bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Properties of C60 and M6C60 (M=K, Rb, Cs) films
Authors: Ren S. L. , Wang Ying , Holden M. , Rao A. M. , Ni F. , Lee W. , Hager G. T. , Eklund P. C. 
Published: March 2011

ABSTRACTWe report the optical properties of C60 determined from the variable angle ellipsometry and near normal incidence reflection / transmission (R.T) experiments, and of M6C60 from the R, T experiments. The measurements were performed on thin films (d∼1000 Å) of C60 and M6C60 deposited on both Si(100) and suprasil substrates. The onset for strong absorption across the HOMO-LUMO gap in CgQ is measured to be -2.3 eV, slightly larger than the gap values obtained from the x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) experiments. The observed peak positions in ε2(ω) for M6C60 and C60 compares well with the recent band structure calculations and suggests that the M6C60 compounds exhibit only a weak hybridization between the C60 and M states.
Electronic Effects of Adducts on C60: A Molecular Orbital Analysis
Authors: Fann Y. C. , Singh D. , Jansen S. A. 
Published: March 2011

ABSTRACTBuckmisterfullerene, C60, has attracted great interest because of its carbon-cage structure and potential applications in the field of superconductivity when doped with alkali metals. The icosahedral framework of C60 has been confirmed by X-ray analysis of an osmylated C60, called ‘Bunnyball’. Little theoretical work has been done to understand the electronic mechanism of C60 and substituted C60. This work has focused on electronic properties of C60 and the bunnyball with hypothetical analogs metal substitutions to understand the electronic effects of adducts on the bunnyball. In this analysis, the osmylated C60and hypothetical analogs were studied by extended Hückel methods. Molecular orbital(MO) interaction diagrams constructed from Density of States (DOS) analysis of the bunnyballs are presented. The results suggest electronic effects induced by substitution /adduct strongly affect electronic population in the C60 unit.
Nonlinear Optical Properties of Buckminsterfullerene, C60, in the Near-Infrared
Authors: Kafafi Z. H. , Lindle J. R. , Pong R. G. S. , Bartoli F. J. , Lingg L. J. , Milliken J. 
Published: March 2011

ABSTRACTTime-resolved degenerate four-wave mixing experiments were conducted on films of pure Qo using a 35 ps Nd:YAG laser. The measurements wavelength 1.064 μm was far off resonance with any one-photon absorption bands. A small linear absorption coefficient α=6 cm−1 was measured at this wavelength. The third-order optical susceptibility χxxxx(3) of C60, derived from its phase conjugate signal, is 7 × 10−12 esu. The nonlinear optical temporal response was largely laser-pulse limited. Evidence for a fifth-order contribution to the nonlinear optical response was observed at high laser intensities.
Magnetic Properties in Charge-Transfer Complexes of High-Symmetry Organic Acceptors
Authors: Sugimoto Toyonari , Murahashi Eiji , Ikeda Kaoru , Yoshida Zen-Ichi , Nakatsuji Hiroshi , Yamauchi Jun , Kai Yasushi , Kasai Nobutami 
Published: March 2011

ABSTRACTTris(l, 2-benzodithio)- and tris(l, 2-ethylenedithio)-trimethylenemethane dication salts were synthesized for the purpose of using as an acceptor in the formation of charge-transfer (CT) complexes with some dianionic donors. In the CT complexes of these dications with hexacyanotrimethylenecyclopropane and tetrafluorotetracyanoquinodimethane dianions, in which the CT degree is albeit small, the spin-spin interaction between the cation radical and the anion radical was antiferro magnetic in the temperature range of 60–293 K, but changed to a ferromagnetic one in the lower temperature range till 15 K, the lowest temperature used in this experiment. This provides the first demonstration of ferromagnetic spin-spin interaction in purely organic/molecular CT complexes. It is conceivable that the ferromagnetic spin-spin interaction is caused by a“spin polarization”mechanism rather than a“CT configurational mixing”mechanism.
Finding of Bulk Ferromagnetism in Stable Organic Radical Crystal
Authors: Kinoshita Minoru 
Published: March 2011

ABSTRACTTransition to a ferromagnetic long range ordered state was found at 0.60 K in the orthorhombic β-phase crystal of p-nitrophenyl nitronyl nitroxide (or 2-(4′-nitrophenyl)-4, 4, 5, 5-tetramethyl-4, 5-dihydro-lH-imidazol-1-oxyl-3-N-oxide in the IUPAC nomenclature). This finding provides the first example of an organic bulk ferromagnet consisting of light elements and having a definite molecular and crystal structure.
Characterization of Glassy State Relaxations in Styrene and Methacrylate Based Nonlinear Optical Materials
Authors: Schen Michael A. , Mopsik Fred I. 
Published: March 2011

