bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel Conjugated Polymers Containing Ferrocene
Authors: Lee Jin-Kyu , Cho Sung In 
Published: May 2011

ABSTRACTConjugated inorganic/organic hybrid polymers, poly(phenylene vinylene ferrocenyl vinylene), was prepared by condensation polymerization of bisphosphonate reagent and ferrocenedialdehyde. Conjugated polymers having long alkyl side chains is very soluble in various organic solvents and thin polymer films can be easily produced by spin-coating technique. UV-Vis., NMR, cyclicvoltammetry, and GPC analysis were used to characterize the properties of conjugated polymers, and the averaged molecular weight was in the range of 7,000~25,000 (vs. PS standard). Electrical conductivity measurement of this processible conjugated polymer either in powder or in thin solid film showed very low conductivity probably due to the slow chain-to-chain hopping process. Third order nonlinear optical property of the conjugated polymers was measured as high as ϰ(3) = 1.24×10−8 esu in spin-coated thin film.
Tetraphenylmethane-Based 1,3,4-Oxadiazole as Electron Transporting Materials in Organic Light-Emitting Devices
Authors: Chen Chin-Ti , Lin Tzu-Yao J. , Yeh Hsiu-Chih , Jan Li-Hsin , Balasubramaniam Easwaramoorthy , Tao Yu-Tai 
Published: May 2011

ABSTRACTA series of tetrahedral tetramers of 2,5-diphenyl substituted 1,3,4-oxadiazole compounds were synthesized and characterized for electron-transporting layer (ETL) in organic light-emitting diode (OLED). The multiple-branch design of the oxadiazole tetramers intends to increase the melting temperature and to generate glass phase of the low molar mass derivative such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). We observed temperatures of the glass phase transition for the oxadiazole tetramer with appropriate peripheral substituents, indicative of amorphous characteristics of the molecule in spite of highly symmetrical molecular framework. The luminescence-current-voltage characteristics of multilayer OLED devices containing the oxadiazole tetramer or PBD as ETL were examined to evaluate the efficiency of our multiple-branch molecular design.
Relationship Between Spectroscopic and Structural Properties of Poly(meta/para Phenylene)
Authors: Dridi Cherif. , Davenas Joël. , Touhami Ahmed. , Ouada Hafedh. Ben , Mâaref Hassen. , André Jean-Jacques. 
Published: May 2011

ABSTRACTWe have used electron paramagnetic resonance (EPR) spectroscopy for investigating the properties of spins, such as those carried by polarons which carry both spin and charge in an electrosynthesized poly (meta/para phenylene) PMPP.Indeed, the study of their mobility provides an insight into the charge transport properties of the conjugated polymer in a microscopic scale.Moreover, we report a correlation between thin film morphology, chainlength and optical gap.Particularly, we show a blue shift upon decreasing chainlength. Furthermore, we have observed a blue shift of the energy band gap with the decrease of the surface grain size deduced from atomic force microscopy (AFM) analyses. This result has been explained in terms of quantum confinement.
New Electron Acceptor for the Control of Crystal Structures and the Generation of High Optical Nonlinearities
Authors: Pu L. S. , Nishikata Y. 
Published: May 2011

ABSTRACTCyclobutenedione (CD) as a new electron acceptor for second order nonlinear optical materials is reported. After syntheses and evaluation of new materials containing CD, it is observed that CD is not only a strong electron acceptor to enhance second order molecular hyperpolarizability (β), but also the first substituent to control the molecular orientation in crystals. Compared with nitro (NO2) subsutitent, CD is shown to be advantageous in higher molecular absorption coefficient (ε), shorter λcut-off and easy introduction of chirality with hydrogen bonds into organic molecules. These advantages are useful to produce higher β values and second order nonlinear optical coefficients (dIJK) than nitro analogue, by controlling the molecular orientation in bulk crystals. In particular, CD substituted with chiral 1-amino-2-propanol is shown by x-ray crystallographic analyses to have a function to control molecular orientation one dimensionally in a mono-molecular plate of crystals with space group P1. By oriented gas model, very large d-values including off-diagonals were obtained. From the analysis of the Maker fringe pattern, the coefficient d11 of DAD ((-)-1-(4-dimethyl aminophenyl)-2-(2-hydroxypropylamino)cyclobutene-3,4-dione) was measured to be 200±40 pm/V.
Influence of the Chemical Structure on the Luminescence Properties of Organic Dye Molecules
Authors: Zojer Egbert , Rant Ulrich , Buchacher Petra , Müllner Ruth , Stelzer Franz , Wudl Fred , Schulte Niels , Schlüter Arnulf-Dieter , Leising Günther , Brédas Jean-Luc 
Published: May 2011

