Synthetic Metals (v.152, #1-3)

Contents (vii-xiii).

Preface (xvii).

Very high conductivities (>1000 S/cm) were obtained in poly(3,4-ethylenedioxythiophene) films oxidized with Fe(III)tosylate when the acidity during the polymerization process was controlled using a basic inhibitor. The best results were obtained with pyridine as inhibitor. The films could either be polymerized from a solution of 3,4-ethylenedioxythiophene (EDT), Fe(III)tosylate and pyridine or by vapor phase polymerization (VPP) of EDT on a surface coated with Fe(III)tosylate and pyridine.By incorporating non-conducting adhesive (up to 75% vol.) in the vapor phase polymerized PEDT system, films with activation energy of 1/3 the value of pure PEDT, were obtained. The reason for this phenomenon could not be explained by changes in the PEDT structure investigated with grazing incidence X-ray diffraction.
Keywords: Polythiophene and derivatives; Polymer/polymer interfaces; Coatings; X-ray diffraction;

The present knowledge regarding the reasons why solutions of conductive polymers (ICP) can not be made, and the most recent status of insight into feasibility and properties of dispersions is being reviewed. Dispersions are now available with conductivity values exceeding 200 S/cm. New applications in the supercapacitor field and in printed circuit board manufacturing are becoming accessible.
Keywords: Melt processing; Dispersion processing; Gel processing; Miscelles and solution self assembly; Polyaniline and derivatives; Other energy conversion devices;

As an electrophoretic core material for the electronic ink display application, polystyrene-TiO2 composite particles were synthesized. Cationic polystyrene (cPS) cores were initially prepared by surfactant-free emulsion polymerization using a cationic initiator, azodiisobutyramidine dihydrochloride (AIBA), and then the coating reaction was performed in ethanol at room temperature by hydrolyzing titanium tetraisopropoxide (TIP) in the presence of cationic polystyrene spheres at two different TIP concentrations. TiO2 coatings on polystyrene particles were characterized by FT-IR, zeta-potential measurement, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS).
Keywords: Core-shell particle; Emulsion polymerization; Titania; Electronic ink;

Characterization of electronically conducting polypyrrole based composite materials by Csaba Visy; Enikő Pintér; Tamás Flüei; Rita Patakfalvi (13-16).
Structure and conductivities (heat and electric) of polypyrrole composites, synthetized chemically and impregnated by silver solutions, have been studied. The silver content and the physical properties of the composite materials compressed into tablets were determined. The presence of silver in the concentration range below 5% had minimal effect on the electric and heat conductances of polyprrole. XRD measurements showed that the form of the incorporated silver was Ag metal or AgCl depending on the anion present in the polymerization solution. The distribution of the silver particles obtained from TEM measurements proved the presence of nanosized metal component.
Keywords: Composites; Polypyrrole; Ag nanoparticles; Electric and heat conductivity;

The optical properties of various conjugated, water-soluble polymers in general, and MPS-PPV [poly (2-methoxy 5-sulfopropoxy) 1,4-phenylene vinylene] in particular, have been found to be useful in the fabrication of sensors for ionic species. We report our investigations on the influence of various ionic species on the fluorescence properties of DPS-PPV, possessing two sulphonate groups per repeating unit. The emission quantum yield of this polymer exceeds that of the mono-sulphonated derivative by a factor of 10, potentially increasing the sensitivity of such sensors. The fluorescence intensity of aqueous DPS-PPV decreases following the addition of certain cations, and some small spectral shifts occur. The origin of these changes will be discussed based on steady state measurements and excited state dynamics. The emission behavior of DPS-PPV adsorbed onto single silica micro spheres is also reported.
Keywords: Fluorescence; Conjugated polyelectrolyte; Sensor; Confocal microscope; Whispering gallery mode emission; Silica micro sphere;

Measurement of molecular order and orientation in nanoscale organic films by B. Watts; L. Thomsen; P.C. Dastoor (21-24).
Self-assembled monolayers (SAMs) have, in recent years, attracted much interest for surface modification, surface coatings and as interfacial coupling agents. X-ray photoelectron spectroscopy (XPS) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) have been used to non-destructively measure the molecular conformation of organic films with thickness of the order of 1nm. Three different types of molecular conformation were found for γ-aminopropyltriethoxysilane (γ-APS) films formed on ZnO surfaces. The orientation of γ-APS films was observed to vary with adsorption time and surface coverage. Thus the molecular conformation of thin films can be controlled through adjustment of the application parameters.
Keywords: X-ray absorption spectroscopy; Coatings; Organic/inorganic interfaces; Polycrystalline surfaces;

Dynamic mechanical analysis of polyvinylalcohol/silica nanocomposite by Zheng Peng; Ling Xue Kong; Si Dong Li (25-28).
Polyvinylalcohol/Silica (PVA/SiO2) nanocomposites with different SiO2 contents are synthesized by employing a novel self-assembly monolayer (SAM) technique. The influence of the silica on dynamic mechanical properties of the nanocomposites is investigated by conducting dynamic mechanical analysis (DMA) and quasi-thermal mechanical analysis (Q-TMA). It is found that the storage modulus (E′), loss factor (tga), glass transition temperature (T g), and activation energy (E a) of prepared nanocomposites all show a strong dependence on the SiO2 content. The Q-TMA results indicate that under a constant force, the elasticity of nanocomposites decreases with SiO2 content, and the softening temperature moves to a higher temperature when more SiO2 is added.
Keywords: Polyvinylalcohol; Silica; Nanocomposites; Dynamic mechanical analysis (DMA);

Glucose sensing with glucose oxidase immobilized covalently on the films of thiophene copolymers by T. Kuwahara; K. Oshima; M. Shimomura; S. Miyauchi (29-32).
Films of 3-methylthiophene/thiophene-3-acetic acid (3MT/T3A) copolymer were prepared by electrochemical polymerization, and glucose oxidase (GOx) was immobilized covalently by condensation reaction with the carboxyl groups of T3A units on the films. By use of the GOx-immobilized films, glucose sensing was carried out to examine the influence of property of the copolymer as a support material on amperometric sensitivity. Conductivity of the copolymer films was found to increase with decreasing content of T3A units. UV-VIS absorption spectra of the copolymer films showed that wavelength of maximum absorption of the copolymer films shifted to lower energy with decreasing content of T3A units. Amperometric response to incremental addition of glucose solution was examined with the GOx-immobilized copolymer films at +0.4 V (vs. saturated calomel electrode) using p-benzoquinone as a mediator. It was confirmed that large response currents were obtained by use of the copolymer films with a small content of T3A units. In addition, electrically dedoped GOx-immobilized films exhibited smaller response currents than doped one. These results suggest that the conductivity of support materials is a very important factor to dominate the efficiency of glucose-sensing devices.
Keywords: Electrochemical polymerization; Electrochemical method; UV-VIS-NIR spectra; Semiconducting films; Polythiophene and derivatives; Detectors;

Immobilization of alcohol dehydrogenase on poly[1-(2-carboxyethyl)pyrrole] film for fabrication of ethanol-responding electrode by Kenji. Oshima; Taichi. Nakamura; Ryoko. Matsuoka; Takashi. Kuwahara; Masato. Shimomura; Sinnosuke. Miyauchi (33-36).
Alcohol dehydrogenase (ADH) was immobilized on the film of poly[1-(2-carboxyethy] pyrrole], which was prepared by electrochemical polymerization of 1-(2-carboxyethyl)pyrrole. The film exhibited a stable conductivity of 10−4-10−3  S/cm over the temperature range 0-200 °C. A significant amount of ADH (50-100 g/cm2) was immobilized on the polymer film by use of a condensing reagent. Although activity of ADH was decreased by the immobilization, the ADH-immobilized polymer film showed amperometric response to ethanol at +0.85 V vs. SCE in the presence of nicotinamide adenine dinucleotide (a redox mediator). These results demonstrate that the polymer film acts as both an ADH-supporting layer and a conductive medium in the alcohol-driven amperometric device.
Keywords: Electrochemical polymerisation; Detectors;

DNA sensor based on functionalized polypyrrole by Jadranka Travas-Sejdic; Hui Peng; Paul A. Kilmaitin; Mark B. Cannell; G.A. Bowmaker; Ralph P. Cooney; Christian Soeller (37-40).
A novel DNA sensor based on a functionalized polypyrrole was prepared. The sensor film was obtained by electrocopolymerizing poly(pyrrole-co-4-(3-pyrrolyl) butanoic acid) onto which an NH2-ODN probe was grafted. The obtained sensor is a simple, label-free DNA sensor with direct electrical read-out. Hybridisation with complementary ODN was investigated by observing changes in die cyclic voltammogram and the AC impedance spectrum. Significant modifications of both the voltammogram and AC impedance spectrum were observed when the sensor was incubated in the presence of complementary ODN. The AC impedance spectra show an increased charge transfer resistance of the film after hybridisation.
Keywords: Polypyrrole derivative; DNA sensor; Cyclic volammetry; AC impedance;

Conducting polymers with a fractal pattern have been prepared electrochemically and have been connected to each other. A network of conducting polymers similar to a neural network has been fabricated. The dopant used in the channels of the network of conducting polymers can be controlled by the current through the channels utilizing the property of a gel-conducting polymer such as poly (alkylthiophene). Thus the signal weight of the network of conducting polymers depends on the signals that flow through the network. This is called learning effect. In the case of a network of a single conducting polymer, it is hard to control the conductivity in the channels. In this paper, double or triple-layer conducting polymers have been used to achieve stable operation. Furthermore an alternative (sine wave) signal has been used to investigate the learning effect on the double layer conducting film.
Keywords: Electrochemical polymerisation; Polythiophene and derivatives; Polypyrrole; Devices;

Preparation of composite materials of polypyrrole and electroactive polymer gel using for actuating system by T. Yamauchi; S. Tansuriyavong; K. Doi; K. Oshima; M. Shimomura; N. Tsubokawa; S. Miyauchi; J.F.V. Vincent (45-48).
In the present work we report on preparation of composite materials of polypyrrole and electroactive polymer gel using for the actuating system. Composite materials of conducting polymer and polymer gel prepared by chemical oxidative polymerization. The gels were stimulated by the application of various electric fields. The elasticity of composite materials was significantly increased with ratio of polypyrrole in the gel. The bending rate of the polymer gel under the electric fields was increased with the ratio of polypyrrole in the composite material and the magnitude of applied voltages. We also succeeded to demonstrate that many cylinders of this conducting electroactive polymer gel embedded in water solution bent uniformly toward the electrode by the application of various electric fields.
Keywords: Polypyrrole; Energy conversion devices; Mechanical devices;

The multifunctional transducers were fabricated by using the piezoelectric poly (vinylidene fluoride) (PVDF) film as active layer and the highly conducting poly (3,4-ethylenedioxythiophene)/poly (4-styrenesulfonate) [PEDOT/PSS (DMSO for solvent)] as electrode. The PVDF active layers and PEDOT/PSS (DMSO) electrodes were modified by using the ion-assisted-reaction (IAR) method for enhancing adhesion. The piezoelectric effect and pyroelectric effect were observed from the PVDF transducer. The tip displacement of the bimorph type transducer with the PEDOT/PSS (DMSO) electrodes was 7.0 mm at resonance frequency of 27 Hz with applying 40 Vrms. The transducers with PEDOT/PSS (DMSO) electrodes operated in a stable manner at 1 MHz with 200 Vrms, while the transducers with the inorganic ITO and Pt electrodes were mechanically or electrically damaged. The bimorph type generator consisted with the PVDF active layers and PEDOT/PSS (DMSO) electrodes produced a sinusoidal output voltage having a maximum voltage of 0.31 V in response to the tip displacement of 3 mm induced by a vibrator, implying energy harvest system. The maximum output voltage of 4.1 V in the pyroelectric PVDF device was generated with the change of temperature.
Keywords: Poly (vinylidenefluoride); Poly (3,4-ethylenedioxythiophene); Piezoelectric; Pyroelectric; Transducer; Electro-active polymer;

Room-temperature ionic liquids have been demonstrated to be advantageous in the development of conducting polymer electrochemical devices. In this paper, we fabricated electrochemical actuators using polyaniline fibers and ionic liquid electrolytes and investigated factors that influence their actuation performance in the ionic liquid [BMIM][BF4], such as the dopant anion, conductive and mechanical properties of the polyaniline fibers, external load, and operational potentials. Long-term testing was also performed on these ionic liquid/polyaniline fiber actuators and the actuators showed an excellent lifetime of over one million redox cycles.
Keywords: Ionic liquids; Conducting polymers; Polyaniline fibers; Electrochemical actuators;

Potential Application of Solid Electrolyte P11 OH in Ni/MH Batteries by C.Y. Wang; J. Sun; H.K. Liu; S.X. Dou; D. MacFarlace; M. Forsyth (57-60).
N,N-Dimethylpyrrolidoium hydroxide (P11 OH) with polymer poly(tetramethyl ammonium acrylate) (PTMA) was investigated as an electrolyte in Ni/MH cells in this work. The efficiency and the performance of the electrolyte was discussed and elucidated with the performance of the cell. Their electrochemical characteristics had been investigated at different temperatures (25 °C and 50 °C) and different discharge current (15 mA g−1 and 30 mA g−1). The results show that the cell with electrolyte polymer-P11OH is dischargeable at these two temperatures, and a discharge capacity of 142 mAh g−1 at 25 °C has been obtained.
Keywords: Polymer electrolyte; N,N-Dimethylpyrrolidoium hydroxide; Ni/MH cell; Discharge capacity;

Extrusion of monofilaments of thermoplastic elastomers by Pavel Spiridonov; Evangelos Lambrinos; Zheng Peng (61-64).
Thermoplastic elastomers (TPE) are widely used in extrusion of weatherseals, tubes and hoses, protective coating for optical fibres and other extruded products. However they are not a common material for fibres’ extrusion. This work presents the results of a pilot study of extrusion of TPEs fibres. The extrusion process comprised of an extruder, cooling water tank, 3 stretching zones, 2 relaxation zones between them and winding machine. The process parameters were set according to the TPE manufacturer's requirements. The stretching ratio varied from 2:1 to 7:1. The monofilaments were extruded in diameters range from 2 to 5 mm. It was found that the stretching ratio significantly influenced mechanical properties of the fibres. Highly stretched fibres showed 2-3 times greater stress at break than lower stretched fibres. This is due to the orientation of polymer macromolecules in the longitudal direction. The maximum strength can be achieved when all macromolecules are highly oriented. However, there is a limit of stretching, determined by both technical and manufacturing reasons. For instance, the analysis of ruptured fibres demonstrated that the orientation of macromolecules occur mostly near the fibres surface resulting from shear deformation of polymer flow in extruder and the stretching force on the surface of rotating rollers. At the same time, there is a core of unstretched or low-stretched polymer, which prevents fibres from reaching the maximum strength. Usage of thermoplastic elastomers in monofilament and fibres production will provide manufacturers and users with a number of benefits: good processability, flexibility, softness, high chemical resistance etc. Our experience can also be useful for engineers and researchers who are looking to work with synthetic monofilaments with high content of electroconductive and magnetic fillers.
Keywords: Extrusion; Monofilaments; Thermoplastic elastomers; Fibres; stretching;

Syntheses of polyaniline tubes (or rods) inside the pores of anodic alumina membrane by electrochemical and chemical methods are reported. A comparison of polyaniline synthesized in polycarbonate track-etched membrane is made. FT-IR spectra show that the products synthesized inside the pores of templates are emeraldine salts. The morphologies of polyaniline tubes (or rods) synthesized electrochemically in anodic alumina membrane are better than those synthesized in polycarbonate track-etched membrane. ESR spectra reveal that the degree of delocalization of those tubes (or rods) synthesized electrochemically in the anodic alumina membranes is better. The tubes synthesized inside the pore of anodic alumina membrane electrochemically show an enhancement of the electronic conductivity compared to polyaniline bulk materials. The polyaniline tubes synthesized by electrochemical method show better properties (morphology, degree of delocalization and conductivity) compared to those tubes synthesized by chemical method in the same templates.
Keywords: Polyaniline and derivatives; Electrochemical polymerization; Scanning electron microscopy; Scanning transmission electron microscopy; Electron spin resonance;

