bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tetranitroquinodimethane (Tnq)—Electron-Deficient Prototype for a New Series of Organic Solid State Materials
Authors: Vanderah David J. , Nielsen A. T. , Hollins R. A. , Baum Chris 
Published: March 2011

ABSTRACTRecently we have synthesized several new aryl compounds substituted with two or more trinitromethyl groups. Vacuum pyrolysis of one of these—±,±,±,±’,±’,±’-hexanitro-p-xylene (p-HNX)—gave the title compound via 1,6-elimination of N2O4. Structural assignment of TNQ is based on spectral evidence (UV, 1H NMR and mass spectrometry) and conversion to the known l,4-bis(bromodinitromethyl)benzene. Evidence for the formation of the TNQ radical anion has been obtained.
Electron Paramagnetic Resonance Studies of Donor-Acceptor Salts in Polymer Media
Authors: Fann Yang-Cheng , Jansen Susan Ann 
Published: March 2011

ABSTRACTCharge transfer complexes, their inherent electrical conductivity, magnetic properties and donor-acceptor redox relationships have been a focus of much research in the last several years. One direction has been in the design of memory devices and applications in molecular electronics.1,2 Our work has focused on analysis of such processes in a polymeric medium. Polycarbonate films of 7,7’,8,8’-Tetracyanoquinodimethane (TCNQ) and o-tolidine (o-T) complexes were studied by EPR spectroscopy from 100-300K. EPR spectra and magnetic susceptibility of the dispersed charge-transfer complexes are presented and compared with the pristine materials. These studies were carried out as a function of donor/acceptor stoichiometry and concentration within the polymer matrix. Saturation studies show significant differences as the composition varies. In addition the g-tensor and linewidth are strongly dependent on temperature and composition.
Low-Dimensional Critical Behaviors and Competition Between Order Parameters in the Organic Metal (Tmtsf)2ClO4
Authors: Pesty F. , Garoche P. , Heritier M. 
Published: March 2011

ABSTRACTIn low-dimensional conductors, the instability of the metallic state can lead to the formation at low temperature of a spin density wave induced by the magnetic field (FISDW). The transition results from the complex interplay between the one dimensional instability of the electronic gas and the quantization of the magnetic field’s flux. This second-order phase-transition line has been investigated by measuring both specific heat and thermal conductivity along the c* direction. The mean-field jump and the gap value have been deduced respectively from the anomaly and the exponential decay of the electronic specific heat. The coupling strength λ has been evaluated, and the λ > 0.3 value indicates clearly a strong coupling behavior at high field. Below 8 teslas, the specific heat displays a double anomaly in relation with the competition between subphases. Above the second-order transition line, critical fluctuations are observed on both specific heat and lattice thermal conductivity. Along this line, one-dimensional fluctuations increase with increasing magnetic field. It is proposed that the very high field reentrance of the metal is to be related to enhancement of the 1D fluctuations.
Sound Propagation in Cdw and Sdw
Authors: Virosztek Attila , Maki Kazumi 
Published: March 2011

ABSTRACTWe present a microscopic theory of the sound propagation in quasi one dimensional charge density wave (CDW), spin density wave (SDW) and field induced spin density wave (FISDW). First, we consider the ideal situation that the phase correlation length in the CDW or the SDW is infinite. In this limit due to the diffusion pole at iω = Dq2 in a variety of correlation functions the sound propagation depends on a) what is the ratio ω/Dq2 and b) if the CDW (or the SDW) is pinned or unpinned where D is the diffusion constant. Second, when the CDW (or the SDW) is unpinned, the phason starts to participate in the screening of the ionic potential. However, since the unpinned part is strongly inhomogeneous, the contribution of the phason term depends on the wave vector of q of the sound wave like (1 + (Lq)2)−1 where L is the Fukuyama-Lee-Rice coherence length. The present theory accounts for a variety of features observed in sound propagation in quasi-one dimensional CDW systems like NbSe3 and TaS3.
Optical Studies of Polyanilines: Effects of Alkyl Ring-Substitution and Solvent Environment
Authors: Ray Anjan , MacDiarmid Alan G. , Ginder John M. , Epstein Arthur J. 
Published: March 2011

