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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
    Bent Tridentate Receptors in Calamitic Mesophases with Predetermined Photophysical Properties:  New Luminescent Lanthanide-Containing Materials
    (American Chemical Society (ACS), 1998)
    Nozary, Homayoun
    ;
    Piguer, Claude
    ;
    Tissot, Paul
    ;
    Bernadinelli, Gérald
    ;
    Jean-claude G. Bünzli
    ;
    Deschenaux, Robert 
    ;
    Guillon, Daniel
    A new synthetic strategy has been developed to introduce bent and rigid tridentate 2,6-bis(benzimidazol-2‘-yl)pyridine cores into rodlike ligands L11-17. The crystal structure of the nonmesogenic ligand L13 (C39H37N5O4, triclinic, P1̄, Z = 2) shows the expected trans−trans conformation of the tridentate binding unit, which provides a linear arrangement of the semirigid aromatic sidearms. The crystal structure of the related mesogenic ligand L16 (C61H81N5O4, triclinic, P1̄, Z = 2) demonstrates the fully extended conformation adopted by the lipophilic side chains, leading to a slightly helically twisted I-shaped molecule. A rich and varied mesomorphism results which can be combined with the simultaneous tuning of electronic and photophysical properties via a judicious choice of the spacers between the rigid central core and the semirigid lipophilic sidearms. Ligands L13,14 react with Ln(NO3)3·xH2O to give quantitatively and selectively the neutral 1:1 complexes [Ln(Li)(NO3)3] (Ln = La to Lu), which are stable in the solid state at room temperature but partially dissociate in acetonitrile to give the cationic species [Ln(Li)(NO3)2]+. The crystal structure of [Lu(L13)(NO3)3]·3CH3CN (30, LuC45H46N11O13, monoclinic, C2/c, Z = 8) reveals a U-shaped arrangement of the ligand strand arising from the cis−cis conformation of the coordinated tridentate binding unit. This drastic geometric change strongly affects the thermal behavior and the photophysical and electronic properties of the lipophilic complexes [Ln(L14)(NO3)3]. Particular attention has been focused on structure−properties relationships, which can be modulated by the size of the lanthanide metal ions.
  • Publication
    Accès libre
    Synthesis and characterization of fullerene-pyridyl arene ruthenium complexes
    Appavoo, Divambal
    ;
    Deschenaux, Robert 
    ;
    Therrien, Bruno 
    Association of [60]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.
  • Publication
    Accès libre
    An optically-active liquid-crystalline hexa-adduct of [60]fullerene which displays supramolecular helical organization
    (2006)
    Campidelli, Stéphane
    ;
    Brandmüller, Torsten
    ;
    Andreas Hirsch
    ;
    Saez, Isabel M.
    ;
    Goodby, John W.
    ;
    Deschenaux, Robert 
    Polyaddition of mesogenic moieties to C60 were found to yield chiral supermolecular nanoparticles which exhibit iridescent helical chiral nematic phases.
  • 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
    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
    Organized Molecular Films from New Ferrocene-Containing Molecular Units
    (1997)
    Deschenaux, Robert 
    ;
    Megert, Sonia
    ;
    Zumbrunn, Cornélia
    ;
    Ketterer, Jurgen
    ;
    Steiger, Rolf
    The design and synthesis of new amphiphilic ferrocene derivatives and their capability for forming Langmuir and Langmuir−Blodgett films are reported. The film formation at the air−water interface was followed by surface pressure−molecular area isotherm, surface potential−molecular area isotherm, and Brewster angle microscopy. The stability and structure of the transferred films were investigated by UV−vis spectroscopy and small angle X-ray experiments. Transfer ratios near unity were obtained. Two hydrophobic alkyl chains combined with either one or two hydrophilic functions gave stable and ordered films. One hydrophobic alkyl chain associated to one hydrophilic headgroup required the presence of an intercalant for obtaining organized molecular films. This behavior clearly illustrated the key role played by the three-dimensional structure of the ferrocene unit which tends to decrease the intermolecular interactions because of its bulkiness; this is in agreement with results reported for ferrocene-containing thermotropic liquid crystals (Deschenaux, R.; Goodby, J. W. In Ferrocenes:  Homogeneous Catalysis, Organic Synthesis, Materials Science; Togni, A., Hayashi, T. Eds.; VCH Verlagsgesellschaft:  Weinheim, 1995; pp 471−495).
  • Publication
    Accès libre
    A dendritic fullerene–porphyrin dyad
    (2006)
    Campidelli, Stéphane
    ;
    Deschenaux, Robert 
    ;
    Swartz, Angela
    ;
    Rahman, G. M. Aminur
    ;
    Guldi, Dirk M.
    ;
    Milic, Dragana
    ;
    Vázquez, Ester
    ;
    Prato, Maurizio
    We describe the synthesis, characterization and photophysical properties of a fullerene derivative whose structure includes a Zn-porphyrin and a second generation liquid-crystalline (LC) dendrimer. The size of the fullerene and porphyrin units with respect to the size of the LC dendrimer prevents the formation of liquid-crystalline phases. However, this system gives interesting photoinduced electron transfer phenomena. Compound 1 has been investigated by steady state and time resolved fluorescence as well as transient absorption spectroscopy in polar and apolar solvents. We demonstrate that the fluorescence of the porphyrin unit in 1 is quenched compared to the Zn-tetraphenylporphyrin used as reference. Femto- and picosecond transient absorption permit to identify the formation of a radical ion pair while nanosecond experiments allowed the determination of the charge recombination lifetimes.
  • Publication
    Accès libre
    Electrochemical properties of a liquid-crystalline mixed fullerene–ferrocene material and related species
    (2002)
    Carano, Maurizio
    ;
    Chuard, Thierry
    ;
    Deschenaux, Robert 
    ;
    Even, Michael
    ;
    Marcaccio, Massimo
    ;
    Paolucci, Francesco
    ;
    Prato, Maurizio
    ;
    Roffia, Sergio
    The electrochemical properties of a fullerene–ferrocene liquid crystal are reported. The electrochemical study was carried out under strictly aprotic conditions: a total of seven reduction peaks were detected in the negative potential region, and two oxidation peaks in the positive potential one. Comparison of the data with those obtained from suitable model compounds (i.e., analogous fullerene- or ferrocene-free materials ) has allowed the assignment of all reduction and oxidation steps. The CV study evidenced the occurrence of a fast follow-up chemical reaction coupled to the third (at 25 °C) or fourth (at –60 °C) reduction of either 1 or 3. Such a reaction, presumably related to the cleavage of one of the cyclopropane bonds, is quantitatively reversed upon re-oxidation. Conversely, under bulk electrolysis conditions (second reduction), the species undergo the retro-Bingel reaction, i.e. the irreversible removal of the bis(alkoxycarbonyl)methano adducts to give the parent C60.
  • 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
    Macrocyclic Effects in the Mesomorphic Properties of Liquid-Crystalline Pillar[5]- and Pillar[6]arenes
    Nierengarten, Iwona
    ;
    Guerra, Sebastiano 
    ;
    Holler, Michel
    ;
    Karmazin-Brelot, Lydia
    ;
    Barberá, Joaquín
    ;
    Deschenaux, Robert 
    ;
    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.