Architectural float glass as a substrate for organic light-emitting diodes by J. Thompson; V. Maiorano; S. Carallo; E. Perrone; A. Biasco; R. Cingolani; A. Croce; A. Daneu; R.I.R. Blyth (69-72).
While ITO has proven a succesful transparent anode material for laboratory-based investigations of OLEDs, it is perhaps less suited to large-scale production. Here we show that float glass with an evaporated gold coating functions extremely well as the transparent anode for OLEDs. We discuss the production of an ultrathin conductive gold layer in terms of the roughness and surface energy of the float glass. We demonstrate large area OLEDs based on these substrates, in particular a green-emitting device using spin-coated films of Poly[(9,9-dioctylfluorenylene-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)] as the active layer, and a white-emitting device using, as the active layer, spin-coated films of Poly(9-vinylcarbazole) doped with the phosphorescent materials Iridium bis(2-(4,6-difluorophenyl)pyridinato-N,C2′)picolinate and Iridium bis(2-(2′-benzothienyl)pyridinato-N, C3′)(acetylacetonate). Atomic force microscopy was used to investigate the morphology during each stage of OLED fabrication. We show that large area OLEDs can be fabricated on such substrates, with the area limited by the deposition techniques used.
Keywords: Glass surfaces; Metal/insulator interfaces; Organic/inorganic interfaces; Light sources;

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) microfibers by T. Takahashi; M. Ishihara; H. Okuzaki (73-76).
The conducting microfibers of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) were fabricated by a wet-spinning technique. When a PEDOT/PSS aqueous solution was extruded into acetone, used as a coagulant, then dehydrated and solidified to form a fiber. At a flow rate of 1–10 μl min−1 using a spinneret with a diameter of 70–180 μm, continuous and meters-long PEDOT/PSS microfibers having a diameter of 6–11 μm could be wound on a winding spool at a speed of about 50 cm min−1. The electrical conductivity of the as-spun microfibers measured by a four-probe method was 0.4–1.0 S cm−1 regardless of the diameter. The electrical and thermal properties of the resulting microfiber were comparable to those of an evaporatively cast film, suggesting the PEDOT/PSS microfibers could be applied to produce fibrous microelectronics devices or artificial muscular filaments for microactuators.
Keywords: Solution processing; Polythiophene and derivatives;

The influence of carbon nanotubes on mechanical and electrical properties of polyaniline fibers by Vahid Mottaghitalab; Geoffrey M. Spinks; Gordon G. Wallace (77-80).
Two possible candidate materials investigated for conductive fibres are polyaniline (PANi) and carbon nanotubes (CNTs). This current research has produced composite fibres consisting of a PANi host reinforced by carbon nanotubes. Many challenges are inherent in the wet-spinning of carbon nanotube/PANi fibres, particularly the preparation of highly dispersed CNTs in the PANi solution and the control of the nature of the CNTs/PANi interface to ensure both charge transport and the transfer of mechanical load. Size distribution studies demonstrate that the quality of the dispersion can be improved by addition of PANi to CNTs in dimethyl propylene urea (DMPU). The mechanical and four probe electrical conductivity tests show a 150% increase in tensile stress and a 110% increase in young's modulus as well as a 30 times enhancement in electrical conductivity with the addition of 2% CNTs. SEM studies confirm the lower porosity of the composite fiber due to a higher viscosity of the composite spinning solution. In addition, Raman spectroscopy reveals specific π-π interactions between PANi (quinoid ring) and CNTs.
Keywords: Polyaniline; SWNTs; Fiber; Wet spinning; Raman spectroscopy;

Photovoltaic (PV) structures based on inorganic photoabsorber CuInS2 (CIS) in combination with conductive polymers polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) were prepared using electrodeposition and spin-casting techniques. The conductive polymer layer is considered as the p-type buffer layer and window layer on CIS absorber layer in the cell structure. The CIS thin films were fabricated using a non-vacuum CISCuT technique on Cu tape substrate. All obtained polycrystalline CIS films were etched in 10% KCN and annealed in vacuum to improve the crystalline structure. PPy films doped with β-naphthalene sodium sulfonate were electrodeposited under white light illumination onto the pretreated CIS films. Thin PEDOT films doped with polystyrenesulfonate (PSS) were deposited onto the CIS films from an aqueous dispersion of PEDOT/PSS mixed with N-methylpyrrolidone, isopropanol, glycerin and epoxysilane additives using the spin-casting technique. In order to prepare stable PPy and PEDOT films with a good adherence to the surface of inorganic semiconductor CIS, the appropriate parameters of electrodeposition and spin-coating were selected experimentally. Significant photovoltage and photocurrent of the fabricated complete structures have been observed under standard white light illumination.
Keywords: Solar cells; Polypyrrole and derivatives; Polythiophene and derivatives; Heterojunctions; Organic/inorganic interfaces; Interface preparation;

Photoconducting polymer nanocomposites with efficient photogeneration and bipolar transport for optoelectronic applications by B.M. Rumyantsev; V.I. Berendyaev; A.Yu. Tsegel'skaya; T.S. Zhuravleva; I.V. Klimenko (85-88).
Photoconducting polymer nanocomposites with high electrophotographic sensitivity for both positive (Sλ +) and negative (Sλ ) signs of corona charging (up to 400 m2/J in 300–620 nm range) and high charge carrier photogeneration quantum yield (β up to 0.6) are developed on the base of p-conducting (Sλ +  ≫ Sλ ) polymer matrices (polyimides (PI), carbazolylcontaining (CzCP) polymers) and n-conducting low molecular mass additive (perylenediimide derivative (PDID)) in aggregated form. For p-composites (PI doped with PDID at content C A up to 50% wt.) the efficient hole photogeneration in PDID absorption band is related to the observed electron transfer from PI donor chain fragments with low ionization potential (ID  = 6.8 eV) to the excited PDID aggregates as acceptors (with affinity EA  = 1.8–2.0 eV). Low Sλ value for p-composites is likely due to potential barrier formation between PDID particles (aggregates and clusters) involved in electron transport network. For n-composites (Sλ  ≫ Sλ +) (CzCP doped also with PDID) high Sλ and β values are explained by the efficient electron photogeneration via excited charge transfer complex (exciplex) between excited PDID molecule as acceptor and CzCP carbazolyl pendant as donor (with ID  = 7.4 eV) as well as electron transport network formation involving PDID particles. As it is only ionization potentials of polymer donor fragments that differ essentially for p- and n-composite, the conclusion is made that charge transfer donor-acceptor interaction in the ground state may be responsible for potential barrier formation between acceptor particles embedded in donor matrix. It is found that films of bipolar sensitive composites (Sλ +  ≈ Sλ ) (obtained by mixing p- and n-composites in solution) which have microsegregated structure are characterized by the highest Sλ +, Sλ and β values. The photovoltaic effect is investigated for sandwich cells with (Al, ITO) electrodes. The best parameters are found for bipolar composite films (0.5–1.0 μm thick).
Keywords: Manipulation of morphology; Photoconductivity; Solar cells; Perylenediimide derivative;

Electrochemical characteristics of multi-functional polymer electrolyte based on dual-layer membrane for lithium metal polymer battery by Young-Gi Lee; Kwang Man Kim; Yong Joon Park; Young-Sik Hong; Xianglan Wu; Kwang Sun Ryu (89-92).
A novel dual-layer type polymer electrolyte was prepared by impregnating the interconnected pores with an ethylene carbonate(EC)/dimethyl carbonate(DMC)/lithium hexafluorophosphate(LiPF6) solution. An incompatible layer is based on a micro-porous polyethylene(PE) and a compatible layer, based on a poly(vinylidenefluoride-co-hexafluoropropylene)(P(VdF-co-HFP)), is submicro-porous and compatible with an electrolyte solution. To enhance the ionic conductivity in the compatible layer, inorganic type Li+ single ion conductor particle based on hydrophilic silica has been synthesized. The maximum apparent ionic conductivity of the dual-layer polymer electrolyte is 7.7 × 10−3  S/cm at the ambient temperature. High rate capability of the Li/the dual-layer polymer electrolytes/Li[Ni0.15Li0.23Mn0.62]O2 cell was significantly improved as the incompatible layer thickness decreases.
Keywords: Dual-layer; Polymer electrolyte; Compatible layer; Inorganic single ion conductor; Ionic conductivity; High rate capability;

Improvement of characteristics on polymer photovoltaic cells composed of conducting polymer - fullerene systems by T. Umeda; Y. Hashimoto; H. Mizukami; T. Shirakawa; A. Fujii; K. Yoshino (93-96).
Photovoltaic properties of the cells consisting of a heterojunction of conducting polymer-fullerene systems and a semiconductor oxide thin film, which is transparent in the visible-wavelength range, have been investigated. Introducing the transparent semiconductor oxide, such as zinc oxide (ZnO), into the photovoltaic cells with conducting polymer - fullerene systems, high performance has been obtained. Especially in the layered photovoltaic cells with the structure of ITO/ZnO/C60/PAT6/Au, the high monochromatic energy conversion efficiency and the external quantum efficiency have been realized. The photovoltaic properties have been interpreted by the effective absorption of incident photons around the interface of conducting polymer and fullerene, the interpenetrated fullerene/conducting polymer interface involving the efficient photo-induced charge transfer, and the short distance between the electron-generation region and electrode, resulting in the enhancement of the electron collection to the electrode.
Keywords: Polythiophene and derivatives; Fullerenes and derivatives; Solar cells;

Chromophoric interactions in [60]fullerene-porphyrin dyads studied by spectral methods by A. Graja; D. Wrobel; A. Boguta; I. Olejniczak; A. Bogucki (97-100).
Electronic absorption, fluorescence, photothermal and vibrational spectra of several fullerene-porphyrin dyads have been investigated. Thermal deactivation of porphyrin moieties are markedly influenced by fullerene. Participation of the excited singlet states in thermal relaxation in fullerene-porphyrin dyads is evident although the contribution of the triplet states cannot be excluded. Our experiments show the existence of a fullerene-porphyrin excimer created from the porphyrin second excited state. The observed differences in spectroscopic properties are discussed in terms of strong interaction between fullerene and porphyrins in dyads.
Keywords: Fullerene and derivatives; Porphyrins; Infrared and optical spectroscopy; Photoelectron spectroscopy;

Probing the local optical properties of layers prepared from polymer nanoparticles by Thomas Kietzke; Burkhard Stiller; Katharina Landfester; Rivelino Montenegro; Dieter Neher (101-104).
It is well known that the performance of solar cells based on a blend of hole-accepting and electron-accepting conjugated polymers as the active material depend crucially on the length scale of the resulting phase separated morphology. However, a direct control of this morphology is difficult if the layer is prepared from an organic solvent. To circumvent this difficulty, recently a universal method to fabricate defined nano-structured blend layer using nanoparticles dispersed in water was demonstrated. These nanoparticles were prepared with the miniemulsion method, which allows for the preparation of semiconducting polymer nanospheres (SPNs) with diameters in the range of 30 to 300 nanometres. Since the process starts from the active material dissolved in a common solvent, it can be applied to the fabrication of nanoparticles of blends of polymers with oligomers or even with inorganic materials.We present here for the first time scanning near field optical microscopy (SNOM) investigations on these novel nanostructured polymer layers. We show that by spin-coating a mixture of two different dispersions a nanoparticle monolayer with a statistically distribution of the nanoparticles can be obtained. Mixing conjugated polymer nanoparticles with some inert particles like polystyrene beads may allow for the preparation of nano-sized light emitters.
Keywords: Control of interface structure and morphology; Solar Cells; Light Sources;

Effect of electron-transport polymer addition to polymer/fullerene blend solar cells by Y. Kim; S. Cook; S.A. Choulis; J. Nelson; J.R. Durrant; D.D.C. Bradley (105-108).
We report on a study of the effect of device annealing on the performance of bulk heterojunction organic solar cells made from a ternary blend of poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Photovoltaic device characteristics before and after annealing were measured under air mass 1.5 simulated solar illumination (100 mW/cm2). Annealing times up to ∼15 min resulted in a sharp increase in short circuit current density and power conversion efficiency, with more gradual improvements upon further annealing. This performance improvement is attributed partly to enhanced optical absorption and partly to improved charge collection, which may result from enhanced charge carrier mobilities.
Keywords: Organic solar cells; Regioregular P3HT; PCBM; F8BT; Device annealing; Power conversion efficiency;

When creating thin films of polymer blends, interesting morphologies are formed because of phase separation. In particular for conjugated polymers, which are used as active material in optoelectronic devices, it is very important to understand the parameters that influence the phase separation process and to achieve control over the morphology. The overall goal of this blend morphology study is to contribute to the design of device structures with desired performance.Here we present results of morphology studies on thin films of polyfluorene-based blends with the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The polymers used are poly(9,9-dioctylfluorene) (F8) and four different copolymers of F8. The thin films are spin coated from chloroform solutions onto silicon substrates and their surface morphology is imaged by tapping mode atomic force microscopy (AFM). We observe that the size and the shape of the domains in the film depend on the structure of the polymer. The nature of the monomer that, together with F8, is building the repeating unit in the copolymers has a strong effect on the phase separation in the polymer: PCBM blend. Since phase separation is influenced by interactions between components of the blend and the solvent, these results indicate that the degree of chemical interaction between polymer, solvent and PCBM, is different for the different blends. For the systems that form larger domains there is a clear correlation between the domain size (area) and the polymer/PCBM blend ratio. We also observe that the spin speed affects the thickness of the films and that the domain size increases with increasing thickness, primarily due to longer drying times.
Keywords: Atomic force microscopy; Spin coating; Morphology; Conjugated polymers; Blend;

Ultrafast field assisted exciton dissociation in oligofluorenes by J. Cabanillas-Gonzalez; M.R. Antognazza; T. Virgili; G. Lanzani; M. Sonntag; P. Strohriegl (113-116).
We report field assisted pump-probe measurements on a 9,9,9′,9′,9″,9″-Hexa-sec-butyl-[2,2′,7′,2″]terfluorene trimer. An electric field as high as 2.2 MV/cm is applied in reverse bias to produce dissociation of the photogenerated singlets without charge injection. The electric field differential transmission dynamics at early times suggest Stark shift of the lower singlet excited state S 1. The magnitude of the shift provides us with a change of polarizability of 0.43 × 10−19  eV m2/V2 between the lower excited and ground states. Differing from poly(9,9-dioctyl fluorene), (PFO), singlet dissociation is not instantaneous but occurs during timescales not inferior to 80 ps. Beyond these timescales we observe a decrease in the signal associated to polarons followed by a repopulation of singlets.
Keywords: Time-resolved fast spectroscopy; Semiconducting films;

The nanoscale phase separation in polymer/fullerene bulk heterojunction plastic solar cells requires the use of high resolution techniques for imaging. In this study we used a high-resolution transmission electron microscope (HR-TEM) together with selected area electron diffraction (SAED) to visualize the polymer and fullerene distributions and their amorphous or crystalline organization in the film. While pristine polymer films exhibited no crystalline order, the fullerene organized in nanocrystals. Upon annealing of the blend film, the accompanying phase separation reaches the micron level and fullerene phases aggregate to larger single crystals, as could be seen by SAED.
Keywords: Scanning transmission electron microscopy; Electron-solid diffraction; Poly(phenylene vinylene) derivative; Fullerenes; Solar cells;

Highly efficient photovoltaic cells composed of interpenetrating conducting polymer/C60 heterojunction by A. Fujii; H. Mizukami; Y. Hashimoto; T. Umeda; Y. Nishihara; M. Ozaki; K. Yoshino (121-124).
Photovoltaic properties of a photovoltaic cell with a structure of indium-tin-oxide (ITO)/C60/conducting polymer (CP)/Au have been investigated. The C60/CP heterojunction in the photovoltaic cell was fabricated by spin-coating the solution of CP onto the C60 thin film formed on ITO. Fabricated by this process, the photovoltaic cell has demonstrated the high efficiency for solar cells based on CPs. From the optical properties of C60/CP heterojunction and the direct surface observation by using scanning electron microscope and atmic force microscope, it has been clarified that the interpenetrating interface of C60 and CP contributes to the high photovoltaic performance.
Keywords: Solar cells; Photoconductivity; Heterojunction; Polythiophene and derivatives; Poly(phenylene vinylene) and derivatives; Fullerenes and derivatives;