ABSTRACTSub-Ts relaxations in polymethylmethacrylate (PMMA) and in narrow molecular weight polystyrene (PS) thin films with and without second order nonlinear optical dyes have been examined using time domain dielectric spectrometry. Dyes used include 4-[N, N-dimethylamino]-4’-nitrostilbene (DANS) and 4-[N-ethyl, N-hydroxyethylaminoJ-4’-nitroazobenzene (DR1) at a level of 0.19 mole percent. In dye/PS blends, dye relaxations are seen to occur at frequencies similar to the frequencies of the β-relaxation of pure PS below the glass transition temperature. Analysis of the glassy phase dispersion leads us to conclude that, at near room temperature, appreciable dye reorientation occurs on a time scale of a few seconds. This dye reorientation is coupled to the dynamic motions of the localized polystyrene subunits. Experiments using dye in PMMA did not conclusively reveal dye motions because of the intrinsically large dispersion of PMMA itself. The β-relaxation frequency range is higher in the PMMA dye/polymer blend than in dye-containing PS implying dye reorientation would likewise occur more rapidly than in PS. Our results indicate that the randomization of dye orientation observed in a dye/polymer system depends on the rapid, local chain motions which continue at temperatures well below the glass transition temperature, as well as on the long range, slow relaxations associated with the glass-to-rubber transition.
Synthesis of New Stable Functionalized Organic Radicals for the Study of their Magnetic Properties
Authors: Chiang Long Y. , Upasani Ravi. B. , Swirczewski John. W. 
Published: March 2011

ABSTRACTSeveral phenoxy radicals were chemically modified in order to probe the intermolecular spin interactions between these radicals. Based on the ketenimine chemistry, we demonstrated an efficient synthetic sequence for the preparation of new dicyano substituted hindered phenols. A series of new polar group substituted nitroxide-nitroxyl radicals were also synthesized. These radicals with polar functionalities include 3, 5-dinitro-phenyl, 3, 5-dimethoxyphenyl, 3, 5-dihydroxyphenyl, 4-hydroxyphenyl, 4-cyanophenyl, 3, 5-dicyano-phenyl, and 3, 5-di-i-butyl-4-hydroxyphenyl derivatives of 4, 4, 5, 5-tetramethylimidazolidine-3-oxide-1-oxyl. They are intended for the study of functional substitution effects on the nature of spin exchanges in solid state.
Interelectronic Exchange Interactions between Organic Radicals in the Solid State
Authors: Rossitto Frank C. , Lahti Paul M. 
Published: March 2011

ABSTRACTThe poly(4'-vinylphenoxy) nonconjugated polyradical was generated by photolysis of an oxalate-functionalized poly(4-hydroxystyrene). Spin-counting experiments in the electron spin resonance spectrum (ESR) showed efficient production of radicals with g = 2.0041, consistent with the expected pendant phenoxyl radicals. The thermal behavior of the ESR signal intensity indicated through-space antiferromagnetic coupling of the pendant radicals. The similarity of the behavior of this nonconjugated system to that of nominally conjugated polyradical systems synthesized by others suggests that geometric effects leading to deconjugation may be a major consideration in the synthesis of organic ferromagnetically exchange coupled polyradicals.
Poled Polyimides for Thermally Stable Electro-Optic Materials
Authors: Wu J. W. , Valley J. F. , Stiller M. , Ermer S. , Binkley E. S. , Kenney J. T. , Lipscomb G. F. , Lytel R. 
Published: March 2011

ABSTRACTUsing polyimide as host in a guest-host electro-optic (EO) thin film a thermally stable poled electro-optic response is demonstrated at temperatures at 150 °C and 300 °C. Electric field poling during curing process including imidization (170 -230 °C) and densification (340 -380 °C) accounts for the highly thermally stable EO response. As a room temperature curing process, chemical imidization is employed as a novel curing process. Dehydration occurring through imidization of the polyamic acid is completed chemically after poling rather than thermally during poling. After thermal aging at 155 °C (above the poling temperature) chemically imidized samples retain over 30% of their original poling induced EO signal while similarly poled samples, which have not been chemically imidized, produce a null EO response. For a class of polyimides possessing aliphatic structure, the thermoplastic behavior of cured guest-host polyimide system allowed the electric field poling at temperatures above the glass transition temperature (Tg). One example of polyimide doped with 10% nonlinear optical molecules exhibits Tg near 200 °C, leading to an excellent thermal stability of the poled EO response with a depoling knee-temperature of 150°C.
Synthesis of a Novel Donor, BTFE-DMB, and Electrical Properties of its Iodine Salt
Authors: Mizutani Makoto , Tanaka Keiji , Ikeda Kiyoshi , Kawabata Kazushige 
Published: March 2011

