bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerization of 10,12‐docosadiyne‐1,22‐ disulfate in self‐assembled multilayers
Authors: Saremi Farnaz , Tieke Bernd
Published: December 2004

The polymerization of diacetylenes in self‐assembled multilayers (see Figure) should lead to a new type of ultrathin films exhibiting interesting optical and electronic properties. Here the preparation of water‐soluble diacetylene derivatives, multi‐layer formation, and the UV polymerization of the derivatives are reported.

magnified image
A blue light emitting polymer with phenylenevinylene segments in the side‐chains
Authors: Hesemann Peter , Vestweber Horst , Pommerehne Jörn , Mahrt Rainer F. , Greiner Andreas
Published: December 2004

Polymer‐based light emitting diodes constructed from amorphous materials with well‐defined conjugated segments and high glass transition temperatures are reproted. It is shown that grafting 4‐vinyl‐trans‐stilbene onto polystyrene results in side‐chain polymers with conjugated segments in the side chains which have amorphous morphologies whereas blends between a conjugated unit and a matrix polymer exhibit unwanted crystallizaion.
Molecular nanoclusters as precursors to conductive thin films and crystals
Authors: Hillier Andrew C. , Hossick Schott Joachim , Ward Michael D.
Published: December 2004

The role of epitaxy and orientation in the morphologies of thin films of organic conductors such as TTF‐TCNQ (see Figure) is discussed. It is found that the anisotropy and direction of molecular bonding with respect to the interface, as well as interfacial interactions have a profound effect on the growth of the thin films.

magnified image
Seven new organic superconductors in the system (ET)2M(CF3)4(solvent) (M = Cu, Ag): effect of solvent replacement**
Authors: Schlueter John A. , Williams Jack M. , Geiser Urs , Dtulek James D. , Kelly Margaret E. , Sirchio Scott A. , Carlson K. Douglas , Naumann D. Dieter , Roy Thomas , Campana Charles F.
Published: December 2004

Superconductivity in k‐phase organic charge transfer salts and its relation to structural differences caused by the solvent present is analyzed on the basis of seven new superconductors in the BEDT–TTF system. The superconducting salts have TcS between 2.6 and 11.1 K. The electrocrystallization of the new materials is described and the structure–proeprty relationships discussed.
Self‐assembled nanoscale tubular ensembles
Authors: Ghadiri M. Reza
Published: December 2004

Nanoscale tubular biomaterials (e.g. see Fig.) produced by the self‐assembly of peptide nanotube structures have a potentially wide range of applications in chemistry, biology, and materials science. The methods of producing such structures are reviewed and a number of potential applications discussed

magnified image

.
The journal of molecular modeling: Electronic chemistry publishing
Authors: Clark Tim
Published: December 2004

The experience of publishing the first fully electronic chemistry journal has exploded many of the myths and legends of the Internet. Tim Clark, editor of the Journal of Molecular Modeling, describes the aims and ideas behind the journal and considers its acceptance among computational chemists at universities and in industry. He briefly outlines how typically “electronic” features can be more fully exploited and concludes that we are at the beginning of an exciting new phase of scientific publishing.
Poly(2,2′‐spaced‐dipyrroles): Bandgap contraction by additive and charge‐transfer mechanisms
Authors: Pagani Giorgio , Berlin Anna , Canavesi Augusto , Schiavon Gilberto , Zecchin Sandro , Zotti Gianni
Published: December 2004

A strategy to decrease the bandgap of polypyrrole in modified pyrrole‐based polymers is the alternation of acceptor (A) and donor (D) groups in the chain. The synthesis of appropriate monomers, their electropolymerization to polyconjugated conducting polymers, and evidence for the narrow bandgap properties of the corresponding neutral systems are described. It is demonstrated that in the presence of specific charge‐transfer interactions between the A and D groups the decrease in the bandgap is strongly enhanced.
Ferromagnetic order in a novel imino nitroxide (IT)Py(C  CH) radical derived from 2‐ethynyl‐pyridine
Authors: Romero Francisco M. , Ziessel Raymond , Drillon Marc , Tholence Jean‐Louis , Paulsen Carley , Kyritsakas Nathalie , Fisher Jean
Published: December 2004

Purely organic ferromagnets are rare, the main problem being the relative orientation of the spins in a three‐dimensional network. The first example of ferromagnetic ordering in an imino‐nitroxide radical is reported. A detailed analysis of the structure reveals that CCHO hydrogen bonds are responsible for both the crystal packing and the ferromagnetic spin interactions within an infinite chain of ordered molecules. This radical is unique: its structure is the first demonstration of the use of terminal acetylenes to generate supramolecular networks.
Semiconductor nanotube formation by a two‐step template process
Authors: Hoyer Patrick
Published: December 2004

Multistep template synthesis offers an easy and general route to complicated nanostructures. A two‐step replication procedure is described that can be used to prepare nanotubes of titanium dioxide (see Figure) or other semiconducting materials. The requirements placed on the starting material, the synthesis route, and the TiO2 deposition mechanism are considered and filling of the tubes is briefly discussed.

magnified image
Rapid prototyping of complex structures with feature sizes larger than 20 μm
Authors: Qin Dong , Xia Younan , Whitesides George M.
Published: December 2004

A rapid, low‐cost technique of microfabrication for feature sizes of 20 μm or more is described, which is useful for the rapid production of limited numbers of microsensor and optical structures. The pattern can be designed on a PC and printed out on transparent films of polymers using a commercial image‐setting system. The Figure shows an SEM image of a relief pattern generated on photoresistant film using this method.

