Vignette d'image

Deschenaux, Robert

Nom
Deschenaux, Robert
Affiliation principale
Fonction
Professeur ordinaire
Email
Robert.Deschenaux@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/384

Résultat de la recherche

Filtres

14
14
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 10 sur 14
  • Publication
    Accès libre
    Aromatic Bent-Core Liquid Crystals:  an Opportunity for Introducing Terdentate Binding Units into Mesophases
    (2012)
    Nozary, Homayoun
    ;
    Piguet, Claude
    ;
    Rivera, Jean-Pierre
    ;
    Tissot, Paul
    ;
    Morgantini, Pierre-Yves
    ;
    Weber, Jacques
    ;
    Bernardinelli, Gérald
    ;
    Bünzli, Jean-Claude G.
    ;
    Deschenaux, Robert 
    ;
    Donnio, Bertrand
    ;
    Guillon, Daniel
    Lipophilic linear semirigid side arms containing two or three successive phenyl rings separated by carboxylate spacers have been connected to the 5 or 6 positions of bent aromatic terdentate 2,6-bis(benzimidazol-2-yl)pyridine binding units to give extended V-shaped (L11) and I-shaped receptors (L12, L12b, and L13). The carboxylate spacers limit the flexibility of the side arms and provide crossed arrangements of the successive aromatic rings in the crystal structure of L12b (C63H61N5O10; triclinic, P1̄, Z = 2) in agreement with semiempirical calculations performed on optimized gas-phase geometries. Moreover, the carboxylate spacers in L11−L13 prevent efficient electronic delocalization between the connected aromatic rings and act as weak π acceptors producing a slight increase of the energy of the 1ππ* and 3ππ* levels centered on the terdentate binding unit. Intermolecular π-stacking interactions observed in the crystal of L12b are invoked to rationalize (i) the peculiar excimer emission of L11 in the solid state and (ii) the rich and varied calamitic (I-shaped L12, L12b, and L13) and columnar (V-shaped L11) mesomorphism observed at high temperature. The ColR mesophase detected for L11 demonstrates that V-shaped bent terdentate binding units are compatible with liquid-crystalline behavior. Complexation of L11 with lanthanide(III) produces I-shaped complexes [Ln(L11)(NO3)3] (Ln = La, Eu, Gd, Tb, and Lu) possessing a large axial anisometry as found in the crystal structure of [Lu(L11)(CF3CO2)3(H2O)] (LuC81H87N5O17F9; triclinic, P1̄, Z = 2), which exists in the solid state as H-bonded dimers. No mesomorphism is detected for the complexes as a result of the large perpendicular expansion brought by the metallic coordination site, but the high energy of the ligand-centered 3ππ* prevents Eu(5D0) → L11 back transfer in the Eu(III) complex, which thus exhibits sizable red luminescence at room temperature, a crucial point for the design of luminescent materials.
  • Publication
    Accès libre
    Liquid-crystalline methanofullerodendrimers which display columnar mesomorphism
    (2008)
    Maringa, Natacha
    ;
    Lenoble, Julie
    ;
    Donnio, Bertrand
    ;
    Guillon, Daniel
    ;
    Deschenaux, Robert 
    Liquid-crystalline methanofullerodendrimers were synthesized via the Bingel addition reaction of mesomorphic malonate derivatives and C60. Second- and third-generation poly(benzyl ether) dendrons were selected as liquid-crystalline promoters to induce columnar mesomorphism. Based on a convergent and modular synthetic methodology, symmetrical (two identical dendrons) and non-symmetrical (two different dendrons) dendrimers were prepared, as well as hemidendrimers (only one dendron). The liquid-crystalline properties of the malonates and fullerodendrimers were investigated by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. All the malonates give rise to hexagonal columnar phases of p6mm symmetry. As for the fullerodendrimers, the second-generation hemidendrimer shows a rectangular columnar phase of c2mm symmetry, while the other materials give rise to hexagonal columnar phases of p6mm symmetry.
  • Publication
    Accès libre
    Liquid-crystalline fullerodendrimers
    (2007)
    Deschenaux, Robert 
    ;
    Donnio, Bertrand
    ;
    Guillon, Daniel
    Addition of liquid-crystalline dendrimers onto [60]fullerene led to thermotropic liquid crystals which displayed various types of mesophases, including chiral nematic, smectic B, smectic A and columnar phases. This approach represents an interesting way for the design of self-organized structures based on [60]fullerene, and opens the way to optoelectronic applications for this carbon allotrope, such as for the development of photovoltaic devices and molecular switches.
  • Publication
    Accès libre
    Liquid−Crystalline Janus-Type Fullerodendrimers Displaying Tunable Smectic−Columnar Mesomorphism
    (2007)
    Lenoble, Julie
    ;
    Campidelli, Stéphane
    ;
    Maringa, Natacha
    ;
    Donnio, Bertrand
    ;
    Guillon, Daniel
    ;
    Yevlampieva, Natalia
    ;
    Deschenaux, Robert 
