bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transfer Integrals and Band Structures in (Et)2X Salts
Authors: Leblanc Oliver H. , Blohm Margaret L. , Messmer Richard P. 
Published: March 2011

ABSTRACTTransfer integrals (tij) between pairs of nearest neighbor ET molecules were calculated by an ab initio method. Tight-binding one-electron energy bands constructed from thetijare similar to those previously calculated by Mori and by Whangbo and their coworkers by semi-empirical, extended Hückel methods, but quite different from those found by Kübler et al. in β-(ET)2I3using the augmented spherical wave (ASW) method. However, all these band models are suspect. The Hubbard on-site repulsion parameter U is estimated to be about twice the band widths, indicating that a full treatment of the Hubbard hamiltonian is needed. Also, polaron effects appear to control transport except at very low temperature.
Electron-Donating Radialenes. Potential Donors for Molecular Organic (Super) Conductors and Ferromagnets
Authors: Yoshida Z. , Sugimoto T. , Misaki Y. 
Published: March 2011

ABSTRACTThe electron-donating [n]radialenes (n=3,4,5) were prepared with the aim of developing both new type of organic (super)conductors and unprecedented organic/molecular ferromagnets. The charge-transfer (CT) complexes of 1,3-dithiole[4]radialene with TCNQ and of 1,3-benzodithiole-[4]radialene with TCNQF4 and DDQ showed comparatively high electrical conductivities in compressed pellets. The single crystals of PF6 and CIO4 salts of 1,3-benzodithiole[4]radialene radical cation revealed temperature change of electrical conductivity characteristic of a semiconductor. The magnetic properties of the bis(trifluoroacetate)salt of thioxanthene[3]-radialene dication and of the CT complexes of 1,3-benzodithiole[5]-radialene with DDQ, TCNQF4, and hexacyanohexamethylenecyclopropane, were also investigated from the ESR and/or magnetic susceptibility measurements.
Aqueous Colloidal Dispersions of Polyaniline Particles
Authors: Armes Steven P. , Aldissi Mahmoud 
Published: March 2011

ABSTRACTColloidal polyaniline has been prepared in acidic aqueous media by a modified chemical polymerization of aniline in the presence of a tailor-made polymeric surfactant. The surfactant which acts as a steric stabilizer used in this study is derivatized poly(vinyl alcohol-co-vinyl acetate). This surfactant contains pendant aniline units which participate in the aniline polymerization, resulting in the formation of sterically-stabilized polyaniline particles which have a non-spherical “rice-grain” morphology.It is shown that this novel form of polyaniline is more processable than the bulk powder that is normally obtained from a conventional chemical synthesis. The solid-state conductivity of solution-cast films or compressed pellets of these dispersions is surprisingly high (⋍ 1 S/cm), despite the presence of the insulating outer layer of chemically-grafted stabilizer.
V2O5 Xerogels as Hosts For Conductive Polymers. Intercalative Polymerization of Aniline, Pyrrole and 2,2’-Bithiophene.
Authors: Wu Chun-Guey , Marcy Henry O. , DeGroot Donald C. , Kannewurf Carl R. , Kanatzidis Mercouri G. 
Published: March 2011

ABSTRACTIntercalative polymerization of aniline, pyrrole and 2,2’-bithiophene in vanadium oxide xerogels results in electrically conductive novel materials which are composed of alternating monolayers of metal-oxide and conductive polymers. The driving force for this intercalation is redox chemistry. The conductivity type in these materials is a function of the polymer/V2O5 xerogel ratio. Low ratios result in xerogel-based charge transport, while high ratios favor polymer-based charge transport properties. Chemical, spectroscopic and electrical data on the intercalative polymerization products of aniline, pyrrole and 2,2’-bithiophene with V2O5 xerogels are presented.
Resonant Raman Scattering of Poly-3-Alkylthiophenes
Authors: Botta C. , Luzzati S. , Bolognesi A. , Catellani M. , Destri S. , Tubino R. 
Published: March 2011

ABSTRACTWe report Raman scattering measurements on poly-3-heptylthiophene and poly-3-undecylthiophenes both on resonance and preresonance conditions. We have studied different samples as solutions ,solution cast films and electrosynthetized as grown films. Our results indicate that the vibrational frequency of the mode which is strongly coupled to the π - π* electronic transition is sensible to “small” torsions between thiophenes rings , which do not necessarly interrupt completely the conjugation path.
Temperature Dependence of the Picosecond Photocurrent in Stretched Trans-Polyacetylene Films with Below Gap Excitation
Authors: Walser A. D. , Dorsinville R. , Tubino R. , Alfano R. R. 
Published: March 2011