magnified image
Third‐harmonic generation from regio‐regular and regio‐irregular poly(3‐dodecylthiophenes). Dependence of χ(3) on conjugation length
Authors: Bjørnholm Thomas , Greve Daniel R. , Geisler Tommy , Petersen Jan C. , Jayaraman Manikandan , McCullough Richard D.
Published: December 2004

The third‐order nonlinear optical susceptibility of regio‐regular poly(3‐dodecylthiophenes) is observed to be enhanced by a factor of 10 as compared to that of regio‐irregular poly(3‐dodecylthiophenes) when pumped at 1907 nm. The increase in the effective conjugation length from regio‐irregular to regio‐regular poly(3‐dodecylthiophene) is estimated from linear absorption data and the reported absolute value measured at 1907 nm represents the nonlinear susceptibility of the most highly conjugated regio‐regular polythiophene film measured to date.
Dyeing salt crystals for optical applications
Authors: Kahr Bart , Jang Sei‐Hum , Subramony J. Anand , Kelley Michael P. , Bastin Loyd
Published: December 2004

Inorganic materials can encapsulate organic dye molecules in a variety of ways. Those considered here are simple inorganic salts that have adsorbed, oriented, and overgrown dyes during growth from solution, which promise spectroscopic and photonic applications. The Figure shows KH2PO4 crystals in which dyes carrying sulfonate or phosphate groups have been incorporated in the {101} growth sectors (see also the cover of this issue).

magnified image
The design and synthesis of Heterogeneous Catalyst Systems
Authors: Herron Norman , Farneth William E.
Published: December 2004

A Maxwell's Demon approach to catalysis, in which individual molecules can be distinguished, has come closer to reality in recent years. Two new approaches to catalyst synthesis are described that are leading the way to catalyst design. The Figure shown n‐octane proceeding through the 8‐ring window of zeolite A toward the iron active site for oxidation. The relative size of the window and alkaline causes selectivity for oxidation towards the end of the chain.

magnified image
Efficient blue‐light emitting devices from conjugated polymer blends
Authors: Birgerson Jonas , Kaeriyama Koji , Barta Piotr , Bröms Per , Fahlman Mats , Granlund Thomas , Salaneck William R.
Published: December 2004

A polymer light‐emitting device with an external quantum efficiency of 2%, one of the highest values in polymer‐based devices reported to date, had been fabricated from a blend of PDHPT (see Figure) and PDPP (poly(2,5‐diheptyl‐2′,5′‐dipentoxybiphenylene)). The optical properties of the polymers and the device are presented. A particularly important point is the processability of the active media.

magnified image
A new method for the preparation of conductive polyaniline solutions: Application to liquid crystal devices
Authors: Harlev Eli , Gulakhmedova Tamila , Rubinovich Ilia , Aizenshtein Gentadi
Published: December 2004

Transparent “all‐polymer” electrodes are promising candidates for applications in LCDs and LEDs and LEDs. A novel approach for making a new polyaniline‐based polymer is described, efficient solubilization of the conductive from of polyaniline is reported, and use of the resulting conductive polymer solutions for LCDs demonstrated. The Figure shows a bent polymer‐dispersed LCD with transparent “all‐polymer” electrodes in the “on” (transparent) state.

magnified image
Oligo(siloxane) rings and cages possessing nickel‐containing liquid crystal side chains
Authors: Saez Isabel M. , Styring Peter
Published: December 2004

A liquid‐crystalline coordination compound immobilized on an oligomeric superstructure free from cross‐linking (see Figure) is reported for the first time. A highly versatile synthetic methodology is described that allows unsymmetrical, mono‐functionalized, metal‐containing liquid‐crystalline coordination complexes to be prepared. Related materials may find uses as novel catalysts.

magnified image
Oriented growth of molecular sieves on inorganic membranes
Authors: Wu Chih‐Ning , Chao Kuei‐Jung , Tsai Tzeng‐Guang , Chiou Yuan‐Horng , Shih Han‐Chang
Published: December 2004

A molecular sieve film with vertically oriented and closely packed crystals has been prepared by a novel method. The Figure shows VAP4‐5 (zeolite‐like) crystals anchored inside the straight channel walls of an anodic alumina membrane. The novel method of synthesis is outlined and the effect of varying the growth conditions, e.g., temperature, solution dilution, chemical composition, reactant source, described.

magnified image
Purification and opening of carbon nanotubes via bromination
Authors: Chen Yao K. , Green Malcolm L. H. , Griffin Julian L. , Hammer Jens , Lago Rachel M. , Tsang Shik C.
Published: December 2004

The purification and opening of carbon nanotubes via bromination is reported. Refluxing raw cathodic soot containing a mixture of nanotubes, nanoparticles, and amorphous carbon in liquid bromine, followed by oxidation in air, is shown to yield 10–20; w/w pure and opened nanotubes. The role of bromine in the purification steps is discussed, based on the results of transmission electron microscopy, temperature programmed oxidation, X‐ray diffraction, and X‐ray photoelectron spectroscopy investigations.
Parallel patterning with nanochannel glass replica membranes
Authors: Pearson Douglas H. , Tonucci Ronald J.
Published: December 2004

Nanochannel glass replica membranes, a recent invention, can be used for parallel patterning of substrates, for example as a shadow mask in reactive ion etching. The preparation of the membranes—formed by physical vapor deposition on wafers that have been cut from bundles of two types of glass fibers that are repeatedly drawn down to the correct dimensions—their uses and their advantages are described. How the size, position, geometric pattern, and packing density of the voids in the membranes can be controlled to a high degree is outlined.
Metal nanoparticle/polymer superlattice films: Fabrication and control of layer structure
Authors: Schmitt Johannes , Decher Gero , Dressick Walter J. , Brandow Susan L. , Geer Robert E. , Shashidhar R. , Calvert Jeffrey M.
Published: December 2004