Oligothiophene-multifullerene linkage molecules as high performance photovoltaic materials by N. Negishi; K. Takimiya; T. Otsubo; Y. Harima; Y. Aso (125-128).
Novel long oligothiophenes incorporated with four fullerenes (2C 60 16T2C 60 and 2C 60 24T2C 60 ) have been synthesized with the aim of developing good single-component photovoltaic materials. The tetracosithiophene derivative 2C 60 24T2C 60 , despite its giant structure, is rather more tractable regarding solubility than the hexadecithiophene derivative 2C 60 16T2C 60 . The electronic absorption and emission spectra of 2C 60 24T2C 60 indicated no electronic interaction in the ground state but efficient intramolecular electron transfer in the excited state. The sandwich device of the Al/2C 60 24T2C 60 /Au structure showed a marked photocurrent upon illumination with monochromatic light from the Al side. The incident-photon to converted-electron ratio (IPCE) is 14%.
Keywords: Polythiophene and derivative; Fullerenes and derivatives; Solar cells; Amorphous thin films; Photoconductivity;

Towards High Power Polypyrrole/Carbon Capacitors by Ali Izadi-Najafabadi; Dawn T.H. Tan; John D. Madden (129-132).
Conducting polymers demonstrate effective capacitances of more than 100 Farads per gram, 5 orders of magnitude higher than traditional capacitors. However polymer discharge times tend to be on the order of seconds, as opposed to the milli or microseconds of conventional capacitors, so that the overall power density is still at least an order of magnitude lower. The polypyrrole devices are essentially electrolytic capacitors in which charging times appear to be limited by rates of ionic mass transport and RC charging times. Electrochemical impedance measurements suggest diffusion time constants of 33 ms in 158 nm thick polypyrrole films with volumetric capacitances of 107  F/m3. The impedance of a highly porous polypyrrole/carbon composite was measured to investigate the achievement of similarly fast response times in much thicker materials. It is shown that increasing the polypyrrole content of the film increases capacitance up to 60 F/g, but also increases the charging time constant. Analysis of the rate limiting factors suggests a method of optimizing capacitor geometry in order to maximize rates, including the prediction of device geometries that will lead to power delivery matching those of traditional capacitors.
Keywords: Polypyrrole; Supercapacitor; Carbon Fiber; Power Density; Impedance; Conducting Polymer;

Understanding ion transport processes in electrically conducting polymers is very important in the light of possible application of these materials in chemical or biosensors. In this work we have studied the ion transport in the electrochemically synthesized inherently conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) induced by the redox switching of the polymer. Mass changes during the synthesis and redox switching of the film have been monitored in-situ by Electrochemical Quartz Crystal Microbalance (EQCM). By doping the conducting polymer film with electroactive materials such as ferrocyanide ions (FCN) the release of the different oxidation state species during the voltage cycling of the polymeric film could be monitored on-line by Scanning Electrochemical Microscopy (SECM). Direct evidence of the exchange capability of Fe(CN)6]4−/3− anions entrapped in PEDOT/FCN film with Cl anion from the solution and doping levels were found by computing the experimental data provided by SECM and EQCM techniques. In addition, SECM measurements showed that during reduction of the PEDOT/FCN films only the release of [Fe(CN)6]4− ion occurs.
Keywords: Polythiophene and derivatives; Electrochemical polymerisation; Electrochemical doping; Scanning electrochemical microscopy; EQCM;

Nitrogen-functionalized polythiophenes: Potential routes to new low band gap materials by Katsu. Ogawa; Jenny.A. Stafford; Scoot.D. Rothstein; Dennis.E. Tallman; Seth.C. Rasmussen (137-140).
Due to the stability and ease of synthetic modification, polythiophenes containing a wide variety of functionalized side chains have been investigated. The majority of functionalized polythiophenes, however, contain functional groups isolated from the polymer backbone by an alkyl spacer. As a result, the side chain acts primarily to modify physical properties and any electronic effect is due to steric-induced conformational changes. The exception to this is the inclusion of alkoxy or alkylmercapto groups, where the heteroatom is directly attach-ed to the polymer backbone. An extension of polyalkoxythiophenes is the investigation of additional heteroatom-functionalized polythio-phenes. Our work has generated an interest in nitrogen-derivatized polythiophenes, thus initiating new synthetic routes to N-function-alized poly(3-aminothiophene)s and poly(dithieno[3,2-b:2′,3′-d]pyrrole)s. Here we report synthetic routes for the necessary monomeric precursors, chemical and electrochemical polymerization studies, as well as initial characterization of the polymeric materials.
Keywords: Polythiophene and derivatives; Steric effects; UV-Vis spectroscopy; Photoluminescence;

Control of the electronic phase transition of the MMX-chain complex Pt2(n-pentylCS2)4I with the uniaxial compression by H. Tanaka; Y. Hasegawa; H. Ito; S. Kuroda; T. Yamashita; M. Mitsumi; K. Toriumi (141-144).
We report the uniaxial compression effect of the electrical resistivity on the quasi-one-dimensional halogen-bridged binuclear metal complex (MMX-chain) Pt2(n-pentylCS2)4I which exhibits successive electronic transitions. At ambient pressure, this complex exhibits first-order phase transition around 210 K between the low-temperature insulating alternate-charge-polarization (ACP; Pt2+-Pt3+-Pt3+-Pt2+) state and the room-temperature conductive averaged-valence (AV; Pt2.5+-Pt2.5+) state, confirmed from the drastic changes of the resistivity and ESR spectra. In the ACP state the thermal activation of the soliton (Pt3+) has been demonstrated from the spin susceptibility enhancement and the motional narrowing of the ESR spectra. Applying the uniaxial piston pressure up to 0.7 GPa, the transition temperature shifts to higher temperatures in both compression directions, parallel and perpendicular to the chain, indicating the stabilization of the ACP state. In the case of the parallel compression, this result is well explained by the increase of the transfer integral (t MX) between platinum and iodine atoms, whereas in the case of the perpendicular one, it should be necessary to consider the modification of the ligand molecules which strongly couples to the phase transition. By comparing with the reported results for Pt2(n-butylCS2)4I with shorter alkyl side chains, the phase stabilization mechanism is discussed.
Keywords: Metal-insulator phase transition; Structural phase transition; Conductivity;

Self-Forming Microtubes of Polypyrrole: Reaction Conditions and Physical Properties by Naoki Toshima; Kazuki Eguchi; Makoto Inokuchi; Masahiro Ueda; Hu Yan (145-148).
Polypyrrole microtubes have myriad promising technological applications. The known synthetic routes for preparing the microtubes involve a shape-guiding template which needs to be removed at final stage of the synthesis. We have recently discovered a new synthetic method, by which polypyrrole microtubes spontaneously form during the electropolymerization of pyrrole without any shape-guiding template. Here the reaction conditions for self-formation of polypyrrole microtubes were examined and the favorable conditions to repeatedly synthesize the microtubes were determined. The reaction processes were also traced by a microscope with a CCD camera. The microtubes were found to grow near the free end of microtubes. In addition a small bubble of hydrogen gas, which was attached at the free end of microtube, was suggested to have an important role in the growth of microtubes. The temperature dependence of electrical resistance suggests that the conduction mechanism of microtubes is similar to that of the conventional polypyrrole films.
Keywords: Polypyrrole and derivatives; Electrochemical polymerisation; Self-organization in macromolecules; Conductivity; Infrared and Raman spectroscopy; Graphite and related compounds;

Vibrational spectroscopic study of a push-pull substituted fluorinated poly(p-phenylenevinylene) copolymer by T. Yohannes; H. Neugebauer; G.M. Farinola; C. Winder; F. Babudri; A. Cardone; F. Naso; N.S. Sariciftci (149-152).
In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroelectrochemistry during oxidation (p-doping) and reduction (n-doping) as well as photoinduced infrared spectroscopy of a random copolymer of 2,3,5,6-tetrafluoro-1,4-phenylenevinylene and 2,5-dioctyloxy-1,4-phenylenevinylene [co(TFPV-DOPV)] is presented. The infrared active vibration (IRAV) patterns obtained during electrochemical oxidation (p-doping) and reduction (n-doping) are different. The copolymer shows photoinduced IRAV bands that are similar to those obtained during electrochemical reduction (n-doping) in contrast to most of the other conjugated polymers which show similarities with oxidation (p-doping) IRAV bands. To our knowledge this is the only p- and n-dopable polymer with different IRAV patterns of charge carriers of both signs, and a similarity between n-doping and photodoping IRAV bands.
Keywords: Electrochemical doping; Infrared spectroscopy; In situ electrochemical spectroscopy; Photoinduced absorption spectroscopy; Poly(phenylene vinylene) and derivatives;

Redox heterogeneity in polyaniline films: from molecular to macroscopic scale by V.F. Ivanov; O.L. Gribkova; S.V. Novikov; A.A. Nekrasov; A.A. Isakova; A.V. Vannikov; G.B. Meshkov; I.V. Yaminsky (153-156).
Heterogeneity relates to the principal features of polyaniline (PAn). For the most part the heterogeneity in PAn belongs to redox type. Our detailed investigation of the vacuum deposited PAn and the study of the luminescence of PAn base (by Shimano and MacDiarmid) reveal the existence of a block structure of PAn molecules formed of quinoid and amine units. There are also direct evidences of existence of the redox heterogeneity in PAn in nano scale (Kelvin scanning microscopy). We have observed by optical and Kelvin the microscopy the formation of various types of the redox heterogeneous structures in microscopic scale in the course of the chemical or electrochemical treatment of the vacuum thermally deposited or electrochemically produced PAn films. Macroscopic scale redox heterogeneity was observed also under chemical oxidation of the vacuum deposited PAn and in the course of PAn matrix synthesis. Hence, multilevel redox heterogeneity from molecular to macroscopic scale takes place in PAn. The fundamental reason for the redox heterogeneity formation is the autocatalytic, non-equilibrium character of the oxidation processes in PAn coupled with non-linear mass transfer processes. Evidently this type of heterogeneity influences markedly the whole range of PAn properties including conductivity.
Keywords: Polyaniline and derivatives; Self-organization in macromolecules; Non-equilibrium thermodynamics;

We present the results of simulation studies of the dependence on temperature, charge carrier density, and electric field of the mobility μ in disordered conjugated polymers. The disorder is modeled by a Gaussian density of states (DOS) with width σ. We base our analysis on an exact numerical solution of the Pauli Master equation. The recently experimentally determined carrier density dependence, ranging from densities typically found in light-emitting diodes (LEDs) up to those found in field-effect transistors (FETs), is fully reproduced. At low temperatures T, we find deviations from the generally accepted μ∼exp[−const.(σ/kT)2] behavior. Our calculations show that the electric field dependence does not play a prominent role at the driving voltages of polymer devices.
Keywords: Computer simulations; Conductivity; Conjugated polymers;

Synthesis and properties of polyfluorenes containing 1,8-naphthalimide moieties for white electroluminescence by Guoli Tu; Quanguo Zhou; Yangxiang Cheng; Yanhou Geng; Lixiang Wang; Dongge Ma; Xiabin Jing; Fosong Wang (161-164).
Two polyfluorenes containing 1,8-Naphthalimide units were synthesized by Yamamoto polycondensation reaction. The 1,8-naphthalimide moieties act as both electron and hole trap in the resulting polymers, leading to the EL spectra different from the PL spectra in film. White electroluminescence with a maximum brightness of 11100 cd/m2, an external quantum efficiency of 2.0% and CIE coordinates of (0.26, 0.36) has been realized through partial energy transfer from polyfluorene to 1,8-naphthalimide moieties.
Keywords: White light-emitting diodes; Polyfluorene; 1,8-Naphthalimide;

Multifrequency EPR study of metal-like domains in polyaniline by V.I. Krinichnyi; S.V. Tokarev; H.-K. Roth; M. Schrodner; B. Wessling (165-168).
The magnetic, relaxation and electronic dynamic parameters of paramagnetic centers, polarons in crystalline domains of polyaniline doped by p-toluenesulfonic acid (PANI-TSA) being in the metallic state (“organic metal”) were studied at 3-cm (9.7 GHz) and 2-mm (140 GHz) EPR wavebands in a wide temperature range. The polarons in PANI-TSA interact strongly at magnetic fields used and demonstrate the Lorentzian single lines with the Dysonian contribution. Room temperature intrinsic conductivity of metal-like domains in air-containing PANI-TSA determined from the Dysonian spectra was ca. 4000 S/cm. This value decreases sufficiently at the sample evacuation. It was shown that polarons interact strongly and weakly below and above the critical temperature T c, respectively, due to a phase transition that leads to an extremal temperature dependence of the polymer linewidth. As the registration frequency increases from 9.7 GHz up to 140 GHz, the T c value is shifted from 160 K down to 130 K. Intrinsic conductivity of PANI does not correlate with its linewidth that indicates polaron localization inside crystalline domains. Charge is transferred according to the Mott variable range hopping mechanism.
Keywords: Electron paramagnetic resonance; Polyaniline and derivatives; Transport measurements;

Field-effect mobility anisotropy in PDA-PTS single crystals by J.Y. Lee; A.N. Aleshin; D.W. Kim; H.J. Lee; Y.S. Kim; G. Wegner; V. Enkelmann; S. Roth; Y.W. Park (169-172).
We studied the current-voltage (I–V) characteristics and the field effect mobility (μFET) of polydiacetylene single crystals in the temperature range 4 K–300 K. Non-Ohmic I–V characteristics reveal the maximum of the Drain-Source current (IDS) at 170 K while the μFET maximum appears at 130 K. The IDS along the backbone chains increases with the positive gate voltage (VG) whereas the IDS between the backbone chains increases with the negative VG. The anisotropy of the conductivity and the μFET are observed. The current parallel to the PDA backbone is ∼ 10–1000 times higher than that perpendicular, while the electron mobility parallel to the PDA backbone is about 100 times higher than that perpendicular.
Keywords: Polydiacetylene and derivatives; Transport measurements; Conductivity;

Conducting polyaniline (PANI)/titanium dioxide (TiO2) hybrid particles were synthesized via an oxidation polymerization in the presence of TiO2, and their electrorheological (ER) characteristics were examined, since the formation of an organic/inorganic hybrid exhibits various advantages from the combination of their unique properties as a part of our efforts to find highly potential ER-active particles using conducting polymers. The TiO2 nanoparticles possess a relatively high dielectric constant which is important for polarization in the ER response, in which the ER fluids are a class of colloidal suspensions which show a transition from a liquid-like to a solid-like state under an applied electric field. Synthesized PANI/TiO2 composites in this study were characterized by an FT-IR, thermogravimetry analysis, and scanning electron microscopy. We then prepared the PANI/TiO2 composites-based ER suspension with insulating oil and investigated its ER behavior as a function of shear rate under an applied electric field. The fast relaxation time of PANI/TiO2 hybrid was expected to enhance electrostatic force over shear force under a shear flow, showing the improved ER performance. Furthermore, it was also found that the properties of TiO2 affect the dielectric of PANI/TiO2 composites to give better ER properties.
Keywords: Electrorheology; Polyaniline; Titanium dioxide; Hybrid; Suspension;

Water Dispersible Low Band Gap Conductive Polymer Based on Thieno[3,4-b]thiophene by Byoungchul Lee; Venkataramanan Seshadri; Gregory A. Sotzing (177-180).
Herein we describe the synthesis and properties of poly(thieno[3,4-b]thiophene) (PT34bT), a new low band gap polymer that shows high optical transparency in oxidized conductive state. Thieno[3,4,b]thiophene was polymerized in water using chemical oxidants in the presence of poly(styrenesulfonic acid). Since poly(styrenesulfonic acid) is water soluble and there are strong interactions between poly(styrenesulfonate) and the oxidized PT34bT, the resulting polymer system is rendered a colloidal dispersion. PT34bT-PSS has a band gap of ca. 1.08 eV (1150 nm) depending on oxidants used as determined by the onset of the π to π* from the Vis-NIR spectrum with a peak at an energy of 1.63 eV (760 nm). Diluted PT34bT-PSS dispersions are transmissive green in the oxidized form and become transmissive blue in reduced state. Electrical conductivities for these polymers are dependent on chemical oxidants used and are varied from 0.01 to 10−4  S/cm.
Keywords: Poly(thieno[3,4-b]thiophene); Intrinsically conductive polymer; Optically transparent polymer;