ABSTRACTThe temperature dependence of the picosecond photocurrent with below gap excitation (1.06 μm) has been measured for a highly oriented form of trans-polyacetylene. The 1-d picosecond photocurrent is independent of temperature. The 3-d picosecond photo-current is temperature dependent with an activation energy of 63 meV. These results demonstrate the photoproduction of nonlinear charged carriers ( solitons and polarons) at energies that are below the principal interband absorption edge.
Novel Photochromic Zwitterions For Multifrequency Data Storage
Authors: Ashwell G. J. , Dawnay E. J. C. , Kuczynski A. P. , Szablewski M. 
Published: March 2011

ABSTRACTZ-β-(N-alkyl-4-pyridinium)-α-cyano-4-styryldicyanomethanide (R-P3CNQ) and its quinolinium analogue (R-Q3CNQ) are photochromic. Their LB films show sharp charge transfer bands at 495 nm (C16H33-P3CNQ) , 565 nm (C16H33-Q3CNQ) and 614 nm (C8H17-Q3CNQ) with half widths at half maximum of 27, 22 and 37 nm respectively. They show interesting nonlinear optical properties and have the potential to store three bits per pixel when addressed at these wavelengths.
L.B. Films Exhibiting Cooperative Spin Transition, for 2D Molecular Memory Devices
Authors: Coronel P. , Ruaudel-Teixier A. , Barraud A. , Kahn O. 
Published: March 2011

ABSTRACTMolecular electronics requires materials of molecular size exhibiting switching or memory properties. The Langmuir-Blodgett method (L.B.) and its variants provide controlled fabrication of molecular films one molecule thick and their transfer onto solid supports. In these 2D monolayers, molecules are highly organized, so that complex organizates aimed at specific properties can be built. One of these, a semi-amphiphilic complex made of two NCS and two amphiphilic phenantrolines in a cis position, exhibits a spin transition around - 20 °C. It switches from high spin (S = 2) at room temperature to low spin (S = 0) at low temperature. The transition does not follow the expected thermal Boltzman statistics, but is rather steep, pointing out molecular cooperation. The L.B. film exhibits a hysteresis about 4 °C in width, while the parent 3D compound exhibits a hysteresis of less than 0.2 °C, but a much sharper transition. This apparently contradictory behaviour is ascribed to the high impurity content and the multicristallinity of the L.B. film in association with high intermolecular coupling. Because of its intrisic properties this new material is a breakthrough on the way to magnetic memories at the molecular scale for molecular electronics.
Optical and Magnetic Processes and the Side Chains of Diacetylenic Materials
Authors: Sandman Daniel J , Hamill Gregory P. , Levinson Mark , Rossoni Philip G. , Yost Elizabeth A , Papaefthymiou Georgia C. 
Published: March 2011

ABSTRACTSimilarities in the molecular energy levels of alkylcarbazoles and aliphatic nitroxides motivate the detailed study of 4,4′-(butadiyne-l,4-diyl)-bis-(2,2,6,6-tetramethyl-4-hydroxypiperidin-l-oxyl) () as a precursor to a ferromagnetic polymer. A more convenient synthetic route to is reported, and an X-ray-induced transformation of the β-phase of to the α-phase has been observed. The magnetic properties of and derived polymers have been studied using a SQUID system. The observed level of ferromagnetism found in samples of polymerized is comparable to the amount of trace iron materials detected in these samples.
Synthesis and Second-Order Nonlinear Optical Properties of New Coumaromethacrylate-Methylmethacrylate Copolymers
Authors: Henry R. A. , Hoover J. M. , Knoesen A. , Kowel S. T. , Lindsay G. A. , Mortazavi M. A. 
Published: March 2011

ABSTRACTThe synthesis and second-order nonlinear optical (NLO) properties of a new family of optically nonlinear coumarin dye-containing polymers is reported. Polymerizable coumaromethacrylate (CMA) monomers having various alkyl spacers (C2 to C5) between the polymerizable group and the chromophore were prepared and copolymerized with methylmethacrylate (MMA) and other vinyl monomers. The CMA copolymers had high chromophoric content (up to 18 × 1020) and glass transitions as high as 132°C. Spin cast films were prepared on BK7 substrates and oriented by corona-onset poling at elevated temperatures (COPET). The poled CMA copolymer films were characterized for spectroscopic absorption and second harmonic properties. A comparison of the nonlinear optical properties of poled CMA-MMA copolymers to poled guest-host systems is made. Relative to guest/host systems, CMA-MMA copolymer films exhibit larger and much more stable second-order nonlinear optical properties.
Electronic Structure of Long Polyenes: States and Transition Dipoles
Authors: Kohler Bryan E. 
Published: March 2011