ABSTRACT1, 4-Bis [2-(tetrathiafulvalen-2-yl)ethenyl] -2, 5-dimethylbenzene (BTFE-DMB) is synthesized and its structure is found to be planar. The single crystal of its iodine salts undergoes a metal-insulator transition about 180K. The compaction pellets of the iodine salts show the current dependent resistive anomaly under high pressure.
Chemical Properties of Porphyrin Thin Films Deposited by ICB
Authors: Usui Hiroaki , Yamada Atsushi , Murayama Kouji 
Published: March 2011

ABSTRACTPorphyrin thin films were deposited by ionized cluster beam from a source material of tetraphenylporphyrin iron(III) chloride. It was found that the chlorine atoms are mostly removed from the original molecules during the film formation process, resulting in a film of tetraphenylporphyrin iron(II) complex. The film is chemically active and showed reversible reaction with O2 and CO gases at an elevated temperature. The formation of μ-oxo dimera, which hinders the chemical activity, was not observed. Electrical conductivity of the film was also measured under various atmosphere.
Structural Aspects of the Polyaniline Family of Electronic Polymers
Authors: Pouget J. P. , Laridjani M. , Jozefowicz M. E. , Epstein A. J. , Scherr E. M. , MacDiarmid A. C. 
Published: March 2011

ABSTRACTRecent structural studies of the polyaniline family of electronic polymers in the base and salt forms are reviewed. We describe the crystalline and amorphous structures of the two classes of emeraldine. The structural evolution with HC1 doping and ring substitutions are also discussed in relationship with the electronic properties of these materials. Implications for charge transport phenomena are also considered.
Heteroaromatics: Exceptional Materials for Second Order Nonlinear Optical Applications
Authors: Jen Alex K-Y. , Wong K. Y. , Pushkara Rao V. , Drost K. , Mininni R. M. 
Published: March 2011

ABSTRACTNew classes of nonlinear optical molecules were synthesized and characterized. It is shown experimentally that molecules with heteroaromatic π-electron systems exhibit exceptional second order nonlinear optical response and good solubility. Measurement of the nonlinear optical properties of molecules containing heteroaromatic moieties with different length scale reveals a power law dependence of Bμ on the number of π-electrons. Also, the effects of two nitro groups as electron acceptors on the aromatic ring are discussed.
The Polymerization of Heterocycles on Clay Templates
Authors: Mahe Loic , Laszlo Pierre , Dubois Jean-Claude 
Published: March 2011

ABSTRACTThe oxidizing power of clays is put to use for the polymerization of heterocycles (pyrrole- and thiophene- types) in the 2D-interfoliar space and on the external surface of the clay particles. A mechanism is proposed for the oxidative polymerization.
An Overview of Conjugated Polymers in their Insulating Forms
Authors: Sandman Daniel J. 
Published: March 2011

ABSTRACTA brief overview is presented of the electrical and linear optical properties of conjugated polymers in their electrically insulating forms. Topics discussed include electronic structure and optical spectroscopy, thermochromism, and device applications, particularly electroluminescence. Structure-property relationships are stressed. Particular emphasis is placed on the properties of polydiacetylenes as they are available as macroscopic single crystals and, hence, are the best defined class of conjugated polymers.
Polyarenemethylidenes, A new Class of low GAP Polymers
Authors: Hanack M. , Hieber G. , Mangold K. -M. , Ritter H. , Röhrig U. 
Published: March 2011

ABSTRACTBased on theoretical calculations Polyarenemethylidenes (PAM) 1 have been predicted to be low gap polymers with good semiconducting and photoelectrical properties. The preparation of such a polymer with a well defined structure affords the synthesis of suitable precursors. We have been able to synthesize and characterize a variety of monomers in which the inner quinonoid system is present. Also more extended systems containing one or two additional benzene rings at the quinonoid system have been prepared. The chemical and electrochemical polymerization of the precursors is reported, leading to polymers 1 in a great structural variety.
Light-Emitting Diodes Based on Conjugated Polymers: Control of Colour and Efficiency
Authors: Burn Paul L. , Holmes A. B. , Kraft A. , Brown A. R. , Bradley D. D. C. , Friend R. H. 
Published: March 2011

