bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generation of Stable Radical Cations (Polarons) and Dications (Bipolarons) on Model Thiophene Oligomers
Authors: Fichou Denis , Horowitz Gilles 
Published: March 2011

ABSTRACTOxidative doping of individual thiophene oligomers nT (n = 3 to 6) with FeC13 in dilute CH2Cl2 solution generates the corresponding radical cations (polarons) nT+.. as evidenced by in-situ visible/near infrared absorption and electron spin resonance spectroscopies. The nT+. species in solution progressively precipitate as conducting (0′300K = 10−1−10−2 S/cm) and strongly paraaagnetic radical cation salts (g = 2.003, ΔHPP ∼ 4–8 G). The conductivity of the 6T+. salt is weakly temperature dependent, with an activation energy of 32 meV above 100 K and a tendency to level Dff at lower temperatures. In the case of the sexithienyl radical 6T+., further doping results in the quantitative conversion into the dication 6T++ (bipolaron).
Photoluminescence and Odmr Studies of Pristine and Photodegraded Poly (3-Hexylthiophene) Films and Solutions
Authors: Swanson L. S. , Shinar J. , Lichty L. R. , Yoshino K. 
Published: March 2011

ABSTRACTThe photoluminescence (PL) and optically detected magnetic resonance (ODMR) spectra of poly(3-hexylthiophene) in solutions of CCl4, toluene, and CH2Cl2, and films cast from these solutions, are described and discussed. In solution, the PL yield is 7%, and increases with increasing temperature. In oxygen-free, protected films cast from these solutions, the room-temperature yield is ∼0.7%, the spectra is red shifted by ∼0.5eV, and strong peaks at 1.52, 1.69, and 1.86eV appear. In films and CH2Cl2 solutions, the ODMR is resolvable into narrow and broad components, and its intensity ΔL/L is ∼5 × l0−5 at room temperature. A strong photoinduced oxidation process quenches the PL upon exposure to O2 but not water, at a rate possibly limited by O2 diffusion.
Determination of Correlation Parameters in π-Conjugated Polymers
Authors: Gammel J. Tinka , Campbell D.K. , Loh E.Y. , Mazumdar S. , Dixit S.N. 
Published: March 2011

ABSTRACTUsing exact finite-size diagonalizations of extended Peierls-Hubbard Hamiltonians for systems of up to 15 sites, we study the excited state spectra of models for the finite oligomer analogs of trans– and cis– polyacetylene. We use a novel “phase randomization” technique and a variety of other methods to extract maximal information from these small systems. For several electron-phonon couplings in the expected range, we discuss the extent to which we are able to find consistent values of the Hubbard on-site (U) and nearest-neighbor (V) correlation parameters such that the band gap, the 2 1Ag state, optical phonon frequency, and the optical absorptions for charged and neutral solitons and dimers occur in the experimentally expected ranges. Our results suggest that these correlation parameters are in the intermediate coupling regime (U ⋍ 2.5t0), beyond the range of perturbation theory.
Reversible Photoproduction of Stable Charged Defects in Trans-Polyacetylene
Authors: Hoener Carolyn 
Published: March 2011

ABSTRACTPhotoproduction and photodepletion of stable charged defects in trans-polyacetylene were observed, at low temperatures, by monitoring the IR signature of these defects: absorptions at 1368, 1289, 640 cm−1 (1053, 600 cm−1 for (CD)x). These absorptions could be observed at long times (two to several hundred minutes) after photolysis, only when the sample was protected from photolysis by the probe beam, by blocking v > 2,300 cm−1.The location of these absorptions and the temperature dependence of their intensities were similar to those of previously observed photoinduced defects reported to have much shorter lifetimes (τ - ms). The stable defects reported here can be produced at much lower photolysis energies (v > 5,000 cm−1) than transient-photoinduced defects (v > 9,000 cm−1). A mechanism for the photoproduction of stable defects, involving a two-photon process catalyzed by existing neutral defects, is proposed to explain this low onset.The slow decay of these defects observed when the sample is kept in the dark is attributed to photoinduced depletion by blackbody irradiation. This process was slow enough to allow the wavelength dependence of photodepletion (observed at 2,800 < v < 8,000 cm−1) to be studied. The photodepletion was fastest near 4,500 cm−1, suggesting that the defects possess an electronic absorption (with a peak near 4,500 cm−1) similar to that observed directly for the transient-photoinduced defects.
Band-To-Band Transitions in Poly (Phenyl Methyl Silane)
Authors: Kepler R. G. , Zeigler J.M. 
Published: March 2011

