Advanced Materials

Cover image for Advanced Materials

March, 1999

Volume 11, Issue 4

Pages 283–344

    1. A Blue-Emitting Organic Electroluminescent Device Using a Novel Emitting Amorphous Molecular Material, 5,5'-Bis(dimesitylboryl)-2,2'-bithiophene (pages 283–285)

      Tetsuya Noda, Hiromitsu Ogawa and Yasuhiko Shirota

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<283::AID-ADMA283>3.0.CO;2-V

      A multilayer, blue-emitting electroluminescent device based on a novel, thermally stable, amorphous molecular material with electron-transport properties, BMB-2T (the title compound, see also the Figure), is described. Its fabrication and performance are reported. It is shown that the device efficiency increases when a thin layer of another new amorphous material is inserted between the BMB-2T and the hole-transporting layer to prevent exciplex formation.

    2. Harvesting Singlet and Triplet Energy in Polymer LEDs (pages 285–288)

      Vicki Cleave, Goghan Yahioglu, Pierre Le Barny, Richard H. Friend and Nir Tessler

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<285::AID-ADMA285>3.0.CO;2-N

      That it is possible to surpass the 25 % limit set by spin statistics and achieve very efficient molecular light-emitting diodes (LEDs) is demonstrated by the experimental results presented here. It is shown that energy can be captured from both singlet and triplet excited states and transformed into emitted light. Studies of LEDs in which platinum octaethylporphyrin (PtOEP), an efficient triplet emitter, is used as a “dopant” in a semiconductor polymer host are described. Time-resolved measurements of light emission are used to determine the mechanism of excitation of PtOEP.

    3. A Simple Colloidal Route to Planar Micropatterned Er@ZnO Amplifiers (pages 288–292)

      Marco Kohls, Thomas Schmidt, Haymo Katschorek, Lubomir Spanhel, Gerd Müller, Norbert Mais, Adriana Wolf and Alfred Forchel

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<288::AID-ADMA288>3.0.CO;2-B

      Erbium-doped fiber amplifiers; are important optical components for telecommunications. That films of nanoparticulate ZnO colloids are a potential route for the preparation of planar micropatterned Er3+ amplifier components is demonstrated by the synthesis of micropatterned films of Er@ZnO, i.e., Er;3+ entrapped in ZnO nanoparticles, with variable refractive index and high optical gain (see Figure).

    4. A High Quantum Yield Diarylethene-Backbone Photochromic Polymer (pages 292–295)

      Francesco Stellacci, Chiaro Bertarelli, Francesca Toscano, Maria C.Gallazzi, Gianni Zotti and Giuseppe Zerbi

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<292::AID-ADMA292>3.0.CO;2-V

      Photochromism that arises from the main polymer backbone is reported for the first time. The synthesized polymer with the diarylethene repeat unit is demonstrated to have photochromic properties superior to those of the monomer. The polymer has high thermal stability and its cyclization quantum yield (0.85) is very high for a photochromic compound. The closed, conjugated form of the polymer, which can be changed into the open, non-conjugated form by irradiation with visible light, is oxidizable, thus opening the way to photoswitchable electronic applications.

    5. Uniaxial Alignment of Cadmium Sulfide on Polymerized Films: Electron Microscopy and Diffraction Study (pages 296–300)

      Amir Berman and Deborah Charych

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<296::AID-ADMA296>3.0.CO;2-F

      Control of crystal growth is the aim of much research. Here the co-aligned nucleation of CdS semiconductor particles onto an acidic poly(diacetylene) (PDA) thin-film membrane is reported. Characterization by electron microscopy and electron diffraction and the relationship between the CdS and PDA are discussed. The Figure shows an electron micro-diffraction pattern of the (011) orientation of CdS crystallites.