ABSTRACTElectronic excitation energies and transition dipoles measured for symmetrically substituted linear polyenes (R-(CH=CH)N-R) with chain lengths n ranging from 2 to 8 are well fit by the functional form A+B/N. Extrapolation to the long chain limit correlates the band gap transition of polyacetylene with the polyene 11Ag to 11Bu transition. The amount by which the highly correlated polyene 21Ag state is lower than the 11Bu state increases with increasing chain length, extrapolating to roughly half of the 11Bu excitation energy. The 11Ag to 11Bu transition dipole magnitude per chain repeat unit attains a maximum value of 3.0 Debye at an effective conjugation length 5 double bonds.Careful studies on linear polyenes provides insight into the electronic structure of polyacetylene.
Quantum Lattice Fluctuations and Nonlinear Optics of Conducting Polymers
Authors: Yu J. , Friedman B. , Su W. P. 
Published: March 2011

ABSTRACTQuantum lattice fluctuations of conjugated polymers in the form of virtual soliton-antisoliton pairs have important effects on the nonlinear optical properties. Quantitative calculations of nonlinear susceptibilities based on the solitonic molecular model are presented.
Effects of In-Plane π’ Bonding on Electronic Transition Energies for Inorganic Polymers
Authors: Ferris Kim F. , Risser Steven M. , Hanson Angela K. 
Published: March 2011

ABSTRACTThe electronic structure of organic and inorganic polymeric systems are well described in terms of their molecular symmetry, even with the large bond polarity shown by such systems as polyphosphazenes. We have performed calculations using the semi-empirical CNDO/1 method to determine the valence electronic structure for a series of model phosphonitrilic and organic compounds. The optical transition energies for phosphonitrilic compounds are greater than their organic counterparts as a result of in-plane π’ bonding interactions. The extent of these interactions is modulated by the electronegativity of the substituent groups on the phosphorus atoms. We report values for the vertical ionization energy and electronic absorption wavelengths, and use molecular orbital contour analysis to show the effects of ligand electronegativity on the π’ network.
Thermal Stability of Magnetic Properties in Dehydrogenated Triarylmethane Resins
Authors: Otani Michiya , Otani Sugio 
Published: March 2011

ABSTRACTThe stability of the magnetic properties of dehydrogenated triaryl-methane resins was investigated both at room temperature and at elevated temperatures. A magnetic property different from that reported in a previous paper was found in the course of studying the reproducibility of synthesis. This new property was examined through a mechanical response of the resins to a set of permanent magnets.
Polyphenoxy Radicals: Synthesis and Homo-Polymerization of 2-(3,5-Dl-t-Butyl-4-Hydroxyphenyl)Isobutyl Methacrylate
Authors: Upasani Ravindra B. , Chiang Long Y. , Goshorn D. P. 
Published: March 2011

ABSTRACTWe evaluated the chemical stability of various polyphenoxy radicals prepared through the modified synthetic methods. The monomeric 3,5-di-t-butyl-4-hydroxyphenyl derivatized olefins and methacrylates were prepared in a multistep synthesis starting from 2,6-di-t-butylphenol. These monomers were polymerized in the presence of radical initiators at the refluxing temperature of aromatic solvents under an inert atmosphere. The most stable polyradicals were found to be highly hindered poly(DBPM) radicals.
Ferromagnetic Interactions in a Series of Schiff-Base Metal-Organic Polymers
Authors: Palacio F. , Lazaro F.J. , Garin J. , Reyes J. , Moron M.C. 
Published: March 2011

ABSTRACTMagnetization and frequency dependence a.c. magnetic susceptibility measurements of the metal-organic polymers of general formula {[M(C13H17N3)2]SO4 6H2O}n, where M = Fe(II) or Co(II), are indicative of superparamagnetic behavior as a consequence of the existence of strong ferromagnetic interactions in the materials. Scanning electron microscopy and X-ray dispersive spectrometry have been used to study the homogeneity in the composition of the iron polymer.
Biocatalytic Synthesis of Polyesters by Enzyme-Catalyzed Transesterification in Organic Media
Authors: Morrow Cary J. , Wallace J. Shield , Bybee Gregory M. , Reda Kristin B. , Williams Mark E. 
Published: March 2011

AbstractEnzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. This paper summarizes our successful use of lipase-catalyzed polycondensations to prepare both a series of achiral [AA-BBJx polyesters from simple bis(2,2,2- trichloroethyl) alkanedioates and diols and of an optically active, epoxy-substituted polyester having a stereochemical purity estimated to be greater than 96%, from racemic bis(2,2,2-trichloroethyl) trans- 3,4-epoxyhexanedioate and 1,4-butanediol. The somewhat less successful polycondensation of a series of A-B monomers is also described. All of the reactions were carried out at ambient temperature in anhydrous, low to intermediate polarity, organic solvents such as ether, THF, and methylene choride, using porcine pancreatic lipase (PPL) as the catalyst. Possible explanations for the difference between the A-B and AA + BB cases, based on NMR analysis of the reactions' progress are considered.
Synthesis of a Collagen Analog in Escherichia Coli Using Recombinant DNA Technology
Authors: Goldberg Ina , Salerno A. J. 
Published: March 2011

AbstractA family of totally synthetic genes coding for multiple tandem repeats of the amino acid sequence (Gly-Pro-Pro) has been prepared and inserted into the Clal cloning site of the expression vector pJL6. A representative recombinant plasmid, pACI, with an insert of about 340 bp, was established in an Escherichia coli strain bearing a defective λ prophage, to study expression of the CII-collagen analog fusion protein produced from pACI upon heat induction. The in vivo levels of synthetic gene expression obtained showed that the fusion protein was synthesized in E. coli, but was labile compared to other cellular proteins. This degradation could be significantly reduced by the genetic inhibition of a bacterial protease system.
Ceramic Oxide Thin Film Formation Utilizing Biological Processes
Authors: Tarasevich B. J. , Rieke P. C. 
Published: March 2011

AbstracMineralization processes used by bioorganisms have been adapted for the nucleation and growth of ceramic oxide thin films onto surfaces from aqueous solutions. These strategies include the use of surfaces derivatized with specific functional groups that control the nucleation and growth and properties of materials deposited. Iron oxide materials were deposited onto functionalized polystyrene surfaces, resulting in the formation of thin films composed of densely packed, nanometer-sized crystallites. Evidence for the formation of oriented crystallites was found. This process may have advantages over conventional thin film processing methods due to the ability to systematically control properties of materials deposited.
Synthesis of Polyimide-Silicate Hybrids Via Sol-Gel Ultrastructure Processing
Authors: Spinu M. , Brennan A. , Rancourt J. , Wilkes G. L. , McGrath J. E. 
Published: March 2011

AbstractNew organic/inorganic hybrid materials were prepared by hydrolysis and co-condensation of tetramethylorthosilicate (TMOS) with trimethoxysilane functionalized polyimide oligomers via sol-gel ultrastructure processing. In the first reaction step, amine terminated, fully imidized, soluble, high Tg polyimides were prepared from appropriate diamines and dianhydrides by solution imidization techniques. The amine end-groups were then quantitativell derivatized to nadimide structures through reaction with cis-norbornene 2,3 dicarboxylic anhydride. Subsequently, the nadimides were quantitatively derivatized to trimethoxysilane functionalities via hydrosilylation reactions in the presence of chloroplatinic acid catalyst. The resulting hexamethoxy functionalized polyimide oligomers were hydrolyzed and co-condensed at elevated temperatures under mild pressure with TMOS via sol-gel processing to generate thermally stable polyimidesilicate hybrids. The synthesis and characterization of these materials is discussed.
Dielectric Relaxation Properties and Alignment Behaviour of Liquid-Crystalline Side-Chain Polymers
Authors: Williams Graham , Nazemi Ali , Karasz Frank E 
Published: March 2011

