Synthetic Metals (v.159, #21-22)

Preferential location of prilocaine and etidocaine in phospholipid bilayers: A molecular dynamics study by Mónica Pickholz; Leonardo Fernandes Fraceto; Eneida de Paula (2157-2158).
In this work, we report a 20-ns constant pressure molecular dynamics simulation of the uncharged form of two amino–amide local anesthetics (LA), etidocaine and prilocaine, present at 1:3 LA:lipid, molar ratio inside the membrane, in the hydrated liquid crystal bilayer phase of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC). Both LAs induced lateral expansion and a concomitant contraction in the bilayer thickness. A decrease in the acyl chain segment order parameter, −S CD, compared to neat bilayers, was also observed. Besides, both LA molecules got preferentially located in the hydrophobic acyl chains region, with a maximum probability at ∼12 and ∼10 Å from the center of the bilayer for prilocaine and etidocaine, respectively.
Keywords: Molecular dynamics; Local anesthetics, Lipid membrane; Order parameter;

Nitric oxide sensing by cytochrome c bonded to a conducting polymer modified glassy carbon electrode by Suélen H. Takahashi; Susana I. Córdoba de Torresi (2159-2161).
A nitric oxide biosensor based on cytochrome c (an heme protein) covalently immobilized to poly(5-amino-1-naphthol) by using cyanuric chloride as a bridge was developed. The immobilization was studied by cyclic voltammetry and quartz crystal microbalance. The nitric oxide detection as a function of poly(5-amino-1-naphthol) amount was recorded, and the best result was obtained with the electrode prepared by 70 cycles. The sensitivity and detection limit were 0.015 μA cm−2/μmol L−1 and 2.85 μmol L−1, respectively.
Keywords: Cytochrome c; Poly(5-amino-1-naphthol); Nitric oxide detection;

Electrochemical biosensor for serum glycoproteins (SG) from patients infected by dengue fever (DF) based on gold nanoparticles (AuNp) and polyvinyl butyral (PVB) adsorbed on gold electrodes has been investigated. Electrochemical impedance spectroscopy (EIS), in the frequency range from 100 mHz to 100 kHz, was performed on these electrodes, in phosphate buffer (PBS) solution containing 10 mM K3[Fe(CN)6]/K4[Fe(CN)6] (1:1) as a redox probe. The electrodes modified with AuNp–Con A–PVB–BSA–SG showed larger electron transfer resistances than those modified with AuNp–Con A–PVB–BSA. The impedance spectra showed an increase in the charge transfer resistance when Con A interacted with SG. Moreover, the charge transfer resistance obtained with DF was larger than that obtained with negative serum. The resulting biosensor is capable to recognize SG from patients infected by DF.
Keywords: Concanavalin A; Dengue viruses; Glycoproteins; Gold nanoparticles; Impedance spectroscopy; Voltammetry;

Cytotoxicity analysis of vertically aligned multi-walled carbon nanotubes by colorimetric assays by A.O. Lobo; M.A.F. Corat; E.F. Antunes; M.B.S. Palma; C. Pacheco-Soares; E.J. Corat (2165-2166).
A new methodology to evaluate the acute cytotoxicity of vertically aligned multi-walled carbon nanotube (VACNT) scaffolds was presented. A comparison between three different colorimetric assays was performed: (i) lactate dehydrogenase, (ii) 2-(4,5-dimethyl-2-thiazolyl)-3,5-diphenyl-2H-tetrazolium bromide, and (iii) neutral red. The results confirmed that a simple removing of VACNT scaffolds from the cell culture before the colorimetric assays, is necessary to obtain a high level of cell viability.
Keywords: MTT; LDH; Neutral red; Carbon nanotube; Colorimetric assays;

Diamond-like carbon films produced from high deposition rates exhibit antibacterial activity by F.R. Marciano; L.F. Bonetti; N.S. Da-Silva; E.J. Corat; V.J. Trava-Airoldi (2167-2169).
The bactericidal activity of diamond-like carbon (DLC) films produced with high deposition rates was measured against Escherichia coli ATCC 25922 (E. coli). Also, the DLC structural quality, hardness and total compressive stress were evaluated by using Raman scattering spectroscopy, nanoindentation and perfilometry. Our results show DLC films produced with good quality, low internal compressive stress and high hardness even with high deposition rates. Antibacterial tests show DLC films kill about 30% of E. coli, which means it is possible to use super-hard DLC films as an antibacterial device produced in a large scale.
Keywords: Diamond-like carbon; High deposition rates; Bactericidal activity;

