Liquid-crystalline cholesterol-based [60]fullerene hexaadducts

Two novel cholesterol-based [60]fullerene hexaadducts I and 2 bearing respectively 12 and 10 mesogenic cholesterol moieties were prepared following Hirsch's methodology. Both hexaadducts I and 2 showed a smectic A phase from slightly above room temperature up to 165 degrees C for 1 and 180 degrees C for 2, whereas the malonate mesogenic promoter 5 displayed two monotropic unidentified phases at 41 degrees C and 67 degrees C and a chiral nematic phase between 67 degrees C and 88 degrees C. An increase of the mesophase stability of about 100 degrees C as well as a near room temperature mesomorphism was thus obtained through C-60-grafting. The design consisting of the polyaddition of cholesterol moieties on the carbon truncated icosahedron used as a spherical template to create new 3D architectures, appears then to be a method of choice to obtain stable anisotropic materials and to prevent the C-60 aggregation tendency. As deduced by X-ray diffraction studies, and supported by molecular modelling calculations, the two supermolecules 1 and 2 self-organize into bi-layer structures which consist of a median C-60-rich slab, sandwiched between cholesteryl-containing outer layers.