Multilayer superlattices incorporating colloidal metal nanoparticles have been synthesized by an approach based on self‐assembly. Teh method of synthesis is described and the results are presented from X‐ray reflectivity measurements, optical spectroscopy, and various microscopies, showing that they provide a consistent picture of the structure of the resulting multilayer superlattices (see Figure). fig.

magnified image
Laser Ablation of Doped Polymer Systems
Authors: Lippert Thomas , Yabe Akira , Wokaun Alexander
Published: December 2004

Laser ablation has become a widely recognized tool for materials processing. In the area of polymeric materials, applications of UV lasers for surface modification, microlithography, cutting, and boring have been explored. With the addition of dopants into the bulk, it has become possible to sensitize most known classes of polymers for UV laser ablation at any desired wavelength, including fluoropolymers. Important features of dopant‐induced ablation are the reduction of threshold energy fluence required for ablation, and the enhancement of the etching rate by factors higher than ten. In the present review the investigated dopant/polymer systems are summarized and compared. Based on the available information, a general scheme including all relevant pathways is suggested, revealing that in each particular case the dominant mechanism depends on the specific system under study.
Efficient blue LEDs from a partially conjugated Si‐containing PPV copolymer in a double‐layer configuration
Authors: Garten Frank , Hilberer Alain , Cacialli Franco , Esselink Eddy , van Dam Yvonne , Schlatmann Bart , Friend Richard H. , Klapwijk Teun M. , Hadziioannou Georges
Published: December 2004

Efficient blue electroluminescent devices based on a novel silicon‐containing poly(P‐phenylene) derivative are described. It is shown that the turn‐on field and internal quantum efficiency can be improved by using a double‐layer device configuration instead of a single‐layer one and by the addition of a transport layer at the cathodic side. The combined study of electrical and optical properties on one hand and morphological aspects on the other is demonstrated to be a fruitful approach to the improved performance of organic electronics.
Hybrid organic‐inorganic electrodes: The molecular material formed between polypyrrole and the phosphomolybdate anion
Authors: Gómez‐Romero Pedro , Lira‐Cantú Mónica
Published: December 2004

Hybrid molecular electrodes, based on a conducting polymer matrix containing a dispersion of an electroactive inorganic component, are reported. The phosphomolydate anion, [PMo12O40]3⊖, is dispersed in polypyrrole to investigate cooperative phenomena between the components. The interactions are shown to influence the magnetic, electrical, photochemical and electrochemical properties of these composite materials.
Nanocrystalline materials prepared through crystallization by ball milling
Authors: Giri Anit K.
Published: December 2004

The process of mechanical milling of amorphous precursors can be used to produce bulk quantities of material with fine crystalline nanostructures. Here, the process and the factors which influence the quality of the materials produced are reviewed. The crystallization induced by mechanical milling and thermal annealing are compared and it is suggested that the induction of crystallization by ball milling may be a promising technique for preparing soft magnetic materials in powder form.
An improved experimental determination of external photoluminescence quantum efficiency
Authors: de Mello John C. , Wittmann H. Felix , Friend Richard H.
Published: December 2004

The external photoluminescence quantum yield of, for example, thin film semiconductors can be conveniently determined using the improved integrating‐sphere method (see Figure) presented here. Spectrally resolved detection allows the excitation source and the emission to be distinguished. The method will be particularly useful for samples with small Stocks' shifts or low photoluminescence quantum yields or for highly scattering samples. Fig

magnified image
5, 5″‐Bis{4‐[bis(4‐methylphenyl)amino]phenyl}2, 2′:5′, 2″‐terthiophene and 5, 5‴‐bis{4‐[Bis(4‐methylphenyl)amino]phenyl}2, 2′:5′, 2″:5″, 2‴‐quaterthiophene as a Novel Family of Amorphous Molecular Materials
Authors: Noda Tetsuya , Imae Ichiro , Noma Naoki , Shirota Yasuhiko
Published: December 2004

A novel family of photo‐and electroactive amorphous molecular materials containing an oligothiophene moiety linked to two triphenylamine moieties has been designed and synthesized (see Figure). Their glass‐forming properties, morphological changes, and molecualr and solid‐state properties are described. They are reported to exhibit multiredox behavior on electrochemical oxidation.

magnified image
Structure and optical property changes of sol‐gel derived VO2 thin films
Authors: Lu Songwei , Hou Lisong , Gan Fuxi
Published: December 2004

The semiconductor–metal phase change in VO2 at approximately 67°C, which results in great changes in its optical, electrical, and magnetic properties, is described in detail. The synthesis of VO2 thin films by the sol‐gel method is outlined and the structure and optical properties are characterized, including hysteresis phenomena in the transmittance–temperature and reflectivity–temperature plots. A mechanism of the phase change—confirmed to be the monoclinic‐to‐tetragonal rutile transition—is proposed based on coordinative field theory.
Bulk synthesis of the 135 K superconductor HgBa2Ca2Cu3O8+δ
Authors: Peacock Graeme B. , Gameson Ian , Edwards Peter P.
Published: December 2004

