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High-Resolution Characterization of Liquid-Crystalline [60]Fullerenes Using Solid-State Nuclear Magnetic Resonance Spectroscopy
Liq.-cryst. materials contg. fullerenes are valuable in the development of supramol. switches and in solar cell technol. In this study, we characterize the liq.-cryst. and dynamic properties of fullerene-contg. thermotropic compds. using solid-state natural abundance 13C NMR expts. under stationary and magic angle spinning sample conditions. Chem. shifts spectra were measured in isotropic, liq.-cryst. nematic and smectic A and cryst. phases using one-dimensional 13C expts., while two-dimensional sepd. local-field expts. were used to measure the 1H-13C dipolar couplings in mesophases. Chem. shift and dipolar coupling parameters were used to characterize the structure and dynamics of the liq.-cryst. dyads. NMR data of fullerene-contg. thermotropic liq. crystals are compared to that of basic mesogenic unit and mesomorphic promoter compds. Our NMR results suggest that the fullerene-ferrocene dyads form highly dynamic liq.-cryst. phases in which mols. rotate fast around the symmetry axis on the characteristic NMR time scale of ?10-4 s. [on SciFinder(R)]
Polar and Electrooptical Properties of [60]Fullerene-Containing Poly(benzyl ether) Dendrimers in Solution
[60]Fulleropyrrolidine-containing poly(benzyl ether) dendrimers 1−4 were synthesized via 1,3-dipolar cycloaddition of amino acid and aldehyde derivatives and [60]fullerene. Their dielectric and electrooptical (Kerr effect) solution properties were studied and compared with poly(propyleneimine) dendrimers, namely DAB-dendr-(alkyl chain)n and DAB-dendr-(CN)n, and with known symmetrical and non-symmetrical poly(benzyl ether) dendrimers carrying benzyl groups ([Gx]-[C]-[Gx]) or benzyl and cyanobenzyl groups (CNn-[Gx]-[C]-[Gx+1]), respectively. It was shown that 1−4 display similar polar and electrooptical characteristics independent of their dendrimer generation. This is in contrast to the reference dendrimers for which a strong dependence of total dipole moment on dendrimer generation was observed.
High-Resolution Characterization of Liquid-Crystalline [60]Fullerenes Using Solid-State Nuclear Magnetic Resonance Spectroscopy
In situ attenuated total reflection infrared spectroscopy in a flow-through cell combined with online UV−vis spectroscopy was used to investigate the oxidation of 2-propanol over Pd/Al2O3 catalyst. The state of the catalyst was driven fast between reduced and oxidized by admitting alternately dissolved hydrogen and oxygen, and the response of the catalytic solid−liquid interface was followed in time. Besides the oxidation product acetone and the water that forms, when hydrogen and oxygen are simultaneously adsorbed on the catalyst surface, an additional species was observed with a characteristic band at ∼1065 cm-1. On the basis of the transient character of the adsorbate and density functional theory calculations, we assign this species to adsorbed 2-propoxide. Its observation indicates that the second dehydrogenation step is rate limiting in an oxidative dehydrogenation mechanism. The results furthermore show that adsorbed hydrogen and oxygen limit the dissociative adsorption of 2-propanol and that 2-propoxide can be hydrogenated back to the reactant in the presence of adsorbed hydrogen.
Conception de dyades liquides-cristallines ferrocène-fullerène
Depuis la découverte des cristaux liquides au XIXième siècle, leur intérêt n’a cessé de croître, menant à des applications toujours plus nombreuses. Très répandue dans la nature, l’architecture dendritique a permis de rendre mésomorphe l’objet anisotrope qu’est le fullerène, celui-ci, dont les propriétés photophysiques sont des plus enthousiasmantes, a souvent été lié à un donneur d’électron, comme le ferrocène. Il paraissait alors intéressant d’assembler les propriétés de transfert d’électron photoinduit observées dans des dyades « donneur-accepteur » avec celles d’auto organisation des cristaux liquides. Ce travail s’est donc intéressé à la synthèse et à la caractérisation de cristaux liquides constitués de dendrimères octyloxybiphényles ou polybenzyléthers, et d’une dyade ferrocène-C60. Cette thèse contient entre autre un premier chapitre décrivant l’état de l’art dans le domaine des cristaux liquides, des dendrimères, du ferrocène, du fullerène et des dyades donneur-accepteur. Suivent ensuite trois chapitres de discussion et une partie expérimentale. Le troisième chapitre de cette thèse est dédié à la synthèse et à la caractérisation de méthanofullerènes de dendrimères octyloxybiphényles contenant un ferrocène mono ou peralkylé. Les composés développent tous des phases lamellaires et des organisations supramoléculaires ont été postulées. Le quatrième chapitre a été consacré à la synthèse et à la caractérisation de méthanofullerènes reliés par un pont ferrocényle permettant ainsi d’augmenter le taux de fullerène dans un composé mésomorphe. Dans la dernière partie, nous avons voulu obtenir des fulléropyrrolidines constituées de dendrons polybenzyléthers présentant des phases cubiques. Les molécules ciblées ont bien été obtenues mais elles ne présentent pas de mésomorphisme. Des études électrooptiques (polarisation diélectrique et effet Kerr) ont cependant mis en évidence une certaine organisation intrastructurelle.
Photophysical, electrochemical, and mesomorphic properties of a liquid-crystalline [60]fullerene–peralkylated ferrocene dyad
Two fullerene–peralkylated ferrocene derivatives were synthesized: (1) a liquid-crystalline dyad (compound 1) was obtained by introduction of nonamethyl ferrocene into a liquid-crystalline fullerene derivative and (2) a reference compound (compound 2) was synthesized by attachment of nonamethyl ferrocene to a fulleropyrrolidine. The liquid-crystalline dyad displayed an enantiotropic smectic A phase from 57 to 155 °C. Oxidation and reduction processes were investigated by cyclic voltammetry, and were in agreement with the electrochemical characteristics of the redox-active units (peralkylated ferrocene, fullerene, dendrimer). Photoinduced electron transfer from ferrocene derivative to fullerene was identified.
Mesomorphic Hexabenzocoronenes Bearing Perfluorinated Chains
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.