ABSTRACTStudies of the effect of different electrode combinations on the device characteristics of simple three layer light-emitting diodes (LEDs) prepared with poly(ρ-phenylenevinylene) (PPV) as the emissive layer sandwiched between two metal contacts have shown that it is generally more difficult to inject electrons than holes. In order to improve the efficiency of such devices it is, therefore, necessary to develop methods to enhance the injection of electrons and we illustrate here one example where we have successfully achieved this by the introduction of a further, electron transport, layer. The result is an eight fold increase in efficiency over our best three layer PPV devices. The efficiency is also dependent on the details of the polymer electronic structure and using a family of copolymers we have been able to produce enhancements in efficiency to values of up to 30 times that of the corresponding PPV devices. Variations in the polymer electronic structure also affect the colour of emission and the same family of copolymers allow control of emission colour from blue/green to orange/red. Supramolecular control of the copolymer electronic structure can be achieved by lithographic patterning and we show that it is possible to produce regions within a single polymer film that possess different π-π* energy gaps.
Optical Spectroscopy and Photochemistry of Thin Films of Propylmethylpolyazine
Authors: Sherman Bradford C. , Euler William B. 
Published: March 2011

ABSTRACTPropylmethylpolyazine, [N=C(R1)-C(R2)=N]X (R1=CH3, R2=CH2CH2CH3), is an organic-soluble linear conjugated polymer. The ultraviolet spectrum of thin films of this material shows two peaks at about 280 nm and 320 nm. These absorptions are ascribed to transitions from different filled valence bands to the same empty conduction band. Oxidative doping of this polymer with iodine gives spectra that are consistent with the generation of bipolarons. Irradiation of pristine thin films with 300 nm light causes a two step photoprocess to occur. The first step happens during the first hour of irradiation and if the film is left in the dark is completely reversible. The second step takes considerably longer to complete (more than 12 hr of irradiation) and is irreversible. The UV spectrum and FTIR spectrum of the step one photoproduct suggest that the imine bond is undergoing an E to Z isomerization photochem-ically which reverses in the dark. The step two product is probably due to a cycloaddition reaction.
A Three-Level Model Useful for Exploring Structure/Property Relationships for Molecular Third Order Optical Polarizabilit1Es
Authors: Dirk C. W. , Cheng L-T. , Kuzyk M. G. 
Published: March 2011

ABSTRACTApproximations are applied to the three-level perturbation theory expressions for the third order optical polarizability. We conclude there will be three competing dominant terms, γ ≈ γc + γn + γtp each of which can be optimized at different molecular electronic structures. The two-photon term, γtp, has been commonly ascribed as the most dominant one for γ. However, the other two terms, which optimize at different structures, potentially offer equivalent or larger overall γ. The term, γn, will be optimized at structures with large second order polarizability β, while the term, γC, optimizes at certain centrosymmetric free electron structures with large first order polarization, α Optimization by γc is the preferred route, since this leads to elimination of the canceling terms which limit optimization by γtp or γn. Recent EFISH results have confirmed our earlier speculations that the free electron squarylium dye structures are particularly good for optimization by way of γc. Strategies are presented to selectively optimize to either of the three structure types and to obtain molecules with even larger γ.
Effects of Humidity and Heat on the Conductivity of Poly(3-Alkylthiophenes)
Authors: Punkka E. , Isotalo H. , Ahlskog M. , Stubb H. 
Published: March 2011

ABSTRACTThe stability of the conductivity of poly(3-alkylthiophenes) has been studied in controlled environmental conditions. High humidity levels at elevated temperatures have been found to strongly influence the dedoping process. Highly FeCl3-doped samples lose their conductivity faster than lightly doped or undoped polymers. The conductivity of undoped poly(3-octylthiophene), however, initially increased by nearly two orders of magnitude as the relative humidity level was raised from 50% to 95% at 70 °C. The largest conductivity decay induced by humidity and heat was observed in thin samples. Measurements of the field-effect mobility reveal that the humidity-induced drop of the conductivity is caused by a decreasing number of active dopants, whereas heating the sample additionally results in a deterioration of the charge carrier mobility.
Layer-by-Layer Molecular Assembly Approaches to the Construction of Thin Films Having High Second-Order Optical Nonlinearities
Authors: Allan David S. , Kubota Fuyuhiko , Kakkar Ashok K. , Marks Tobin J. , Zhang Tongguang , Lin Weiping , Shih Mingchih , Wong George K. , Dutta Pulak 
Published: March 2011