ABSTRACTIn this contribution we compare experimental investigations (of photoluminescence, absorption and modulation spectroscopy) for a number of novel dye molecules to quantum-chemical simulations. The investigated materials contain phenylene-, phenylenevinylene-, naphthylene- and anthrylene units linked either by saturated or non saturated bonds. In the first part of the paper we give a short overview of the principal optical properties of the investigated molecules including a discussion of exciton localization effects. The latter can be accomplished by studying the geometry modifications in the excited state relative to the ground state. To do so, we couple the Austin Model 1 (AM1) approach to a multi-electron configuration interaction technique (MECI). The optical spectra are subsequently obtained from the Intermediate Neglect of Differential Overlap (INDO) Hamiltonian combined with a Single Configuration Interaction (SCI) approach. In the main section of this contribution we show the results of singlet exciton lifetime measurements performed with a modulation technique. An excellent agreement was found between the experimental data and quantum-chemical simulations for the transition dipole moments
Infrared Photospectroelectrochemistry of Germanium/Pedot/Electrolyte Interfaces
Authors: Neugebauer Helmut , Yohannes Teketel , Sariciftci N. Serdar 
Published: May 2011

ABSTRACTDifference infrared spectra between illumination and dark of a polyethylenedioxythiophene (PEDOT) covered germanium electrode in contact with the electrolyte solution and under applied potential are shown. The spectra show a different behavior at different redox (doping) states of the polymer. The photoinduced formation of positive charge carriers was found by illumination of the neutral (undoped) form, wheras no significant spectral changes occur in the oxidized (p-doped) and reduced (n-doped) form of PEDOT.
Electrochemically- and Photo-Induced IR Absorption of Low Band-Gap Polydithienothiophenes: A Comparative Study
Authors: Cravino A. , Neugebauer H. , Sariciftci Niyazi S. , Catellani M. , Luzzati S. 
Published: May 2011

ABSTRACTPoly(dithieno[3,4-b:3',4'-d]thiophene) (pDTT1), poly(dithieno[3,4-b:3',2'-d]thiophene (pDTT2) and poly(dithieno[3,4-b:2',3'-d]thiophene) (pDTT3) are low band-gap polymers that undergo both p- (oxidation) and n- (reduction) type electrochemical reversible doping in organic electrolytes. In this work we report on the in-situ IR spectroscopic characterization of both doping types using attenuated total reflection (ATR) FTIR spectroelectrochemistry. Thin polymer films were prepared on Ge reflection elements by electrosynthesis. During electrochemical potential cycling experiments in a spectroelectrochemical cell, the evolution of infrared active vibrational (IRAV) modes, correlated with the generation of charge within the polymer chain, was studied. In addition to electrochemical doping, the polymers exhibit also charged excitations by photodoping. FTIR spectra recorded by illumination/dark cycles show photoinduced IRAV bands which are similar to those found for the electrochemically p-doped materials. The infrared spectroscopic results are compared with Raman spectra of the neutral polymers. The relationship between vibrational properties and structure of the polymers is discussed in terms of different contribution of the φ-electrons within the repeating units to the electronic structure of the conjugated backbone.
Second Order Nonlinear Optical Films by Alternating Polyelectrolyte Deposition on Hydrophilic and Hydrophobic Substrates
Authors: Roberts M. Joseph , Herman Warren N. 
Published: May 2011

