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  • Publication
    Accès libre
    Ferrocene-Containing Optically Active Liquid-Crystalline Side-Chain Polysiloxanes with Planar Chirality
    (2005)
    Brettar, Julie
    ;
    Bürgi, Thomas
    ;
    Donnio, Bertrand
    ;
    Guillon, Daniel
    ;
    Klappert, Rolf
    ;
    Scharf, Toral
    ;
    Optically active liquid-crystalline side-chain polysiloxanes have been prepared by grafting planar chiral ferrocene-based vinyl monomers onto commercially available polyhydrosiloxane. Two ferrocene monomers have been synthesized: a linear-type monomer, which displays a monotropic chiral smectic C (SC*) phase and enantiotropic smectic A (SA) and chiral N (N*) phases, and a laterally branched monomer, which shows an enantiotropic N* phase. X-ray diffraction analysis indicates a monomolecular organization of the monomeric units within the smectic layers. The polymers retain the liquid-crystalline phases of their corresponding monomers. The UV-vis and circular dichroism (CD) spectra are in agreement with the structure of the monomers and polymers. The molar absorption coefficient (Δε) and molar circular dichroic absorption coefficient (ε) values of the polymers are proportional to the number of monomeric units grafted onto them. The absolute configuration of the ferrocene carboxylic acid intermediate, used to synthesize the monomers, has been determined on the basis of CD spectra. The helical twisting power (HTP) of the nematogenic monomer and polymer have been determined in E7, and indicate that such materials could be used as chiral dopants. Finally, this study demonstrates that the nature of chiral phases can be controlled by structural engineering of the organic groups only, with ferrocene acting as the source of chirality.
  • Publication
    Accès libre
    Olefin Cross-Metathesis: a Versatile Synthetic Reaction for the Design of Janus Liquid Crystals
    Trinh, Thi Minh Nguyet
    ;
    Nguyen, Thanh Tung
    ;
    Kopp, Cyril
    ;
    Pieper, Pauline
    ;
    Russo, Virginie
    ;
    Heinrich, Benoît
    ;
    Donnio, Bertrand
    ;
    Nguyen, Thi Le Anh
    ;
    The olefin cross-metathesis reaction using the second-generation Grubbs catalyst was employed to prepare non-symmetrical thermotropic liquid crystals from various mesomorphic or nonmesomorphic type I and type II olefinic constructs, including linear, chiral, dendritic and ferrocenyl olefins. Smectic C, smectic A and nematic phases, as well as chiral smectic A and chiral nematic phases were observed in agreement with the structure and nature of the mesogens. The olefin cross-metathesis proved to be a valuable chemical reaction in designing dimeric and Janus-like thermotropic liquid crystals built from two different molecular entities.
  • Publication
    Accès libre
    Macrocyclic Effects in the Mesomorphic Properties of Liquid-Crystalline Pillar[5]- and Pillar[6]arenes
    Nierengarten, Iwona
    ;
    ;
    Holler, Michel
    ;
    Karmazin-Brelot, Lydia
    ;
    Barberá, Joaquín
    ;
    ;
    Nierengarten, Jean-François
    Whereas the reaction of 1,4-bis(2-bromoethyloxy)benzene (4) with paraformaldehyde in the presence of BF3·Et2O afforded exclusively the cyclopentameric pillar[5]arene derivative (5), both cyclopenta- and cyclohexameric macrocycles 5 and 6 were obtained when the reaction of 4 with paraformaldehyde was performed at 45 °C in CHCl3 with FeCl3 as the catalyst. Treatment of compounds 4–6 with sodium azide provided the corresponding polyazides, to which a cyanobiphenyl building block was subsequently grafted to generate model compound 1, pillar[5]arene 2, and pillar[6]arene 3, bearing two, ten and twelve mesomorphic subunits, respectively. The liquid-crystalline and thermal properties of the compounds were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Comparison of the liquid-crystalline properties of macrocycles 2 and 3 with those of 1 revealed the strong influence of the macrocyclic pillar[n]arene core on the mesomorphic properties. Whereas only a monotropic mesophase was observed for 1, a broad enantiotropic mesophase was evidenced for both pillar[n]arene derivatives.