Chiral hexacatenar metallomesogens: supramolecular organization versus steric demand of chiral cores

Abstract

Hexacatenar chiral oxazoline complexes were prepared in a stereospecific synthesis. Metals (Pd, Ni, Cu, Zn), lateral alkoxy chains (OC6H13, OC12H25), sterically demanding alkyl groups (CH3, C4H9) on the chiral rigid centre and the number of nuclei incorporated in the complex core (mononuclear, orthopalladated dinuclear) were varied in order to achieve supramolecular organization of the phasmid-like molecules in liquid crystal phases. Mesomorphic properties were not observed in neat materials, but phase diagrams of binary mixtures with TNF demonstrate that steric repulsion can be overcome by intercalation of the electron-acceptor TNF. In spite of the presence of six lateral chains, SmA phases were found exclusively. The structures of the SmA phases were found to have additional order with respect to SmA phases formed by calamitic molecules. Further examination of the complexes in host nematic materials demonstrated their use as chiral dopants to induce cholesteric LC phases.