    Janus-type liquid−crystalline fullerodendrimers were synthesized via the 1,3-dipolar cycloaddtition of two mesomorphic dendrons and C60. By assembling poly(aryl ester) dendrons functionalized with cyanobiphenyl groups, displaying lamellar mesomorphism, with poly(benzyl ether) dendrons carrying alkyl chains, which display columnar mesomorphism, we could tailor by design the liquid−crystalline properties of the title compounds as a function of each dendron size. The liquid−crystalline properties were examined by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Depending on the dendrimer generations, smectic (SmC and/or SmA phases) or columnar (Colr-c2mm or Colr-p2gg phases) mesomorphism was obtained. The supramolecular organization is governed by (1) the adequacy of the cross-sectional area of the dendrons, (2) the microsegregation of the dendrimer, (3) the deformation of the dendritic core, and (4) the dipolar interactions between the cyanobiphenyl groups. Comparison of the mesomorphic properties of two fullerodendrimers with those of model compounds (fullerene-free analogues) indicated that the C60 unit does not influence the type of mesophase that is formed. Molecular properties determined in solution (permanent dipole moment, specific dielectric polarization, molar Kerr constant) confirm that microsegregation persists in solution and strengthen the models proposed for the structure of the mesophases.
  • Publication
    Accès libre
    Encoding calamitic mesomorphism in thermotropic lanthanidomesogens
    (2006)
    Terazzi, Emmanuel
    ;
    Bocquet, Bernard
    ;
    Campidelli, Stéphane
    ;
    Donnio, Bertrand
    ;
    Guillon, Daniel
    ;
    Deschenaux, Robert 
    ;
    Piguet, Claude
    Peripheral cyanobiphenyl dendrimers impose a microphase organization compatible with smectic mesomorphism, in which the bulky nine-coordinate lanthanide core is located between the decoupled mesogenic sublayers made up of parallel cyanobiphenyl groups.
  • 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
    ;
    Deschenaux, Robert 
    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
    Mesomorphic Hexabenzocoronenes Bearing Perfluorinated Chains
    (2005)
    Alameddine, Bassam
    ;
    Aebischer, Olivier F.
    ;
    Amrein, Walter
    ;
    Donnio, Bertrand
    ;
    Deschenaux, Robert 
    ;
    Guillon, Daniel
    ;
    Savary, Corinne
    ;
    Scanu, David
    ;
    Scheidegger, Oliver
    ;
    Titus A. , Jenny
    Synthesis and characterization of new hexabenzocoronene (HBC) derivatives bearing perfluoroalkylated chains are described. These disc-shaped polycondensed aromatic hydrocarbons are known to self-assemble by π-stacking into columnar architectures. The peripheral decoration with perfluorinated chains, well-known for their low van der Waals forces, leads as expected to reduced intercolumnar interactions. Powder X-ray diffraction and differential scanning calorimetry of these perfluoroalkylated HBCs proved liquid crystalline (LC) properties whose transition temperatures, mesophase stability, and nature depend on the detailed structure of these side chains, i.e., the ratio between aliphatic and perfluorinated parts. On the other hand, the insertion of a phenyl spacer between the aromatic core and the lateral chains increases the LC transition temperature and, surprisingly, switches the mesophase structure from columnar to smectic.
  • Publication
    Accès libre
    Liquid-Crystalline [60]Fullerene-TTF Dyads
    (2005)
    Allard, Emmanuel
    ;
    Oswald, Frédéric
    ;
    Donnio, Bertrand
    ;
    Guillon, Daniel
    ;
    Delgado, Juan Luis
    ;
    Langa, Fernando
    ;
    Deschenaux, Robert 
    [60]Fullerene was functionalized with a TTF derivative and a bis-mesogenic fragment. The synthetic methodology was based on the addition of a malonate derivative to C60 (Bingel-type reaction). Both the malonate and dyad showed smectic B and A phases. The supramolecular organization within the smectic layers was of the monolayer type for the malonate and of the bilayer type for the fullerene derivative. In the latter case, the supramolecular organization was governed by the C60 unit.
  • Publication
    Accès libre
    Hexacatenar liquid-crystalline complexes of palladium(II) and platinum(II) based on trialkoxystilbazole esters
    (2002)
    Plasseraud, Laurent
    ;
    Gonzalez Cuervo, Laura
    ;
    Guillon, Daniel
    ;
    Süss-Fink, Georg 
    ;
    Deschenaux, Robert 
    ;
    Bruce, Duncan W.
    ;
    Donnio, Bertrand
    The synthesis and characterisation of 4-(3,4,5-trialkoxybenzoyloxy)pyridines (1a–e), and of their corresponding palladium(II), (2a–e), and platinum(II), (3a–e), complexes are described. The pyridine-based ligands are not mesomorphic, but upon complexation to PdCl2 or PtCl2, new hexacatenar mesogens are formed which show exclusively the hexagonal columnar mesophase. The mesomorphic behaviour of the complexes was characterised by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. The metal seems to influence the crystal phase and mesophase stability as well as the mesomorphic temperature range.
  • Publication
    Accès libre
    A Ferrocene-Containing Carbohydrate Surfactant:  Thermotropic and Lyotropic Phase Behavior
    (2000)
    Donnio, Bertrand
    ;
    Seddon, John M.
    ;
    Deschenaux, Robert 
    A ferrocene-containing carbohydrate surfactant has been synthesized and shown by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction to exhibit both thermotropic and lyotropic liquid-crystalline phase behavior. This new class of materials should prove useful for the design of redox-active lyotropic liquid crystals, allowing fine electrochemical control of the phase structure and symmetry.