The electronic transport properties of a number of materials with nanoscale or microscale structure show some remarkable similarities despite the differing conduction mechanisms expected in different materials, for example similar nonlinearities in their current-voltage characteristics. We propose a generic expression for the nonlinear current-voltage characteristics based on our numerical calculations for metallic conduction interrupted by small barriers. We discuss the general features of the experimental data and show that our expression gives a very good description of the observed nonlinearities in carbon nanotube networks, vanadium pentoxide nanofibrcs and polyacctylene nanofibres, as well as half-metallic granular Sr2FeMoO6 that is of interest for spintronics.
Keywords: Conducting polymers; Carbon nanotubes; Conductivity; Spintronics;

Electrochemistry and spectroelectrochemistry of regioregular oligooctylthiophenes by Jerzy Zak; Mieczyslaw Lapkowski; Stephane Guillerez; Gerard Bidan (185-188).
In this work we report on the electrochemical and spectroelectrochemical characterization of the series of α-monochloro substituted regioregular 3-alkylthiophene consisting of 4–8 units of (3-octylthiophene) in solution. The shortest in the series tetramer molecules undergo a fast dimerization process, whereas longer oligomers are not subject to consecutive reactions when oxidized to form the radical cation. Each oxidation stage corresponds to one-electron process; single radical cation and dication are initially produced, which in turn are doubled within each oligomer molecule. Studies of these compounds in solution species were carried out in the thin layer cell on optically transparent electrodes. Clear tendencies are observed with increasing number of thiophene units for the peak potential of the redox reactions and positions of maximum absorbance. Formation of additional electronic bands within the band gap, shifted to the lower energies, has been also observed.
Keywords: Regioregular oligomers; Oligothiophenes; Electrochemistry; Spectroelectrochemistry;

ESR spectroelectrochemistry of functionalised long side chain derivatives of poly(3,4-ethylenedioxythiophene) by T. Moskwa; W. Domagala; A. Czardybon; B. Pilawa; M. Lapkowski (189-192).
Electrochemically synthesised polymers of ω-bromine 2-oxaalkyl derivatives of 3,4-ethylenedioxythiophene (EDOT) have been studied using in-situ ESR spectroelectrochemistry. While these compounds are versatile intermediates en route to EDOT derivatives bearing special functional groups, their polymers themselves show interesting properties. Results indicate differences in potential dependencies of concentration of spins, ΔBPP width and g-factor between the two polymers, indicating an influence of the alkyl side chain length on specific properties of paramagnetic charge carriers appearing in these polymers in the course of their redox processes. Compared to their parent polymer-PEDOT, some similarities in the behaviour of charge carries may be observed notably the hysteresis of potential dependence of concentration of spins and ΔBPP width, indicating that the doping-dedoping mechanism of these polymers may resemble the one in PEDOT.
Keywords: Electrochemical doping; PEDOT derivatives. Electron spin resonance; Polythiophenes; Polarons; Bipolaons;

Several spin dynamics techniques (ESR linewidth variation as a function of applied oxygen pressure and temperature, NMR relaxation time frequency dependence) have been used to comparatively investigate the electronic transport properties of HCl doped poly(aniline) and HCl doped tetra-aniline at a nanoscopic scale. DC-conductivity measurements and X-ray diffraction have also been carried out. From the data, the following conclusions can be derived: (i) at room temperature, the effective polaron hopping frequency at the nanoscopic scale, is one order of magnitude higher in the polymer than in the tetramer, (ii) new data support the Elliott mechanism as the origin of the ESR line broadening at high temperature and therefore bring a clear evidence in favor of the existence of a metallic state in the polymer. No evidence for such a metallic state exist in the tetramer. (iii) the polaron diffusion frequency appears to be highly anisotropic in both systems.
Keywords: Polyaniline and derivatives; X-ray diffraction; Nuclear magnetic resonance; Electron spin resonance; Transport measurements; Conductivity;

A series of poly(thiophene)s, poly(3-(2-benzothiazolyl)thiophene) (PBTT) and poly(3-(2-benzothiazolyl)oxyethyl thiophene) (PBTOET), containing a benzothiazole moiety in the side chain have been synthesized by a cross-coupling reaction using Ni catalyst. PBTT and PBTOET were characterized by FT-IR and 1H-NMR spectra. Both polymers showed fluorescence peaks in the visible region. The HOMO and LUMO energies were estimated by cyclic voltammetry. PBTT was more suitable as a hole transporting material than PBTOET. The turn-on voltages of PBTT and PBTOET single layer EL devices were 5.0 V and 6.5 V, respectively.
Keywords: Polythiophene and derivatives; Coupling reaction; Electroluminescence;

An alternating copolymer composed of phenothiazine and thiophene heterocycles, poly(PTZV-alt-TV), was synthesized through the Witting polycondensation reaction. The synthesized polymers were characterized using UV-visible, photoluminescence (PL) and electroluminescence (EL) spectroscopy. The poly(PTZV-alt-TV) showed a maximum UV-visible absorption and peak PL emission at 442 nm and 584 nm, respectively. The optical band gap of the polymer was obtained to be 2.74 eV from the absorption onset. The ionization potential of poly(PTZV-alt-TV) was determined to be 5.04 eV. Electroluminescent device was fabricated in an ITO/PEDOT/ poly(PTZV-alt-TV)/Ca/Al configuration. Light emission from this device was observable at voltages greater than 4.0 V. The EL device showed a maximum brightness of 140 cd/m2 and a luminous efficiency of 1.3 × 10−2  cd/A.
Keywords: Light-emitting diode; Phenothiazine; Thiophene; Copolymer;

White LEDs using conjugated polymer blends by Do-Hoon Hwang; Moo-Jin Park; Changhee Lee (205-208).
We fabricated white light-emitting devices using blends of two conjugated polymers. Poly[9,9-bis(4′-n-octyloxyphenyl)fluorene-2,7-diyl-co-10-(2′-ethylhexyl)phenomiazine-3,7-diyl] [poly(BOPF-co-PTZ)] was employed as a blue host polymer and stereo-regular poly(3-hexylthiophene) (P3HT) was employed as a red doping material. The PL emission spectra of the blend systems depended on its blend ratio. Each emission bands of poly(BOPF-co-PTZ) and P3HT were observed at 480 nm and 570 nm in the PL spectra of blend systems. As the P3HT content in the blend system increase the intensity of emission at 570 nm increases. The EL devices were fabricated with ITO/PEDOT/blend/LiF/Al configuration and white light-emission was obtained for a certain blend ratio.
Keywords: White light-emitting diode; Organic semiconductor; Electroluminescence;

Photopumped multimode blue laser emission from cylindrical microcavities of conducting polymers with heteroatoms in main chains by Y. Yoshida; T. Nishimura; Y. Nishihara; A. Fujii; M. Ozaki; H.K. Kim; N.S. Baek; S.K. Choi; K. Yoshino (209-212).
We have studied optical and electric properties of conducting polymers with heteroatoms such as Si and Sn in main chains. Heteroatoms, which are the same group with carbon atom, in each monomer unit of polymer main chains, are expected to possess unique characteristics and functionalities. The strong photoluminescence (PL) with high quantum efficiency and electroluminescence have been clarified, and these polymers have been exhibited the excellent optical properties and spectral narrowing. We also demonstrated pulsed, photopumped multimode laser emission from cylindrical microcavities formed by the polymer thin films deposited around optical fibers and the polymer microdisks. The bright blue laser emission could be observed.
Keywords: Conducting polymers; Photoluminescence; Stimulated luminescence; Electroluminescence; Lasers;

The light emitting devices using ruthenium(II)(4,7-diphenyl-1,10-phenanthroline)3 ([Ru(dphphen)3]2+) complex as dopant and emitter in poly(N-vinylcarbazole) (PVK)-based blend matrix have been studied in different structures. In comparison with the indium-tin-oxide glass (ITO)/PVK:2-(4-biphenyl)-5-(4-ter-butylphenyl)-1,3,4-oxadiazole (PBD):[Ru(dphphen)3]2+/tris-(8-hydroxyquinoline) aluminum (Alq3)Al,ITO/PVK:PBD:[Ru(dphphen)3]2+/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/Alq3/LiF/Al, and ITO/PVK:N,N′-diphenyl-N,N′ -bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD):PBD:[Ru(dphphen)3]2+/BCP/Alq3/LiF/Al devices, the ITO/PVK:PBD:[Ru(dphphen)3]2+/Alq3/BCP/Alq3/LiF/Al device shows efficient improvement in device brightness and efficiency. Furthermore, the chromacity-tunable electroluminescence is obtained by the hybrid emission from [Ru(dphphen)3]2+ and Alq3 species in such a device structure.
Keywords: Electroluminescence; Conducting polymer; Heterojunctions;

Two new poly(arylene ether sulfone)s containing second-order nonlinear optical chromophores by Zhaoqiang Lu; Jun Li; Jianli Hua; Xue Li; Jingui Qin; Anjun Qin; Cheng Ye (217-220).
Two new poly(arylene ether sulfone)s, P1 and P2, with pendant nonlinear optical (NLO) chromophores (60 and 84%, respectively) have been easily prepared by post-esterification reaction of poly(arylene ether sulfone) P under mild conditions. P1 and P2 are readily soluble in common organic solvents at room temperature and thermally stable up to 200 °C in both air and argon. The glass transition temperatures (Tg's) of P1 and P2 are 174 and 189 °C, respectively. The resonant nonlinear optical coefficient (d33) values were estimated to be 29.2 and 16.5 pm/V for P1 and P2, respectively, by in situ second harmonic generation (SHG) measurements at 1064 nm fundamental wavelength. By using the approximation two-level model, the nonresonant NLO coefficient (d33(∞)) values of P1 and P2 were estimated to be 6.6 and 4.8 pm/V, respectively.
Keywords: Non-linear optical methods; Poly(arylene ether sulfone);

PPV-derivatives containing phenothiazine and alkyloxy-substituted oxadiazole/Phenyl units for OLED by Feng Xu; Chen Wang; Liying Yang; Shougen Yin; Armin Wedel; Silvia Janietz; Hartmut Krueger; Yulin Hua (221-224).
The heterocycle of phenothiazine unit was investigated as the backbone of organic light-emitting polymeric materials because of its strong luminescence, potential ability of anti-oxidation and p-type semiconductor properties. The dialdehyde and dibromo-substituted phenothiazines were synthesized successfully by Vilsmeier method and bromination respectively. The homo and co-polymers from phenothiazine and substituted oxadiazole were synthesized successfully. Their photo- and electroluminescent properties were investigated.
Keywords: Conducting polymers; Electroluminescence; Heterocycle synthesis;

Two new iridium(III) complexes with two cyclometalated ligands (2-phenylpyridinato-C2,N) and one monoanionic dithiolate (N,N′-dialkyl-dithiocarbamate or O,O′-dialkyl-dithiophosphate) as ancillary ligands have been synthesized, and characterized by 1H-NMR, IR, MS and EA. They are all emissive in both solid state and in solution at room temperature. The replacement of β-diketonate ligand (acac) by dithiolate ligand results in blue shift of emission wavelength in solution photoluminescence spectra. The OLED using complex (ppy)2Ir (Et2dtc) as dopant in emitting layer gives a maximum current efficieny of 2.9 cd/A and a maximum brightness of 2525 cd/m2 at 13 V.
Keywords: Optical absorption and emission spectroscopy; Electroluminescence; Photoluminescence;

Blue light-emitting materials based on terfluorenes with carbazole terminal units by Q. Zhang; J.S. Chen; Y.X. Cheng; Y.H. Geng; L.X. Wang; D.G. Ma; X.B. Jing; F.S. Wang (229-232).
Three thermally stable ter(9,9-disubstitutedfluorene)s with hole-transporting carbazole moieties at two terminals (DCTFs) have been synthesized by modified Ullmann reaction and Pd-catalyzed Suzuki coupling. The resulting compounds are amorphous with glass transition temperature (T g) in the range of 201–205 °C. The electroluminescence efficiency up to 1.6 cd/A has been achieved with the device structure of ITO/NPB (30 nm)/DCTF-3(30 nm)/BCP (20 nm)/Alq3 (30 nm)/LiF/Al. A 60% increase of efficiency along with the CIE coordinates of (0.16, 0.11) was demonstrated compared with terfluorene (TF) analogue based device.
Keywords: Electroluminacence; Blue emitter; Glass transition temperature;

Synthesis and properties of polyfluorenes containing 1,8-naphthalimide moieties for white electroluminescence by Guoli Tu; Quanguo Zhou; Yangxiang Cheng; Yanhou Geng; Lixiang Wang; Dongge Ma; Xiabin Jing; Fosong Wang (233-236).
Two polyfluorenes containing 1,8-Naphthalimide units were synthesized by Yamamoto polycondensation reaction. The 1,8-naphthalimide moieties act as both electron and hole trap in the resulting polymers, leading to the EL spectra different from the PL spectra in film. White electroluminescence with a maximum brightness of 11100 cd/m2, an external quantum efficiency of 2.0% and CIE coordinates of (0.26, 0.36) has been realized through partial energy transfer from polyfluorene to 1,8-naphthalimide moieties.
Keywords: White light-emitting diodes; Polyfluorene; 1,8-Naphthalimide;

Polyfluorenes containing 1.8-naphthalimide dye as endcapping groups by Jianxin Cao; Quanguo Zhou; Yanxiang Cheng; Yanhou Geng; Lixiang Wang; Dongge Ma; Xiabin Jing; Fosong Wang (237-240).
A series of polyfluorene derivatives endcapped by 0.1–2 mol% 1,8-naphthalimide dye were synthesized by Yamamoto coupling reaction. The resulting polymers show the promising electroluminescence (EL) performance with emission predominantly from the 1,8-naphthalimide unit due to energy transfer and charge trapping from polyfluorene backbone to 1,8-naphthalimide dye. Single-layer devices were fabricated with a device configuration of ITO/PEDOT/polymer/Ca/Al. Among all the devices tested, the device of NFP50 exhibited the current efficiency of 7.40 cd/A, the power efficiency of 2.89 lm/W and the maximum brightness of 19280 cd/m2, about 30 times more efficient than that of polyfluorene without endcapping groups.
Keywords: Polyfluorene; 1,8-naphthalimide; Energy transfer;

Geometries of ground (S0) states of mer-tris(8-hydroxyquinolinato)metal (Mq3, M = Al3+, Ga3+, In3+, Tl3+) are optimized by B3LYP/6-31G(d) methods. In order to investigate the distribution for unequal individual ligands in mer-Mq3 as key materials for OLED, the bonding interactions either between the metal fragment Mq2 and a single ligand q have been analyzed with the energy decomposition scheme. The bonding analysis has been carried out at the BP86 level using TZ2P quality basis functions with small core. All the calculated results suggest that the HOMOs for Mq3 are mainly localized on A-quinolate ligand, which are responsible to the optical characteristics. The calculated phenomena about optical and structural properties of mer-Mq3 can be simply traced back to the lowest electrostatic attractive interaction energy between fragments A-quinolate ligand and the Mq2 due to the special arrangement, resulting in the easy of geometry relaxation for excited state or interaction with metal atoms.
Keywords: Bonding analysis; Energy partitioning; Mq3; OLED;

Synthesis and Luminescent Properties of Alq3 Complex by K.S. Yang; H.K. Shin; C. Kim; Y.S. Kwon (245-248).
New luminescent material, 6,11-dihydoxy-5,12-naphtacene-dione ·Alq3 complex(Alq2-Ncd), 1,4-dihydoxy-5,8-naphtaquinone ·Alq3 complex(Al2Nq4) was synthesized. The Alq2-Ncd and Al2Nq4 has big molecular weight and many π-electrons more than widely known Alq3. And extended efforts have been made to obtain high-performance electroluminescent(EL) devices. We used hole transfer layer of powdered TPD to improve hole transfer and characteristics of interface in OLED. Current-voltage characteristics, luminance-voltage characteristics and luminous efficiency were measured by Flat Panel Display Analysis System(Model 200-AT) at room temperature. Photoluminescence spectra were measured by LS45(PerkinElmer instruments) at room temperature. This study indicates not only the sterical effect but also some other effects that would be responsible for the change of the emission wavelength, improvement of luminance and etc.
Keywords: OLED; Alq3 complex; Electroluminescence; Photoluminescence; Cyclic voltammetry;