Bulk synthesis of the high‐temperature superconductor HgBa2Ca2O8+δ (Hg‐1223)—an important step towards realizing its technological potential—is described. In the reaction discussed, the formation of bulk samples (up to 20 g) with excellent phase purity and transition temperatures above 130 K at ambient pressure proceeds from the binary oxides by a solid‐state route. The significant advantages of this method compared to the high‐pressure routes currently used are pointed out.
Fabrication of polymeric microstructures with high aspect ratios using shrinkable polystyrene films
Authors: Zhao Xiao‐Mei , Xia Younan , Qin Dong , Whitesides George M.
Published: December 2004

High‐aspect‐ratio polymeric structures have been fabricated using a process that combines reactive ion etching (RIE) and stress‐oriented, shrinkable polystyrene films. It is reported how, after pattering of the surface of the polystyrene film by RIE, heating of the film caused it to shrink by a factor of 4–5 in the lateral dimensions while the thickness of the film and the features on it increased by a factor of ∼20 (see Figure). Fig.

magnified image
The synthesis of micrometer‐ and submicrometer‐size spheres of ordered mesoporous oxide MCM‐41
Authors: Grün Michael , Lauer Iris , Unger Klaus K.
Published: December 2004

Spherical particles of the mesoporous material MCM‐41 have been synthesized and are reported for the first time. The results of characterization of the samples by X‐ray diffraction, scanning electron microscopy, and nitrogen sorption at 77 K (which provides information about the pore system) is described. It is shown that all the properties of the spherical MCM‐41 particles are essentially the same as those of the MCM‐41 materials synthesized by well‐established methods. Finally, possibilities for future research are outlined.
Persistent photoinduced effects in high‐Te superconductors
Authors: Hoffmann Axel , Reznik Dmitry , Schuller Ivan K.
Published: December 2004

The reaction of high‐temperature cuprate superconductors to illumination differs from the reaction produced in conventional superconductors. Two such effects, reviewed here, are persistent photoconductivity and persistent photoinduced superconductivity. For example, REBa2Cu3Ox thin films show a decrease in the normal state resistance and an increase of Tc which persist for a long time at low temperatures (< 100 K). The experimental investigations and results are briefly presented, before two alternative theoretical models are considered.
Progress and perspectives in solar energy conversion
Authors: Kuwano Yukinoro
Published: December 2004

Photovoltaic (PV) power generation can surely be considered a critical technol‐ ogy for overcoming global environmental problems and energy problems. This essay will review the current status and application technologies of PV power gene‐ ration, concluding with a discussion of the prospects of a future global‐scale energy supply system based on PV power generation.
Growth mode of HgBa2Ca2Cu3O8+δ superconducting films prepared by a Sol‐Gel method on a Yo0.15Zr0.85O1.93 Substrate
Authors: Reich Shimon , Tsabba Yzhak
Published: December 2004

The growth mode and structure of superconducting films of Hg‐1223 (HgBa2Ca2Ca2Cu3O8+δ) are described. The results from atomic force microscopy and X‐ray studies are presented and the implications for the unit cell discussed. The positions of the atoms relative to the substrate Y0.10Zr0.85O1.93 are calculated by computer simulation—showing that the growth is epitaxial. Hg‐1223 is a member of the family of superconducting cuprates HgBa2Can−1CunO2n‐2+δ, which are important for both science and technology.
The structure of small GaAs clusters
Authors: Jiang Jiechao , Schaper Andreas K. , Schäfer Rolf , Hihara Takehiko , Becker JöRg A.
Published: December 2004

Semiconductor clusters, particularly gallium arsenide, have potential applications in nonlinear optical devices. Special interest is generated by the fact that their optical and electronic behavior depends on the size of the cluster. Direct evidence is presented for the occurrence of hexagonal, i.e., wurtzite‐type structure, GaAs in clusters, whereas bulk GaAs has zinc‐blende structure. High‐resolution transmission electron microscopy, atomic force microscopy and electron diffraction results are reported and interpreted. Suggestions are made for further work.
Magnetic properties of nitronyl nitroxide radicals substituted in phenylboronic acid the BOH ⃛O hydrogen bond as a constituent unit of a one‐dimensional suprastructure exhibiting a ferromagnetic spin interaction
Authors: Akita Takeyuki , Kobayashi Keiji
Published: December 2004

The NO…︁HOB hydrogen bond has recently been shown to play a role as an intermolecular ferromagnetic spin coupler. Studies of this bound in phenylboronic acid derivatives substituted by the nitronyl nitroxide radical moiety are presented, in particular the synthesis, crystal structure, and magnetic properties of the para‐substituted phenylboronic acid shown in the Figure and the corresponding meta compound. Boronic acid derivatives bearing the NO radical center are shown to be promising precursors for molecular magnetic materials.

magnified image
Microlithographic process for patterning conjugated emissive polymers
Authors: Renak Michelle L. , Bazan Guillermo C. , Roitman Daniel
Published: December 2004

The spatially confined synthesis of emissive conjugated polymers—compatible with existing 1C fabrication technology—is described, which can be used to create well‐defined micrometerscale patterned organic LEDs (see cover). The Figure shows the first step in the photolithographic process, which is followed by irradication, to produce a latent image, and development, resulting in patterned polymer.

magnified image
Measurements of optical electric field intensities in microcavities using thin emissive polymer films
Authors: Burns Seamus E. , Pfeffer Nicola , Grüner Johannes , Remmers Marcus , Javoreck Thomas , Neher Dieter , Friend Richard H.
Published: December 2004