AbstractWe describe the alignment behaviour of different liquidcrystalline (LC) side-chain polymers when they are subjected to electrical/thermal treatments. It is shown that the alignment behaviour is determined by several variables for a given polymer, including the amplitude and frequency of the applied electric field and both the thermal and electrical history of the sample and its low-field dielectric relaxation properties. It is shown that the dielectric relaxation spectra vary systematically with the degree of macroscopic alignment of the sample and its temperature. The anisotropy of dielectric properties may be understood in terms of the anisotropic reorientational motions of the dipolar mesogenic groups. The permittivity data allow the degree of macroscopic alignment to be determined, via a director order parameter Sd for samples prepared in different ways and also for samples being realigned, as a function of time, by directing electric fields. We illustrate these principles through data we have obtained for a copolymer having the mesogenic groups attached longitudinally and transversely to the main chain.
Dielectric Properties of Polymeric Liquid Crystals with Strong Lateral Dipole Groups
Authors: Haase Wolfgang , Pfeiffer Matthias 
Published: March 2011

AbstractUsing broad band dielectric spectroscopy on well oriented microdomains of mesogenic polymethacrylates the influence of strong lateral dipole groups on the dielectric parameters could be verified. The mesogenic groups investigated were phenylbenzoates with fluorine substituents at the phenyl ring. The orientation of the samples was maintained in a superconducting magnet with field strength of 7.2 T. The results are compared with those obtained for non-substituted compounds.
Thermotropic Chiral Nematic Polymers as Optical Materials
Authors: Chen S.H. , Tsai M.L. , Jacobs S.D. 
Published: March 2011

AbstractChiral nematic copolymers based on optically active cholesterol, dihydrocholesterol, (R)-(+)- and (S)-(−)-1-phenylethylamine, and (+)- and (−)- isopinocampheol were synthesized and characterized for the investigations of thermotropic and optical properties. Although helical sense does not appear to correlate with the sign of [α]D of the precursor chiral compound as suggested by the observations of cholesteryl and dihydrocholesteryl copolymers, the inversion of chirality in the pendant group, (R)-(+)- vs (S)-(−)-1-phenylethylamine, does lead to the opposite handedness in the resultant helical structure. To better understand the structure-property relationships involving helical sense and twisting power, systematic studies of the roles played by both nematogenic and chiral structures as well as other structural features of the comonomers should be conducted.
New Synthesis/Processing Routes to Materials Exhibiting Large Optical Nonlinearity
Authors: Dalton L. R. , Yu L. P. 
Published: March 2011

AbstractSynthesis/processing schemes for the preparation of optical quality thin films of π-electron containing organic and organometallic materials are discussed. Fabrication approaches range from preparation of molecular/polymer composites, to preparation of copolymers containing pendant electroactive moieties, to preparation of copolymers with electroactive units incorporated into the polymer backbone, to the preparation of polymer/polymer composites. Such fabrication methodologies (particularly the latter three approaches) have the advantage of facilitating control over polymer solubility and of avoiding aggregation of electroactive units. The synthetic schemes discussed here yield materials with well-defined electroactive units; thus, diffuse bandedges associated with a distribution of π-electron conjugation lengths are avoided. Degenerate four wave mixing (DFWM) measurements at 532, 579–600, and 1064 nm are used to determine third order susceptibilities. Investigation of the frequency dependence of χ(3)/α established that resonance contributions dominate non-linear optical activity near the π-iπ* bandedge. A variety of electroactive moieties have been investigated with the largest values of χ(3)/α (= 10−12 esu cm) being observed for triphenodioxazine, metal phthalocyanine, metal tetraazaannulene, 6,6′-dimethoxy-quinolidine cyanine units.
Inorganic and Organometallic Principles in the Design of Multifunctional Materials
Authors: Michael D. , Mingos P. 
Published: March 2011

AbstractThe prospects of using the properties of inorganic solids with infinite structures in combination with the spectral, magnetic and chemical characteristics of co-ordination and organometallic compounds are reviewed with particular reference to their potential applications in the electronics, sensors and optoelectronic fields.Solid state inorganic chemistry provides a great variety of thermally stable and optically transparent host materials which have sufficiently large cavities for the incorporation of small molecules. These include zeolites with either spherical or cylindrical three dimensional cavities, layered compounds with infinite two-dimensional spaces and a variable third dimension, and pillared materials with intersecting one-dimensional channels. These structures may be chosen on the basis of a particular function and a second introduced via the incorporation of molecules in the cavities. Alternatively, they may be viewed as neutral structural materials and the multifunctionality can be introduced via the incorporation of molecules with different spectral or chemical properties.As guest materials co-ordination and organometallic compounds have the following properties which are important in the context of multifunctionality: the ability to co-ordinate small molecules such as O2, SO2, H2 reversibly, distinct reversible electrochemical properties, electronic transitions which show an enormous variation in extinction coefficients and oscillator strengths, polarised spectral transition and electrical conductivity properties.