We synthesized two new siloles with thiophene linkage to the silicon atom that could show aggregation-induced emission (AIE), and observed that their PL emissions strongly depended on the aggregation states. The siloles are virtually nonemissive in solutions but their aggregates or solid films are highly luminescent, and the PL spectra of crystals of the siloles show large and unusual blue shift compared to the amorphous state. These phenomena are unique since PL quantum yields of conjugated organic emitters normally decrease in solid states, along with red shift of PL spectra at higher aggregation extent. Different and variable PL spectra of aggregates of the siloles formed in water/acetone mixtures were found. At certain water fraction, the solvent mediated aggregation morphology changing from the amorphous state to the crystalline state probably resulted in the variable PL emissions of the silole aggregates. Our results reveal that the novel thiophene containing siloles are crystalline blue emitters, and only their crystalline forms, rather than the amorphous forms, can emit lights with stable PL spectra.
Keywords: Silole; Photoluminescence spectra; Aggregate-induced emission; Blue shift; Crystal;

Multi-color emission of polymer light-emitting diodes with multi-layer structure by Y. Zhang; J. Peng; W. Gao; K. Yang; Y. Cao (253-256).
Polymer light-emitting diodes, which possess a multi-layer structure and produce blue, green and red emissions on an ITO substrate, were successfully fabricated. The basic device structure is ITO/PEDOT/blue polymer/Ba/Al/green polymer/Ba/Al/red polymer/Ba/Al, where PEDOT is poly(styrene sulfonic acid), functioning as the hole transportation, injection, and ITO surface modification, Ba: barium electron injection cathode, Al: aluminum, acting as the protecting layer from Ba oxidized. All polymer layers were prepared by spin-coating technique. The blue, green and red emission intensities can separately be controlled. Possible electroluminescence (EL) mechanisms were discussed in this paper.
Keywords: Electroluminescence; Multi-layer;

Synthesis and Characterization of Polyfluorene electrolytes as Green and Red Light-emitting Layers for High-Efficiency PLEDs by Huilin Shen; Fei Huang; Lintao Hou; Hongbin Wu; Wei Cao; Wei Yang; Yong Cao (257-260).
A series of ammonium-ended alkyl-substituted polyfluorene copolymer with narrow band-gap comonomer benzothiadiazole (BTDZ) and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DBT) were synthesized of by Suzuki polycondensation. The resulting polymers can be processed as an RGB active layer in polymer light emitting devices from environment friendly solvents such as alcohols. It is found out that devices from such polymers show equal or higher external quantum efficiencies (QE) with the high work-function metal cathode such as Al than by using the low work-function (Ca or Ba) cathode. The added BTDZ and DBT units not only change the polymers’ emission color, but also greatly improved the device performances of the polymers, as a result of the suppression of excimer formation which is common to rigid polyelectrolyte chains.
Keywords: Conjugated polymers; Polyfluorene; Polyelectrolytes; Light-emitting diode;

Recent theoretical developments on topological materials, Möbius nanographite and Möbius conjugated polymers, are reported. (I) In nanographite systems with the Möbius boundary condition, there appears a novel magnetic domain. However, this domain state competes against the helical magnetic states. Total energies of the latter states are always lower than that of the former state. Additionally, the domain wall appears in the charge density wave states. (II) Optical properties of Möbius conjugated polymers are studied. We discuss that oligomers with a few structural units are more effective than polymers, in order to measure effects of discrete wave numbers which are shift by the Möbius boundary from those of the periodic boundary. Certain components of the optical absorption for the electric field perpendicular to the polymer axis mix with the absorption spectra for the electric filed parallel with the polymer axis. The polarization dependences of electric field of light can detect whether conjugated polymers have the Möbius boundary or not.
Keywords: Electron density; Excitation spectra calculations; Many-body and quasiparticle theories; Special-purpose functionalized conjugated polymers; Graphite and related compounds;

Electronic absorption and emission data of M(CO)4(phen) complexes, where M = Cr, Mo or W; phen=1,10-phenanthroline are reported using density functional theory (DFT). Electronic absorption spectra of [M(CO)4(phen)] show a strong band in the visible region of the spectrum, whose metal to ligand charge transfer (MLCT) M → phen and M → COax character is indicated by high molar absorptivity. This assignment is investigated by theoretical calculations, which differ from the early interplay of M → L metal to ligand charge transfer MLCT and ligand-filed (LF) electronic transitions, occurring between d-orbitals. The phosphorescence of each complex was identified as a lowest, triplet metal to ligand charge transition (MLCT) around 740 nm.
Keywords: Absorption; Emission; DFT; Excited states;

Electronic structures of bis-sillicon-bridged trans-stilbene homologues were theoretically analyzed from the viewpoint of electronic effect occurring from geometrical difference in the vicinity of the stilbene bridged moiety using DFT B3LYP method. Absorption and emission energies were reported on the basis of TD-DFT and ZINDO approaches, establishing good agreement with experimental data. As compared with the carbon analogue, the absorption and emission maxima of silicon-bridged stilbene analogues have substantial red shifts. These significant red shifts are attributable to the electronic contribution of the silicon bridges. EL peak was predicted to be about 393 and 483 nm for them. The effects of hole and electron injection are clarified by the ionization potentials (IPs) and electron affinities (EAs) calculations. It is suggested that bis-sillicon-bridged trans-stilbene homologue should be more efficient at trapping the electron than carbon species.
Keywords: Trans-stilbene; Silicon-bridge; Density functional calculations; Excitation spectra calculations;

There is a growing interest in the structures and properties of gold complexes because of their especial chemical bonds. The crystal structure of [Au(SeC2B10H11)(PPh3)]2 has been determined by X-ray diffraction studies recently. The Au(I)...Au(I) interaction, electronic structures of ligands and nonlinear optical(NLO) properties of systems were discussed by means of DFT and finite field methods in this paper. The calculation results indicate that the second order NLO coefficient of [Au(SeC2B10H11)(PPh3)]2 is as high as 10−29 esu, which is superior to common organic conjugated systems.
Keywords: DFT/finite field method; Dinuclear gold complex; Electronic structure; Nonlinear optical property;

Neat Alq3 thin film and metal/Alq3 interfaces studied by NEXAFS spectroscopy by Takahiro Yokoyama; Hisao Ishii; Noritaka Matsuie; Kaname Kanai; Eisuke Ito; Atsuhiro Fujimori; Tohru Araki; Yukio Ouchi; Kazuhiko Seki (277-280).
Thin film of Alq3 and its interfaces with various metals (K, Li, Ca, Al)/Alq3 and the Al/LiF/Alq3 interface were investigated using NEXAFS spectroscopy. The assignments of structures in NEXAFS spectra at the C, N and O K-edges were performed using theoretical calculations taking account of the core-excitonic effect. The NEXAFS spectra at the three edges are well reproduced by the simulated results. The spectra at the N and O K-edges of Alq3 are similar to the partial density of unoccupied states (PDOUS) of the ground state, but the spectrum at the C K-edge is different from the PDOUS of ground state due to the core-excitonic effect. The present study is the first trial of the detailed analysis of the C K-edge spectrum of Alq3.The spectral changes at the metal/Alq3 and Al/LiF/Alq3 interface were found to depend on the metal. By the comparison with the theoretical simulations based on the 1:1 metal-Alq3 complex, we found that the electron transfer and orbital overlap occur at the interfaces of K/Alq3 and Li/Alq3, while the observed changes at the Ca/Alq3 and Al/Alq3 interfaces could not be understood by the simulated results. At the LiF/Alq3 interface, we observed the spectral changes which may result from some chemical interaction. Some of the spectral changes at Al/LiF/Alq3 interface differ from those of Al/Alq3 interface, indicating chemical interaction specific for the co-existence of Al, LiF, and Alq3.
Keywords: NEXAFS spectroscopy; Alq3; Interface;

Basic model for molecular sensing with molecular wires by Shuji Abe; Takako Iizuka-Sakano (281-284).
We examine the feasibility of a molecular wire system for sensing a molecule. For a general theoretical argument on this problem, we set up a model of a short conjugated molecular wire attached on both ends to metal electrodes. The binding of a target molecule is presumed to exert an effective local perturbation in the wire. We calculate the quantum transport through the molecular wire in terms of the Green's function method. Coulomb interactions are treated in the mean field approximation with the image charge effect taken into account. The electrostatic potential and the electron charge densities on the molecular wire are determined in a self-consistent manner. It is demonstrated that the current modulation by the local perturbation grows with increasing the applied voltage, thus making the molecular sensing feasible. The magnitude of modulation depends sensitively on the position of the local perturbation, implying that a precise molecular design is necessary for optimizing the device performance.
Keywords: Semi-empirical models and model calculations; Green's function method; Electron density; Excitation spectra calculations; Organic semiconductors based on conjugated molecules; Detectors;

Observation and Electrical Properties of Functionalized Dendrimer Monolayers by Using SPMs by K.H. Jung; S.B. Jung; H.K. Shin; C. Kim; Y.S. Kwon (285-288).
We synthesized dendrimers containing light switchable units, azobenzene group. We also report the example of a dendrimer containing 48 azobenzene that is electrically conducting using STM. The dendrimer with azobenzene group compared trans form and cis form at electrical properties. By irradiation of 365 [nm] light, the trans state current of G4-48 Azo dendrimer was increased, which was originated by the photoisomerization process of the azobenzene group on the periphery from trans to cis form. All of the conductivities were ohmic, there is no evidence of polarization on switching the current direction, and the conductivity values remained constant for several hours. This demonstrates that the conductivity is electronic, not ionic. This suggests that optical behavior and conductivity change are affected by the functional group and symmetric chain.
Keywords: Dendrimer; Azobenzene; Scanning probe microscopy; Photoisomerization; Organic monolayer;

A new optical doping method toward molecular electronics by T. Naito; T. Inabe; H. Niimi; K. Asakura (289-292).
Molecular materials have been recently spotlighted as promising candidates for advanced functional materials. We have developed a novel and simple doping method for a molecular material which utilizes a light-induced solid state reaction. The electrical behavior of a single crystal of a molecular charge-transfer salt of silver(I) ion qualitatively becomes differed after illumination with ultraviolet-visible (UV-VIS) light. The X-ray photoelectron spectroscopy also demonstrated that there was neutral silver species concentrated in the illuminated part of the pressed pellet sample, while only silver (I) ions were detected in the rest part and non-illuminated samples. Raman spectra of the pressed pellet sample showed that the formal charge of the constituent organic π-acceptor molecule, which is responsible for the conductivity of this material, varied in accordance with the time of illumination. Illumination with UV-VIS light upon only half of a thin single crystal of the same material transformed it to junction structure, exhibiting a rectifying character. This doping method has opened a new way for fabrication of devices from molecular solids.
Keywords: Organic conductors based on radical cation and/or anion salts; Metal/semiconductor interfaces; Interface preparation; Transport measurements; Conductivity; Hall effect; Magnetotransport;

Transport mechanism of rectifying D-σ-A-SAc molecule in the structure of vertical metal-molecule-metal (MMM) has been investigated by using variable temperature measurement. We successfully synthesized a novel D-σ-A-SAc molecule and fabricated the molecular rectifying array device by using self-assembly technique. The results of variable temperature measurements suggest that electron injection in the interface between electron donor molecule and Ti/Au electrode is dominated by a thermal emission with a barrier height of around 0.29 eV while carrier injection between thiolated A-σ-D molecule and gold electrode is dominated by tunneling with a barrier height of around 0.8 eV. Therefore, we suggest that the origin of rectification comes from energy differences of two interfacial barriers in MMM device.
Keywords: Self-assembly using surface chemistry; Organic semiconductor based on conjugated molecules; Heterojunctions;

Fine structure of the highest occupied band in OTi-phthalocyanine monolayer by H. Yamane; H. Fukagawa; H. Honda; S. Kera; K.K. Okudaira; N. Ueno (297-300).
Ultraviolet photoelectron spectra were measured for ultrathin films of OTi-phthalocyanine (OTiPc), which has an electric dipole perpendicular to the molecular plane, prepared on highly oriented pyrolytic graphite in order to study effects of the molecular orientation and the electric dipole layer on the organic electronic states. For the as-grown films, the observed highest occupied molecular orbital (HOMO) band consists of two prominent peaks that can be assigned to different molecular orientations. For the oriented monolayer obtained by annealing the as-grown film, we detected a very sharp HOMO band at 290 K. The binding-energy (E B) difference between the HOMO bands of the as-grown and annealed films was found to agree with the shift in the vacuum level. For the oriented monolayer, the observed sharp HOMO band involves at least four components that are ascribed to the coupling between the HOMO hole and the molecular vibration. Upon cooling the sample to 95 K, the HOMO bandwidth became sharper than that at 290 K. From the peak fitting using Voigt function, additional components are expected in the HOMO band at 95 K. Moreover, we detected the E B shift in the HOMO band for the oriented monolayer upon cooling, which can be originated from decrease in the HOMO-hole screening due to the change in the film structure and/or the molecule-substrate interaction.
Keywords: Organic semiconductors based on conjugated molecules; Organic/inorganic interfaces; Photoelectron spectroscopy;

Substrate Dependent Anisotropic Diffusion Of Indium Atoms On Ptcda Thin Films Studied by Peem by M. Shionoiri; I. Yamamoto; M. Onoue; S. Kera; K.K. Okudaira; N. Ueno (301-304).
Anisotropic surface diffusion of In atoms was observed by photoelectron emission microscopy (PEEM) when a square-shaped microstructure of In metal was deposited onto thin films of perylene-3,4,9,10-tetracarboxyric acid-dianhydride (PTCDA) grown on cleaved MoS2 and GeS surfaces. For In microstructure on PTCDA/MoS2 system, the PEEM images showed a triangle pattern, although the deposited shape of the In microstructure was square, indicating that In atoms diffuse to three directions on PTCDA/MoS2. Such triangle pattern was not observed on PTCDA/GeS but an oval structure was observed, revealing that In atoms diffuse to two directions on PTCDA/GeS with different diffusion constant. The two directions correspond well with surface crystal axes of GeS. Since the unit cells of PTCDA adsorbed on these two crystal surfaces are nearly the same, it is suggested that different anisotropic diffusion of In in these systems is related to strong In-PTCDA interaction which may be affected by the surface structure of underlying substrate.
Keywords: Photoelectron emission microscopy (PEEM); PTCDA; Indium; Metal-organic interface; Diffusion;

Three series of multifunctional polysiloxanes containing charge-transporting agents and electro-optical chromophores have been prepared for the photorefractive application. The structural characterization of these polymers is presented by IR, UV, 1H-NMR spectra and elemental analysis. The poled films of polymer 1, 3, 8 reveal resonant d 33 values of 21,31 and 19 pm/V by second harmonic generation (SHG) measurements.
Keywords: Polysiloxane; Multifunctional polymer; Synthesis; Non-linear optical methods;

Victor J. Emery and recent applications of his ideas by Serguei Brazovskii (309-312).
Victor Emery made seminal contributions to the theory of one-dimensional electronic systems and to its applications to organic metals. His inventions became illuminated recently when the joint effect of the ferroelectricity and the charge disproportionation has been discovered in (TMTTF)2X compounds and beyond. Several of his contributions came to agenda at once: separate gaps in spin/charge channels and the route to solitons, 4kF anomaly, dimerization gap, role of ionic transitions. New phenomena unify an unusual variety of concepts: ferroelectricity of good conductors, structural instability towards Mott-Hubbard state, Wigner crystallization in a dense electronic system, ordered 4kF density wave, richness of physics of solitons, interplay of structural and electronic symmetries. The ferroelectric state gives rise to several types of solitons carrying the electron charge, a noninteger charge, spin or both the spin and the charge in special cases. They are clearly observed via conductivity, electric and magnetic susceptibilities. Solitons are challenging for optics where they already seem to determine the pseudogap in adsorption. Various features also appear, or are expected, from collective electronic and coupled electron-phonon modes. The last topic, as well as some aspects of physics of solitons, recalls also the contributions of M.J. Rice. Moreover, the observation of Mott-Hubbard states refers to classical results of A. A. Ovchinnikov.
Keywords: One-dimensional systems; Interacting electrons; Ferroelectricity; Charge disproportionation; Solitons; CDW; Wigner crystal;

