Diastereoisomerically Pure Fulleropyrrolidines as Chiral Platforms for the Design of Optically Active Liquid Crystals

Incorporation of [60]fullerene (C60) within self-organizing systems is conceptually challenging but allows us to obtain materials which combine the characteristics (anisotropy, organization) of condensed mesophases with the properties of C60 (photo- and electrochem. activity). Here, the authors report on the synthesis, characterization, and liq.-cryst. properties of four optically active fullerodendrimers, which are chiral at the point of conjunction between the fullerene scaffold and the mesogenic moieties. Thus, the novelty of this study is to take advantage of the asym. carbon atom created during the 1,3-dipolar cycloaddn. reaction on C60 in order to induce mesoscopic chirality in the materials. Four diastereoisomeric fulleropyrrolidines ((R,S)-1, (R,R)-1, (S,R)-1, and (S,S)-1) were synthesized and assocd. with a second-generation nematic (N) dendron to give fullerodendrimers ((R,S)-2, (R,R)-2, (S,R)-2, and (S,S)-2) which display chiral nematic (N*) phases. The abs. configurations of the stereogenic centers were detd. by X-ray crystallog., 1D and 2D NMR expts., and CD spectroscopy. The liq.-cryst. properties of the fullerodendrimers were studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The fulleropyrrolidine derivs. 2 exhibit supramol. helicoidal organizations with a right-handed helix for the (R,S)-2 and (R,R)-2 diastereoisomers and a left-handed helix for the (S,R)-2 and (S,S)-2 diastereoisomers. This result suggests that the self-organization of such supermol. materials can be controlled at the mol. level by the introduction of only one chiral center. [on SciFinder(R)]