ABSTRACTWe have measured the quantum efficiency for carrier generation as a function of photon energy and the electroabsorption spectrum in poly (phenyl methyl silane). The experimental data are consistent with a band gap of about 4.6 eV. A strong absorption peak which is observed at 3.7 eV is shown to be an exciton band.
Nonlinear Optical Polymers: Challenges and Opportunities in Photonics
Authors: Garito A. F. , Wu J. W. , Lipscomb G. F. , Lytel R. 
Published: March 2011

ABSTRACTIn polymer structures, highly correlated virtual excitations of the π-electrons are responsible for the exceptionally large nonresonant nonlinear optical responses observed. Extremely large resonant nonlinear optical responses are also achievable in certain π-electron systems, which can be treated as optical Bloch systems. In addition to their obvious scientific importance, these large optical nonlinearities potentially make possible the implementation of powerful, new nonlinear optical devices and systems. After a description of nonlinear optical processes in polymers, two examples are presented. First, saturable absorption and optical bistability in ultrathin organic polymer films are described, illustrative of resonant third order processes. Saturable absorption studies of glassy polymer films consisting of quasi two-dimensional conjugated disc-like structures of silicon naphthalocyanine demonstrate that on-resonance the system behaves as an optical Bloch system with a linear absorptivity coefficient α0 of 1 × 105 cm−1 and an intensity dependent refractive index n2 of 1 × 104 cm2/kW in the wavelength range of standard laser diodes. A resonant nonlinear optical response of π-electron excitations provides the nonlinear interaction essential to the onset of bistability. Electronic absorptive optical bistability is observed on a nanosecond time scale in a nonlinear Fabry-Perot interferometer employing the saturably absorbing naphthalocyanine film as the nonlinear optical medium. As a second example, the nonresonant second order process of linear electrooptic effects in poled polymer films, is discussed. For such a second order nonlinear optical process, the broken global centrosymmetry is achieved by electric field poling of a thin polymer film. With high electrooptic coefficients of 10–50 pm/V and low dielectric constants of 3–4, poled polymers have potentially great advantages over inorganic crystals as electrooptic materials. As one device illustration, the application of poled polymers in electrooptic waveguide operations is presented.
Quadratic Nonlinear Optical Properties of Diva Crystal
Authors: Wada T. , Grossman C. H. , Yamada S. , Yamada A. , Garito A. F. , Sasabe H. 
Published: March 2011

ABSTRACTNew organic nonlinear optical crystal : dicyanovinyl anisole (DIVA) has been grown from vapor by low pressure sublimation and from saturated solution by solvent evaporation. Crystallographic structure and quadratic nonlinear optical properties were investigated. Molecular orientation in DIVA crystal with space group P21, is favorable for the highest possible value of bulk phase-matchable coefficient. Both type I and type II phase matched second harmonic generation (PMSHG) were observed from naturally grown faces of single crystals. Efficient PMSHG was achieved at a fundamental wavelength of 812 and 1064 nm. The efficient type I PMSHG coefficient was determined as deff = 4.9 × 10−8 esu = 40 × (d11 of α-quartz) at a wave.LH length of 1064 nm. Blue light generation was demonstrated by both PMSHG and sum-frequency mixing of the 812 nm laser with 1064 nm.
Organic Polymer Semiconductor Superlattices
Authors: Jenekhe Samson A. , Chen Wen-Chang 
Published: March 2011

ABSTRACTWe describe the synthesis and study of the first organic polymer semiconductor superlattices designed as periodic block conjugated copolymers, (−AxBy−)m. The observed variation of electronic spectra and wavelength of the lowest energy absorption maxima with block length y are interpreted in terms of quantum confinement size effects predicted for semiconductor superlattices. The periodic block conjugated copolymers were synthesized by a two-step strategy that ensure strict control of sequence, block length and periodicity. It is suggested that organic semiconductor superlattices provide a rational and systematic approach to the molecular engineering of electronic, optical, nonlinear optical, and electro–optical properties in polymeric materials and hold promise for molecular electronics and molecular photonics.
Synthesis and Characterization of Third Order Nonlinear Optical Materials
Authors: Yu L. P. , Chen M. , Dalton L. R. , Cao X. F. , Jiang J. P. , Hellwarth R. W. 
Published: March 2011