We review an analytically treatable method to account for multi-electronic interactions for electronic and optical properties of conjugated polymers. Our model combines the long range electron-hole (e-h) Coulomb attraction with a specific effect of strong effective intramonomer e-h repulsion. The theory operates with a few parameters which can be determined experimentally or from ab initio calculations. The model explains, exploits and organizes various experimental and numerical findings. E.g. we connect such different questions as shallow singlet and deep triplet excitons in phenylenes, common 1/L energy dependencies in oligomers, etc.This presentation is dedicated to memory of Michael Rice for whom conducting polymers were a great passion. More details on scientific part can be found in the contribution to the memorial volume [1].
Keywords: Conjugated polymers; Oligomers; Optical absorption; Singlet and triplet excitons; Electronic correlations;

Magnetic vs. charge ordered states, and electric capacitance in zigzag nanographite ribbons by K. Harigaya; A. Yamashiro; Y. Shimoi; K. Wakabayashi (317-320).
Nanographite materials show novel electronic properties: spin glass like behaviors [1], the on/off switching of magnetism with molecule adsorptions [2], and so on. Here, we study electronic states in nanographite ribbons with zigzag edges. Effects of the nearest neighbor Coulomb interactions are investigated using the extended Hubbard model. The nearest Coulomb interactions stabilize a novel electronic state with the opposite electric charges separated and localized along both edges, resulting in a finite electric dipole moment pointing from one edge to the other. Next, electric capacitance is calculated to examine nano functionalities. We find that the behavior of the capacitance is widely different depending on whether the system is in the magnetic or charge polarized phases. In the magnetic phase, the capacitance is dominated by the presence of the edge states while the ribbon width is small. As the ribbon becomes wider, the capacitance remains with large magnitudes as the system develops into metallic zigzag nanotubes. It is proportional to the inverse of the width, when the system corresponds to the semiconducting nanotubes and the system is in the charge polarized phase also. The latter behavior could be understood by the presence of an energy gap for charge excitations.
Keywords: Electron density; Excitation spectra calculations; Many-body and quasiparticle theories; Graphite and related compounds;

In the present study, the isothermal crystallisation kinetics and behaviour of polyvinylalcohol/silica (PVA/SiO2) nanocomposite prepared with self assembly monolayer (SAM) technique are characterized by conducting differential scanning calorimetric (DSC) analysis. Several kinetics equations are employed to describe the isothermal crystallisation of PVA/SiO2 nanocomposite compared to the pure PVA. During the isothermal crystallisation, the peak crystallisation time (t p ), half time of crystallisation (t 1/2), degree of crystallinity (X c ), relative degree of crystallinity (X t ) and kinetic rate constant (k) all show a strong dependence on the crystallisation temperature and the presence of SiO2, while the Avrami exponent (n) is hardly affected by crystallisation temperature and SiO2. Activation energy (E) for pure PVA and PVA/SiO2 nanocomposite are 235.8 kJ/mol and 319.7 kJ/mol, respectively.
Keywords: Polyvinylalcohol; Silica; Nanocomposite; Isothermal crystallisation; Differential scanning calorimetry (DSC); Self assembly;

Theoretical studies of the relative stabilities and electronic properties on B endohedral and exohedral fullerenes by X.M. Pan; Z. Fu; B. Hong; L. Zhao; Y.Q. Qiu; Z.M. Su; R.S. Wang (325-328).
Possible structures of C60Bn and C60Bn n+ (n = 1–4) endohedral and exohedral fullerene complexes have been calculated using semiempirical AMI and DFT/B3LYP methods at the level 6–31 G in order to determine the most stable structures, to investigate the underlying causes of their stabilities and to predict their redox characteristics. In principle, the stabilities decrease with increasing number of the endohedral atoms. The most possible structures of the fullerene adducts investigated in this paper are determined. The correlation differential between the stable of B-doped heterofullerenes and that of fullerene adducts have been found. The chemical reactivity of all adducts were enhanced.
Keywords: DFT/B3LYP method; Fullerene complexes; B endohedral and exohedral fullerene; Electronic properties;

The interactions of hydrogen with graphitic C16H10 and B8N8H10 clusters are investigated by performing hybrid density functional electronic structure calculations. The B3LYP results are presented for both the H-C16H10 and H-B8N8H10 clusters. For H-C16H10, significant structural relaxation of the C16H10 substrate is observed, while for H-B8N8H10 the B8N8H10 substrate is allowed to keep a planar structure at their optimized geometry. From the analyses of electron density and potential energy surface, the former interaction is shown to be chemisorption and the latter physisorption. The mechanism of hydrogen adsorption on the substrates is discussed using energetic diagram in the HOMO-LUMO region.
Keywords: Ab initio quantum chemical methods and calculations; Density functional calculations; Models of surface and interface chemistry and physics; Graphite and related compounds; Fuel storage devices;

Preparation and characterization of nanosized Pt/Au particles on TiO2-nanotubes by Shu-Hua Chien; Yuh-Cherng Liou; Ming-Chih Kuo (333-336).
TiO2-nanotubes were prepared by hydrothermal treatment of TiO2 powders in concentrated NaOH solution at 110 °C for 90 h. The immobilization of Pt and Au was carried out by photochemical deposition method with TiO2-nanotubes suspending in an aqueous solution containing H2PtCl6·6H2O or HAuCl4·3H2O. Transmission electron micrographs revealed that the diameter of the as-made TiO2-nanotube is about 10 nm with an inner diameter around 6 nm. The nanotube shows layered structures similar to the carbon nanotubes. The layer spacing is about 0.88 nm. Nanosized Pt (∼2 nm) and Au (∼10 nm) particles were dispersed uniformly on the surface of the nanotubes. The BET surface area of the nanotube is ∼200 m2/g as estimated by N2 adsorption isotherm, that was not significantly affected after the immobilization of Pt or Au. In-situ IR spectroscopic studies revealed that the Pt/TiO2-nanotube is highly active for CO2 hydrogenation, while Au/TiO2-nanotube exhibits pronounced activity for CO oxidation at room temperature. In general, Pt/TiO2-nanotubes presents a relatively higher activity than Au/TiO2-nanotubes, and the catalytic activities of TiO2 supported Pt and Au catalysts are significantly enhanced by the high surface area of TiO2-nanotube.
Keywords: TiO2-nanotubes; Pt; Au nanocatalysts; In-situ IR; CO2 hydrogenation; CO oxidation;

Synthesis and electrorhelogy of multi-walled carbon nanotube/polyaniline nanoparticles by S.J. Park; S.Y. Park; M.S. Cho; H.J. Choi; M.S. Jhon (337-340).
Nanoparticles with multi-walled carbon nanotube (MWNT) and polyaniline (PANI) were synthesized via an oxidative dispersion polymerization using poly(vinyl alcohol) (PVA) as a polymeric stabilizer and HCl as a dopant. Prior to the synthesis, the MWNT was treated with strong acidic solutions via a reflux process to eliminate impurities including metallic catalysts. These MWNT/PANI nanoparticles were well dispersed in water because the hydrophilic PVA was stably adsorbed onto the nanopartcle surface. These MWNT/PANI nanoparticles were used as suspended particles for an electrorheological (ER) suspension, and the rheological properties for this ER fluid including yield stress and shear viscosity under several different applied electric field strengths were examined via a rotational rheometer equipped with a high DC voltage generator.
Keywords: Multi-walled carbon nanotube; Polyaniline; electrorheology;

Nanostructured films of various conjugated polymers can be obtained through electrophoretic deposition process. Unlike the conventional deposition techniques based on the solutions of conjugated polymer, the methods employing colloidal suspensions like one proposed here make it to possible to separate the solidification of material from the film formation and drying steps. This unique feature provides nanostructure in the films deposited.A simple method, pouring a dilute solution of target material into an excess of non-solvent liquid, was used to obtain suspensions of conjugated polymers. Since this method is similar to a step of purification of the polymers after polymerization and does not use any additives such as surfactant, the polymers in the suspension and therefore the films obtained through the electrophoretic deposition may keep at least the purity of the original material.The unique morphology found in the electrophoretically deposited films opens up the new application of polymer light-emitting devices other than displays, the artificial fingerprint devices for anti-forging technology applicable to smartcards. Additionally, a unique process to obtain polymer-fullerene nanocomposite for photovoltaic application through the electrophoretic deposition is also proposed.
Keywords: Solution processing; Coating; Nanostructure; Electrophoretic deposition; Light sources; Solar cells;

Writing of Conducting Polymers using Nanoelectrochemistry by S.-Y. Jang; M. Marquez; G.A. Sotzing (345-348).
Nano-writing of intrinsically conducting polymer was achieved via a novel electrochemical nanolithographic technique using tapping mode electrochemical atomic force microscopy. Conducting polymer nanolines as small as 58 nm width were obtained and the line width is controlled as a function of the writing speed and writing potential. Higher writing potential and slower writing speed produce wider conducting polymer nanolines due to enhanced propagation. No specific restriction in the choice of substrates and the ease of controlling feature size is expected to facilitate to fabrication of all plastic nano-electronic devices.
Keywords: Conducting polymers; Polythiophene; Atomic force microscopy; Electrochemical polymerization; Coupling reaction;

Electrical and mechanical properties of nanocomposites of single wall carbon nanotubes with PMMA by V. Skákalová; U. Dettlaff-Weglikowska; S. Roth (349-352).
The electrical conductivity and mechanical characteristics of nanocomposites from pristine and doped single wall carbon nanotubes (SWNT) with polymethylmethacrylate (PMMA) were measured. In highly purified HiPCO SWNT, a percolation threshold as low as 0.17 weight percent has been found. The conductivity value at saturation is about 17 S/cm. If the purified HiPCO SWNTs are doped with SOCl2, the percolation threshold does not change but the saturation conductivity rises to about 100 S/cm. The mechanical properties were investigated for the PMMA composite mixed with SOCl2-doped SWNT. A small content of doped nanotubes dramatically changed Young modulus, toughness and tensile strength as well.
Keywords: Carbon and related materials; Solution processing; Conductivity; Insulating Films; Semiconducting films; Raman spectroscopy;

Ultra microelectrodes from MWCNT Bundles by M. Kaempgen; S. Roth (353-356).
Bundles of Multi Wall Carbon Nanotubes (MWCNT) are used as ultra microelectrodes. They show featureless cyclic voltammograms in 0.1 m KCl indicating the absence of surface functionalities. Typical behavior for radial diffusion was found for faradaic processes as expected for low dimensional electrodes. Since CNTs are hydrophobic by nature, strategies are explored overcome the surface tension of aqueous electrolytes. Additionally, methods to cut the MWCNT bundle to a desired length and to get insulating coatings are demonstrated. These more technological aspects are very interesting in terms of practical use for all applications of individual CNT electrodes.
Keywords: Carbon nanotubes; Ultra microelectrodes; Electrochemical Polymerization;

Electronic Structure of Metallofullerene, Tm@C82 (II) by S. Hino; N. Wanita; K. Iwasaki; D. Yoshimura; N. Ozawa; T. Kodama; K. Sakaguchi; H. Nishikawa; I. Ikemoto; K. Kikuchi (357-360).
Ultraviolet photoelectron spectra of one of three Tm@C82 isomers, Tm@C82 (II), were measured with synchrotron radiation light source. The spectra resemble those of Ca@C82 (III), which indicates that these two metallofullerenes have analogous valence electronic structures as well as the cage structures. The spectra of Tm@C82 (II) and Ca@C82 (III) are well reproduced by a simulated spectrum obtained with ab initio calculation based on the C 2 (no.5) cage geometry. This finding supports symmetry group determination carried out with NMR measured on Tm@C82 (II). Because of spectral resemblance, the electronic structure of metallofullerenes seems to be determined solely by the fullerene cage and entrapped atom species.
Keywords: Photoelectron spectroscopy; Fullerenes and derivatives;

Titanium Oxide and Polyaniline Core-Shell Nanocomposites by Feng-Yi Chuang; Sze-Ming Yang (361-364).
The surfaces of titanium oxide nano-crystals were modified with γ-aminopropyl-triethoxy silane and N-phenyl-γ-aminopropyl-trimethoxy silane. Polymerizations of aniline on the modified titanium oxide nano-crystals were conducted. The composites were characterized by FTIR, ESCA and TEM. FTIR spectra indicate the formation of polyaniline. ESCA spectra of the composites show peaks of N with similar environment of N in polyaniline indicating the formation of polyaniline on the surface. The shape of the particles in the composite is spherical which is different from that of titanium oxide crystal and fibular structure of polyaniline polymerized under the same condition.
Keywords: Core-shell nanocomposites; Titanium oxide; Polyaniline;

We present a comparative study on supported and suspended carbon nanotubes, using room temperature scanning tunneling microscopy measurement, in order to assess the effect of substrate interactions on the electronic properties. Our results show two remarkable differences between suspended and supported molecules; first there is about 0.1 eV less shift in the band structure toward higher energies which indicates less doping from the Au(1 1 1) substrate; second there are persistent coherent oscillations that are very sensitive to the bias voltage. The undamped behaviour of these oscillations is a manifestation of long coherence length, suggesting that the electron-electron interactions between nanotube and substrate is the main mechanism for phase relaxation. The origin of these oscillations is the constructive interference of electron waves that are scattered from defects on the nanotube. We present a high-resolution topographic image of a unique type of such defects where a void on the wall of a pristine nanotube is observed for the first time.
Keywords: Carbon nanotubes; Scanning tunnelling microscopy;

Re-excited states of solitons and polarons in conjugated polymers by D.C. Zhang; D.S. Liu; L.M. Mei; S.J. Xie; X. Sun (369-372).
π-Conjugated polymers have become an important class of materials for electronic devices. It was suggested recently that a charge flipping of spin carrier will take place when a charged polaron is re-excited by a photon. A possible photo-control valve or switch can be designed from this phenomenon. In the framework of the tight-binding approximation we studied the re-exciting process both in degenerate and non-degenerate polymers and checked all the possible re-excited states.
Keywords: Re-excited states; Soliton; Polaron; Polymer;

Structures and Physical Properties of New β′-BEDT-TTF Tris-Oxalatometallate (III) Salts Containing Chlorobenzene and Halomethane Guest Molecules by A. Akutsu-Sato; A. Kobayashi; T. Mori; H. Akutsu; J. Yamada; S. Nakatsuji; S.S. Turner; P. Day; D.A. Tocher; M.E. Light; M.B. Hurstho (373-376).
We report the structures and physical properties of new β′-(BEDT-TTF)4[Fe(oxalate)3]·G salts where A = H3O+, G = PhCl; A = Rb+ G = Pyridine. The structure of the PhCl salt is isomorphous with β′-(BEDT-TTF)4[(H3O)M(oxalate)3] with other guest molecules. PhCl is ordered in die hexagonal pockets formed by the [(H3O)Fe(oxalate)3] layer. The electrical conductivity is metallic down to 100 K, below which the resistivity increases with decreasing temperature. The specific conductivity at room temperature is about 10 S/cm. We also report the salt β′-(BEDT-TTF)4[RbFe(oxalate)3]·Pyridine where Rb+ replaces H3O. The electrical resistivity shows metallic behavior down to 100 K. and turns up gradually to a maximum at 65 K below which the system re-enters the metallic state down to liquid helium temperature. Neither salt shows superconductivity down to 2 K. In addition, other new β′-(BEDT-TTF)4[(H3O)M(oxalate)3]·salts with M = Cr, Ga, Fe; G = CH2Cl2, CH2ClBr, CH2Br2 are also reported.
Keywords: Organic conductors based on radical cations and/or anion salts; Metal-insulator phase transitions; Magnetic measurements; Bectrocrystallisation;

We report here four novel purely organic magnetic conductors containing common electron donors together with an organic anion including an organic free radical, (TTF)(TEMPO-NHCOCH2SO3)·0.5H2O (1), (TMTSF)(TEMPO-NHCOCH2SO3)·2H2O (2), (BEDT-TTF)3(TEMPO-NHCOCH2SO3)2·2H2O (3), and α-(BEDT-TTF)3(TEMPO-NHCOCH2SO3)2·6H2O (4). The TTF complex was prepared by metathesis of (TTF)3(BF4)2 and the PPh4 salt of the anion (5). The other complexes were obtained by electrocrystallization of the corresponding donors with the salt 5 as an electrolyte. Crystal structures of 2–4 have been solved. The salts 1 and 2 show relatively high resistivities (>107 and 5 × 103  Ω·cm), whilst the BEDT-TTF salts 3 and 4 have rather low room temperature resistivities (1.2 and 5.1 Ω·cm) with small activation energies (0.041 and 0.050 eV). The magnetic behavior of complex 1 obeys the Curie-Weiss law (C  = 0.379 emu·K/mol and θ  = −3.29 K) and those of the other complexes obey the 1-D Heisenberg model (C/J  = 0.366/−0.32 for 2, 0.373/−0.81 for 3, and 0.380 emu·K·mol−1/+0.42 K for 4). The relationships between the crystal structures and the physical properties are discussed.
Keywords: Organic conductors based on radical cation and/or anion salts; Magnetic measurements;

