Advanced Functional Materials

Cover image for Advanced Functional Materials

August, 2003

Volume 13, Issue 8

Pages 587–658

    1. Star-Shaped Oligothiophenes for Solution-Processible Organic Field-Effect Transistors (pages 591–596)

      S.A. Ponomarenko, S. Kirchmeyer, A. Elschner, B.-H. Huisman, A. Karbach and D. Drechsler

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304363

      New semiconducting star-shaped oligothiophenes have been synthesized and investigated for operation as solution-processible organic field-effect transistors (FETs) were found. FETs made by spin-coating 1,3,5-tris(5″-decyl-2,2′:5′,2″-terthien-5-yl)benzene (see Figure) from a chloroform solution showed a mobility of 2 × 10–4 cm2 V–1 s–1, a 102 on/off ratio at the gate voltages 0 and –20 V and a threshold voltage close to 0 V.

    2. The Origin of Green Emission in Polyfluorene-Based Conjugated Polymers: On-Chain Defect Fluorescence (pages 597–601)

      L. Romaner, A. Pogantsch, P. Scandiucci de Freitas, U. Scherf, M. Gaal, E. Zojer and E.J.W. List

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304360

      The low emission band at 2.2–2.3 eV in polyfluorene-based conjugated materials is studied by various spectroscopic methods using defined fluorene–fluorenone copolymers. Absorption and photoluminescence in the film and dilute solution reveal the optical properties of the low-energy emission band emerging in polyfluorene-type polymers upon degradation. All the experimental evidence presented yield direct evidence against excimer or aggregate formation as the primary source of this band. Instead emission from keto defect sites, i.e., fluorenon molecules can be shown to be responsible for the low-energy emission band.

    3. Improved Efficiency of Single-Layer Polymer Light-Emitting Devices with Poly(vinylcarbazole) Doubly Doped with Phosphorescent and Fluorescent Dyes as the Emitting Layer (pages 603–608)

      S. Kan, X. Liu, F. Shen, J. Zhang, Y. Ma, G. Zhang, Y. Wang and J. Shen

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304304

      Novel organic light-emitting diode (LED) materials are demonstrated, which contain a green phosphorescent dye and a red fluorescent dye as dopants in a polyvinylcarbazole (PVK) host. The energy transfer efficiency from PVK host to the fluorescent dye is increased by the phosphorescent co-dopant, which is effectively used as an energy coupler, providing the possibility to harvest both singlet and triplet energy in the devices. By optimizing the concentration of both dyes, a maximum EL quantum efficiency of 0.42 cd A–1 at a current density of 9.5 mA cm–2 was obtained.

    4. New Conjugated Ladder Polymer Containing Carbazole Moieties (pages 609–614)

      S.A. Patil, U. Scherf and A. Kadashchuk

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304344

      A new ladder polymer incorporating a polar carbazole group within the main chain, poly(para-phenylene carbazole) LPPPC (see Figure), was synthesized and characterized by luminescence techniques. Its properties are compared to that of the well-known methyl substituted ladder-type poly(para-phenylene) MeLPPP.

    5. Analysis of Metallo-Supramolecular Systems Using Single-Molecule Force Spectroscopy (pages 615–620)

      M. Kudera, C. Eschbaumer, H.E. Gaub and U.S. Schubert

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304359

      Metallo-supramolecular complexes have been investigated on the molecular level using single-molecule force spectroscopy (see Figure and cover). The rupture force of an individual bisterpyridine ruthenium(II) complex was found to be 95 pN and thus comparable to biotin–streptavidin binding forces. Such systems are therefore particularly suited for the construction of functional nanomaterials.

    6. Fully Reversible Homogeneous and Heterogeneous Li Storage in RuO2 with High Capacity (pages 621–625)

      P. Balaya, H. Li, L. Kienle and J. Maier

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304406

      A completely reversible Li storage in RuO2 with a high capacity of 1130 mA h g–1 (see Figure) and a nearly 100 % coulombic efficiency at the first cycle is achieved through heterogeneous solid-state electrochemical reactions. Such an unusually good performance is due to the nanostructures formed in situ and favorable transport properties of RuO2.

    7. Well-Defined Fullerene Nanowire Arrays (pages 626–630)

      Y.-G. Guo, C.-J. Li, L.-J. Wan, D.-M. Chen, C.-R. Wang, C.-L. Bai and Y.-G. Wang

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304362

      Well-defined C60 nanowire arrays have been fabricated within the pores of anodic alumina templates by electrodeposition (see Figure and inside cover). The nanowires are mainly polycrystalline, but a rhombohedral polymeric phase is also observed in their vibration spectra. The fabrication of such pre-designed arrays represents an important step toward the development of chemical sensors and nanoscale electronic devices based on fullerenes.

    8. Formation of Thick Porous Anodic Alumina Films and Nanowire Arrays on Silicon Wafers and Glass (pages 631–638)

      O. Rabin, P.R. Herz, Y.-M. Lin, A.I. Akinwande, S.B. Cronin and M.S. Dresselhaus

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304394

      Large-area porous anodic alumina films lacking a barrier layer, and nanowire arrays of high aspect ratio nanowires (∼102) in direct contact with a conductive film, have been formed on rigid substrates. The effect of different substrates on the morphology of the film and the barrier layer was examined, and the ease of manipulation of the structures was demonstrated by patterning the films and by nanowire transport measurements.

    9. General Synthesis of Single-Crystal Tungstate Nanorods/Nanowires: A Facile, Low-Temperature Solution Approach (pages 639–647)

      S.-H. Yu, B. Liu, M.-S. Mo, J.-H. Huang, X.-M. Liu and Y.-T. Qian

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304373

      Large-scale synthesis of a family of single-crystalline transition metal tungstate nanorods/ nanowires by a mild hydrothermal crystallization technique using inorganic salts as precursors is reported. Uniform tungstate nanorods/nanowires, such as MWO4 (M = Zn, Mn, Fe (as shown in the Figure)), Bi2WO6, Ag2WO4, and Ag2W2O7 with diameters of 20–40 nm, lengths of up to micrometers, and controlled aspect ratios can be readily obtained.

    10. Building Quantum Dots into Solids with Well-Defined Shapes (pages 648–656)

      C. Mao, J. Qi and A.M. Belcher

      Version of Record online: 12 AUG 2003 | DOI: 10.1002/adfm.200304297

      Quantum dots (QDs) have been built in situ into a variety of close-packed QD ensembles (QD solids): needles, disks, rods, spheres, bundles, stars, ribbons, and transition structures. Design strategies using a cold treatment (–25 to 0 °C, see Figure for the result of treatments on thiol-stabilized QDs) immediately after synthesis provides control, no matter which II–VI material is used.