ABSTRACTChromophoric multilayer thin films exhibiting efficient second harmonic generation have been constructed on inorganic substrates via a stepwise layer-by-layer process using molecular self-assembly techniques. In each step, chemical species bearing appropriate functional groups form covalent bonds with functional groups deposited in the previous step. Bulk acentricity is achieved by the orientation of chromophore-containing layers outward from the substrate surface. A new chromophore having comparable hyperpolarizability but different steric and transparency characteristics than the stilbazolium chromophore used previously has been incorporated into self-assembled films. The large effects of octachlorotrisiloxane capping on the structure of these films have been investigated by second harmonic generation and X-ray reflectivity measurements. Novel in situ measurements of second harmonic generation efficiency as a function of chromophore layer growth are described and provide information useful for optimizing deposition conditions and understanding the film growth process.
A Two-Legged Spacer Molecule for Alternate Layer LB Film Deposition with Optically Nonlinear Dyes
Authors: Ash Well G. J. , Crossland W. A. , Martin P. J. , Thompson P. A. , Hewson A. T. , Marsden S. D. 
Published: March 2011

ABSTRACTSecond harmonic generation from Langmuir-Blodgett films of E-N-octadecyl-4-(2-(4-dimethylaminophenyl)ethenyl)pyridinium iodide (a hemicyanine) interleaved with 4, 4'-dioctadecyl-3, 5, 3', 5'-tetramethyldipyrrylmethene hydrobromide (spacer) increases quadratically with the number of active layers, the second-order nonlinear optical susceptibility of film structures comprising from 1 to 150 bilayers being 70 pm/V. The synthesis and nonlinear optical properties are reported.
Thin Film Crystalline Organic Semiconductors: A New Class of Engineered Materials for Optoelectronics
Authors: Haskal E. I. , So F. F. , Zang D. Y. , Forrest S. R. 
Published: March 2011

ABSTRACTWe have demonstrated that a class of stable aromatic compounds based on perviene and naphthalene can be deposited in extensive single crystalline thin films using the ultrahigh vacuum process of organic molecular beam deposition (OMBD). Furthermore, highly ordered “quasi-epitaxial” structures consisting of alternating, ultra-thin (to 10A) layers of two or more crystalline organic compounds have also been grown using this novel process, thus opening the door to a wide range of artificially “engineered” structures analogous to conventional semiconductor multiple quantum wells (MQWs). Unlike the case of inorganic semiconductors, however, organic materials bonded by the flexibly van der Waals forces are free of the need to choose layer compositions from materials whose crystal structures are matched. In this paper we summarize many of the unusual growth and materials characteristics of quasi-epitaxial organic thin films grown by OMBD.
Nanoscopic Molecular Engineering: Organic MBE and STM
Authors: Hara Masahiko , Garito Anthony F. , Sasabe Hiroyuki 
Published: March 2011

ABSTRACTApplication of molecular beam epitaxy (MBE) and scanning tunneling microscopy (STM), especially for organic molecular systems, has been drawing our attention as a new approach to realizing novel material structures with low dimensionality, which are expected to exhibit important electronic and photonic properties. The following is an outline of our work in progress, including an overview of “nanoscopic” molecular engineering. Future possibilities of fabrication, modification and characterization for organic low-dimensional materials are reviewed with the new concept embraced by “nanoscopic” science and technology.
Quantum Well Formation in One-Dimensional Polymer Films by Molecular Layer Deposition and Chemical Vapor Deposition
Authors: Yoshimura Tetsuzo , Tatsuura Satoshi , Sotoyama Wataru 
Published: March 2011

ABSTRACTQuantum wires and dots were fabricated in one-dimensional conjugated polymer films by chemical vapor deposition. In the wires, a sharp exciton absorption peak, and in the dots, a blue shift in the absorption band due to electron confinement were observed. We showed that acceptors could be substituted into the conjugated polymer chain. We also demonstrated that molecular layer deposition (MLD), in which molecules are stacked on substrates one by one in order of preference in a vacuum, is feasible in fabricating one-dimensional conjugated polymers.
Mechanisms of Photo Currents in Phthalocyanine Thin Film Solar Cells
Authors: Siebentritt Susanne , Gunster Stefan , Meissner Dieter 
Published: March 2011

ABSTRACTPhotocurrents in phthalocyanine ohmic samples and in phthalocyanine/perylene solar cells are shown. In principle current spectra follow the absorption spectra of the materials. Deviations from this behaviour can be accounted for by filtering effects. The influence of intensity, bias light and applied voltage is discussed.