ABSTRACTAlternating polyelectrolyte deposition (APD) is a room temperature process that can be used to produce noncentrosymmetric ordered films of nonlinear optical polymers (NLOP). In this study, second-order NLOP APD films of a stilbazolium-substituted polyepichlorohydrin, poly (diallyldimethylammonium chloride), and polyacrylic acid were prepared by alternately dipping a substrate into aqueous solutions of each polymer. Evidence for uniform layer to layer deposition includes a linear increase of UV-Visible absorbance, thickness measurements, and quadratic increase of second harmonic generated light intensity as a function of film thickness. Films have been uniformly deposited up to 0.1 micrometer thick. The surface morphology, roughness, and film thickness have been characterized by Tapping Mode Atomic Force Microscopy (TM AFM ). Work is in progress to deposit thicker films of the same quality and to improve NLO figures of merit.
Low Halfwave Voltage Electrooptic Polymer Modulator Technology
Authors: Shi Yongqiang , Lin Weiping , Olson David J. , Bechtel James H. 
Published: May 2011

ABSTRACTThe recent development in nonlinear optical polymer materials and device fabrication technologies has resulted in a significantly reduced halfwave voltage for high-speed optical communications. In this paper, optical push-pull and active cladding approaches are discussed for low halfwave voltage electrooptic polymer modulator design and fabrication. Based on these new designs, experimental polymer modulators were fabricated and a halfwave voltage-interaction length product of 2.2 V-cm was achieved using optical push-pull and a highly active electrooptic polymer system.
Design and Synthesis of New Acceptor Molecules for Photo-Induced Electron Transfer Reverse Saturable Absorption
Authors: Bader M. , Moser J. , Li H. , Tarter S. , Spangler C. 
Published: May 2011

ABSTRACTWith the advent of efficient and relatively inexpensive pulsed and CW laser systems for both civilian and military applications, the need for adequate eye and sensor protection is becoming increasingly important. While it is possible to filter out harmful wavelengths if the laser frequency is known, the proliferation of frequency agile laser sources underscores the need for “smart” passive materials that can sense the incident wavelength and provide protection. There has been considerable progress made in recent years in the design of optical power limiting (OPL) materials that can function by a variety of mechanisms, most of which derive their limiting behavior from some type of nonlinear absorption process. The most well-studied of these processes involve excited state absorption in which the absorption cross-sections of the photo-generated transient species are much greater than the original S0 to S1 transition. In this presentation we will discuss the efficacy of charge transfer species for optical limiting, and the need for more and better electron acceptor species.
Interfacial Design of Silicon/Polypyrrole Junctions
Authors: Kim Namyong Y. , Vermeir Inge E. , Laibinis Paul E. 
Published: May 2011

ABSTRACTHydrogen-terminated silicon surfaces exposing a molecular film of covalently grafted pyrrole units were formed by a solution-phase reaction using the organolithium reagent 5-(N-pyrrolyl)pentyllithium. Electrochemical polymerization of pyrrole onto native hydrogen-terminated silicon surfaces and these chemically modified supports produced silicon/polypyrrole junctions that showed diode-like characteristics, with those formed on the latter substrate exhibiting higher current densities and better ideality factors. The presence of the grafted pyrrole films on silicon provided a better electrochemical control over the polymerization process and yielded smoother polypyrrole films than on the native hydrogen-terminated silicon supports. Impedance measurements revealed that the electrical improvements to the silicon/polypyrrole junctions were a consequence of incorporating sites on the silicon surface for direct contact between the conducting polymer and the semiconductor, as the barrier height of the junction appeared to be unaffected by the chemical modification.
A Route to Stable Interfaces Between Dissimilarly Doped Conjugated Polymers
Authors: Zhou Xin , Langsdorf Brandi , Lonergan Mark C. 
Published: May 2011

ABSTRACTA route to kinetically stable interfaces between dissimilarly doped conjugated polymers is proposed. The route relies on the use of internally compensated conjugated polymers to kinetically control interfacial redox chemistry. As a demonstration of the feasibility of the proposed route, the enhanced stability of an interface between an oxidatively doped, internally compensated poly(acetylene) and an undoped poly(acetylene) is reported.
Vibronic Structure of PTCDA Stacks: Monomer-Dimer Equilibrium
Authors: Soos Zoltán G. , Hennessy Margaret H. , Bulovic Vladimir 
Published: May 2011