ABSTRACTMethyl and ethyl ring-substituted polyaniline derivatives have been synthesized and characterized by UV-visible-near IR spectroscopy. Optical spectra of the base forms in DMF solution suggest that the torsion angle between adjacent rings is increased by steric hindrance due to the alkyl groups in the substituted polymers, leading to blue shifts in the ∼4 eV (“bandgap”) and ∼2 eV (“exciton”) absorptions and an accompanying decrease in the relative intensity of the “exciton” band.The methyl ring-substituted derivative, poly(o-toluidine), is shown to exhibit solvatochromism. The “exciton” absorption shifts from 2.03 eV in pure NMP to 2.19 eV in CH2CI2, accompanied by a loss in intensity relative to the “exciton” absorption.The phenomenon is attributed to the presence of a more “rod-like” state in NMP as compared to a more “coil-like” state in CH2CI2.The effects of alkyl substituents on acetic acid solution spectra of “emeraldine” salt will be discussed with respect to polaron band formation in these systems.
Ferromagnetic Intermolecular Interaction and Crystal Structure of α-Nitronyl Nitroxide
Authors: Awaga Kunio , Inabe Tamotsu , Maruyama Yusei 
Published: March 2011

ABSTRACTThe temperature dependence of the magnetic susceptibilities for several ±-nitronyl nitroxides have been measured. It is found that the intermolecular magnetic coupling in these radical crystals changes from antiferromagnetic to ferromagnetic depending on the substituents at ±-position. X-Ray crystal analysis and MO calculation have been carried out on the ferromagnetic ±-nitronyl nitroxide, 2-(4-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy 3-oxide, revealing a two-dimensional ferromagnetic network linked by the Nδ+...0δ− Coulomb attraction.
Synthesis, Structure, Infrared Spectra, and Iodine Doping of Unsubstituted Polyazines
Authors: Euler William B. , Gill Benjamin C. 
Published: March 2011

ABSTRACTPolyazines, -[N=CH-CH=N]x-, are environmentally stable conjugated polymers that can be doped with iodine into an electrically conductive state. These polymers are prepared by the condensation of glyoxal and glyoxal di-hydrazone with acid catalysis. IR spectra of the undoped polymers, independent of the synthetic conditions, exhibit a broad band centered around 3240 cm−1 indicative of the presence of OH groups in the polymer. Solid state NMR spectra show that the OH groups are covalently bound to the polymer chain so that the polymer chain has a number of defect and/or cross-linking sites present. The polymer can be doped with iodine into a poorly conducting state. Iodine doping introduces one new vibrational band into the IR spectra at 1490 cm−1, associated with a bipolaronic charge carrier.
Helical Conformations of Conducting Polymers
Authors: Kertesz Miklos , Cui Changxing 
Published: March 2011

ABSTRACTHelical conformations of polymers occur due to a variety of factors, some of which are electronic in origin. We briefly review the situations in which there is an electronic driving force towards a helix including a case that might be called a helical Peierls distortion. Energetics and geometries of helical conformations of polythiophene and polypyrrole are also analyzed.
Hall Effect and Magnetoresistance in Undoped Poly(3 Hexylthiophene)
Authors: Assadi Azar , Svensson Christer , Willander Magnus 
Published: March 2011

ABSTRACTWe report studies of transport properties of thin films of undoped poly(3-hexylthiophene) (P3HT) fabricated by spinning a polymer solution onto oxidised silicon or glass. The film thicknesseswere on the order of 1000 Å. We studied magnetoresistance, the effect of magnetic field on field effect mobility and Hall effect.Transverse magnetoresistance was measured on films on glass. A positive anomalous magnetoresistance with a saturation value of about 0.1 % was found. Transverse magnetoresistance was also studied by measuring the change of a field effect mobility with magnetic field. This measurement was performed using the field effect transistor structure. An initial mobility of 6.5 × 10−5 cm2/Vs was reduced by about 15 % in a transverse magnetic field.We also carried out Hall effect measurements on films on glass using a Van der Pauw contact configuration. The measured Hall mobility was 2.17 × 10−5 cm2/Vs. Finally we measured the temperature dependence of the Hall mobility and found it follow the exp(T-l/4) law of variable range hopping.
Insulator-Metal Transition and Conduction Processes in Trans-Polyacetylene
Authors: Conwell Esther M. , Mizes Howard A , Jeyadev Surendar 
Published: March 2011

ABSTRACTWe show by calculations for a chain of stage-1 (16.7%) potassium-doped (CH)x that the metallic state is obtained by adding to the Su-Schrieffer-Heeger Hamiltonian the Coulomb potential of the doping ions and solitons on other chains. Good agreement with the measured Pauli susceptibility is obtained. Adding interchain coupling is found to lead to essentially the same density of states.
Thermally Activated Charge Hopping Transport Studies in a Σ-Conjugated Polymer
Authors: Samuel L. , Sanda P. N. , Miller R. D. , Thompson D. 
Published: March 2011