The behavior of chromophores in microcavities—Fabry‐Perot resonators with thickness of the order of the wavelength of light that are introduced into light‐emitting devices to improve performance—is reported. Strong modification of the absorption and the spontaneous emission rates of the chromophores is demonstrated for thin luminescent layers of polyphenylene derivatives placed at different positions in the cavities. The technique of measurement is detailed and the implications of the results are discussed.
Electrochemical redox behavior and electroluminescence in the mixed energy‐sufficient system thianthrene and 2‐(4‐Biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole
Authors: Janietz Silvia , Wedel Armin
Published: December 2004

Efficient use of organic compounds in electroluminesent devices requires detailed knowledge of their redox potential values and their ability to form stable radical ions, information available from electrochemical investigations. The electrochemical behavior of the title compounds (TH and PBD) is described, followed by the preparation of light‐emitting diodes (LEDs) based on them. The characteristics of mixed single‐layer and separated double‐layer devices presented here suggested that PBD and TH could be used for the construction of LEDs.
Surface chemistry of Luminescent Silicon Nanocrystallites
Authors: Sailor Michael J. , Lee Eric J.
Published: December 2004

The rational modification of porous and single‐crystalline silico surfaces is of particular interest for technologies based on silicon. Porous silicon, such as the layer shown in the Figure, has many potential technological applications. In this review of chemical reactions developed for Si surface modification, both extensions of the chemistry of molecular Si compounds to surfaces and new surface chemistry are treated.

magnified image
Ultrathin cellulose ether network as a host matrix for alkylthiophene polymerization
Authors: Henry Christelle Denise , Tebbe Heiko , Wegner Gerhard , Arrnand Frank , Ruaudel‐Teixier Annie
Published: December 2004

New insights into the mechanism of chain growth and phase formation in electropolymerization are expected from the work on ultrathin films described here. The Figure shows that the very rapid electrochemical polymerization of a thiophene derivative that occurs inside a multilayered assembly of a cellulose derivative on an electrode can be used as the basis of an imaging process.

magnified image
Molecular rectification in oriented polymer structures
Authors: Sentein Carole , Fiorini CéLine , Lorin André , Nunzi Jean‐Michel
Published: December 2004

Oriented diode‐like molecules in a polymer binder are the new approach described here for overcoming the problems associated with Schottky and p‐n junctions in semiconductor devices. The principles relies on the intrinsic polar nature of the organic molecules used–which causes them to orient in an applied static electric field–and is expected to improve significantly the efficiency of polymeric semiconductor devices. The principle is outlined and experimental evidence presented for molecular rectification equivalent to ad distributed p‐n homojunction.
Induction of high‐temperature superconductivity in pulsed laser ablated La2CuO4 thin films by room temperature chemical oxidation
Authors: Lees Simon T. , Edwards Peter P. , Gameson Ian , Jones Martin O. , Slaski Marcin , Rial Carmen , Amador Ulises , Morán Emilio
Published: December 2004

Facile fabrication of high‐temperature superconducting La2CuO4 thin films through the combination of two seemingly disparate techniques is reported. Pulsed laser ablation is used to produce stoichiometric, c‐axis oriented La2CuO4 thin films −3700 Å in thickness. The convenient method of controlled room‐temperature chemical oxidation using aqueous sodium bromite is then utilized to introduce excess holes in the valance band of La2CuO4. This induces superconductivity in the otherwise antiferromagnetic semiconductor.
The photovoltaic stability of, bis(isothiocyanato)rlutheniurn(II)‐bis‐2, 2′bipyridine‐4, 4′‐dicarboxylic acid and related sensitizers
Authors: Kohle Oliver , Grätzel Michael , Meyer Andreas F. , Meyer Tobias B.
Published: December 2004

The photovoltaic stability of RuII(LH2)2(NCS)2 (where LH2 = 2,2′‐bipyridyl‐4,4′‐dicarboxylic acid), a potential sensitizer for solar cells based on anatase, is examined. Its suitability for this role is demonstrated by a 7000 h endurance test, at the end of which no discernible signs of degradation can be detected. An explanation for its remarkable stability of provided by an investigation of its photo‐ and thermally induced reactions in alcoholic solution. Recommendations as to how to avoid ligand substitution reactions that may be undesirable for certain applications are also made.
Soluble organosilicon micronetworks with spatially confined reaction sites
Authors: Baumann Frank , Deubzer Bernhard , Geck Michael , Dauth Jochen , Sheiko Sergio , Schmidt Manfred
Published: December 2004

Extremely small monodisperse micronetworks have potential applications as molecular containers or reaction vessels. The advantages of the sol‐gel synthesis reported here, involving endcapping with Si‐O‐SiR3 groups, are pointed out and the characterization of the resulting spherical particles (radius between 5 nm and 20 nm), see Figure, is described. The variety of functional groups and the high density of potential reaction sites are stressed.

magnified image
Unprecedented thermo‐ and ion‐responsive behavior of a non‐ionic water‐soluble polysilane
Authors: Cleij Thomas J. , Jenneskens Leonardus W. , Kluijtmans Sebastiaan G. S. J. M.
Published: December 2004

Polysilanes display remarkable optical and electronic properties that are affected by teh degree of σ‐conjugation, which depends on the conformation of the silicon backbone. The thermo‐ and ion‐responsive behavior of aqueous solutions of 1 (Figure) is described, including «inverse» abrupt termochromism and the tunability of the lower critical solution temperature (LCST) by addition of inorganic salts.

magnified image
Giant magnetoresistance, charge‐ordering, and related aspects of manganates and other oxide systems
Authors: Rao C. N. R. , Cheetham Anthony K.
Published: December 2004

