Liquid-Crystalline Bisadducts of [60]Fullerene

Abstract

A second-generation cyanobiphenyl-based dendrimer was used as a liquid-crystalline promoter to synthesize mesomorphic bisadducts of [60]fullerene. Liquid-crystalline trans-2, trans-3, and equatorial bisadducts were obtained by condensation of the liquid-crystalline promoter, which carries a carboxylic acid function, with the corresponding bisaminofullerene derivatives. A monoadduct of fullerene was also prepared for comparative purposes. All the compounds gave rise to smectic A phases. An additional mesophase, which could not be identified, was observed for the trans-2 derivative. The supramolecular organization of the monoadduct derivative is governed by steric constraints. Indeed, for efficient space filling, adequacy between the cross-sectional areas of fullerene (∼100 Å 2 ) and of the mesogenic groups (∼22-25 Å 2 per mesogenic group) is required. As a consequence, the monoadduct forms a bilayered smectic A phase. The supramolecular organization of the bisadducts is essentially governed by the nature and structure of the mesogenic groups and dendritic core. Therefore, the bisadducts form monolayered smectic A phases. The title compounds are promising supramolecular materials as they combine the self-organizing behavior of liquid crystals with the properties of fullerene.

Fullerene‐Containing Liquid Crystals

“…Fullerene-ferrocene derivative 3 was later designed to elaborate multifunctional liquid-crystalline materials by associating an electron acceptor unit (C 60 ) and electron donor units (ferrocene). Both 3 (Cr → 66 → SmA → 118 → I) and its precursor 4 (Cr → 73 → SmA → 134 → I) gave rise to smectic A phases.…”

“…This result should be related, at least in part, to the respective arrangement of the mesogenic moieties and the C 60 unit, and also to the intermolecular interactions such arrangements generate. Second, as a consequence of its bulkiness, C 60 decreases the stability of the liquid-crystalline phases of their precursors.…”

“…Such ingenious approach allowed exploring the relationship between molecular structure, intermolecular interactions, and macroscopic organization in relation to chirality transfer. The novelty of this study was to take advantage of the asymmetric carbon atom created during the 1,3-dipolar cycloaddition reaction on C 60 to induce macroscopic chirality in the materials. Either diastereoisomers (R,S)-7, (R,R)-7, (S,R)-7, and (S,S)-7 or enantiomers (R)-8, (S)-8, they all displayed an N * phase (Table 6.1).…”

“…However, the development of functional devices very often requires dedicated engineering of the molecules, that is, functionalization of the molecules for controlling their self-organization. This requires that some shape anisotropy should be imparted to C 60 , which is perfectly spherical. There are two main approaches to design fullerene-containing liquid crystals either based on covalent and noncovalent modifications.…”

“…There are two main approaches to design fullerene-containing liquid crystals either based on covalent and noncovalent modifications. Two examples of the noncovalent approach involve the formation of inclusion complexes in which C 60 either resides within cavities of host molecules. Within the covalent approach, a number of different mesogenic units have been introduced to yield a variety of fullerene-containing thermotropic liquid-crystalline materials.…”