Electronic and vibrational spectra of a gel of single-wall carbon nanotubes in an ionic liquid

A gel of single-wall carbon nanotubes in an ionic liquid has been prepared using the technique of mixing nanotubes with ionic liquids. The gel obtained has a high concentration of nanotubes (～1%). The absorption spectra of the gel and its individual components have been measured. The absorption spectrum of the gel exhibits reconstruction of the electronic and vibrational spectra of the gel with respect to its individual components. This reconstruction is explained by the interaction of nanotubes with the ionic liquid in the gel structure. Reconstruction of the electronic subsystem of nanotubes has also been observed in a suspension of nanotubes in an aqueous solution of a surfactant.     

7-Aryl-3-(hydroxymethyl)-5-oxo-1,2,3,5-tetrahydro[1,2,4]triazolo[1,5-a]pyridine-6,8-dicarbonitriles: Synthesis and Predicted Biological Activity

Russian Journal of General Chemistry - Aminomethylation of 1,6-diamino-4-aryl-2-oxo-1,2-dihydropyridine-3,5-dicarbonitriles under the action of excess of formaldehyde in ethanol has led to the...     

Electrochemical method in determination of antioxidative activity using ferrocene derivatives as examples

Electrochemical method for the evaluation of antioxidative activity of compounds based on their reaction with the stable radical, 2,2-diphenyl-1-picrylhydrazyl, was suggested with monitoring of the reaction by cyclic voltammetry (CVA). Antioxidative properties of new ferrocene derivatives Fc(L)R (where Fc is the ferrocenyl, R is the fragment of 2,6-di-tert-butylphenol or its aromatic analog, L is the spacer) were studied. Anodic oxidation of the compounds Fc(L)R, which contain azomethine and 2,6-di-tert-butylphenol moities, proceeds in three steps, that suggests a possibility of intramolecular proton-coupled electron transfer process. Conjugates of ferrocene and 2,6-di-tert-butylphenol are efficient antioxidants.     

Formation of the second superhydrophobic shell around an encapsulated metal ion: synthesis, X-ray structure and electrochemical study of the clathrochelate and bis-clathrochelate iron(II) and cobalt(II, III) dioximates with ribbed perfluoroarylsulfide substituents

The nucleophilic substitution of six chlorine atoms of the n-butylboron-capped clathrochelate iron and cobalt(II) precursors with perfluoroarylthiolate anions afforded the hexaperfluoroarylsulfide macrobicyclic iron and cobalt(II) tris-dioximates. The complexes obtained are soluble in aromatic and aliphatic hydrocarbons as well as in polar aprotonic solvents due to the presence of the superhydrophobic fluorine-containing molecular periphery. As it follows from the X-ray data for five iron and cobalt mono- and bis-clathrochelates, the geometry of their macrobicyclic frameworks is affected by both the nature of an encapsulated metal ion and that of the ribbed substituents. Bis-capping fragment Co(II)O(6) of the Co(III)Co(II)Co(III) bis-clathrochelate possesses a trigonal antiprismatic geometry, all the Co(II)N(6) coordination polyhedra are trigonal-prismatic, and those of the encapsulated iron(II) and cobalt(III) ions are intermediate between them. The wide range of Co-N distances as well as the significant shifts of the encapsulated cobalt(II) ions from the centres of their N(6)-coordination polyhedra were explained by the Jahn-Teller distortion. The EPR and magnetometry data are also characteristic of the low-spin cobalt(II) complexes with this distortion. The parameters of the (57)Fe M?ssbauer spectra of the iron macrobicycles are characteristic of the low-spin iron(II) complexes. The cyclic voltammograms (CVs) for the complexes studied contain the one-electron oxidation and reduction waves assigned to metal-centered redox-processes. The Fe(2+/3+) and Co(2+/3+) oxidations are quasi-reversible or irreversible. The anionic clathrochelate species resulting from the reversible Co(2+/+) reductions are stable on the CV time scale, whereas their iron(I)-containing analogs are unstable.     