Giant magnetoresistance, and spin‐, charge‐, and orbital‐ordering are some of the properties displayed by manganates that make these materials of interest in magnetic recording, sensor, and actuator technology. New and significant results on the giant magnetoresistance found in films as well as polycrystalline and single‐crystal samples of rare earth manganates are reviewed along with related aspects. The unique features of these systems and the as‐yet unsolved problems are highlighted. Charge‐ordering as opposed to spin‐ordering is also discussed and suggestions for future directions are given.
Low molecular weight and polymeric triphenylenes as hole transport materials in organic two‐layer LEDs
Authors: Bacher Andreas , Bleyl Ingo , Erdelen Christian H. , Haarer Dietrich , Paulus Wolfgang , Schmidt Hans‐Werner
Published: December 2004

The benefits of using hexa‐alkoxytriphenylenes as hole transport materials for two‐layer light‐emitting diodes are reported. Both low molecular weight and polymeric triphenylenes are investigated. The polyacrylate shown in the figure is demonstrated to have excellent film‐forming properties and combines sufficient charge carrier mobility with good hole injection properties to make it a very suitable hole transport material.

magnified image
Stability improvement of high‐performance photorefractive polymers containing eutectic mixtures of electro‐optic chromophores
Authors: Meerholz Klaus , Bittner Reinhard , De Nardin Yessica , Bräuchle Christoph , Hendrickx Eric , Volodin Boris L. , Kippelen Bernard , Peyghambarian Nasser
Published: December 2004

Amorphous organic photorefractive materials, which are useful for reversible holographic applications such as real‐time optical processing and holographic data storage, have excellent performance but limited self life, often owing to the crystallization of one of the components. A technique is presented for improving the long‐term stability of composites based on poly(N‐vinylcarbazole) that uses mixtures of two isomeric electrooptically active chromophores. The self‐life is shown to be significantly increased and the photorefractive device performance as good as that of the best materials known previously.
Solution‐phase synthesis of luminescent materials libraries
Authors: Sun Xiao‐Dong , Wang Kai‐An , Yoo Young , Wallace‐Freedman William G. , Gao Chen , Xiang Xiao‐Dong , Schultz Peter G.
Published: December 2004

The application of combinatorial methods to the synthesis and characterization of novel materials is described for the case of solution‐phase synthesis of phosphors based on rare‐earth‐activated refractory metal oxides. A scanning multiinkjet system is shown to be suitable for the fabrication of a liberry such as (LamGd1‐m)‐AlnOx:Eu, the photoluminescence image of part of which is shown in the Figure.

magnified image
Electrical and optical properties of Processable Polythiophene Derivatives: Structure‐Property relationships
Authors: Leclerc Mario , Faid Karim
Published: December 2004

Control of the electrical and optical properties of different polythiophene derivatives can be achieved, to some extent, by adjusting the nature of their substituents. The effects of flexible side chains (increase in solubility, modification of the stability of the conducting state, induction of thermo‐, iono‐, photo‐, or biochromism) such as alkyl or alkoxy moieties are reviewed and the promising self‐doped polythiophenes (see Figure) discussed.

magnified image
Novel photorecording langmuir‐blodgett films
Authors: Liu Minghua , Ushida Kiminori , Nakahara Hiroo , Kira Akira
Published: December 2004

A photocontrolled reaction of Langmuir‐Blodgett (LB) films with transition metal ions is demonstrated to be suitable as the basis of a new method of photorecording. The setup required for recording is described and experiments on TARC18 and PARC18 films (a thiazolylazophenol and a pyridylazophenol derivative, respectively) are reported. Advantages compared to previously known techniques of photorecording in LB films are pointed out, for example, that differently colored states can be achieved with a single chelating reagent simply by changing the metal ions.
Rewritable full‐color recording on a thin solid film of a cholesteric low‐molecular‐weight compound
Authors: Tamaoki Nobuyuki , Parfenov Alexander V. , Masaki Atsushi , Matsuda Hiro
Published: December 2004

Rewritable full‐color recording is potentially technologically important but has not yet been realized. A cholesteric low‐molecular‐weight compound (see Figure) is presented that, in the form of a thin film, displays iridescent colors at room temperature (see the cover picture of this issue) that can be recorded and erased repeatedly to form images by thermal treatment.

magnified image
Large third‐order nonlinear optical response from molecules with effective multidirectional charge‐transfer transitions: New design of third‐order nonlinear chromophores
Authors: Greve Daniel R. , Schougaard Steen B. , Geisler Tommy , Petersen Jan C. , Biørnholm Thomas
Published: December 2004

Enhanced values of the second molecular hyperpolarizability, γ, are reported for molecules that undergo significant multidirectional charge redistributions between the ground and excited states, e.g., charge is displaced from the periphery to the center, or vice versa, upon excitation, in during large changes in electric moments higher than dipole moments. The γ‐values are compared with those for polyene‐like molecules having a similar number of π‐electrons. It is demonstrated that the “periphery‐to‐center charge‐transfer” design concept is fruitful and should lead to new molecules with high γ‐values.
Micropatterning fluid membranes
Authors: Ulman Nick , Groves Jay T. , Boxer Steven G.
Published: December 2004

An application of photolithographic patterning is described for producing a self‐assembled membrane that is fluid over some areas and immobilized or absent in others, as directed by the patterning on the support (see Figure). This is an important step towards forming a specific interface between living cells and silicon electronics. (Figure reprinted from Science 1997 275, 651–653; ©1997 AAAS)

magnified image
Does Microgravity Influence Self‐Assembly??
Authors: Dag Ömer , Ahari Homayoun , Coombs Neil , Jiang Tong , Aroca‐Ouellette Patricia P. , Petrov Srebri , Sokolov Igor , Verma Atul , Vovk Gregory , Young David , Ozin Geoffrey A. , Reber Christian , Pelletier Yanick , Bedard Robert L.
Published: December 2004