ABSTRACTTime of flight (TOF) and thermally stimulated current (TSC) measurements were performed on poly(methylphenylsilane) (PMPS), poly(ethyl-p-methoxyphenylsilane) (PMeOPhEtS) and poly(ethylphenylsilane) (PEtPhS), to study the mechanism of interchain charge hopping transport. The value of the hole mobility at a given electric field and temperature varied with the substituent side groups. The activation energies, which were assigned to the hopping transport, ranged between 0.1-0.3eV and were dependent on the applied electric field. The nature of this dependence also varied with the substituent side groups. In the TSC spectra, a well defined current peak was observed in the temperature range between 100K-160K. The peak temperature was dependent both on the electric field and the heating rate. For a constant electric field and heating rate it was also dependent on the side groups, in a manner which was consistent with the results obtained by TOF. When the samples were exposed to high doses of UV radiation, a secondary peak at ∽180K was observed, which was attributed to surface defect sites produced by the UV exposure.
Synthesis, Thermal Behavior, and Second-Order Nonlinear Optical Properties of Conjugated, Acceptor/Donor Compounds
Authors: Wolfe James F. , Ermer Susan P. , Lovejoy Steven M. , Leung Doris S. , Aron Kenneth P. , Hansen Glenn A. , Bitler Steven P. 
Published: March 2011

ABSTRACTNew noncentrosymmetric compounds having both electron-accepting and electron-donating substituents on a conjugated, aromatic heterocyclic structure were synthesized and their spectroscopic, thermal, and solubility properties were determined. D.C. electric field-induced second harmonic generation (EFISH) experiments were performed to provide values of the second-order nonlinear optical susceptibility/dipole moment product βμ. Long alkyl substituents were required in heterocycle-containing compounds for sufficient solubility to conduct EFISH analysis. 2,4-Dinitro-substitution on these imine-linked materials gave the highest βμ in the series.
Electro-Optic and Nonlinear Optical Properties of 2, 6-Dibromo-N-Methyl-4-Nitroaniline (Dbnmna) Crystals
Authors: Nahata Ajay , Horn Keith A. , Yardley James T. 
Published: March 2011

ABSTRACTWe report a new organic nonlinear optical crystal, 2, 6-dibromo-N-methyl-4-nitroaniline (DBNMNA). The refractive indices of DBNMNA were measured at several wavelengths between 500 and 1100 in and fit to a single oscillator Sellmeier equation. Second harmonic Maker fringe data yielded d33 values through comparison with y-cut crystalline quartz. We also report measurements of the electro-optic coefficients, (na3r13-nc3r33) r42, and r51 at several wavelengths. We find good agreement between the observed dispersion and that predicted by the simple two level dispersion model. However, the second order susceptibility is not well described by a single tensor component hyperpolarizability.
The Effect of Matrix Attachment on the Third Order Nonlinear Optical Properties of Dyes
Authors: Polis David W. , Bader Mamoun M. , Dalton Larry R. 
Published: March 2011

ABSTRACTIn order to discern the source of the third order nonlinear optical (NLO) phenomenon both morphological and electronic considerations are required. A series of styrene copolymers with varying amounts of p-aminostyrene or p-chloromethylstyrene were prepared as anchoring sites for chemically reactive electrophilic and nucleophilic dyes. For comparison, the same dyes were incorporated into composites of polycarbonate. Preliminary degenerate four wave mixing results for all materials indicate that the copolymeric support allowed incorporation of greater amounts of electroactive units, versus composites, and hence allowed high third order nonlinear responses (X(3)/α of approximately 10−13 esu cm). Third order NLO responses were absent in some composite systems due to limited solubility and/or phase separation difficulties.
Synthesis and Properties of a Fully Conjugated Polydiacetylene: Poly(1,4-Bis (3-Quinolyl)-1,3-Butadiyne)
Authors: Talwar Satya S. , Kamath Manjunath B. , Babu K. N. 
Published: March 2011

ABSTRACTSynthesis of a new fully conjugated polydiacetylene i.e. poly(l,4-bis(3-quinolyl)-l,3-butadiyne) is described. Reflectance spectra of partially polymerised samples and the polymer are reported. The spectra show long wavelength absorption band at 750 nm. with the visible absorption edge above 800 nm. DC electrical conductivity measurements on pristine and Iodine doped Poly-DQ are reported. The results are discussed in terms of side group - backbone electronic interactions.
Large Cubic Nonlinear Optical Properties of Organic Semiconductor Superlattices
Authors: Jenekhe Samson A. , Chen Wen-Chang , Lo Saukwan , Flom Steven R. 
Published: March 2011

