Advanced Materials

Cover image for Advanced Materials

May 1995

Volume 7, Issue 5

Pages fmi–fmi, 435–502

  1. Masthead

    1. Top of page
    2. Masthead
    3. Essay
    4. Articles
    5. Communications
    6. Research News
    1. Masthead (page fmi)

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070501

  2. Essay

    1. Top of page
    2. Masthead
    3. Essay
    4. Articles
    5. Communications
    6. Research News
    1. Laser spectroscopy and organic dyes (pages 435–436)

      Prof. Josef Friedrich and Prof. Siegfried Schneider

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070502

      Laser Spectroscopy and Organic Dyes is the topic of this specal issue. The Review, many of the Communications, and several of the Research News articles this month are devoted to various aspects of the applications of this technology in areas ranging from the application of this technology in areas ranging from the application shown on the cover and discribed above, nonlinear optics and optical data storage, and the study of disorder phenomena in glasy materials, to artificial light-collecting antennae mimicking, for example, photosynthetic systems. The significance and potential of organic dyes and the exploitation of their interesting optical properties are introduced.

  3. Articles

    1. Top of page
    2. Masthead
    3. Essay
    4. Articles
    5. Communications
    6. Research News
    1. Scheibe Aggregates (pages 437–444)

      Prof. Dietmar Möbius

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070503

      Scheibe agregates (J-aggregates), highly ordered systems of strongly interacting chromophores (e.g. see figure), are characterized by a strong and narrow absorption band shifted to lower energy with respect to the band of the monomer, and a narrow resonance emission band with a very small Stokes shift. The formation of such aggregates, their organization and reorganization, their structure and their optical and photophysical properties are reviewed.

  4. Communications

    1. Top of page
    2. Masthead
    3. Essay
    4. Articles
    5. Communications
    6. Research News
    1. Mono- and bi-excitonic states in j-aggregates of pseudoisocyanine studied by nonlinear polarization and nonlinear absorption spectroscopy (pages 445–448)

      Dr. Holger Stiel, Dr. Bernd Voigt, Dr. Jürgen Hirsch, Dr. Klaus Teuchner and Dr. Dieter Leupold

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070504

      The aggregation of pseudoisocyanine (PIC) is of interest because of the unusual properties of the aggretages which make them useful in photographic science as sensitizers as well as in photosynthesis research as model systems. Here, the room-temperature substructure of the J-absorption band of PIC–Cl aggregates is discussed on the basis of the results from nonlinear polarization spectroscopy in the frequency domain. The results are compared with the known substructure at 4.2 K.

    2. The primary steps in photography: Excited J-aggregates on AgBr Microcrystals (pages 448–450)

      B. Trösken, Prof. F. Willig, K. Schwarzburg, Dr. A. Ehret and Dr. M. Spitler

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070505

      The primary process in the photographic emulsion is interfacial electron transfer. The electron is transferred from the excited state of a dye species to empty electron acceptor states in silver bromide. There have been no detailed measurements of the rate constants of this commercially important process. The fluorescence decay curves of thiocarbocyanine dye (see figure) yield these rate constants.

    3. On the electronic and vibronic structure of PIC-aggregates (pages 451–453)

      Dr. Philipp O. J. Scherer

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070506

      Intermolecular excitonic interactions in one-dimensional molecular aggregates are strong enough to delocalize the electronic excitation coherently over a large number of milecules. Model calculations usually make a number of assumptions, for example that only te nearest neighbor molecules are involved or that te dipole–dipole coupling has a dependence of 1/R3. Here, the electronic structure of the PIC excitations is investigated on the basis of quatum chemical calculations, allowing the validity of the assumptions to be assessed.

    4. Molecular arrangement and thermal reorganization of merocyanine J-aggregate monolayers on solid substrates (pages 453–457)

      Dr. Lydia Wolthuus, Dr. Michael Gnade and Prof. Dietmar Möbius

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070507

      Amphiphilic merocyanine dyes form J-aggregates at the air–water interface. For any application the thermal behavior of the monolayers in an important issue and hermally induced phase transitions in monolayers have been intensively studied. Langmuir–Blodgett monolayers of two merocyanine dyes mixed with matrix molecules (see figure) have been examined and the optimization of the thermal stability of such systems discussed.

    5. Shaping of phase and amplitude of ultrashort laser pulses with organic spectral hole burning materials (pages 457–460)

      Dr. Heinrich Schwoerer, Daniel Erni, Dr. Alexander Rebane and Prof. Urs P. Wild

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070508

      Thin films of spectral hole burning materials (dyes such as chlorin or phthalocyanines in a matrix) are shown to serve well as highly spectrally selective, linear filters for ultrashort laser pulses. The materials exhibit a large ratio of width of the inhomogeneously broadened absorption band to the width of the zero phonon lines of the photochromic materials and have been used to shape both the phase and amplitude of the output of a Ti:sapphire laser. The preparation of the materials and a variety of their applications are presented.