The templated syntheses of TMA2Sn3S7 and TBA2Sn4S9 (where TMA is tetramethylammonium and TBA is n‐tetrabutylammonium) microporous layered tin(iv) sulfides have been carried out under both microgravity (μG) and earth (1G) conditions in order to elucidate the influence of gravity on the self‐assembly and crystal‐growth processes of this class of materials. The μG experiments were conducted on board the May 1996 Endeavour STS‐77 NASA space‐shuttle flight. It was determined that the long‐range ordering of the porous layers and the population of defects but not the short‐range ordering within the layers is influenced by gravity. Bulk and surface crystallinity, smoothness of crystal faces, optical quality, crystal habits, registry of the porous layers, and accessible void volume to adsorbates were found to be improved in the space‐grown crystals. This is probably because the forces associated with the organization of the porous layers are expected to be weak and sensitive to the elimination of buoyancy‐driven convective flows and Stokes sedimentation effects in a microgravity environment. One can draw an analogy to the weak forces between protein macromolecules and the established effect of microgravity on improving the diffraction quality of crystals harvested in space.
The first ZnBr2‐based upconversion glass fiber waveguide
Authors: Egger Philipp , Trusch Bernhard , Rogin Peter , Giovanoli Rudolf , Hulliger Jürg
Published: December 2004

Visible solid‐state lasers based on upconversion glass fiber waveguides are attractive because upconversion, the resonant conversion of near‐infrared (NIR) to visible light, permits high laser power in narrow bands and the fiber geometry guarantees a high exciting NIR radiation density along the entire absorption medium. The synthesis of the first upconversion fibers based on a heavier halide (ZnBr2) is reported. A modified fiber preparation process that decreases the risk of attack by moisture is described and the losses along the fiber investigated.
A blue‐emitting triazole‐based conjugated polymer
Authors: Grice Alan W. , Tajbakhsh Ali , Burn Paul L. , Bradley Donal D. C.
Published: December 2004

Improved performance of light‐emitting devices is reported for devices containing the newly synthesized, triazole‐containing polymer TRIDSB (see Figure). This fully conjugated material has a high solid‐state photoluminescence quantum efficiency, unlike other triazole polymers investigated previously, and emits blue light. TRIDSB holds promise as an electron‐transporting material.

magnified image
Caspase‐1–processed interleukins in hyperoxia‐induced cell death in the developing brain
Authors: Felderhoff‐Mueser Ursula , Sifringer Marco , Polley Oliver , Dzietko Mark , Leineweber Birgit , Mahler Lieselotte , Baier Michael , Bittigau Petra , Obladen Michael , Ikonomidou Chrysanthy , Bührer Christoph
Published: December 2004

Infants born prematurely may develop neurocognitive deficits without an obvious cause. Oxygen, which is widely used in neonatal medicine, constitutes one possible contributing neurotoxic factor, because it can trigger neuronal apoptosis in the developing brain of rodents. We hypothesized that two caspase‐1–processed cytokines, interleukin (IL)–1β and IL‐18, are involved in oxygen‐induced neuronal cell death. Six‐day‐old Wistar rats or C57/BL6 mice were exposed to 80% oxygen for various time periods (2, 6, 12, 24, and 48 hours). Neuronal cell death in the brain, as assessed by Fluoro‐Jade B and silver staining, peaked at 12 to 24 hours and was preceded by a marked increase in mRNA and protein levels of caspase 1, IL‐1β, IL‐18, and IL‐18 receptor α (IL‐18Rα). Intraperitoneal injection of recombinant human IL‐18–binding protein, a specific inhibitor of IL‐18, attenuated hyperoxic brain injury. Mice deficient in IL‐1 receptor–associated kinase 4 (IRAK‐4), which is pivotal for both IL‐1β and IL‐18 signal transduction, were protected against oxygen‐mediated neurotoxicity. These findings causally link IL‐1β and IL‐18 to hyperoxia‐induced cell death in the immature brain. These cytokines might serve as useful targets for therapeutic approaches aimed at preserving neuronal function in the immature brain, which is exquisitely sensitive to a variety of iatrogenic measures including oxygen. Ann Neurol 2005;57:50–59
Glut‐1 deficiency syndrome: Clinical, genetic, and therapeutic aspects
Authors: Wang Dong , Pascual Juan M. , Yang Hong , Engelstad Kristin , Jhung Sarah , Sun Ruo Peng , De Vivo Darryl C.
Published: December 2004

Impaired glucose transport across the blood‐brain barrier results in Glut‐1 deficiency syndrome (Glut‐1 DS, OMIM 606777), characterized by infantile seizures, developmental delay, acquired microcephaly, spasticity, ataxia, and hypoglycorrhachia. We studied 16 new Glut‐1 deficiency syndrome patients focusing on clinical and laboratory features, molecular genetics, genotype–phenotype correlation, and treatment. These patients were classified phenotypically into three groups. The mean cerebrospinal fluid glucose concentration was 33.1 ± 4.9mg/dl equal to 37% of the simultaneous blood glucose concentration. The mean cerebrospinal fluid lactate concentration was 1.0 ± 0.3mM, which was less than the normal mean value of 1.63mM. The mean Vmax for the 3‐O‐methyl‐D‐glucose uptake into erythrocytes was 996 fmol/106 red blood cells per second, significantly less (54 ± 11%; t test, p < 0.05) than the mean control value of 1,847. The mean Km value for the patient group (1.4 ± 0.5mM) was similar to the control group (1.7 ± 0.5mM; t test, p > 0.05). We identified 16 rearrangements, including seven missense, one nonsense, one insertion, and seven deletion mutations. Fourteen were novel mutations. There were no obvious correlations between phenotype, genotype, or biochemical measures. The ketogenic diet produced good seizure control. Ann Neurol 2005;57:111–118
Nonconsensus intronic mutations cause episodic ataxia
Authors: Wan Jijun , Carr Janai R. , Baloh Robert W. , Jen Joanna C.
Published: December 2004