Highly thermal conductive metal/carbon composites by pulsed electric current sintering by Toshiyuki Ueno; Takashi Yoshioka; Jin-ichi Ogawa; Nobuaki Ozoe; Kiminori Sato; Katsumi Yoshino (2170-2172).
Various composites with metals such as aluminum and copper, and carbons such as pitch based carbon fiber and carbon nanotube, and scale-like graphite have been prepared to realize high thermal conductive materials utilizing pulsed electric current sintering method. The composites have high thermal conductivity and one- or two-dimensional low thermal expansion coefficient.
Keywords: Composite; Thermal conductivity; Thermal expansion; Aluminum; Copper; Carbon fiber; Carbon nanotube; Graphite; Pulsed electric current sintering;

In this paper, we present the anti-Stokes Raman scattering as a technique allowing investigations of materials at a nanoscale level. When the energy of the excitation light coincides with the energy of an electronic transition, a strong anti-Stokes Raman spectrum with respect to the prediction of the Maxwell–Boltzman (MB) law is regularly observed. Under a tight-focusing of the excitation light, the anti-Stokes Raman emission is reminiscent of Coherent anti-Stokes Raman Scattering (CARS). It has been detected on carbon nanotubes (CNTs), prototypes of nanometric materials, as well as on other compounds such as copper phthalocyanine (CuPc), poly(bithiophene) (PBTh), poly(3,4-ethylene dioxythiophene) (PEDOT), polyparaphenylene vinylene (PPV) layered as thin films on a metallic support in which are generated surface plasmons. We demonstrate that nanostructures by themselves can be of importance by generating non-linear phenomena that can be exploited for studying such materials and in particular carbon nanotubes.
Keywords: Optical techniques; Raman scattering; SERS; Carbon nanotubes; Non-linear phenomena;

Macroscopic-scale carbon nanotube alignment via self-assembly in lyotropic liquid crystals by Stefan Schymura; Eva Enz; Siegmar Roth; Giusy Scalia; Jan P.F. Lagerwall (2177-2179).
By dispersing carbon nanotubes (CNTs) in a lyotropic liquid crystalline matrix, uniaxial alignment of the nanotubes can easily be achieved over macroscopic areas. We briefly describe the principles behind the technique and then show that it can be applied to multiwall as well as single-wall nanotubes and that a variety of different dispersing materials can be used, from industrial surfactants to DNA. We also present a new microfluidics-based method for transferring the liquid crystal-dispersed CNTs to a substrate, maintaining a fair control of tube direction.
Keywords: Carbon nanotubes; Lyotropic liquid crystal; Alignment;

Optical properties of polyfluorene–thiophene copolymers having chiral side chains by T. Hirahara; M. Yoshizawa-Fujita; Y. Takeoka; M. Rikukawa (2180-2183).
A series of alternating copolymers consisting of chiral thiophene and fluorene, poly[9,9-dihexylfluorene-alt-(3-{2-[(S)-(+)-1-methyloctyloxy]ethyl}thiophene)] (P1), and poly[9,9-dihexylfluorene-alt-(3-{2-[(S)-(+)-1-methyloctyloxy]ethyl}-2,2′-bithiophene)] (P2), were synthesized by Suzuki coupling method. P1 and P2 were characterized by 1H NMR spectra and elemental analyses. Both of the copolymers showed clear solvatochromism and circular dichroism in methanol/chloroform mixed solutions. These two polymers had different spacer lengths between the chiral side chains along the main chain, and accordingly the circular dichroism spectra were apparently different.
Keywords: Polythiophene; Polyfluorene; Circular dichroism;

Synthesis and optical properties of poly(thiophene-fluorene) copolymers with benzothiazole moiety by K. Esashika; M. Yoshizawa-Fujita; Y. Takeoka; M. Rikukawa (2184-2187).
Poly[9,9-dihexylfluorene-co-(benzothiazol-2-yl)thiophene-co-9,9′-spirobifluorene] (PF x B y S z ) were synthesized by palladium-catalyzed Suzuki coupling reaction. PF x B y S z were characterized by FT-IR, elemental analysis, and 1H NMR. All the copolymers showed decomposition temperatures above 400 °C and glass transition points above 180 °C, suggesting that these materials had excellent thermal stability. As the benzothiazolylthiophene content in copolymers was increased, the band gaps of copolymers decreased. All the copolymers exhibited fluorescence peaks in the visible region, and the energy transfer from fluorene to benzothiazolylthiophene units were observed.
Keywords: Polythiophene; Coupling reaction; Electroluminescence; Benzothiazole; Thermal stability;