ABSTRACTNew polymers incorporating a variety of electroactive moeities with defined π-electron conjugation lengths have been synthesized and characterized by degenerate four wave mixing (DFWM) techniques. The χ(3)/α values for these materials varied from 10−12 to 10−13 esu cm. This work has identified several promising structures with nonlinear optical activity including organometallic and purely organic materials. The preparation of composite materials has also permitted the measurement of χ(3)/α as a function of the electroactive unit concentration.
Enhanced Third Order Optical Nonlinear Response in Polythiophene Films—Polaron Contributions
Authors: Yang Lina , Dorsinville R. , Zamboni R. , Taliani C. , Tubino R. , Alfano R. R. 
Published: March 2011

ABSTRACTThe enhancement of the third order nonlinear susceptibility χ(3)) of an homologous series of polycondensed thiophene based polymers was observed about photoinduced polaronic bands by a novel “pump-probe” degenerate four wave mixing echnique. Enhancement of the degenerate four wave mixing signal for more than an order of magnitude was achieved with response time of less than 25 ps. The intrachain polarons contribution is proposed as the possible mechanism responsible for the observed enhancement.
Nonlinear Optical Studies of Mixed π-Conjugated Polymer Multilayers by Second Harmonic Generation
Authors: Koezuka H. , Kurata T. , Tsumura A. , Fuchigami H. 
Published: March 2011

ABSTRACTThe structures of the mixed LB monolayers, composed of two different kinds of π-conjugated system, poly(3-hexylthiophene) (PHT) and pentacosa-10, 12-diynoic acid (DA), have been investigated mainly by a second harmonic generation (SHG) Maker fringe method. The mixed LB films partly contain a double-layered structure consisting of PHT and DA. The second harmonic radiation has been produced from slightly twisted PHT in the double layer. Both UV-polymerization of DA and successive heat-treatments enhanced the SHG intensities. The enhancement of the SHG intensities has been elucidated by the enlargement of the PHT twisting and the interaction between PHT and a newly formed π-conjugated system.
Preparation and Properties of Organic Superconductor κ-(Bedt-TTF)2 [Cu(NCS)2] and Its Related Materials
Authors: Saito Gunzi 
Published: March 2011

ABSTRACTκ-(BEDT-TTF)2 [Cu(NCS)2] has a two-dimensional (2D) layered structure. The compound is metallic with the room temperature conductivity of 10–40 S/cm within the 2D plane but showed a semiconductive-like anomaly between 270 and 90K. The superconducting transition was observed at Tc=10.4K and Tc increased by 10% on the sample of deuterated BEDT-TTF (Tc=11.4K). The upper critical field, Hc2, was more than 20 Tesla below 2K within the 2D plane which is more than the expected value from the simple BCS theory. The transport critical current density was estimated as 100 A/cm2 (5.1K, 0 Tesla, l//b, H//c) which is an order of magnitude smaller than that obtained from the magnetization curve hysteresis. 1H-NMR showed a big enhancement of the relaxation rate well below Tc. The tunneling spectra showed anisotropic gap and the magnetic field penetration depth measurements strongly suggest that this system is a gapless superconductor. (BEDT-TTF)2[KHg(SCN)4] is an organic metal and showed both Shubnikov-de Haas effect and angle-dependent quantum oscillation indicating that this system has a warped 2D Fermi surface.
The Microstructures of the Biomineralized Bivalvia Shells
Authors: Huang L.J. , Li H.D. 
Published: March 2011

AbstractThe paper presents the detailed study of the structural features of the biomineralized bivalvia shells. The Cristaria plicata(Leach), Anodonta woodianal(Lea) and Lamprotula Leai(Gray) are selected as the prototype in the present study. Scanning electron microscope (SEM), X-ray diffraction, laser Raman spectroscope and electron spectroscopy for chemical analysis (ESCA) are employed to study the structures of the shells. It is found that three different layers of the shells possess distinct morphologies and structures with a clear boundary between every two layers. The prismatic layer can be further divided into two sub–layers. The preferential growth orientation of the biominerahzed phases were different from the natural ones. The Raman spectra present the detailed vibrational states of these biomineralized phases, while ESCA reveals that the chemical environments of the atoms in pearl layer are less varied than those in the other two layers.
Hierarchical Structure of the Intervertebral Disc
Authors: Cassidy J. J. , Hiltner A. , Baer E. 
Published: March 2011

