Advanced Materials

The research center in Jülich is the largest of the 16 national research centers in the Federal Republic of Germany. This year, the center is 40 years old and has an anual budget of DM 485 million. In the early years the center concentrated on nuclear power-related technologies but now research carried out at the center is very interdisciplinary and very diverse. The development of the center is described, the current research priorities presented and a view of an interdisciplinary materials research future is discussed.

Ensembles of graphite-based nanotubes (see Fig.) have been produced by extending a template approach successfully used for metals and semiconductors to carbons. The outer andinner diameters of the tubules can be controlled by varying the time allowed for the polymerization of acrylonitrile within the pores of a nanotubes formed in the pores are subsequently graphitized at high temperatures to form the graphitized nanotubes

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Electron transport polymers containing aromatic oxadiazole side chain chromophores have been designed and synthesized. They have been found useful for improving the quantum efficiency, lowering the turn-on voltage, and enabling the use of the more stable aluminum cathode in the fabrication of polymer LEDs. As the oxadiazole units are chemically bound to the polymer chain, rather than being simply dispersed in a polymer matrix, the materials are expected to exhibit long-term morphological stability. The synthesis and several different applications are presented.

The extension of the emission region or organic LEDs into the ultraviolet region is reported. Emission at 394 nm is achieved by modifying the geometry of a device based on poly(octylphenyl)bithiophene (PTOPT) and poly(octylphenyl)oxadiazole (PBD) which had previously been shown to emit white light. Through changing the geometry the red and green emission peaks have been suppressed and the UV band (from the PBD) enhanced

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The optical and electronic properties of new soluble derivatives of poly(naphthalene-vinylene) (PNV) with different length alkyl side groups are reported. Quantum efficiencies of up to 10% and power efficiencies of up to 0.02% have been attained from polymer-LEDs based on these materials, and the polymers themselves are found to have a well-defined chemical structure and exhibit little main-chain stiffness.

Poly(bithiophene) dervatives unsymmetrically substituted with strong electron-donating groups and strong electron-withdrawing groups (e.g. see Fig.) have been synthesized. The substituents induce electronic push–pull effects along the conjugated chain which could be exploited in the design of organic-based multiple quantum well structures

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Photorefractive polymers have gret potential in applications such as all-optical switching and optical communication. Here, new charge-transporting polymers are presented based on a polysiloxane backbone with pendant carbazole groups, which provide both transport and room-temperature poling properties without the need for additional plasticizing components. A quantitative evaluation of the phase behavior of holographic gratings based on the new materials is also presented.

An optical sensor for organic solvents with a detection limit of 10⁻² v/v-% for methanol in mixed hydrocarbons is presented. The system, a fiber optic chemical sensor based on Reichardt's dye covalently bound to an insoluble Merrifield peptide resin (see Fig.), is shown to have a response time of ca. 1 minute

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σ-conjugated polysilanes and polygermanes are known to possess interesting linear optical properties as well as unique physical and chemical properties. Unlike π-conjugated carbon-based polymers these materials are transparent in the visible and strongly absorbing in the near ultraviolet region. Here, the nonlinear optical properties, in particular those for third harmonic generation, for several polygermane homopolymers and a polygermane-polysilane copolymer are presented.

The type of alignment achieved with discotic liquid crystals is important for a number of applications. It is found to depend decisively on the structure of the substrate. Infrared dichroism experiments are used to study the alignment of truxene and triphenylene cores (see Fig.) on amorphous silicon and polycrystalline ZnSe substrates, revealing considerable differences and hinting at the opportunity to tune the alignment of the materials

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Anisotropic charge transport, or polarized photo- and electroluminescence are possible applications for materials combining the optical properties of arylenevinylene polymers with the characteristic orientational order of the liquid-crystalline state. Thermally stale, soluble materials with a broad mesophase, which can be oriented macroscopically using conventional processing techniques and when exhibit highly anisotropic luminescence behavior of use in polarized LEDs are presented.

The preparation of the superconductor Hg-1223 (see this month's title picture) with 60-70% phase purity by a simplified route is reported. The material is produced in a single step from air-stable mono-oxides and exhibits a sharp superconducting transition, possibly due to the lack of observable defects (see Fig.)

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The conductivity of bulk polysilanes is reported to occur via the migration of holes. Since there is considerable σ delocalization along the backbone of polysilanes these materials can be considered as a one-dimensitonal molecular wire, the backbone being the wire and the alkyl side groups acting as the insulator, Here, quantum mechanical calculations on the polysilane model compound Si₁₇(CH₃)₃₆ aimed at elucidation of the electronic properties related to electrical conductance are presented.

Hollow aluminophosphate microspheres, based on mesolamellar surfactant bilayer aluminophosphate composite material, have been synthesized in polyethylene glycol by an alkylamine surfactant based method. The surface of the spheres displays patterns of surface impressions as well as fine morphological detail withi the spherical features.

Extended dendritic, ladder, and cross-linked polyradical frameworks empolying π-conjugated backbones (e.g. see Fig.) show promise in the development of ferromagnetic polymers. Recent progress in this field is reviewed and the various classes of materials, for example polyacetylene-, or polyphenylenevinylene-based radicals, compared

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Hierarchical inorganic materials chemistry has been taken a step further by the “molecular beaker synthesis” of elaborately structured aluminophosphate morphologies. A unified surfactant-based cellular-type vesicle templating model is reported that is able to explain the origin of the macroscopic forms and surface patterns of synthetic inorganic-organic composite ultrastructures, many of which resemble those found in natural siliceous biomineralized structures.

Are the ideas behind the recently published developments in biomimetic inorganic materials chemistry really as novel as they seem? This article is about rediscovery in science. The focus is on biomimetic inorganic materials chemistry and the 1872 classic published work of Pieter Harting, a Dutchman from Utrecht, on synthetic morphologies, particularly artificial calcareous formations. It would seem that one of the founding fathers of this burgeoning field of endeavor has (almost) been forgotten.