    6. Exciton band structures in 2D aggregates of cyanine dyes (pages 460–463)

      Dr. Stefan Kirstein and Prof. Helmuth Möhwald

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070509

      Herring-bone structures (see figure, where the rectangles are the dye molecules and the arrows indicate the oscillation of the transition dipoles) can be classified on the basis of the angle of mutual orientation of the two molecules per unit cell. Those with small angles showing nearly resonant fluorescence emission from the most redshifted transition (J-aggregates).

    7. Surface emitting SHG light by counter propagation of guided waves in a plane parallel poled DANS side chain polymer (pages 463–465)

      Dr. Silvia Mittler-Neher, Dr. Akira Otomo, Dr. George I. Stageman, Dr. Christian Bosshard, Dr. Winfried H. G. Horsthuis and Dr. Gustaaf R. Möhlmann

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070510

      Large nonlinear optical coefficients and easy processing and fabrication techniques make organic materials, especially polymers, very attractive condidates for counter propagating mixing applications. Here a spincoated waveguide based on a 4-dimethylamino-4'-nitrostilbene side chain polymer is shown to generate surface emitted second harmonic light. The preparation of the waveguide, its experimental operation, and the theoretical background are discussed.

    8. Novel photocrosslinkable systems for nonlinear optics (pages 465–468)

      Dr. Thomas Hanemann, Caroline Noël and Dr. Wolfgang Haase

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070511

      The development of electroopic devices exploiting second harmonic generation in thin polymer films is hindered by the low stability of the dipole orientation of the chromophore in the surrounding matrix. New polymers (see figure) containing cinnamic acid derivatives as potential network-forming units, in combination with new synthetic dyes as nonlinear optical active moieties are presented. The crosslinking leads to higher stability in the films.

    9. Luminescent RuII-polypyridine complexes in poly-2-hydroxyethylmethacrylate matrices as oxygen sensors (pages 468–471)

      Dr. Gaetano Di Marco, Dr. Maurizio Lanza and Dr. Sebastiano Campagna

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070512

      Oxygen sensors based on polymer-immobilized transitionmetal complexes are reported representing an interesting example of solid-state luminescent sensors. The sensitivity of the luminescence lifetme of these systems is examined in relation to the mechanical properties and it is found that te plasticizing effect due to the monomer is a necessary factor to obtain systems with suitable sensor properties.

    10. Reduction in the size of features of patterned SAMs generated by microcontact printing with mechanical compression of the stamp (pages 471–473)

      Younan Xia and Prof. George M. Whitesides

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070513

      Sub-micron size features can now be produced using the microcontact printing technique. The elastomeric stamp used to produce the features in self-assembled monolayers (see figure) is mechanically compressed both one- and two-dimensionally, resulting in a reduction of the size of the features by up to a factor of almost ten (e.g. 2.5 μm) while retaining the spatial regularities in the pattern.

    11. Doping of polyaniline via pseudoprotonation by an ionic salt (pages 473–475)

      Prof. Show-An Chen and Dr. Liang-Chang Lin

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070514

      Polyaniline can be converted into a conducting form by either protonation of the imine site or oxidative doping at the amine site. Here, a new class of dopant is reported, ionic salts. An ionic-salt-doped polyaniline is obtained by mixing the emeraldine base of polyaniline and solutions of, for example, LiClO4, LiBF4, or Zn(ClO4)2 in 1-methyl-2-pyrrolidone, and then casting the solution to form films. Materials synthesis, film production, and the demonstration that the material is intrinsically, rather then ionically, conducting are discussed.

    12. Ferromagnetic order in the sulfur-containing nitronyl nitroxide radical, 2-(4-thiomethyl)phenyl-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide, NIT(SMe)Ph (pages 476–478)

      Dr. Andrea Caneschi, Fabrizio Ferraro, Prof. Dante Gatteschi, Dr. Antoine le Lirzin, Prof. Miguel A. Novak, Dr. Eva Rentschler and Dr. Roberta Sessoli

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070515

      Low-temperature magnetic measurements on powdered samples of the title nitronyl nitroxide radical (see figure) are reported. Evidence for ferromagnetic order with a Tc of ca. 0.2 K is found. It is proposed that the diffuse electronic cloud of the sulfur atom in the radical substituent generates sufficiently strong ferromagnetic interactions even at large distances.