New Organic Functional Anions: Ferrocenyl-(CONHCH2SO3 ) n (n = 1–2) and their TTF Salts by Keigo Furuta; Hiroki Akutsu; Jun-ichi Yamada; Shin’ichi Nakatsuji (381-384).
New organic functional anions that includes the ferrocenyl group, CpFeCp-CONHCH2SO3 and Fe(Cp-CONHCH2SO3 )2, are prepared as tetraphenylphosphonium (PPh4) salts. They reacted with (TTF)3(BF4)2 to give TTF monocation salts. The X-ray analyses indicate that for all salts TTF forms a dimer which is separated by the relatively larger anions. The oxidation reaction of (PPh4)(CpFeCp-CONHCH2SO3) with I2 gave the Zwitter-ion, CpFe+Cp-CONHCH2SO3 , which shows a Curie-Weiss behavior (C  = 0.800 emu·K/mol, θ  = −1.13 K) with weak antiferromagnetic interaction. This magnetic moment is found to be attributed to the ferrocenyl radical.
Keywords: Organic conductors based on radical cation and/or anion salts; Magnetic measurements;

Photocarrier injection to organic compounds by Jun-Ichi Yamaura; Yuji Muraoka; Takaki Muramatsu; Touru Yamauchi; Zenji Hiroi (385-388).
Photocarrier injection (PCI) is efficient method of the carrier control for the inorganic thin films, where the photo-excited holes in the wide-gap semiconductor under the UV light irradiation are injected to the film through the interface. We examine the PCI method to various organic films provided on the inorganic wide-gap semiconductor substrate. We prepared organic films deposited on the surface of a Nb-doped TiO2 (SrTiO3) single crystal substrate, possessing a band gap of 3.0 eV (3.2 eV), by using casting or vacuum evaporation. Fabricated organic films were polythiophene (1), Ni phthalocyanine (2), polyaniline (3), C60 (4), and DNA (Herring Sperm) (5) on Nb-doped TiO2 substrate. We determined the carrier injection to the organic films from the across-plane open-circuit voltage measurement under the UV light. The values of the surface density of the injected holes to organic films are estimated at 1.4 × 1013  cm−2 (1), 4.2 × 1012  cm−2 (2), 6.9 × 1012  cm−2 (3), 1.5 × 1011  cm−2 (4), and 8.1 × 1012  cm−2 (5) at the irradiance of 10 mW/cm2. Moreover, we also measure the photovoltages for polythiophene films provided on Nb-doped SrTiO3 substrates with various Nb concentrations.
Keywords: Polythiophene and derivatives; Semiconducting films; Other heterostructures; Photoconductivity;

Effect of Hydrostatic Pressure on Molecular Conductors, Pd(dmit)2 Salts by Y. Ishii; M. Tamura; R. Kato; M. Hedo; Y. Uwatoko; N. Môri (389-392).
A series of molecular conductors β′-(cation)[Pd(dmit)2]2 (cation  = Et2Me2 P and Me4P) exhibit various complicated pressure-induced phenomena. Resistivity measurements under high pressure up to 8 GPa have been carried out using a clamp-type piston-cylinder cell and cubic anvil type high pressure apparatus. The Et2Me2P salt shows non-metallic phases at low and high pressure regions, between which a metallic phase appears. The application of pressure suppresses the low-temperature resistivity of this salt. However, the non-metallic behavior still remains at low temperature under 8 GPa. For the Me4P salt, the metal-to-non-metal transition temperature reaches a minimum at 0.83 GPa and turns to increase with increasing pressure up to 8 GPa, showing no metallic state stable at low temperature
Keywords: Organic conductors based on radical anion salts; Conductivity; Metal-Insulator transition;

NMR Study of the Spin-Liquid State and Mott Transition in the Spin-Frustrated Organic System, κ-(ET)2Cu2(CN)3 by Y. Shimizu; Y. Kurosaki; K. Miyagawa; K. Kanoda; M. Maesato; G. Saito (393-396).
The 1H and 13C NMR experiments of the Mott insulator κ-(ET)2Cu2(CN)3 with highly frustrated spin structure were performed under ambient and hydrostatic pressures. No indication of long-range antiferromagnetic ordering (moment, if any, <0.01 μB) was observed in the 1H NMR spectrum under ambient pressure, indicating the spin liquid state in the compound. The 13C NMR, a more sensitive probe of electron spins, showed field-dependent inhomogeneous broadening at low temperatures, which suggests the staggered magnetization partly induced by magnetic field. The Mott transition to Fermi liquid under hydrostatic pressure was observed in the resistivity and the 1H NMR spin-lattice relaxation rate.
Keywords: Nuclear magnetic resonance spectroscopy; Organic superconductor; Metal-insulator phase transition;

A series of anion radical salts of [Pd(dmit)2] with tetrahedral cations such as Me4P+ are paramagnetic Mott insulators under ambient pressure. Recently, we have found that sufficiently pure samples of the Et2Me2Sb salt undergo a novel first-order phase transition at about 70 K. The spin susceptibility exhibits a sharp drop to zero as temperature decreases below this temperature, accompanied by a steep rise of resistivity. We have attributed this transition to the charge separation, 2[Pd(dmit)2]2  → [Pd(dmit)2]2+[Pd(dmit)2]2 2−. We discuss the possible mechanism of this phase transition, emphasizing the role of strong dimerization in [Pd(dmit)2]2. It is pointed out that the observed charge separation is favored by the HOMO-LUMO interplay in [Pd(dmit)2]2, which stabilizes the doubly occupied state of me dimer by forming double-bond. This mechanism is never expected for the conventional charge-ordered systems such as the ET salts with quarter-filling, in which the intermolecular Coulomb repulsion is believed to play a dominant role in charge separation.
Keywords: Organic conductors based on radical anion salts; Structural phase transitions; Semi-empirical models and model calculations;

The radical cation salt (Fluoranthen)2PF6 is an organic quasi-1d conductor showing a Peierls transition at TP  = 186 K. Model calculations predicted that the Peierls transition is suppressed by an increased density of defects which can be influenced by irradiating the crystals with high-energetic protons (EP  = 25 MeV). This prediction could be verified by microwave conductivity measurements investigating a homogeneously irradiated crystal. In order to eliminate possible sample dependence, a high quality crystal was irradiated through a periodic grid to result in a stripy pattern. A detailed spatially resolved X-band-pulse-ESR-analysis quantifies the resulting defect concentration and proves that the Peierls transition can be nonuniformly suppressed.
Keywords: Organic conductors based on radical and/or anion salts; Metal-insulator phase transitions; Electron spin resonance;

2D Peierls state in a square lattice – Effect of anisotropy by Yoshiyuki Ono; Shutaro Chiba; Tetsuya Hamano (405-408).
In recent studies, we have shown that the lowest energy state in a 2D square lattice SSH-type model with a half-filled electronic band is not a simple Peierls state involving only distortions with the nesting wave vector Q but complicated multimode states involving distortions with various wave vectors parallel to Q and that there are many degenerate non-equivalent distortion patterns yielding the same ground state energy. In the present work we discuss the effect of anisotropy on these multimode Peierls states. It is indicated within the pertubational treatment combined with numerical calculations that the multimode states can survive as far as the anisotropy is small. Furthermore it is pointed out that the degeneracy can be lifted by the anisotropy. These studies will shed light on the understanding of the Peierls-like behaviors of 2D materials as layered organic conductors.
Keywords: Equilibrium thermodynamics and statistical mechanics; Metal-insulator phase transitions; Structural phase transitions; Organic conductors based on radical cation and/or anion salts;

The Bechgaard salts and their sulfur analogs are considered to be in quasi-one-dimensional correlated electron systems with a quarter-filled π band and exhibit various types of charge and/or spin ordering. A variety of mechanisms have been proposed in an attempt to interpret the variety of instabilities, featuring dimensionality, which can be turned by pressure as well as chemically, intrachain dimerization due to the anion columns, and competing on-site and even long-range Coulomb repulsions.Here we investigate quantum and thermal phase transitions in the Bechgaard salts and their sulfur analogs with particular emphasis on lattice degree of freedom. We consider the one-dimensional extended Peierls-Hubbard model with long-range Coulomb and electron-lattice interactions. Due to the intrinsic dimerization accompanied by the anion columns, we introduce alternation to transfer integrals, nearest-neighbor Coulomb interactions and spring constants. We fully demonstrate the interplay between charge ordering and lattice instability within the Hartree approximation. Besides the purely electronic charge and spin density waves which are well established both experimentally and theoretically, we reveal a lattice-tetramerized phase stabilized essentially in Peierls-Hubbard model. Our results inspected and compared with the results of experiments.
Keywords: Equilibrium thermodynamics and statistical mechanics; Order-disorder phase transitions; Organic conductors based on radical cation and/or anion salts;

We investigated the bandwidth-control Mott transition in the quasi-two-dimensional organic conductor, κ-(BEDT-TIF)2Cu[N(CN)2]C1, by conductance measurements under continuously controllable pressure of helium gas at zero and high magnetic fields. Several fundamentals of the Mott transition were revealed: (i) the Mott transition is of the first order with the clear conductance jump, and terminates at a finite-temperature critical endpoint, (ii) the low-temperature marginal metallic phase near the Mott transition is found to undergo the localization transition by magnetic field, which is also of the first order, and (iii) the critical endpoint is characterized by critical divergence in the pressure derivative of conductance and the vanishing of the conductance jump. The critical phenomena indicate that the conductance around the critical endpoint reflects the singularity of the order parameter of the Mott transition. The preliminary evaluation of the critical exponents suggests that the criticality of Mott transition in two dimensions is unconventional.
Keywords: Transport measurements; Metal-insulator phase transitions; Organic superconductors;

μSR studies of layered organic superconductors: vortex phases, penetration depth and anomalous superfluid properties by F.L. Pratt; S.J. Blundell; T. Lancaster; M.L. Brooks; S.L. Lee; N. Toyota; T. Sasaki (417-420).
Muon-spin rotation (μSR) measurements have been used to study the superconducting vortex properties of layered organic superconductors based on molecular donors such as BEDT-TTF. The μSR is particularly sensitive to the degree of local ordering of pancake vortices and can detect when the pancake layers become decoupled by intrinsic or defect-driven decoupling mechanisms, or by thermally driven motion. Further novel features of the vortex system occur when the field is tilted away from a crystal axis. Knowledge of the vortex phase behaviour allows appropriate parameter regions to be selected for reliable determination of the superconducting penetration depth λ and studies of the temperature dependence of λ have shown a T-linear term at low fields that is suppressed with increasing field. Systematic studies of λ across the range of organic superconductors have revealed a strong correlation between λ and Tc. In contrast to the linear scaling Tc ∝ λ−2 seen in high Tc cuprates, the organics show an overall correlation better described as Tc ∝ λ−3. One interpretation is that the superconducting carriers are only a small fraction of the total carrier concentration in these low-Tc superconductors. Understanding this result may give us some important clues about the nature of the superconductivity in the organics.
Keywords: Organic superconductors; Magnetic measurements;

Optical studies of shear stress effect on organic thin films by M. Inokuchi; A. Nagaoka; M. Yamamoto; I. Shirotani; J. Hayashi; K. Yakushi; H. Kawamura; H. Inokuchi (421-424).
We have studied the effect of shear stress by using the sapphire-anvil cell, which was developed to generate shear stress on a thin film under high pressure. We have tried to synthesize the charge-transfer (CT) salt of TMPD (N,N,N′,N′-tetramethyl-p-phenylenediamine) and TCNQ (7,7,8,8,-tetracyanoquinodimethane) by the shear stress effect. The shear deformation caused a change of the color of the thin film to blue-black at the outer part on the sapphire culet, while the color at the center part remained as orange of neutral TCNQ. The thin film on the anvils was examined by Raman spectroscopy under a microscope. The Raman bands attributed to C=C of TCNQ were observed at 1386 cm−1 and 1452 cm−1 for the CT salt and neutral TCNQ, respectively. For the blue-black thin film at the outer part, the Raman band appeared at 1386 cm−1, while at the center part, it was observed at 1452 cm−1. From the Raman spectra, the formation of the CT salt from TMPD and TCNQ by the shear stress effect was confirmed. In addition, the estimation of the shear stress effect on Pt(dpg)2, bis(diphenylglyoximato)-platinum(II), was performed by comparing the Raman band under the shear stress with one under hydrostatic pressure. It was noted that the shear stress with the sapphire anvil cell was applied more strongly at the outer part on the culet than at the center part.
Keywords: Infrared and Raman spectroscopy; Optical absorption and emission spectroscopy; Organic conductors based on radical cation and/or anion salt; Amorphous thin films;

Is the resistance upturn around 50 K related to the Fermi surface area in τ-(EDO-R, R-DMEDT-TTF)2(AuBr2)1+y? by T. Nakanishi; L. Li; H. Yoshino; S. Yasuzuka; D. Graf; E.S. Choi; J.S. Brooks; G.C. Papavassiliou; K. Murata (425-428).
From our previous observation, it is known that τ-(EDO-R,R-DMEDT-TTF)2(AuBr2)1+y (y  ≤ 0.875) exhibits strong sample dependence in the temperature dependence of its resistance R(T). Some samples are metallic down to 4.2 K, while others show upturn below around 50 K. To investigate the origin of the sample dependence, we performed Shubnikov-de Haas (SdH) effect for four samples. Here two samples show metallic behavior, while other samples exhibit nonmetallic below 50 K. From the observation of the SdH oscillation, we detect two series of two-dimensional (2D) Fermi surfaces (FS's) pockets for all samples. Interestingly, we find slight scatter in the area of FS, but no correlation is found between R(T) and FS area. The origin of the slight difference in the FS areas is discussed in terms of possible difference in the band filling.
Keywords: Transport measurements; conductivity; magnetotransport; Organic conductor based on radical cation and/or anion salts;

Novel TTF vinylogues containing phenyl groups at the vinyl positions by M. Osada; T. Kumagai; M. Sugimoto; J. Nishida; Y. Yamashita (429-432).
Novel TTF vinylogues containing phenyl substituents at the vinyl positions were prepared by using oxidative coupling reactions of the 1,4-dithiafulvenes, where fused-pyrazine rings, 1,3-dithiole-2-thione rings, acenaphtho[1,2-b][1,4]dithiine units and ethylenedioxy groups were introduced at the 1,3-dithiole parts. Mono-phenyl substituted derivatives were also prepared to reduce the steric interactions. The cyclic voltammetry and X-ray structure studies revealed the substituent effects on the redox behavior.
Keywords: Heterocyclic synthesis; Coupling reactions; Electrochemical methods; X-ray emission; diffraction and scattering; Organic conductors based on radical cation and/or anion salts;

Dibenzotetrathiafulvalene with Amino Groups: New Electron-Donor Molecule with Hydrogen-Bonding Functionalities by Yasushi Morita; Eigo Miyazaki; Kozo Fukui; Suguru Maki; Kazuhiro Nakasuji (433-436).
Dibenzotetrathiafulvalene (DBTTF) with two amino groups, DADBTTF, has been designed as a new TTF derivative with intermolecular hydrogen-bonding functionalities and synthesized as a stable solid in air. The first oxidation potential of DADBTTF was negatively shifted by 0.24 V compared with that of DBTTF, suggesting a noticeable change in the electronic structure induced by the substitution effect of the two amino groups. The crystal structure of DADBTTF shows the E-type configuration of this molecule and columnar stacking structure through the π…π interaction with interplanar distance of 3.5 Å.
Keywords: X-ray diffraction; Electrochemical methods; Single-crystal growth; Organic conductors;

