermediates and target compounds were confirmed by Fourier transform infrared and proton nuclear magnetic resonance spectroscopy. The thermal phase behaviour of the synthesised tetramers were investigated by polarising optical microscopy coupled with hot stage and differential scanning calorimetry. All of these liquid crystal tetramers showed only one chiral nematic mesophase on a very large temperature domain (100 degrees C), and the clearing temperature above 250 degrees C.