AbstractThe intervertebral disc is a complex hierarchical structure composed of the annulus fibrosus and nucleus pulposus which are anchored to the vertebral bodies by cartilaginous endplates. The hierarchical structure of the collagenous components of the intervertebral disc is characterized using optical microscope techniques. In the lamellae of the annulus, collagen fibers exhibit a planar crimped morphology similar to that seen in other collagenous tissues. A model of the intervertebral disc has been developed that incorporates the structure of the collagen fibers on the macro- and microscopic scales.Mechanical testing in load-deflection, stress relaxation, and creep modes reveals the response at each level of organization to compression. These mechanical data are analyzed with models that reflect the hierarchical composite structure.
Mechanical Properties of Bacterial Fibres
Authors: Thwaites John J , Mendelson Neil H. 
Published: March 2011

AbstractBacterial thread is the name given to a fibrillar fiber produced from cell-separation-suppressed mutants of Bacillus subtilis. which grow in long cellular filaments and produce in cultures aggregates that resemble randomly-laid textile webs. Threads are produced by steady withdrawal at the end of a sterile toothpick - for all the world like Carothers, 50 years ago! Individual filaments are drawn radially into the forming thread and adhere strongly to each other with axial alignment. Uniform threads up to 1 meter in length and 180 μm in diameter can be produced. Such threads contain about 50,000 filaments and upwards of 1010cells Tests on thread show that peptidoglycan, which is the load-bearing polymer of the bacterial cell wall, behaves mechanically like other visco-elastic polymers. When dry its behavior is glassy, with high modulus; when wet, it is relatively weak and of low initital modulus. Relaxation data indicate a very wide spectrum of relaxation times. All the mechanical properties depend strongly on the RH of the test environment; they are also influenced by the ionic environment at the time threads are drawn. Available evidence indicates that peptidoglycan is not crystaline. Nonetheless there is some degree of orientation in the bacterial cell wall. This is shown by the effect of enzyme attack on mechanical properties and by the twisted growth pattern of bacteria.
Enzymatic Synthesis of Chiral Lactones and Polyesters
Authors: Gutman Arie L. 
Published: March 2011

AbstractLipases in organic solvents catalyse lactonisation or polymerisation of ω-hydroxyesters. Under these conditions the enzymes exhibit both enantioselectivity and prochiral selectivity. This approach was used to develop the synthesis of chiral γ-lactones and polyesters.
Biological Production of Uniform Polypeptides for Optical Applications
Authors: Lawton Carl W. , Klei Herbert E. , Strausbaugh Linda D. , Crane Robert 
Published: March 2011

AbstractRecent advances in recombinant DNA technology have created the potential for engineering of protein molecules to specific uses beyond those normally considered for biomaterials. This research project has demonstrated the feasibility of producing polypeptides useful for narrow band filters and nonlinear optical applications.Synthetic genes, ranging in size from 36 to 576 base pairs, have been constructed from oligonucleotides using a restriction doubling technique. The synthetic genes have been inserted into a Protein A fusion expression system. Fused polypeptides from induced cells have been purified by affinity chromatography (IGG), and analyzed by polyacrylamide gel electrophoresis.
Sugar Coated Semiconductors: Model Surfaces to Study Biological Adhesion
Authors: Mastandrea Mark , Bednarski Mark D. 
Published: March 2011

AbstractCertain molecules when placed in contact with a surface can bind to form well-ordered two dimensional arrays. This process is called molecular selfassembly (MSA), and it is emerging as an important method to control the interactions between a surface and its environment (interfacial properties). Molecular self-assembly uses the fundamental forces between molecules (Van der Waals interactions, hydrophobic effects and hydrogen bonding) to form highly ordered macromolecular systems. This process has been used to synthesize molecular films on a variety of surfaces including glass, gold, alumina, platinum, and silicon. The objective of this paper is to describe the application of molecular self-assembled films to the study of biological systems. Specifically, we will describe methods to synthesize and characterize surfaces that contain molecules that bind to bacteria and viruses. We will also evaluate the use of surface science techniques to characterize the physical and chemical properties of these surfaces, and we will attempt to correlate these properties with the adhesion of biological molecules.
Calcium Mineral-Peptide Interactions
Authors: Wheeler A. P. , Sikes C. Steven 
Published: March 2011

