Advanced Materials

Cover image for Advanced Materials

May, 1999

Volume 11, Issue 7

Pages 519–585

    1. Transient Electroluminescence from Poly(phenylenevinylene)-Based Devices (pages 519–531)

      Vadim Savvateev, Aharon Yakimov and Dan Davidov

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<519::AID-ADMA519>3.0.CO;2-E

      Conjugated polymers such as poly(phenylenevinylene) are an attractive target for electroluminescent (EL) devices because of their ease of preparation, processability, and color tunability. The authors review theoretical and experimental progress in polymer EL devices with special emphasis on device degradation under strong pulses. The Figure shows the morphology of a degraded Al cathode.

    2. Orange Electroluminescence from a Divalent Europium Complex (pages 533–536)

      Christopher P. Shipley, Simone Capecchi, Oleg V. Salata, Mark Etchells, Peter J. Dobson and Victor Christou

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<533::AID-ADMA533>3.0.CO;2-U

      Divalent molecular lanthanide complexes are shown to offer promise as tunable light emitting materials in thin film electroluminescent displays for the first time in this study. Bright orange luminescence is obtained from thin film EL device structures containing bis[tris(dimethylpyrazolyl)borate]europium(II) (1), which has a high quantum efficiency in the solid state. The effect of device structure upon device efficiency and light purity is discussed and an optimum EL device structure for 1 detailed.

    3. Electrooptical Chromophores for Nonlinear Optical and Photorefractive Applications (pages 536–541)

      Stefan Beckmann, Karl-Heinz Etzbach, Peter Krämer, Katarzyna Lukaszuk, Ralf Matschiner, Andreas J. Schmidt, Peter Schuhmacher, Rüdiger Sens, Günther Seybold, Rüdiger Wortmann and Frank Würthner

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<536::AID-ADMA536>3.0.CO;2-I

      A new series of dyes for nonlinear optical (NLO) and photorefractive(PR) applications investigated by optical and electrooptical absorption spectroscopy. Optimized PR and NLO chromophores are obtained based on the exceptionally strong heterocyclic thiazolidenemalononitrile acceptor unit, combined with the proper choice of electron donor unit and conjugation length (see Figure).

    4. Non-Electrochemical Synthesis, and Structural and Physical Properties of the Polymorphic Organic Superconductors βCO-(ET)2I3 (Tc = 7.5 K) and κ-(ET)2I3 (Tc = 3.6 K) (pages 541–546)

      Harald Müller, Andrew N. Fitch, Maren Lorenzen, S. Olof Svensson, Sven Wanka and Jochen Wosnitza

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<541::AID-ADMA541>3.0.CO;2-Y

      Superconducting radical cation salts derived from the donor molecule bis(ethylenedithio)tetrathiafulvalene (ET) are an important class of molecular organic conductors. Superconducting ET–iodine phases, owing to relatively high transition temperatures, are playing a key role in the development of prototypic devices. Here is reported a novel redox preparation of the organic metal α-(ET)2I3, as well as a study of the thermally induced conversion of this material and the structural characterization and superconducting properties of the transformation product.

    5. Electroluminescent Materials with Feature Sizes as Small as 5 μm Using Elastomeric Membranes as Masks for Dry Lift-Off (pages 546–552)

      David C. Duffy, Rebecca J. Jackman, Kathleen M. Vaeth, Klavs F. Jensen and George M. Whitesides

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<546::AID-ADMA546>3.0.CO;2-E

      High resolution displays require simple, reliable methods to pattern electroluminescent materials. Here is reported the fabrication of soft, elastomeric membranes containing holes with diameters ranging from 5 μm (see Fig.) to 50 μm. By use of two membranes, the authors demonstrate multicolor photoluminescent patterns of organic materials with a solvent-free, non-photolithographic method.

    6. Colloidally Prepared HgTe Nanocrystals with Strong Room-Temperature Infrared Luminescence (pages 552–555)

      Andrey Rogach, Stephen V. Kershaw, Mike Burt, Mike T. Harrison, Andreas Kornowski, Alexander Eychmüller and Horst Weller

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<552::AID-ADMA552>3.0.CO;2-Q

      Room-temperature infrared luminescence with high quantum yield (48 %) has been observed from HgTe nanocrystals. The colloidal preparation, reported for the first time, gave rise to nanocrystals of size 3 to 6 nm with coloradoite structure. The thiol-capped quantum dots, precipitated as a white powder from the colloidal solution with 2-propanol, and readily redissolved in water, are stable towards oxidation and display luminescence covering the 1.3 μm telecommunications fiber window.

