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Deschenaux, Robert

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

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  • Publication
    Accès libre
    Fullerene-containing liquid-crystalline dendrimers
    (2001)
    Dardel, Blaise
    ;
    Guillon, Daniel
    ;
    Heinrich, Benoît
    ;
    Deschenaux, Robert 
    Addition reaction of mesomorphic malonate-based dendrimers (up to the fourth generation) with C60 gave liquid-crystalline fullerene derivatives. The cyanobiphenyl unit was used as liquid-crystalline promoter. The malonates presented nematic and/or smectic A phases. The fullerenes showed only smectic A phases, with the exception of the second generation dendrimer for which smectic A and nematic phases were observed. The supramolecular organization of the fullerene-based molecular units within the smectic A layers was investigated by X-ray diffraction. Two structural regimes were determined. For the low generation dendrimers, the supramolecular organization is determined by steric factors. For the high generation dendrimers, the mesogenic groups impose a microphase organization: due to lateral extension of the branching part of the molecule, the cyanobiphenyl groups arrange in a parallel fashion as in classical smectic A phases, the rest of the macromolecule being located between the mesogenic sublayers.
  • Publication
    Accès libre
    A Mixed Fullerene-Ferrocene Thermotropic Liquid Crystal: Synthesis, Liquid-Crystalline Properties, Supramolecular Organization and Photoinduced Electron Transfer
    (2001)
    Even, Michaël
    ;
    Heinrich, Benoît
    ;
    Guillon, Daniel
    ;
    Guldi, Dirk M.
    ;
    Prato, Maurizio
    ;
    Deschenaux, Robert 
    Grafting of a ferrocene-containing liquid-crystalline malonate derivative to C60 led to the mixed fullerene-ferrocene material 1 which gave rise to a smectic A phase. Cholesterol was used as liquid-crystalline promoter. X-ray diffraction experiments and volumetric measurements indicated that 1 is organized in double layered structures. The corresponding supramolecular organization within the mesomorphic lamellar phase is characterized by a microsegregation of the different units (ferrocene, fullerene, and cholesterol) in distinct sublayers. In such a smectic A phase, C60 imposes the arrangement of the other molecular moieties. Photophysical studies revealed that electron transfer occurs from the donor ferrocene to the electron accepting fullerene. The formation of a long-lived radical pair, with lifetimes of the order of several hundred nanoseconds, was confirmed by time-resolved spectrometry, especially in the near infrared region, in which the radical anion of the fullerene moiety displays its characteristic fingerprint absorption.
  • Publication
    Accès libre
    Ferrocene-Containing Thermotropic Side-Chain Liquid-Crystalline Polysiloxanes
    (1998)
    Deschenaux, Robert 
    ;
    Jauslin, Isabelle
    ;
    Scholten, Ulrich
    ;
    Turpin, François
    ;
    Guillon, Daniel
    ;
    Heinrich, Benoît
    The synthesis, purification, characterization, and liquid-crystalline properties of side-chain polysiloxanes bearing mesomorphic 1,1‘- or 1,3-disubstituted ferrocene units are reported. The polymers were prepared by grafting the appropriate vinyl-containing ferrocene monomer onto commercially available poly(hydrosiloxane)s following a standard procedure. The monomers gave smectic A or smectic A and smectic C phases depending on the length of the flexible chains connected to the ferrocene unit. X-ray diffraction indicated that the polysiloxanes exhibited disordered smectic phases. Variation of the d-layer spacing determined for the polymers containing either 100% or 15−18% of the 1,1‘-disubstituted ferrocene monomer (with the longest terminal alkyl chain) revealed the presence of smectic A and smectic C phases. Thermogravimetry showed a good thermal stability for the polymers.
  • Publication
    Accès libre
    Design, Synthesis, and Self-Assembly Behavior of Liquid-Crystalline Bis-[60]Fullerodendrimers
    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
    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
    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.