Advanced Functional Materials

Cover image for Advanced Functional Materials

July, 2004

Volume 14, Issue 7

Pages 631–730

    1. Photoswitching of Ferroelectric Liquid Crystals Using Unsymmetrical Chiral Thioindigo Dopants: Photoinduced Inversion of the Sign of Spontaneous Polarization (pages 637–642)

      J. Z. Vlahakis, M. D. Wand and R. P. Lemieux

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200400039

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      Photoswitching of a surface-stabilized ferroelectric liquid crystal is achieved by inversion of the sign of spontaneous polarization PS induced by an ambidextrous thioindigo dopant (see Figure) with two competing stereo-polar units of opposite handedness. The photoinversion is achieved without a photomechanical effect and using visible light.

    2. Reinforcing Epoxy Polymer Composites Through Covalent Integration of Functionalized Nanotubes (pages 643–648)

      J. Zhu, H. Peng, F. Rodriguez-Macias, J. L. Margrave, V. N. Khabashesku, A. M. Imam, K. Lozano and E. V. Barrera

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200305162

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      A fully integrated nanotube–polymer composite has been developed using amino-functionalized single-walled carbon nanotubes (see Figure). The nanotubes become an integral part of the crosslinked epoxy structure through covalent bonding. Significant reinforcement of epoxy was demonstrated—up to 70 % increase in mechanical strength with the addition of only a small amount of functionalized nanotubes.

    3. 1,3,6,8-Tetraphenylpyrene Derivatives: Towards Fluorescent Liquid-Crystalline Columns? (pages 649–659)

      V. de Halleux, J.-P. Calbert, P. Brocorens, J. Cornil, J.-P. Declercq, J.-L. Brédas and Y. Geerts

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200400006

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      Ten new potentially discotic liquid-crystalline derivatives of 1,3,6,8-tetraphenylpyrene (see Figure) have been synthesized. The molecular design, thermotropic, and photophysical properties are discussed in relation to their structure. Quantum-chemical calculations performed using the structure of one of the compounds rationalize the high solid-state emission observed for all the derivatives.

    4. New Organic Metals Based on BDH-TTP Radical Cation Salts with the Photochromic Nitroprusside Anion [FeNO(CN)5]2– (pages 660–668)

      I. Shevyakova, L. Buravov, V. Tkacheva, L. Zorina, S. Khasanov, S. Simonov, J. Yamada, E. Canadell, R. Shibaeva and E. Yagubskii

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200305170

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      Two new quasi-2D metallic salts of the organic donor molecule BDH-TTP with the photochromic nitroprusside anion as well as a semiconducting one have been prepared and characterized. κ-(BDH-TTP)4[FeNO(CN)5]·NB (projection along a-direction, see Figure) is the first κ-phase with two different dimers exhibiting metallic behavior down to low temperatures.

    5. Conventional Electron Microscopy and Electron Holography of Organic Solar Cells (pages 669–676)

      P. Simon, B. Maennig and H. Lichte

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200304498

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      Layered organic semiconductor solar cells have been characterized with regard to morphology and structure by means of electron holography and electron diffraction. The layer sequence and interface could be imaged with high contrast at the nanometer scale (see Figure). The first electron microscopy analysis of a 1:1 mixture of C60 and zinc phthalocyanine was performed. High-resolution phase images of zinc phthalocyanine and C60 were successfully recorded.

    6. Electron-Enhanced Hole Injection in Blue Polyfluorene-Based Polymer Light-Emitting Diodes (pages 677–683)

      T. van Woudenbergh, J. Wildeman, P. W. M. Blom, J. J. A. M. Bastiaansen and B. M. W. Langeveld-Vos

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200305178

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      Electrons play an important role in poly(9,9-dioctylfluorene) (PFO)-based polymer light-emitting diodes. They assist in hole injection by accumulating at the hole contact. As a result the hole injection is strongly enhanced. The electron transport itself is strongly improved by suitable end-capping (see Figure).

    7. Chain-Length Dependence of Singlet and Triplet Exciton Formation Rates in Organic Light-Emitting Diodes (pages 684–692)

      D. Beljonne, A. Ye, Z. Shuai and J.-L. Brédas

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200305176

      Charge recombination in polymer-based light-emitting diodes (LEDs) occurs as a two-step process. First, initially free polarons coalesce into singlet or triplet charge-transfer (CT) excitons; these then decay into lower singlet or triplet exciton neutral states, with rates kS and kT, respectively. Overcoming spin statistics requires that the second step be significantly slower for triplet than for singlet CT states: Here, this is found to be the case from the results of quantum-chemical calculations performed on long oligomer chains. Thus, in polymer devices, the resulting singlet/triplet ratio can significantly exceed the spin-statistical limit.

    8. The Effect of Hydrogen Bonding on Self-Assembled Polyaniline Nanostructures (pages 693–698)

      L. Zhang, Y. Long, Z. Chen and M. Wan

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200305020

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      Polyaniline nanotubes have been synthesized through a self-assembly process in the presence of various carboxylic acids such as propionic acid, lactic acid, succinic acid, malic acid, tartaric acid, and citric acid. It is shown that the size, aggregated morphology (e.g. dendrites; see Figure), and thermal and electrical properties of the nanotubes are affected by the number of OH and COOH groups of the carboxylic acids.

    9. Highly CO2-Permeable and -Selective Membranes Derived from Crosslinked Poly(ethylene glycol) and Its Nanocomposites (pages 699–707)

      N. P. Patel, A. C. Miller and R. J. Spontak

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200305136

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      Factors governing the mechanical and gas-transport properties of highly CO2-permeable and -selective membranes derived from crosslinked poly(ethylene glycol) diacrylate (PEGda) and its nanocomposites are investigated. Material considerations such as PEGda chain length (see Figure) and nanofiller type/concentration govern network flexibility and molecular transport through the polymer matrix.

    10. Microscopic Morphology of Polyfluorene–Poly(ethylene oxide) Block Copolymers: Influence of the Block Ratio (pages 708–715)

      M. Surin, D. Marsitzky, A. C. Grimsdale, K. Müllen, R. Lazzaroni and P. Leclère

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200305191

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      The synthesis and morphological characterization of poly(fluorene)–poly(ethylene oxide) block copolymers are described. Depending on the block ratio of the copolymer and the sample preparation condition, different microscopic morphologies are observed, from well-defined nanoribbons (see Figure) to non-textured deposits.

    11. Siliceous ZSM-5 Membranes by Secondary Growth of b-Oriented Seed Layers (pages 716–729)

      Z. Lai, M. Tsapatsis and J. P. Nicolich

      Version of Record online: 22 JUL 2004 | DOI: 10.1002/adfm.200400040

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      A thin, well-intergrown and b-oriented siliceous ZSM-5 membrane (see Figure) has been synthesized through a modified seeded growth technique. A b-oriented seed layer was altered via secondary growth into a dense b-oriented ZSM-5 membrane. High permeance, as well as ahigh separation factor, was reproducibly achieved for the separation of xylene isomers.