ABSTRACTWe have measured extremely large second hyperpolarizabilities〈γxxxx〉 in solutions of two recently prepared organic polymer semiconductor superlattices. These block copolymers are of alternating aromatic and quinoidal moieties and structurally differ by a side group substituent. The values observed are 1.6 × 10−29 esu for the parent copolymer (PBTBQ) and 3.7 × 10−30 esu for its acetoxy derivative (PBTABQ). The corresponding values of χ(3) are estimated to be 2.7 × 10−7 esu and 4.5 × 108 esu. The measurements, made by picosecond degenerate four wave mixing at 532 nm, showed that the dynamics of the larger χ(3) valued copolymer were faster than the 30 ps resolution of the instrument while the derivative exhibited a slower response. The large magnitude and rapid response of the cubic optical nonlinearities in these novel materials suggest theiT potential for further development and photonic device applications.
Nonlinear Optical Properties of Two Thiophene-Based Polyconjugated Systems: Photoinduced Absorption and Third Harmonic Generation Spectroscopy
Authors: Zamboni R. , Taliani C. , Ruani G. , Pal A. J. , Kajzar F. 
Published: March 2011

ABSTRACTNonlinear optical properties of two thiophene-based conjugated polymers (PTT and PDTB) were studied by the photoinduced absorption spectroscopy and the third harmonic generation spectroscopy. The results obtained with these two methods are used to estimate the value of χ(3) in these materials. Resonant χ(3) are (2.0 ± 0.2) × 10−11 e.s.u. and (1.0 ± 0.1) × 10−11 e.s.u. for PTT and PDTB, respectively. χ(3) is shown to be related to the width of the optical gap through a sixth-power law. In PTT a vibronic structure due to the C = C stretching mode appears in the χ(3) spectrum.
Rotational Diffusion of Chromophores Inside a Glassy Polymeric Film Studied By Electrooptical Interferometry
Authors: Meyrueix R. , Mignani G. 
Published: March 2011

ABSTRACTPerot Fabry interferometry under oblique incidence provides a powerful tool for the determination of the complex values of the independant components of the tensors χ2(−ω;ω,ο) and χ3(−ω;ω,ο,ο) of poled films. Deorientation of Disperse Red One chromophore in a poled film can be followed by the decrease with time of two order parameters. In the short term regime, the relaxation times of this process are spread over a broad spectrum. By comparing the chromophore dynamics in PMMA, PS and SAN at different temperatures, it appears that free volume and secondary transition concepts cannot fully explain the chromophore behavior. Chromophore dipole/Polymer dipole interactions are invoked in order to explain the slow deorientation rate in SAN.
Optical Characterization of Polydiacetylene Langmuir Blodgett Film on Silicon Substrates
Authors: Miller P. , Rahman A. K. M. , Broude S. V. , Tripathy S. 
Published: March 2011

ABSTRACTA bilayer of a surfactive polydiacetylene (15–8 PDA) has been deposited by Langmuir-Blodgett technique on a smooth Silicon substrate using a commercial Lauda film balance [1] . The morphology of the deposited film has been studied by cross-polarized optical microscopy, and laser light scattering microscopy. Usual crystalline domains with size ranging from 5 to 50 μm can be seen between cross polarizers. Nonuniformities and voids in the film are observed by imaging the scattered light from a visible laser beam incident at grazing angle onto the film.Raman scattering study on these bilayers have been carried out to investigate their vibronic structure. Information about vibronic levels from PDA has been used to define the extent of disorder and crystalline phase of the bilayer.
Theoretical Calculations on Nonlinear Susceptibilities of Organic Crystals
Authors: Itoh Yuzo , Hamada Tomoyuki , Kakuta Atsushi , Mukoh Akio 
Published: March 2011

ABSTRACTTheoretical calculations on nonlinear susceptibilities of organic crystals are made. Under the oriented gas model approximation, nonlinear susceptibility of a crystal can be calculated both from the molecular hyperpo1arizability and crystal structure data. Molecular hyperpolarizabilities are calculated by an ab initio molecular orbital (MO) method and the energy minimum crystal structures are obtained by an empirical atom-atom pairwise potential method. Finally the effect of intermolecul ar interactions on molecular hyperpolarizabilities, which is neglected in the above approximation, is investigated quantitatively by using a “super molecule” method of ab initio MO calculations.
Efficient Second Harmonic Generation in Hydrazone, Derivatives of Substituted Aromatic Aldehydes
Authors: Potember Richard S. , Hoffman Robert C. , Stetyick Karen A. 
Published: March 2011

