Synthesis of cholesterol containing unsymmetrical dimers: a new series of liquid crystals

Abstract

We report an efficient and practical procedure for the synthesis of cholesterol containing unsymmetrical liquid crystals dimers. Liquid crystalline and thermal properties were studied by POM, TGA, DSC, and SAXS analysis. All final products (3a-d) presented liquid crystal properties. The presence of smectic (compounds 3a, 3b, and 3d) and chiral nematic (3 c) mesophases evidenced by polarised optical microscopy (POM) and further confirmed by small-angle X-ray scattering (SAXS) analyses. The compound 3 c remains supercooled until room temperature and presented enantiotropic mesomorphism at a low temperature. This characteristic of organisation and mesomorphism at room temperature makes compound 3 c an ideal candidate for technological applications. The SAXS analyses further suggest possibly the presence of smectic clusters within the nematic liquid crystalline phase. All compounds presented high thermal stability at around 300°C when tested for their thermal properties. The highest occupied molecular orbital (HOMO) energies were estimated from cyclic voltammetry (CV) and used together with the optical absorption measurements to determine the band gap and lowest unoccupied molecular orbital (LUMO) energies. The values obtained were: HOMO (–5.81 to – 6.03 eV), LUMO (–1.53 to – 2.12 eV), and band gap (3.88 to 4.28 eV).