Voici les éléments 1 - 10 sur 157
- PublicationAccès libreBuilding liquid crystals from the 5-fold symmetrical pillararene coreComparison of the liquid-crystalline properties of a pillararene core functionalized with 10 mesogenic cyanobiphenyl units with those of a corresponding model compound revealed the strong influence of the macrocyclic pillararene core on the mesomorphic properties.
- PublicationAccès libreFerrocene-Containing Optically Active Liquid-Crystalline Side-Chain Polysiloxanes with Planar Chirality(2005)
;Brettar, Julie ;Bürgi, Thomas ;Donnio, Bertrand ;Guillon, Daniel ;Klappert, Rolf ;Scharf, ToralOptically 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.
- PublicationAccès libreLiquid-crystalline mixed fullerene–ferrocene materials(1998)
; ;Even, MichaelGuillon, DanielFullerene was functionalized with a mesomorphic malonate derivative containing two ferrocene units; the targeted compound showed thermotropic liquid-crystalline properties.
- PublicationAccès libreDesign, Synthesis, and Self-Assembly Behavior of Liquid-Crystalline Bis-Fullerodendrimers
;Russo, Virginie ;Pieper, Pauline ;Heinrich, Benoît ;Donnio, BertrandBis-fullerodendrimers were synthesized by assembling fullerene-containing type I (terminal olefin) and type II (a,ß-unsaturated carbonyl olefin) olefins through the olefin cross-metathesis reaction. The synthetic modular approach developed in this study allowed the preparation of mono-fullerodendrimers and their fullerene-free analogues. First- and second-generation poly(aryl ester) dendrons carrying cyanobiphenyl mesogens were used as liquid-crystalline promoters. The liquid- crystalline properties were studied by polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. In agreement with the nature and structure of the dendrimers, nematic, smectic, and multisegregated lamellar phases were observed. Owing to its versatility and tolerance towards many functional groups, olefin cross-metathesis proved to be a reaction of choice for the elaboration of molecular materials with complex architectures.
- PublicationAccès libreSupramolecular Metallomesogens: Hydrogen-Bonded Ferrocene-Containing Liquid Crystals Which Display Bicontinuous Cubic Phases(2005)
;Massiot, Philippe ;Impéror-Clerc, Marianne ;Veber, MichèleTwo series of hydrogen-bonded liquid-crystalline ferrocenes have been prepared by reacting ferrocene derivatives carrying a carboxylic acid function and two flexible alkyl chains (containing n = 8, 10, or 12 carbon atoms) with stilbazoles bearing a flexible alkyl chain (containing m = 6 or 10 carbon atoms). The first family of materials (m = 6; n = 8, 10, 12) gave rise to smectic A/C and/or cubic (Ia3̄d space group) phases, and the second series of complexes (m = 10; n = 8, 10, 12) displayed cubic phases (Ia3̄d space group). A subtle balance between the volume occupied by the central core and the flexible chains, as well as the surface between both parts, are responsible for the formation of the mesophases. Hydrogen bonding is an elegant alternative to covalent bonding for the design of ferrocene-containing liquid crystals.
- PublicationAccès libreLiquid-Crystalline Fulleropyrrolidines, Preliminary Communication(2001)
;Campidelli, StéphaneA fulleropyrrolidine showing a smectic A phase was synthesized by 1,3-dipolar cycloaddition of a liquid-crystalline aldehyde derivative and sarcosine to C60.
- PublicationAccès libreSupramolecular Fullerene Materials: Dendritic Liquid-Crystalline Fulleropyrrolidines(2005)
;Campidelli, Stéphane ;Lenoble, Julie ;Barberá, Joaquín ;Paolucci, Francesco ;Marcaccio, Massimo ;Paolucci, DemisFullerene-containing liquid-crystalline dendrimers were synthesized from the first to the fourth generation by applying the 1,3-dipolar cycloaddition reaction from a mesomorphic dendritic-type aldehyde derivative, sarcosine (N-methylglycine) or glycine and C60. The cyanobiphenyl unit was used as a liquid-crystalline promoter. With the exception of the first-generation fullerene dendrimer, which was found to be nonmesomorphic, all fullerene-based dendrimers gave rise to a smectic A phase. The liquid-crystalline fullerenes led to two different supramolecular organizations within the smectic layers: for the second-generation dendrimers, the molecules are oriented in a head-to-tail fashion within the layers; for each molecule the cyanobiphenyl units point in the same direction. For the dendrimers of third and fourth generations, the dendritic core extends laterally, parallel to the layer planes; the mesogenic units are oriented above and below the dendritic core. For the aldehyde precursors, only one organization inside the layers was obtained, similar to the one observed for the third and fourth fullerene-based dendrimers. Cyclic voltametry investigations displayed several one-electron and multielectron reduction processes; no significant interaction in the ground state between the fullerene and the dendrimer was noticed. The title compounds showed the typical electrochemical stability of fulleropyrrolidines.
- PublicationAccès libreFerrocene-Containing Thermotropic Side-Chain Liquid-Crystalline Polymethacrylate from a Mesomorphic Trisubstituted Ferrocene Monomer(1997)
;Guillon, DanielThe synthesis and mesomorphic properties of a methacrylate-containing ferrocene monomer bearing two flexible chains at the 1,1‘-positions and the corresponding side-chain homopolymer are described. Both polymer and monomer showed enantiotropic smectic C and smectic A phases. The liquid-crystalline phases were fully characterized by means of X-ray diffraction experiments. Dilatometric measurements pointed to a head-to-tail molecular arrangement of the monomeric units within the smectic A phase. The results described in this report confirm that ferrocene-containing thermotropic side-chain liquid-crystalline polymethacrylates respresent a valuable family of metallomesogenic polymers.
- PublicationAccès libreEncapsulation of Pyrene-Functionalized Poly(benzyl ether) Dendrons into a Water-Soluble Organometallic CageTwo generations of lipophilic pyrenyl functionalized poly(benzyl ether) dendrimers (P1 and P2) have been synthesized. The thermal properties of the two functionalized dendrimers have been investigated, and the pyrenyl group of the dendritic molecules encapsulated in the arene–ruthenium metalla-cage, [Ru6(p-cymene)6(tpt)2(donq)3]6+ (6+) (tpt=2,4,6-tri(pyridin-4-yl)-1,3,5-triazine; donq=5,8-dioxydo-1,4-naphthoquinonato). The host–guest properties of [P1⊂1]6+ and [P2⊂1]6+ were studied in solution by NMR and UV/Vis spectroscopic methods, thus allowing the determination of the affinity constants. Moreover, the cytotoxicity of these water-soluble host–guest systems was evaluated on human ovarian cancer cells.
- PublicationAccès libreSynthesis and characterization of fullerene-pyridyl arene ruthenium complexesAssociation of fullerene with arene ruthenium moieties has been achieved for the first time. Two fullerenopyrrolidine derivatives (Npyr-C60) were synthesized via a 1,3-dipolar cycloaddition, and coordinated to arene ruthenium complexes to form two half-sandwich complexes of the general formula (p-cymene)RuCl2(Npyr-C60). The coordination of the fullerenopyrrolidines to the arene ruthenium unit was evidenced by NMR spectroscopy and mass spectrometry, thus confirming the formation of these novel arene ruthenium complexes.