ABSTRACTHydrazone, 1,1-dimethylhydrazone, methylhydrazone, phenylhydrazone and p-nitrophenyl hydrazone derivatives of substituted aromatic aldehydes were prepared and screened for second harmonic generation using the Kurtz powder technique. One compound, 4-nitro-3-methoxybenzaldehyde hydrazone exhibited a second harmonic signal up to 32 times that of ammonium dihydrogen phosphate (ADP) and 4-nitrobenzaldehyde hydrazone exhibited a second harmonic signal five times higher than previously reported, up to 40 times that of ADP. 3-methyl-4-nitrobenzaldehyde hydrazone, 4-nitrobenzaldehyde phenylhydrazone, 1-naphthaldehyde phenylhydrazone, 1-pyrenecarboxaldehyde phenylhydrazone exhibited second harmonic signals 25, 2.5, 5 and 20 times that of an ADP standard.
Calcium Phosphate Precipitation in Liposomal Suspensions
Authors: Eanes Edward D. 
Published: March 2011

AbstractArtificial lipid vesicles (liposomes) provide anin vitroapproach for microencapsulating calcium phosphate precipitation reactions in a manner similar to that which occurs in matrix vesicles, the initial loci for extracellular mineralization in many skeletal tissues. Apatitic precipitates readily form within the aqueous interiors of liposomes prepared from phosphatidylcholine, dicetylphosphate, and cholesterol when the liposomal membranes enclosing pH 7.4 buffered PO4solutions are made permeable to external Ca2+with ionophores. If the external Ca solution is rendered metastable with PO4, the apatitic precipitates rapidly expand to outside the liposomes as well. The present paper describes the basic features of liposomal mineralization and presents some specific examples on how compositional alterations in the liposomal membrane and external Ca solution can affect the progress of this mineralization.
The Bernal Icosahedral Spiral
Authors: Vazquez-Polo G. , Jose-Yacaman M. 
Published: March 2011

AbstractIn the present work we study the means to produced icosahedral and decahedral spiral structures based on the ideas of Mackay and Bernal. It is found that indeed it is possible to generate spirals with five-fold or ten fold symmetry axes which might be structural unit for Quasicrystals. These types of structures are already present in many biological systems
Biomineralization: New Routes to Crystal Engineering
Authors: Mann Stephen , Heywood Brigid R. , Didymus Jon M. , Rajam Sundara , Wade Vanessa J. , Walker Justin B. A. 
Published: March 2011

AbstractThis paper discusses the principal features of biomineralization in relation to the controlled crystallization of inorganic materials, and the modelling of these conceptsin vitro. The biological strategies adopted in the regulation of nucleation and growth are; (a) the use of constrained reaction environments, (b) the synthesis of chemically and structurally specific organic macromolecules, and (c) the secretion of tailor-made additives of low and high molecular weight. Underlying these strategies is the concept of molecular recognition at interfaces comprising organic and inorganic surfaces. The structural, electrostatic and stereochemical aspects of these interfacial interactions in systems involving supramolecular asemblies, Langmuir monomolecular films and tailored additives will be described.
Dental Enamel Biomineralization: A Prospectus
Authors: Slavkin Harold C. , Snead Malcolm L. , Zeichner-David Margarita , Lau Eduardo C. , Fincham Alan G. 
Published: March 2011

AbstractIt is becoming increasingly evident that recombinant DNA technology, physical-chemistry and selected biological processes can be coupled leading to the development of new “synthetic” biomaterials. This summary and prospectus will highlight selected features related to dental enamel biomineralization towards the development of human dental enamel as a restorative biomaterial.
The Effects of Particle Size and Solution Chemistry on the Formation of Hydroxyapatite
Authors: Fulmer Mark , Brown Paul W. 
Published: March 2011

AbstractThe effects of varying the particle sizes of particulate reactants which form hydroxyapatite by a dissolution-precipitation reaction is considered. The effect of Mg2+ ion, known to inhibit hydroxyapatite formation in vivo. on the reaction to form hydroxyapatite is discussed.
Synthetic Surfaces as Models for Biomineralization Substrates
Authors: Rieke Peter C. , Bentjen Susan B. , Tarasevich Barbara J. , Autrey Thomas S. , Nelson David A. 
Published: March 2011

AbstractPolyethylene and oxide substrates were derivatized with functional groups commonly associated with biomineralization substrates. These groups include carboxylate, phosphate, hydroxy, sulfonate, thiol, and amine. FTIR, XPS, and contact angle wetting were used to identify and characterize the products at each step. The efficacy of these groups toward inducing mineralization will be compared with naturally occurring substrates.