    6. Three-Dimensional Manipulation of an Azo Polymer Liquid Crystal with Unpolarized Light (pages 300–302)

      Yiliang Wu, Tomiki Ikeda and Qijin Zhang

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<300::AID-ADMA300>3.0.CO;2-Y

      Manipulation of azobenzene moieties in polymer liquid crystals (PLCs) in three dimensions by means of unpolarized light is demonstrated here. When cis-azobenzenes, produced by irradiation for 1 min with unpolarized light at 366 nm, were subsequently irradiated at 436 nm, the resulting trans-azobenzenes could be aligned in any direction, according to the direction of propagation of the irradiating light, it was found. Transmittance measurements, UV absorption spectra, and conoscopic observations (see cover) are reported. Azobenzene-containing PLCs have potential applications in optical data storage.

    7. Fluoride-Induced Hierarchical Ordering of Mesoporous Silica in Aqueous Acid-Syntheses (pages 303–307)

      Patrick Schmidt-Winkel, Peidong Yang, David I. Margolese, Bradley F. Chmelka and Galen D. Stucky

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<303::AID-ADMA303>3.0.CO;2-M

      Hierarchical ordering of mesoporous silica induced by fluoride addition is described for aqueous acid-syntheses. The authors report that small amounts of fluoride make it possible to control the organization of the mesoporous materials on different length scales. At low pH, fluoride addition brings about the formation of large hydrothermally stable silica rods (see Figure) consisting of aligned bundles of mesoporous silica fibers.

    8. Synthesis of Mesoporous Silica from Sodium Silica Solutions and a Poly(ethylene oxide)-Based Surfactant (pages 307–311)

      Ligia Sierra, Betty Lopéz, Humberto Gil and Jean-Louis Guth

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<307::AID-ADMA307>3.0.CO;2-6

      Preparation of mesoporous silica by the neutral route has advantages compared with that by electrostatic routes, however, until now the starting materials were alkoxysilanes-rather expensive silica sources. A synthesis is presented that starts from sodium silicate solutions, as an inexpensive inorganic silicon source, and a poly(ethylene oxide)-based neutral surfactant. The communication focuses on the influence of the polycondensation conditions, e.g., pH, synthesis temperature, aging time, and surfactant-to-silica molar ratio, on the stability and pore size of the materials.

    9. Preparation of Titania Foams (pages 311–314)

      Arnout Imhof and David J. Pine

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<311::AID-ADMA311>3.0.CO;2-Q

      Interesting and potentially useful macroporous materials can be made by exposing non-aqueous emulsions, e.g., water-sensitive metal alkoxides in formamide, to water, it is reported. The Figure shows an SEM image of a titania foam made by the addition of water to a non-aqueous emulsion of titanium isopropoxide and isooctane. The microstructure is robust and preserved even after calcination.

    10. Dendrimer-Based Self-Assembled Monolayers as Resists for Scanning Probe Lithography (pages 314–318)

      David C. Tully, Kathryn Wilder, Jean M. J. Fréchet, Alexander R. Trimble and Calvin F. Quate

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<314::AID-ADMA314>3.0.CO;2-E

      Ultra-thin dendrimer films are effective resists for high-resolution lithography using a scanning probe. The authors describe dendritic monolayer formation via covalent attachment to a silicon wafer surface and the field-enhanced oxidation of the dendrimer monolayers using scanning probe lithography to create features with dimensions less than 60 nm. Poly-(benzyl ether) dendrimers, terminated with either benzyl or tert-butyldiphenylsilyl ether groups, were used because of their relative ease of preparation and derivatization.

    11. The Culture of Mammalian Cells on Nanostructured Silicon (pages 318–321)

      Sue C. Bayliss, Robert Heald, D. Ian Fletcher and Lorraine D. Buckberry

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<318::AID-ADMA318>3.0.CO;2-Z

      For biologically interfaced sensing applications, nanostructured porous silicon (PSi) is a very promising candidate, since mammalian cells can be cultured directly onto it. The development of cell culture systems for a PSi–cell interface is described, together with the development of a more “nature-identical” simulated plasma (SP). The Figure shows an SEM image of crystallites that have formed on nanoporous Si exposed to SP for 25 days.