The effect of spontaneous polarization on two-dimensional elasticity of smectic liquid crystals

The influence of polarity on orientational elasticity and on structures formed in the director field is studied in free-standing smectic films. Periodic stripe patterns and 2π-walls in a magnetic field are investigated. Measurements are performed on a nonpolar racemic mixture, on an optically pure ferroelectric compound, and in mixtures with different concentrations of the chiral isomers of opposite signs. The structure of periodic stripes changes drastically with the polarity of the film. The ratio of the bend K _B and splay K _S elastic constants for smectic films is determined as a function of polarization from the structure of periodic stripe patterns and 2π-walls. We find that the elastic anisotropy K _B /K _S increases essentially with increasing the polarity of the film. Changes of the elasticity and the structure of periodic stripes are explained by polarization charge effects.     

Photonic liquid crystals: Optical properties and their dependence on light polarization and temperature

Optical properties of cholesteric photonic crystals and their dependences on light polarization and temperature have been studied. The transmission spectra associated with diffraction depend on the direction of linear polarization of a light wave. The temperature dependence of the photonic band gap is determined. The experimental results are compared with theoretical predictions.     

Self-organization of N<Superscript>*</Superscript> inclusions in SmC<Superscript>*</Superscript> free-standing films

The behaviour of freely suspended smectic-C* ( SmC^*) films at the bulk SmC^*-cholesteric ( N^*) phase transition has been investigated using polarized-reflected-light microscopy. Our experimental observations show that above the bulk SmC^*- N^* phase transition the N^* order appears in different ways according to the film thickness. In thin films, the conventional layer-by-layer thinning occurs. In films of intermediate thickness N^* inclusions nucleate inside the SmC^* film. The distortions of the in-plane orientational order of the SmC^* host phase induce elastic interactions between the inclusions and lead to their self-organization in chain-like structures. Both the dynamic of the chaining and the parameters driving the equilibrium distance between the inclusions in the chain are investigated. In thick films, N^* fingers grow inside the film. The influence of the experimental conditions on the various processes is analysed. Received 1 July 2002 / Published online: 15 April 2003 RID="a" ID="a"e-mail: Philippe.cluzeau@univ-lille1.fr     

Free-standing smectic films at high temperature

Optical reflectivity studies on free-standing liquid crystal films above the bulk smectic temperature range have revealed different melting phenomena. Our measurements are performed on tilted smectic phases (smectic C*, smectic C) using optical microscopy in polarized light in order to visualize the changes of the film structure. We observe the formation of twodimensional defect structures from string-like lines in very thick (about 1000 layers) as well as in thin (about 20 layers) films. In thick films these structures nucleate around the temperature of the bulk smectic-cholesteric phase transition, while in thin films the formation of the defects occurs well above this temperature and just before the thinning transitions. In thick and intermediate thickness films, cholesteric or nematic droplets and a 'quasi-smectic' structure are observed. The films exhibiting the 'quasi-smectic' structure definitely exist at higher temperatures than the smectic films with the same thickness.     

A diffraction and spectroscopic study of the solid states of EBBA

The solid states and phase transitions were studied in the nematogen EBBA. Differential scanning calorimetry, neutron diffraction and Raman scattering provided well-correlated results on the structure and dynamics of the solid phases. It was concluded that (a) EBBA has four different solid phases, (b) there is a difference between the dynamics, viz. the coherence length of phonons in the rapidly-cooled phases of MBBA and EBBA, (c) the molecular shape in the nematic phase can be determined by using the solid state structures.     

Light-induced layer by layer thickening in photosensitive liquid crystal membranes

Photosensitive smectic membranes of pure liquid crystal (LC) were studied under white light illumination. A thickness increase is observed in the illuminated film area. Appropriate light and thermal conditions lead to a thickening layer by layer process. This unusual phenomenon is opposite to the well-known step-by-step thinning transitions under heating. We give a phenomenological interpretation for thickening based on layer transport of LC matter towards the illuminated area.