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Deschenaux, Robert

Nom
Deschenaux, Robert
Affiliation principale
Fonction
Professeur.e ordinaire
Email
Robert.Deschenaux@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/384
_
0000-0002-1142-0022

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  • Publication
    Accès libre
    Design, Synthesis, and Self-Assembly Behavior of Liquid-Crystalline Bis-[60]Fullerodendrimers
    (2016)
    Russo, Virginie
    ;
    Pieper, Pauline
    ;
    Heinrich, Benoît
    ;
    Donnio, Bertrand
    ;
    Deschenaux, Robert 
    Bis-[60]fullerodendrimers were synthesized by assembling [60]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-[60]fullerodendrimers and their [60]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.
  • Publication
    Accès libre
    Olefin Cross-Metathesis: a Versatile Synthetic Reaction for the Design of Janus Liquid Crystals
    (2015)
    Trinh, Thi Minh Nguyet
    ;
    Nguyen, Thanh Tung
    ;
    Kopp, Cyril
    ;
    Pieper, Pauline
    ;
    Russo, Virginie
    ;
    Heinrich, Benoît
    ;
    Donnio, Bertrand
    ;
    Nguyen, Thi Le Anh
    ;
    Deschenaux, Robert 
    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
    Designing Supramolecular Liquid-Crystalline Hybrids from Pyrenyl-Containing Dendrimers and Arene Ruthenium Metallacycles
    (2014)
    Pitto-Barry, Anaïs
    ;
    Barry, Nicolas P. E
    ;
    Russo, Virginie
    ;
    Heinrich, Benoît
    ;
    Donnio, Bertrand
    ;
    Therrien, Bruno 
    ;
    Deschenaux, Robert 
    The association of the arene ruthenium metallacycle [Ru4(p- cymene)4(bpe)2(donq)2][DOS]4 (bpe = 1,2- bis(4-pyridyl)ethylene, donq = 5,8-dioxydo-1,4-naphtoquinonato, DOS = dodecyl sulfate) with pyrenyl-functionalized poly(arylester) dendrimers bearing cyanobiphenyl end- groups is reported. The supramolecular dendritic systems display mesomorphic properties as revealed by polarized optical microscopy, differential scanning calorimetry and small- angle X-ray scattering measurements. The multicomponent nature of the dendrimers and of the corresponding host–guest supramolecules (i.e., end-group mesogens, dendritic core, pyrene unit, aliphatic spacers, and metallacycle) leads to the formation of highly segregated mesophases with a complex multilayered structure due to the tendency of the various constitutive building-blocks to separate in different organized zones. The pyrenyl dendrimers exhibit a multilayered smectic A-like phase, thereafter referred to as LamSmA phase to emphasize this unaccustomed morphology. As for the corresponding Ru4–metallacycle adducts, they self-organize into a multicontinuous thermotropic cubic phase with the Im3¯m space group symmetry. This represents a unique example of liquid- crystalline behavior observed for such large and complex supramolecular host–guest assemblies. Models of their supramolecular organizations within both mesophases are proposed.
  • 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 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
    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
    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
    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
    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.