    12. Low Surface Energy Coatings from Waterborne Nano-Dispersions of Polymer Complexes (pages 321–324)

      Andreas F. Thünemann, Antje Lieske and Bernd-Reiner Paulke

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<321::AID-ADMA321>3.0.CO;2-M

      Strategies for obtaining low surface energy coating materials; include those for realizing surfaces rich in CF3 groups. Of these, ones that are low in cost and environmentally friendly (for example, avoid organic solvents) have a good chance of being introduced for everyday use. It is shown that waterborne nanodispersions with supramolecular ordering—produced from a commercially available polyelectrolyte and a fluorinated

    13. Morphosynthesis of Calcium Carbonate (Vaterite) Microsponges (pages 324–328)

      Dominic Walsh, Benedicte Lebeau and Stephen Mann

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<324::AID-ADMA324>3.0.CO;2-A

      Preparation by morphosynthesis–the chemical construction and patterning of inorganic materials with complex forms–will only be technologically relevant if inexpensive routes with high product yields can be developed. A facile, one-step, high-yield preparation of vaterite (calcium carbonate) microsponges is presented, the proposed mechanism for the formation of which is illustrated in the Figure.

    14. ‘Tailor-made’ Polymers for the Removal of Lamellar Twinning: Resolution of α-Amino Acids by Entrainment (pages 328–331)

      Maria Berfeld, David Zbaida, Leslie Leiserowitz and Meir Lahav

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<328::AID-ADMA328>3.0.CO;2-V

      Pure enantiomers are frequently prepared by the technique of resolution by entrainment. However, this does not work if the samples are lamellarly twinned conglomerate crystals, which is often the case for α-amino acid salts, especially amphiphilic ones. A method based on the addition of chiral /6tailor-made′ enantioselective crystal nucleation inhibitors is presented that prevents lamellar twinning and allows resolution of hydrophobic racemic α-amino acids by kinetic crystallization. The role of the /6tailor-made′ additive is shown to provide evidence for the presence of structured clusters in supersaturated solutions.

    15. Monolayers of Cyclopeptides: A New Concept for Molecular Recognition and Enantiomeric Discrimination (pages 331–335)

      Tilo Weiß, Dietmar Leipert, Michael Kaspar, Günther Jung and Wolfgang Göpel

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<331::AID-ADMA331>3.0.CO;2-I

      The suitability of the combinatorial chemistry approach for the design of a broad spectrum of new molecular-recognition compounds is demonstrated. A model system consisting of a monolayer of two synthetic cyclohexapeptides–one of which is illustrated in the Figure–containing three L-cysteine amino acids is reported to be able to distinguish more than 20 amino acids.

    16. Chiral Lipid Tubules (pages 337–340)

      Mark S. Spector, Ronald R. Price and Joel M. Schnur

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<337::AID-ADMA337>3.0.CO;2-V

      The control of the structure of lipid-derived tubules is discussed, with particular emphasis on recent advances and their resulting impact on materials applications. Since lipid tubules reflect the chiral nature of the lipids that form them, results from chiral dichroism studies are summarized. It is shown how tubule morphology can be improved, for example by structural modification of the commercially available lipid DC8,9PC, or how the mechanical strength of the tubules can be increased by cladding them with metal. Applications, in particular in the pharmaceutical and electronics industries, are considered.

    17. Structural Studies of Langmuir Films of Disc-Shaped Molecules (pages 341–344)

      Oksana Y. Mindyuk and Paul A. Heiney

      Article first published online: 8 APR 1999 | DOI: 10.1002/(SICI)1521-4095(199903)11:4<341::AID-ADMA341>3.0.CO;2-E

      Langmuir films composed of disc-shaped molecules (rather than traditional amphiphiles) are briefly reviewed. The molecules investigated typically have a flat, conjugated core and flexible side chains, such as the triphenylene derivatives shown in the Figure. Information obtainable from pressure–area isotherms is discussed and the techniques suitable for direct structural studies are mentioned.