We discovered intronic mutations in two episodic ataxia type 2 (EA2) families: a four‐nucleotide GAGT deletion at IVS41+(3–6) and a single nucleotide insertion (insT) at IVS24+3. We expressed minigenes harboring the mutations in cell lines to demonstrate exon skipping from the deletion mutation and the activation of a cryptic splice donor site from the insertion mutation. The identification of these disease‐causing mutations expands the spectrum of EA2 mutations and emphasizes the importance of intronic sequences in regulating gene expression. Ann Neurol 2005;57:131–135
Conformation studies on the sodium and cesium salts of calf thymus deoxyribonucleic acid (DNA)
Authors: Cohen Gerald , Eisenberg Henryk
Published: December 2004

Solutions of calf thymus NaDNA in 0.2M NaCl and CsDNA in 0.2M CsCl (fragmented by sonic irradiation to a molecular weight of about 5 × 105) were examined by electron microscopy, light scattering, and viscosity measurements. Electron microscopy showed that the molecular fragments are rodlike in shape and that the distribution of their lengths is sharp (Lw/Ln ∼ 1.06). The weight‐average number of nucleotides Zw per DNA molecule derived from light scattering was found to be in very good agreement with the value Lw derived from electron microscopy. The z‐average length Lz derived from light scattering at 25°C. was found to be about 89% of the corresponding value derived by electron microscopy. Similarly, the value of Lw derived from intrinsic viscosity at 25°C. on the basis of a rodlike model was found to be about 87% of the corresponding value derived by electron microscopy. It is concluded that the molecules are slightly flexible and do not, assume their full contour length in solution because of the disorienting effect of Brownian motion. The intrinsie viscosity was found to increase linearly with decreasing temperature toward a limiting value corresponding to the fully stretched length of the macromolecules at 0°K.: a reasonable value for the modulus of elasticity could be calculated. It was also found that, no differences in conformation could be delected in t he two systems CsDNA‐0.2M CsCl and NaDNA‐0.2M NaCl.
Infrared absorption spectrum of keratin. II. Deuteration studies
Authors: Bendit E. G.
Published: December 2004

A number of new bands have been found in the spectra of deuterated α‐ and β‐keratin. In particular, the deuteration difference spectrum has been useful for the determination of frequencies of previously unsuspected bands. Thus it is found that the amide A and II frequencies of the nonhelical component in α‐keratin occur at 3310–3320 and 1520 cm.−1, respectively, and that both bands exhibit dichroism consistent with polypeptide chains which have a measure of alignment parallel to the fiber axis. The parallel dichroism of the amide II′ band of this phase at about 1435 cm.−l also indicates some alignment. A nondichroic residual band at 1513 cm.−1 in highly deuterated α‐keratin is assigned to the tyrosine residue, as a sharp band near this frequency is found in the spectrum of polytyrosine. The ν‖(o) component of the α‐helix is weak or absent in α‐keratin, and the relatively sharp band observed near this frequency is thought to be due to the tyrosine residue, while its dichroism is caused by the presence of dichroic nonhelical material. A band near 1575 cm.−1 in deuterated α‐ and β‐keratin is tentatively assigned to the deuterated guanidinium group of arginine. This band becomes progressively more prominent during deuteration, which indicates that some arginine side chains arc slow to exchange, possibly because their environment prevents interaction with D2O. The deuteration difference spectrum also shows that, contrary to earlier views, helical material in α‐keratin exchanges significantly during the early stages of deuteration, although at a slower rate than the nonhelical material, while part of the nonhelical phase does not exchange as rapidly as had been thought and makes a contribution even after many hours or days.
Solution properties of synthetic polypeptides. II. Sedimentation and viscosity of poly‐γ‐benzyl‐L‐glutamate in dimethylformamide
Authors: Fujita Hiroshi , Teramoto Akio , Yamashita Tsuneko , Okita Koichi , Ikeda Shoichi
Published: December 2004

Nine samples of poly‐γ‐benzyl‐L‐glutamate (PBLG), ranging in M̄w from 19,000 to 410,000, were examined viscomctrically and by ultracentrifugation with dimethylforma‐mide (DMF) at 25°C. as helicogenic solvent. The data for [η] and s0 (limiting sedimentation coefficient) as functions of M̄w were fitted well by the theories for a rigid prolate ellipsoid of revolution whose major axis increases linearly with M̄w, but whose minor axis is independent of M̄w. This implies that the overall shape of the PBLG molecule in DMF is represented by a straight cylinder whose cross section is independent of its length. The length per monomeric residue h evaluated from [η] is about 1.3 A., whereas that from s0 is about 1.6 A. No adequate explanation for this difference in h can be found at present. More serious is the fact that these hydrodynamically evaluated values of h are appreciably larger than, the value obtained from our light‐scattering measurements reported previously. All these values of h from our studies are not consistent with the value characteristic of the α‐helix, for which h is 1.5 A. The concentration dependence of s0 was found to agree well with the recent theoretical prediction of Peterson for cylindrical macromolecules.