ABSTRACTSolution spectra of perylenetetracarboxylic dianhydride (PTCDA) show an equilibrium between monomers and dimers, with fluorescence exclusively from monomers and absorption from both. The dimer absorption follows closely the spectrum of PTCDA stacks in crystalline films, which indicate strong coupling to a molecular vibration and mixing of Frenkel and charge-transfer excitons. The same model accounts for solution spectra.
Photoexcitations in Oligothiophenes: The Role of Conformation Mobility and Intermolecular Interactions.
Authors: Botta Chiara , Destri Silvia , Porzio William , Bongiovanni Gianni , Mura Andrea , Loi Maria A. , Garnier Francis , Tubino Riccardo 
Published: May 2011

ABSTRACTThe optical properties of substituted and unsubstituted oligothiophenes are analysed with respect to their supramolecular organization in the solid state. The spectra typical of the isolated molecules are obtained by reducing the intermolecular interactions by both lateral chain substitution and by inclusion in a host organic crystal. The photophysical properties of the weakly interacting oligothiophenes are strongly influenced by their backbone conformation and conformational mobility. Oligomers included in the channels of a guest crystal show fast torsional relaxation processes during the photoexcitation. Powders of β-substituted oligomers display optical properties dependent on the conformation of their particular chain packing arrangement.
Photonic Properties of Dendrons and Dendrimers Incorporating Bis-(Diphenylphosphino)Diphenylpolyenes
Authors: Madrigal L. , Kuhl K. , Spangler C. 
Published: May 2011

ABSTRACTSubstituent effects are quite important in fine tuning the photonic properties of conjugated molecules. In designing new chromophores, electron-donating or withdrawing substituents affect the electron distribution in the conjugation sequence, and previous studies to establish structure- property relationships have noted that when second row elements replace first row elements in the structure (e.g. S for O in donor groups), large enhancements of both the second and third order optical nonlinearity are observed. However, along with the observed enhancement of the nonlinearity, a red-shift in the absorption spectra occurs, often with peak broadening and tailing. This absorptivity-nonlinearity trade-off has been a constant concern in proposing organic materials for electro-optic device applications. In this presentation we will review our recent activity in designing new chromophores wherein P replaces N in donor groups and dendrimer building blocks, and the consequences and opportunities resulting from the observed large blue shifts in the spectra.
Photovoltaic Effect in Multilayer Organic Systems
Authors: Meinhardt G. , Moderegger E. , Schröder R. , Winter G. , Hanack M. , Quante H. , Geerts Y. , Müllen K. , Tillmann H. , Hörhold H.-H. , Leising G. 
Published: May 2011

ABSTRACTThe organic materials presented here, e.g. cyano-ether-PPV, different bisarylamidine-perylenes and conventional as well as substituted forms of phthalocyanines exhibit the advantages of low processing costs and the simplicity of tuning their optical properties. Hence they are promising candidates to be used in large area photovoltaic applications. The investigated cells consist of one or two organic layers sandwiched between electrodes of indium tin oxide (ITO) and aluminum. The experimental techniques of electroabsorption(EA)- spectroscopy, photocurrent-action spectroscopy and current voltage characterization were used to gain further insight into the process of charge generation, charge separation and transport of the charged species to the electrodes. To enhance the quantum efficiencies of the photovoltaic cells, combinations of organic materials with electron-accepting and electron- donating properties in multilayer devices were investigated. We chose the organic materials copper-phthalocyanine and a bisarylamidineperylene whose HOMO and LUMO level alignment should favor a charge transfer process in order to increase the photocurrent(PC) responsivity by enhanced exciton dissociation. Additionally, one of the two layers of a double layer device was blended with small amounts of the material constituting the second layer to further increase charge carrier generation by extending the dissociation zone.
Influence of Colloids in Experimental Solubility Studies of Ni in Natural and Synthetic Aqueous Media
Authors: Vuorinen Ulla , Carlsson Torbjörn , Kekki Tommi 
Published: May 2011