    13. New routes to metal-organic precursors; growth of high purity AIGaAs by CBE using a novel amine adduct of triisopropylgallium (pages 478–481)

      Dr. Richard W. Freer, Dr. Timothy J. Whitaker, Dr. Trevor Martin, Dr. Phillip D. J. Calcott, Dr. Michael Houlton, Dr. David Lee, Dr. Antony C. Jones and Simon A. Rushworth

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070516

      High-purity AlGaAs has been grown using chemical beam epitaxy employing a new gallium precursor, triisopropylgallium·NEt3 in combination with AlH3(NMe2Et). The materials exhibit low oxygen concentrations and excellent optical and electrical characteristics, comparable with the best materials grown using molecular beam epitaxy or metal-organic vapor phase epitaxy. The use of amine solvents and the complete absence of eters from the precursors has important consequences for the growth of III–V alloys by CBE, as oxygen-containing solvents are known to lead to materials degradation.

    14. Molecular aggregation-induced photocarrier generation in layered organic photoreceptors incorporating azo compounds (pages 481–483)

      Dr. Tatsuya Niimi and Dr. Minoru Umeda

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070517

      The high photosensitivity of azo-compound-based photoreceptors is considered to be due to molecular-aggregation-induced geminate-pair dissociation rather than a photo-induced electron-transfer reaction. Both agregated and non-aggregated carrier-generating materials are employed on order to investigate the mechanism of this process, which has practical implications for the development of electrophotography.

    15. Real space evidence for reversible metal–metal bond rearrangement induced by AFM tip force (pages 483–486)

      Hardy Bengel, Prof. Hans-Joachim Cantow, Dr. Sergei N. Magonov and Prof. Myung-Hwan Whongbo

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070518

      The reversible rearrangement of weak metal‒metal bonds in layered transition metal chalcogenides is shown to be induced by the force exerted by the tip of an atomic force microscope. The figure shows how the ribbon chains which make up the layers of NbTe2 are reversibly switched by 60° by increasing ad decreasing the force at the tip.

  5. Research News

    1. Top of page
    2. Masthead
    3. Essay
    4. Articles
    5. Communications
    6. Research News
    1. Polymeric microcapsule arrays (pages 487–488)

      Prof. Charles R. Martin and Ranjani V. Parthasarathy

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070519

      Enzyme immobilization in polymeric microcapsule arrays could provide an interesting method for the development of biosensors. Produced via the template synthesis method under mild conditions, the arrays exhibit high loadings of the enzyme, provide a large surface area for enzyme–substrate contact, ad are mechanically robust. A recently developed microencapsulation method is described and the potential of these materials for furter development discussed.

    2. Aligned carbon nanotubes in a thin polymer film (pages 489–491)

      Dr. Pulickel M. Ajayan

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070520

      Carbon nanotubes (see figure) constitute one of the smallest one-dimensional and nearly perfect structures available and these materials should exhibit a wide range of interesting properties. Most of these properties, however, will only be of use if te structures can be manipulated into a controlled configuration here the alignment of nanotubes in thin polymer films is discussed.

    3. Nanometric surface design of size-quantized semiconductor microcrystals (pages 492–494)

      Prof. Hiroshi Yoneyama and Dr. Tsukasa Torimoto

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070521

      Semiconductor microcrystals (Q-particles) with diameters less that 100 Å, modified with viologen have recently been produced. One potential application for such particles would be for light energy conversion devices such as photocatalysts and photosenstizers in wet solar cells. The viologen moieties have the ability to function as electron mediators between the semiconductor particles and acceptors in solution. The preparation and potential applications of these ineresting materials are discussed.

    4. Present limits of data storage using dye molecules in solid matrices (pages 495–499)

      Dr. Rong Ao, Prof. Lothar Kümmerl and Prof. Dietrich Haarer

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070522

      Optical data storage offers the potential advantages of high storage densities, fewer mechanical problems, low reading and writing energies, ruggedness, and higher data rates. Currently, the only true photonic optical storage medium is the spectral hole burning scheme. The features of the technique are presented, the materials (e.g. see figure) and necessary laser technology presented, and a view is given of the prospects and requirements for future commercial development.

    5. Collective nonlinear optical properties of disordered J-aggregates (pages 500–502)

      Prof. Jasper Knoester

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19950070523

      Collective molecular optical responses can be studied in detail in J-aggregates. The aggregates are usually studied in a medium having intrinsic disorder (solutions, glasses, Langmuir–Blodgett films) and therefore disorder plays an important role when modeling their properties. Here, recent progress in the theoretical treatment of the optical properties of the aggregates is reviewed.