    7. Ultrathin Microstructured Polypeptide Layers by Surface-initiated Polymerization on Microprinted Surfaces (pages 555–558)

      Thomas Kratzmüller, Dietmar Appelhans and Hans-Georg Braun

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<555::AID-ADMA555>3.0.CO;2-E

      Polypeptide surfaces are regarded as key compounds; e.g. for the control of biomimetic steps in biomineralization processes. Here is described the application of microcontact printing in the patterning of gold surfaces with monolayers of an initiator, which was used to polymerize a thin layer of polypeptide. The Figure reveals that the geometrical features introduced to the surface by microprinting are accurately retained during polymerization.

    8. Increasing the Coercivity in Layered Molecular-based Magnets A[MIIMIII(ox)3] (MII = Mn, Fe, Co, Ni, Cu; MIII = Cr, Fe; ox = oxalate; A = organic or organometallic cation) (pages 558–561)

      Eugenio Coronado, José R. Galán-Mascarós, Carlos J. Gómez-García and José M. Martínez-Agudo

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<558::AID-ADMA558>3.0.CO;2-2

      A spectacular increase in the coercive field with values as high as 1.7 Tesla has been observed in the family of layered molecular magnets A[MIIMIII(ox)3] for the FeIII/CrIII mixed metal alloys, where MII = Mn, Fe, Co, Ni, Cu; MIII = Cr, Fe; ox = oxalate; and A = organic or organometallic cation. In these novel molecular magnets, the transition temperature can be easily tuned by simply varying x, the FeIII/CrIII ratio. x was also found to affect the thermal dependence of the magnetic hysteresis for this series, particularly interesting behavior being observed in the iron (II) compounds having x close to 1.

    9. Oriented FAU Zeolite Films on Micrometer-Sized EMT Crystals (pages 561–564)

      Ann M. Goossens, Bart H. Wouters, Veronique Buschmann and Johan A. Martens

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<561::AID-ADMA561>3.0.CO;2-Q

      Permeability is a crucial aspect of zeolite films, and is a characteristic that is dependent on the orientation of the individual zeolite crystals that compose the film. In this communication is reported oriented zeolite films of FAU structure-type on compositionally different, micrometer-sized EMT zeolite crystals. The Figure depicts the edge of such a film, and shows that the FAU overgrowth is oriented and highly crystalline.

    10. Nanostructured Rhenium Dioxide: Synthesis and Characterization (pages 564–567)

      Michael Fröba and Olaf Muth

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<564::AID-ADMA564>3.0.CO;2-E

      Nanostructured rhenium oxides,which belong to the technically important group 7 transition metal oxides, have been inaccessible until now due to the lack of appropriate precursors and reaction templates. Using methyltrioxorhenium as the organometallic rhenium precursor and long-chain alkylamines as supramolecular templates, these authors have synthesized nanostructured rhenium dioxide for the first time. The products are nanocomposites that are composed of rhenium dioxide and the organic structure-directing agent used in the preparation.

    11. Gradient Refractive Index Polymers Produced in a Centrifugal Field (pages 567–570)

      Frank van Duijnhoven and Cees Bastiaansen

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<567::AID-ADMA567>3.0.CO;2-2

      Transparent glasses with a refractive index gradient are useful in a variety of optical applications; however, their low-cost mass-production is difficult, and their stability is poor. Here is reported a new method for the preparation of these materials, whereby a centrifugally produced gradient in a solution of polymer-in-monomer is fixed by polymerization of the monomer. The Figure reflects the optical properties of the produced optical preforms.

    12. Photo-Induced Diffusion in Polymerizing Chiral-Nematic Media (pages 573–578)

      Dirk J. Broer, Grietje N. Mol, Johannes A. M. M. van Haaren and Johan Lub

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<573::AID-ADMA573>3.0.CO;2-E

      Photo-assembly of reactive liquid crystals by simultaneous diffusion and polymerization can give rise to interesting new polymeric architectures. In this report, the authors summarize recent results, which show how deformation of the molecular helix in a cholesteric network can give rise to interesting new optical properties, such as higher order reflection bands and built-in optical retardation. When the deformed helix is combined with a pitch gradient over the film thickness, the built-in retardation can be used for wide-band cholesteric polarizers that directly generate polarized light.

    13. Evaporation-Induced Self-Assembly: Nanostructures Made Easy (pages 579–585)

      C. Jeffrey Brinker, Yunfeng Lu, Alan Sellinger and Hongyou Fan

      Version of Record online: 6 MAY 1999 | DOI: 10.1002/(SICI)1521-4095(199905)11:7<579::AID-ADMA579>3.0.CO;2-R

      Simple and efficient methods of organizing materials are key to the realization of a nanotech world. These authors report on recent developments in simple evaporation-induced self-assembly processes, which enable the rapid production of patterned porous or nanocomposite materials. The Figure shows a calcined particle exhibiting vesicular mesophase, which was generated by aerosol self-assembly of the tri-block copolymer P123.