ABSTRACTThe estimation of nickel solubility values for performance assessment is impaired by the lack of experimentally verified solubility values in conditions relevant to actual nuclear waste disposal sites. For this reason, experimental nickel solubility studies were conducted in conditions relevant to a possible Finnish disposal site, Olkiluoto. Using an initial nickel concentration of 10−3 M, nickel solubility was approached from over-saturation in three aqueous media – natural fresh groundwater, synthetic saline groundwater, and cement-conditioned groundwater with added ferrous iron and sulfide. In addition to the nickel solubility values, nickel association with the particle and colloidal phases was measured. Almost 100%of the initial nickel was found associated with the separated particle phase in the natural groundwater and the cement-conditioned groundwater, and in only the natural groundwater about 0.04%or 0.4%with the separated colloidal fraction depending on the initially added amount of ferrous iron and sulfide. In the synthetic saline groundwater, all the nickel was found in the soluble fraction except for a minor fraction sorbed onto the walls of the sample bottle. Colloid-bound nickel did not have any practical influence on the solubility values obtained. The inverse behavior of Ni solubility and sorption in the natural groundwater compared to that in the other two aqueous phases studied was suspected to be caused by the unidentified yellow color of the groundwater for which indications of both possible organic and inorganic nature was obtained. Based on the measured results, the presence of sulfide and ferrous iron would decrease the amount of mobile nickel, both soluble and colloidal, in non-saline natural and cement-conditioned groundwater, whereas in saline groundwater nickel remains in the mobile phases.
Insights to Repository Performance through Study of a Nuclear Test Site
Authors: Smith D.K. , Kersting A.B. , Thompson J.L. , Finnegan D.L. 
Published: May 2011

ABSTRACTUnderground nuclear test sites offer an unprecedented opportunity to evaluate processes relevant to high-level waste repository performance in the absence of engineered barriers. Radionuclide migration programs at the Nevada Test Site represent a twenty-five year systematic investigation of the diverse radiologic source terms residual from weapons testing and the evolution of the hydrologic source term which comprises those radionuclides dissolved in or otherwise available for transport by groundwater. The Nevada Test Site shares actinide source terms, correlative geology, an identical tectonic setting, similar climate, and a thick unsaturated zone with the adjacent potential Yucca Mountain high-level waste repository and provides a natural laboratory to assess long-term radionuclide transport in the near field. Analog studies may ultimately help validate predictions of radionuclide transport from the potential Yucca Mountain repository.
Surface Conductivity and Diffusion Models - Comparison and Evaluation -
Authors: Ohlsson Y. , Arnerdal K. , Neretnieks I. 
Published: May 2011

ABSTRACTThe interest for studying the mobility of near surface cat-ions in rock and clay pores has increased during the last 3-4 years. Several researchers have worked experimentally with liquid phase diffusion experiments and with electrical conductivity measurements, and on developing models describing the phenomenon. Our own measurements have shown that surface mobility can contribute substantially to ionic transport in crystalline rock. Some recently proposed models for surface mobility are discussed.Part of the problem in comparing different surface transport models lies within the different definitions of what the diffuse layer and the Stern layer really comprise. There are also differences in what is actually considered to be adsorbed ions and what part of these ions that can be considered mobile. We attempt to reconcile some of the different approaches by describing some very simplified concepts upon which all the models are based. This permits us to discuss the different views within one framework. Experimental results interpreted using the various models are discussed in the context of the simplified framework.
Use of Multi-Dimensional Sorption Data-Sets to Constrain Models of Radionuclide-Solid Interactions
Authors: Payne T. E. , Waite T. D. , Lumpkin G.R. 
Published: May 2011

ABSTRACTIn order to adequately constrain surface complexation models for radionuclide sorption, large ‘multi-dimensional’ data-sets, showing the dependence of sorption on numerous experimental parameters, are required. This paper describes how large sorption databases were used to develop surface complexation models of U(VI) uptake on kaolinite and ferrihydrite. It is shown that the shape of U uptake curves as a function of pH and total U (εU) can be used to distinguish between U adsorption and the precipitation of amorphous uranyl hydroxide. The U sorption data-set obtained in this work also includes the effects of several complexing ligands, including phosphate. The dependence of U uptake on these variables can be used to assess the formation of various types of surface complexes (including ternary surface complexes) and the possibility of precipitation reactions. Adsorption experiments with different sorbing materials were also useful in developing models for U sorption and for excluding some possible surface and precipitation reactions. This study shows how combining multi-dimensional sorption databases with advanced spectroscopic or microscopic techniques (such as EXAFS or AEM) can lead to improved models of interactions at mineral-water interfaces.