Pressure Effect on Fermi Surface in β″-(ET)(TCNQ) by S. Yasuzuka; S. Uji; K. Enomoto; T. Konoike; M. Nishimura; T. Terashima; D. Graf; E.S. Choi; J.S. Brooks; H.M. Yamamoto; R. Kato; K. Yokogawa; Keizo Murata (437-440).
In order to investigate the electronic state, we have performed the resistance measurements of β″-(ET)(TCNQ) under pressures. At ambient pressure, the resistance shows metallic behavior down to 0.5 K with three hump anomalies at T 1(=20 K), T 2(=60 K), and T 3(=250 K). As the sample is pressurized, the anomalies at T 1 and T 3 are strongly suppressed, and only the anomaly at T 2 is observed at 5.1 kbar. The angular-dependent magnetoresistance shows resonance structures under fields in both b*-c and b*-a planes, which arises from one-dimensional Fermi surfaces of the ET and TCNQ bands, respectively. The results are consistent with the band calculation, and also suggest that the Fermi surface is not reconstructed at T 2. The origin of the anomaly at T 2 is still an open question.
Keywords: Transport measurements; Metal-insulator phase transition; Organic conductors based on radical cation and/or anion salts;

Magnetic, thermoelectric, and pressure studies of the magnetic field-induced metal to insulator transition in tau-phase organic conductors by J.S. Brooks; D. Graf; Y. Oshima; E.S. Choi; K. Murata; T. Konoike; G. Papavassiliou (441-444).
We have investigated the magnetic field induced metal-insulator transition (FIMI) in τ-phase organic conductors, which occurs in fields above 35 T, and below 12 K. We report magnetization, thermoelectric, and pressure dependent transport measurements. Our results show that the transition is a bulk thermodynamic process where a magnetic field-dependent gap opens upon entry into the insulating state. The FIMI is rapidly suppressed with pressure. Preliminary ESR measurements at low fields suggest the presence of magnetic order below 12 K.
Keywords: Organic conductors based on radical cation and/or anion salts; Magnetic field induced transitions; Metal-insulator transitions;

Pressure-induced low resistive and insulating phases in τ-(EDO-R, R-DMEDT-TTF)2(AuI2)1+y by Lin Li; H. Yoshino; T. Nakanishi; G.C. Papavassiliou; G.A. Mousdis; T. Sakaki; Keizo Murata (445-448).
A sudden drop of resistance below 7 K was observed in the two-dimensional organic τ-conductor, τ-(EDO-R, R-DMEDT-TTF)2(AuI2)1+y. However, this low resistive state was not associated with superconductivity, since the resistance becomes lower by increasing field. The temperature of the resistance anomaly increased by increasing pressure. Further, the low resistive state turns into high resistive one beyond 1.6 GPa. These behaviors have been observed neither in τ-conductors nor in other organic conductors. Although the electronic properties look quite different from other τ-conductors, Fermi surface areas are only 20% different from the isostructural τ-conductors, i.e. τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y or τ-(P-S,S-DMEDT-TTF)2(AuBr2)1+y. Why so much variety of electronic properties are found in each salt in spite of having similar Fermi surface areas, is an attractive problem but unanswered.
Keywords: Transport measurements; Magnetotransport.; Metal-insulator phase transition; Other phase transitions; Organic conductors based on radical cation and/or anion salts;

Persistent photo-excited conducting states in functionalized pentacene by T. Tokumoto; J.S. Brooks; D. Graf; E.S. Choi; N. Biskup; D.L. Eaton; J.E. Anthony; S.A. Odom (449-452).
We report a study of long-lived photo-excited states in single crystals of functionalized forms of pentacene: 6,13-bis (triisopropylsilylethynyl) pentacene, 6,13-bis (triethylsilylethynyl) pentacene, and 6,13-bis (triethylgermylethynyl) pentacene, organic semiconductors with band gaps ≈1 eV. The relaxation rates are thermally activated, as determined from time and temperature-dependent measurements of the photo-conductivity after illumination. These states can be produced in a stable population at temperatures below 150 K. Hence, after low temperature illumination, thermally stimulated current (TSC) is observed as temperature increases. Trap energies associated with these states can be estimated by analysis of the TSC signal.
Keywords: Photoconductivity; Organic semiconductors based on conjugated molecules;

ESR measurements were carried out for α-(BEDT-TTF)2PF6 and ζ-(BEDT-TTF)2PF6(THF). The temperature dependences of the spin susceptibility of the two salts are very similar to each other and seem to behave as typical paramagnetic insulators with low-dimensional antiferromagnetic interaction. The absolute values of the macroscopic antiferromagnetic interaction, J/k B, are also very close. However, there are obvious differences in their ground states and microscopic behaviors. ζ-(BEDT-TTF)2PF6(THF) undergoes an antiferromagnetic transition at around 5 K., while α-(BEDT-TTF)2PF6 shows no long-range magnetic ordering down to 2 K. The temperature dependent behaviors of the ESR linewidth, ΔH PP, are quite different: The ΔH PP of ζ-(BEDT-TTF)2PF6(THF) is almost temperature independent in the paramagnetic region and shows an abrupt increase below about 30 K, while the ΔH PP of ζ-(BEDT-TTF)2PF6 gradually decreases as the temperature decreases. The low temperature electronic states of these salts are discussed from the microscopic point of view.
Keywords: (Electron spin resonance. Magnetic phase transitions; Organic conductors based on radical cation and/or anion salts);

Iron mixed-valence complex (n-C3H7)4N-[FeIIFeIII(dto)3] (dto = C2O2S2) shows a new-type of phase transition coupled with spin and charge around 120 K, where the charge transfer between the FeII and FIII sites occurs reversibly, and shows the ferromagnetic transition at 7 K. The charge transfer phase transition at 120 K can be explained by the crossover of free energy between the higher temperature phase with FeII (S  = 2) and FeIII (S  = 1/2) and the lower temperature phase with FeII (S  = 0) and FeIII (S  = 5/2). Recently, we have succeeded in preparing an (n-C3H7)4N[FeIIFeIII(dto)3] analogue, (n-C3H7)4N[FeIIFeIII(tto)3] (tto = C2OS3). From the magnetic susceptibility measurement, (n-C3H7)4N[FeIIFeIII(tto)3] shows the ferromagnetic phase transition at 9.5 K, There is a hysteresis behavior in the wide range of temperature, whose upper limit cannot be observed obviously below 340 K. This result suggests that the bistability between the higher and the lower temperature phases in dit complex is realized for tto complex at room temperature region. Judging from ESR and 57Fe Mössbauer spectra on heating process, the spin states are consistent with the lower temperature phase with FeII (S  = 0) and FeIII (S  = 5/2) between 2 K and 340 K.
Keywords: Magnetic measurements; Magnetic phase transition; Mössbauer spectroscopy; Electron spin resonance;

Intercalation of an organic photochromic molecule into the magnetic system provides multifunctionalities such as photomagnetism. In order to build up a photosensitive multifunctional-material, we have synthesized an organic-inorganic hybrid system consisting of layered-perovskite-type copper halides and photochromic diarylethenes. By mixing the stoichiometric amounts of CuCl2 and 2,2′-dimethyl-3,3′-(perfluorocyclopentene-1,2′-diyl)bis-(benzo-[b]thiophene-6-ammonium)(1) in aqueous hydrochloric acid and methanol solution, we obtained (1)CuCl4. In the dark synthetic condition, the resulting compound with open-form 1a has an intralayer ferromagnetic interaction whose exchange coupling constant is estimated at J/k B  = 10.7 K. Additionally, this compound shows antiferromagnetic transition at T N  = 3 K because of the antiferromagnetic interaction between adjacent sheets. In UV irradiated synthetic condition, the resulting compound with close-form 1b has a weaker intralayer ferromagnetic interaction (J/k B  = 6.9 K) and shows no magnetic phase transition above 2 K. By the photo-irradiation, we can control the antiferromagnetic transition and the intralayer magnetic interaction.
Keywords: Magnetic measurements; Magnetic phase transition;

Towards a novel magnetoresistance (MR) device with a carbon nanotube, we propose “nonmagnetic metal/zigzag nanotube encapsulating magnetic atoms/nonmagnetic metal” junctions. We theoretically investigate how spin-polarized edges of the nanotube and the encapsulated magnetic atoms influence on transport. When the on-site Coulomb energy divided by the magnitude of transfer integral, U/|t|, is larger than 0.8, large MR effect due to the direction of spins of magnetic atoms, which has the magnitude of the MR ratio of about 100%, appears reflecting such spin-polarized edges.
Keywords: Greens function method; Magnetotransport;

Optical and electronic control of spin-alignment in molecular magnets by Ping Huai; Yukihiro Shimoi; Shuji Abe (469-472).
We theoretically demonstrate that spin alignment in π-conjugated radical molecules can be controlled by photoexcitation and charge doping, accompanying transition from low-spin to high-spin states. To clarify the mechanism of such controllable spin alignment, we designed a model Hamiltonian, in which π electrons in fused carbon-ring systems are coupled, through exchange interactions, with two localized spins on stable radicals. The Hamiltonian is exactly solved in excited states as well as doped states, including all the correlation effects. In the lowest π-exited state of an anthracene-based molecular magnet, spin triplet in the π-electron system aligns the localized spins in parallel, giving rise to a high-spin state. Such meta-stable state would be reached through relaxation processes following photoexcitation. Furthermore, we study the doping-controlled spin-alignment in a thianthrene-based molecular magnet. Hole-doping induces ferromagnetic correlation between the localized spins, resulting in a high-spin state. Spin alignment around heteroatoms in thianthrene can be understood based on the superexchange mechanism. Our results are consistent with the recent experimental demonstration of spin-alignment control by photoexcitation and electronic doping, and provide useful insights into molecular design of controllable organic magnets.
Keywords: Many-body and quasiparticle theories; Magnetic phase transitions; Organic semiconductors based on conjugated molecules (not polymers) (anthracenes, perylenes; etc.);

In order to investigate the possibility of a redox-switchable intramolecular magnetic interaction converting system, the electronic structures of the model compounds of 1,2-bis[x-(N-tert-butylaminoxyl)phenyl]-1,2-bis[4-{N,N-bis(4-methoxyphenyl)amino}phenyl] ethylene (x = 4, p,p′-1; x = 3, m,m′-1) were examined theoretically with the hybrid DFT method. It was found that these molecular systems can operate as a redox switch and change their electronic structures depending on the substituted position of nitroxide radicals.
Keywords: Density functional calculations;

Transport properties of organic spin-gapped antiferromagnets by Tôru Sakai; Shoji Yamamoto (477-480).
Transport properties of one-dimensional quantum systems have been attracing considerable interest in recent years. Heat transport can directly be observed through thermal conductivity measurements, while spin transport can be deduced from nuclear spin-lattice relaxation-time measurements. Numerous experiments have indeed been performed in an attempt to settle the argument about whether finite-temperature energy transport should be diffusive or could be ballistic. From the theoretical point of view, there is an argument that integrable Hamiltonians may exhibit ballistic transport, whereas nonintegrable ones are generally diffusive, at finite temperatures.In order to reveal the transport properties of spin-gapped antiferromagnets, which are generally described by nonintegrable Hamiltonians and thus almost unexplored theoretically, we take an interest in organic Haldane-gap antiferromagnets such as Cu(C14H24N4)CuCl4, and (CH3)2CHNH3CuCl3, both of which consist of ferromagnetic and antiferromagnetic bond-alternating spin-1/2 chains. We calculate their level statistics by means of exact numerical diagonalization and finite size scaling. We argue the possibility of diffusive spin transport occurring and propose model experiments on these materials.
Keywords: Computer simulations; Non-equilibrium thermodynamics and statistical mechanics; Nuclear magnetic resonance spectroscopy; Transport measurements; Metal-insulator phase transitions; Magnetic phase transitions;

Brief encounter at the molecular level: what muons tell us about molecule-based magnets by Stephen J. Blundell; Tom Lancaster; Michael L. Brooks; Francis L. Pratt; Eugenio Coronado; Joése R. Galán-Mascarós; Jamie L. Manson; Cyril Cadiou; Richard E. Winpenny (481-484).
Spin-polarized muons can be implanted in various molecular magnetic materials in order to measure static and dynamic magnetic field distributions at a local level. The positively-charged muon is an unstable, radioactive particle which has spin–1/2, a lifetime of 2.2 μS, about one-ninth of the proton mass and a magnetic moment of approximately 1/200 μB. Both pulsed and continuous beams of muons can be produced with almost 100% spin polarization and significant intensity at various accelerator facilities. The subsequent decay of the muon into a positron allows the extraction of the muon-spin autocorrelation function which can be related to the magnetic field distribution inside a sample. This experimental technique has found particular application to the problem of hydrogen in semiconductors, as well as the study of the vortex lattice in both high-temperature and organic superconductors. Nevertheless, it has been most widely employed in the field of magnetism. We describe how our experiments using spin-polarized muons have been used to provide information about organic ferromagnets, molecular magnets, spin-chains and single molecule magnets.
Keywords: Magnetic measurements; Magnetic phase transitions; Molecular magnets;

Synthesis and Magnetic Characterization of TTM-TTF intercalated into Lamellar MnPS3 by Xuan Zhang; Xu Su; Huiqiong Zhou; Yang Fu; Xingguo Chen; Chuluo Yang; Jingui Qin; Makoto Inokuchi; Minoru Kinoshita (485-488).
A new intercalation compound of TTM-TTF (tetrathiomethyl tetrathiafulvalene) into MnPS3 was obtained by treating the pre-intercalate Mn0.83PS3(bipy)0.51 with (TTM-TTF)Ix in acetonitrile. The new intercalate was characterized by X-ray powder diffraction, IR and element analysis. Its magnetic property was studied with SQUID. Three magnetic transitions occur in the range between 40 K and 5 K. The first magnetic transition at 40 K indicates a weak ferrimagnetic transition, but in the range of 30 K to 5 K, the antiferromagnetism plays the main role in it. The third magnetic transition at 5 K indicates that the intercalate exhibits bulk spontaneous magnetization below 5 K.
Keywords: Organic/inorganic interfaces; Magnetic measurement; Magnetic phase transition;

Intercalation of stilbazolium chromophores into layered MnPS3: synthesis, characterization and magnetic properties by Chuluo Yang; Xuan Zhang; Xingguo Chen; Jingui Qin; Kyuya Yakushi; Yasuhiro Nakazawa; Kenji Ichimura (489-492).
Two new intercalation compounds of stilbazolium chromophores into MnPS3 have been synthesized, and characterized by X-ray powder diffraction, IR and element analysis. The lattice spacing of the intercalates have expanded by 5.47–8.63 Å with respect to the pristine MnPS3. The magnetic property of one intercalate has been studied with SQUID. The result indicates that it shows bulk spontaneous magnetization below 40 K.
Keywords: Organic/inorganic interfaces; Magnetic measurement; Magnetic phase transition;

Dynamics of polaron in polymers by C.Q. Wu (493-496).
In a polymer chain, an extra electron or hole will distort the chain to form a charged polaron. Under the influence of an applied electric field, the polaron will be accelerated for a short time and then move at a constant velocity while it will be dissociated for the field being stronger than a threshold. Within a dynamical non-adiabatic evolution method, we simulate the motion of polaron under the influence of the electric field which is present for different periods. (1) We find the lattice oscillation behind the polaron is a moving multi-breather excitation, which bears the incresed energy due to the electric field acting on the polaron, so that the polaron can move at a constant speed even in the presence of an electric field. (2) We present a full picture for the polaron scattering from an impurity, which may trap or repulse the charged polaron.
Keywords: Electron-solid interactions; Elastic and inelastic scattering; Polyacetylene and its derivatives; Switches; Other opto-electronic devices;

Conductivity measurements of PEDOT nanowires on nanoelectrodes by S. Samitsu; T. Iida; M. Fujimori; S. Heike; T. Hashizume; T. Shimomura; K. Ito (497-500).
We have prepared very thin, conducting polymer nanowires of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) with diameters under 5 nm on a thermally grown SiO2/Si substrate by a molecular combing method. We have measured the conductivity of the nanowires using nanoelectrodes. Ohmic behavior of the PEDOT nanowires was obtained when applied voltages were smaller than 100 mV. The conductance of the nanowires decreased with decreasing temperature and the temperature dependence of the conductance was explained by the quasi one-dimensional variable range hopping (VRH) model. After all the nanowires placed on the gap of the nanoelectrodes were cut, the current was drastically decreased, down to the background level. We have thus provided direct evidence that the PEDOT nanowires were responsible for conduction between the nanoelectrodes.
Keywords: Nanowire; Nanofibers; PEDOT/PSS; Molecular combing; Nanoelectrode; Single molecular conductivity;