AbstractPeptides have been synthesized by solid phase methods with structures which are in part based on experimentally-determined features of a major class of organic matrix phosphoproteins isolated from the calcium carbonate shell of the oyster. The matrix structures mimicked in the synthetic peptides included runs of aspartic acid (Asp), which were contrasted with peptides having other deployments of Asp with serine (Ser) and glycine (Gly). In addition, peptide-Ser was phosphorylated (PSer) and the hydrophobic carboxyterminus of natural matrix was mimicked using polyalanine tails. The interaction of the various peptides with CaCO3as well as calcium phosphates was determined using a variety of crystallization assays and studies of adsorption of radio-labelled peptides to crystal surfaces.In general, peptides that include runs of Asp regulate crystal nucleation and growth more effectively than those which contain (Asp-X)nor (Asp-X-Y)nsequences with X and Y being either Gly or Ser. Further, CaCO3crystals have a much higher binding capacity for polyAsp than for peptides with other deployments of Asp. Phosphorylation increases the regulatory activity and the crystal capacities of Asp/Ser - containing peptides. PolyAsp peptides having terminal PSer's are especially effective as regulators of CaCO3nucleation and the conversion of amorphous calcium phosphate to apatite. The activity of Asp15molecules in CaCO3nucleation assays is markedly increased by the addition of polyalanine tails.
The Effects of Citrate and Phosphocitrate on the Kinetics of Mineralization of Calcium Oxalate Monohydrate.
Authors: Richardson C. F. , Johnsson M. , Bangash F. K. , Sharma V. K. , Sallis J. D. , Nancollas G. H. 
Published: March 2011

AbstractThe adsorption of citrate and phosphocitrate on calcium oxalate monohydrate (COM) surfaces has been measured in saturated solutions of calcium oxalate monohydrate at 37°C. In separate adsorption experiments, the uptake of phosphocitrate was markedly greater than that of citrate. When both additives were present, the adsorption of phosphocitrate was further increased. In constant composition studies of the crystallization of CON from supersaturated solution, phosphocitrate was more effective as an inhibitor than was citrate.
Organic, Organometallic and Polymeric Materials with Nonlinear Optical Properties
Authors: Marder S. R. , Perry J. W. , Schaefer W. P. , Ginsburg E. J. , Gorman C. B. , Grubbs R. H. 
Published: March 2011

AbstractNew approaches to both second-order and third-order nonlinear optical materials are presented. A series of organometallic and organic salts, in which the cation has been designed to have a large molecular hyperpolarizability, has been prepared and the SHG efficiencies were measured. Partially substituted derivatives of polyacetylene are synthesized via the ring-opening metathesis polymerization (ROMP) of cyclooctatetraene (COT) and its derivatives. Certain poly-COT derivatives afford soluble, highly conjugated polyacetylenes. These materials exhibit large third-order optical nonlinearities and low scattering losses.
Third-Order Optical Nonlinearity in a Polymer Composite
Authors: White K. M. , Harelstad R. E. , Francis C. V. , Gerbi D. J. , Stevens J. , Leung P. C. 
Published: March 2011

AbstractThird-order optical nonlinearity in organic materials has generally been sought from molecules and polymers having extended i-electron delocalization in conjugated bonding schemes. In an alternative approach, we have investigated the third-order optical response of a polymeric composite containing charge transfer complexes in which the nonlinearity originates from intermolecular electron delocalization between π-electron clouds in charge transfer stacks. The material, which is composed of a polymer having electrondonating pendant side groups that complex with dopant electron-acceptor molecules, has been processed into an optically clear thin film. Nonlinear characterization of the film by means of third-harmonic generation suggests enhancement of the third-order response arising from charge transfer interactions.
Synthesis and Properties of Multifunctional Polymers
Authors: Goldberg H.A. , East A.J. , Kalnin I.L. , Johnson R.E. , Man H.T. , Keosian R.A. , Karim D. 
Published: March 2011

AbstractRecent work aimed at developing new polymers which exhibit useful optical, electro-optical, and piezoelectric properties is presented. The materials under study are polymers with methacrylate backbones and oxynitrostilbene side chains. The synthesis is outlined, and pyro-electric, electro-optic, and thermal property data are reported and discussed.
Molecular Design of Synthetic Polypeptides for Nonlinear Optics
Authors: Ishii T. , Wada T. , Garito A. F. , Sasabe H. , Yamada A. 
Published: March 2011

AbstractSecond order molecular susceptibilities β of poly(γ – benzyl L–glutamate)(PBLG) and poly(γ – p–nitrobenzyl L–glutamate) (PNBLG) were determined by means of dc-induced second harmonic generation (dc-SHG technique in solutions at a wavelength of 1064nm as 1.5×10–−29 esu and −4.9×10−29 esu, respectively. Among PBLG, PNBLG and nitrobenzene, it was found that only PNBLG has negative value of β. It follows that the effect of nitrophenyl groups in side chains is dominant for β whereas the contribution of carbonyl groups in main chain is dominant for the permanent dipole moment μ in PNBLG.