Columnar liquid crystalline benzenetrisamides with pendant 1,3,4-oxadiazole groups

Novel liquid crystal materials based on 1,3,5-benzenetrisamide derivatives with three pendant 2-phenyl-5-(mono-, di-, and/or tri-n-alkoxyphenyl)-1,3,4-oxadiazole arms (Ia–c, IIa–c) were prepared. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The formation of a columnar mesophase was found to be dependent on the number of alkoxy side chains. The compounds Ib and IIb, with a total of six alkoxy chains, and compounds Ic and IIc, with nine alkoxy chains, exhibited an enantiotropic hexagonal columnar (Col_h ) phase with high isotropisation temperatures; however, compounds Ia and IIa with a total of three alkoxy chains formed a crystalline phase. Compounds IIb and c were room temperature liquid crystals.     

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.     

Multifunctional Supramolecular Dendrimers with an s‐Triazine Ring as the Central Core: Liquid Crystalline,Fluorescence and Photoconductive Properties

Novel liquid crystal (LC) dendrimers have been synthesised by hydrogen bonding between an s‐triazine as the central core and three peripheral dendrons derived from bis(hydroxymethyl)propionic acid. Symmetric acid dendrons bearing achiral promesogenic units have been synthesised to obtain 3:1 complexes with triazine that exhibit LC properties. Asymmetric dendrons that combine the achiral promesogenic unit and an active moiety derived from coumarin or pyrene structures have been synthesised in order to obtain dendrimers with photophysical and electrochemical properties. The formation of the complexes was confirmed by IR and NMR spectroscopy data. The liquid crystalline properties were investigated by differential scanning calorimetry, polarising optical microscopy and X‐ray diffractometry. All complexes displayed mesogenic properties, which were smectic in the case of symmetric dendrons and their complexes and nematic in the case of asymmetric dendrons and their dendrimers. A supramolecular model for the lamellar mesophase, based mainly on X‐ray diffraction studies, is proposed. The electrochemical behaviour of dendritic complexes was investigated by cyclic voltammetry. The UV/Vis absorption and emission properties of the compounds and the photoconductive properties of the dendrons and dendrimers were also investigated     

Supermolecular Columnar Liquid‐Crystalline Phosphorus Dendrimers Decorated with Sulfonamide Derivatives

A series of supermolecular liquid crystals has been synthesized by combining phosphorus dendrimers of the zero, first, and fourth generations with sulfonamide derivatives, thus generating dendromesogens bearing 6, 12, and 96 mesogenic units on their surfaces. The relevant reactions could be monitored by ¹H, ¹⁹F, and ³¹P{¹H} NMR spectroscopies. The thermal and mesomorphic properties of the products have been studied by optical microscopy, differential scanning calorimetry, and X‐ray diffraction. All of the new macromolecules prepared in this work have been found to show mesomorphic properties over a wide temperature range; moreover, for all of the compounds, the columnar mesophases observed were maintained or vitrified at room temperature. On increasing the generation of these dendromesogens, mesophases appear at lower temperatures and remain stable over a wider temperature interval. In all cases, on the basis of X‐ray analysis, a cylindrical symmetry of the molecules can be proposed to promote the supramolecular columnar arrangement observed in the mesophases. In this type of model, the height of the dendrimer clearly increases with increasing dendrimer generation, whereas its cross‐ sectional area increases only slightly, probably due to compression of the highly hyperbranched structures as a consequence of their progressive steric constraints. The mesomorphic arrangement is governed by the peripheral sulfonamide units.     

Electronic and Structural Properties of Highly Aluminum Ion Doped TiO2 Nanoparticles: A Combined Experimental and Theoretical Study

This study presents the experimental and theoretical study of highly internally Al‐doped TiO₂ nanoparticles. Two synthesis methods were used and detailed characterization was performed. There were differences in the doping and the crystallinity, but the nanoparticles synthesized with the different methods share common features. Anatase to rutile transformation occurred at higher temperatures with Al doping. X‐ray photoelectron spectroscopy showed the generation of oxygen vacancies, which is an interesting feature in photocatalysis. In turn, the band‐gap energy and the valence band did not change appreciably. Periodic density functional calculations were performed to model the experimentally doped structures, the formation of the oxygen vacancies, and the band gap. Calculation of the density of states confirmed the experimental band‐gap energies. The theoretical results confirmed the presence of Ti⁴⁺ and Al³⁺. The charge density study and electron localization function analysis indicated that the inclusion of Al in the anatase structure resulted in a strengthening of the Ti?O bonds around the vacancy.     

Analytical theory for ion transfer–electron transfer coupled reactions at redox layer–modified/thick film–modified electrodes

Electrodes modified by liquid films or plasticized polymeric membranes containing a redox species offer valuable alternatives for the study of ion transfers and bimolecular electron transfers at liquid–liquid interfaces with conventional electrode arrangements and stable interfaces. The ion-to-electron (or electron-to-electron) transducer affects the electrochemical signal, complicating the accurate analysis of experimental data. This can be reduced through the use of an electrode surface-attached redox species of well-defined electrochemical behaviour. As will be demonstrated, the voltammetry of these systems show significant deviations with respect to individual charge transfers, which must be considered for appropriate diagnosis and quantitative analysis. For this, a simple analytical theory is presented here, deducing mathematical expressions for the current–potential response, as well as for the potential difference at the two polarized interfaces, the surface excess of the redox species and the ion interfacial concentrations.     

Magnetite, a model system for mixed-valence oxides, does not show charge ordering

We have investigated the charge ordering (CO) in magnetite below the Verwey transition. A new set of half-integer and mixed-integer superlattice reflections of the low-temperature phase have been studied by x-ray resonant scattering. None of these reflections show features characteristic of CO. We demonstrate the absence of CO along the c axis with the periodicity of either the cubic lattice q=(001) or the doubled cubic lattice q=(001/2). This result suggests that the Verwey transition is caused by strong electron-phonon interaction instead of an electronic ordering on the octahedral Fe atoms.     

A new class of tethered-arene ruthenium(II) complexes with pendant P and C donor atoms: synthesis of eta6:eta1:eta1 phosphonio-azabutadienyl ruthenabicycles via allenylidene intermediates

The activation of 1,1-diphenyl-2-propyn-1-ol by complexes [RuCl(eta(6)-p-cymene)[eta(2)-P,N-Ph(2)PCH(2)P([=NR)Ph(2)]](+) results in the formation of the unusual tethered (eta(6)-arene)-ruthenium(ii) derivatives, via an unprecedented iminophosphorane-allenylidene coupling process.     

Effect of interface fracture on the tensile deformation of fiber-reinforced elastomers

The influence of interface properties (strength and toughness) on the tensile behavior of fiber-reinforced elastomers deformed perpendicularly to the fibers was studied using computational micromechanics. Numerical simulations were performed by means of the finite element analysis of a representative volume element of the composite microstructure. The effect of finite deformations and of interface fracture was included in the simulations, the latter through a bidimensional and quadratic interface element inserted at the fiber/matrix interfaces. A parametrical study was carried out to assess the effect of interface strength and toughness on the tensile strength and damage micromechanisms. It was found that the onset of damage and tensile strength were controlled by interface strength while the evolution of damage depended on interface toughness.