DC conductivity study of polyaniline and poly(acrylonitrile-butadiene-styrene) blends by Fernando H. Cristovan; Fernando R. de Paula; Sherlan G. Lemos; Adilson J.A. De Oliveira; Ernesto C. Pereira (2188-2190).
In this study, conducting blends of poly(acrylonitrile-butadiene-styrene) and polyaniline doped with dodecylbenzene sulfonic acid were prepared by solution blending. In order to understand the electrical conduction mechanism of the samples, DC electrical conductivity measurements of the blends were carried out in the temperature range of 80–320 K. The experimental results fit well with Mott's model of three-dimensional variable range hopping conduction. The values of Mott's temperature, density of states at the Fermi energy, average hopping distance and barrier height for the composites were calculated and presented.
Keywords: Conducting polymers; Polyaniline; Poly(acrylonitrile-butadiene-styrene); Variable range hopping;

Pyridine-2,6-dicarboxylic acid reacts as the first ligand (L1) under hydrothermal conditions with different metal ions such as CoII, NiII, and CuII to form two 1D polymeric complexes [M(L1)(L2)2·H2O] n (M = Co2+ or Ni2+) and a tetranuclear cluster with formula [Cu4(L2)4(L1)4]·2H2O in the presence of 5-(4-bromophenyl)-2,4′-bipyridine as the second ligand (L2). Intramolecular interactions were observed in the three compounds, being antiferromagnetic in both cobalt and nickel 1D coordination polymers and ferromagnetic interaction in the tetranuclear copper cluster.
Keywords: Crystal structure; Tetranuclear cluster; 1D chain; Magnetic property;

Ab initio MO–CI based quantum master equation approach: Exciton dynamics of weakly and strongly coupled J-type aggregates by Ryohei Kishi; Masayoshi Nakano; Takuya Minami; Hitoshi Fukui; Hiroshi Nagai; Kyohei Yoneda; Hideaki Takahashi (2194-2197).
In order to investigate the time evolutions of electron and hole distributions in weakly and strongly coupled H2 dimer models, we employ a novel dynamic exciton expression derived from the exciton density matrices calculated by the quantum master equation combined with the ab initio molecular orbital (MO)–configuration interaction (CI) method. The oscillation of exciton distribution over the monomers is observed in case of small inter-monomer distance, where the coupled dipole approximation is invalid. The result originates in the covalent character of inter-monomer interaction in the first excited state, i.e., delocalized character of LUMO distribution.
Keywords: Exciton; Polarization; Ab initio MO method; Quantum master equation;

Preparation of helical carbon and graphite films using morphology-retaining carbonization by Satoshi Matsushita; Mutsumasa Kyotani; Kazuo Akagi (2198-2201).
Helical carbon and graphite films were prepared from iodine-doped helical polyacetylene (H-PA) film using currently developing morphology-retaining carbonization. It was found from scanning electron microscopy (SEM) observations that the hierarchical helical morphology of the H-PA film remains unchanged even after the carbonization at 800 °C. Besides, the weight loss of the film due to the carbonization was very small, which was only a few percent to the weight of the film before doping. Furthermore, the graphite film prepared by the subsequent heating at 2600 °C still retained the same morphology as those in the original H-PA film and in the helical carbon film prepared at 800 °C. X-ray diffraction (XRD) and Raman scattering measurements were then pursued. The results showed that graphitic crystallization proceeds in the carbon film through the heat treatment at 2600 °C. Transmission electron microscopy (TEM) image of a single helical graphitic fibril was also observed by ultrasonicating the graphite film in ethanol. Carbonization of the H-PA films by way of iodine doping was found to afford helical carbon and graphite films, where spiral morphologies and even helical fibril structures were completely preserved.
Keywords: Chiral nematic liquid crystal; Helical polyacetylene; Iodine doping; Morphology-retaining carbonization;

New derivatives of phenylamine as novel building blocks of conducting polymers by Mieczyslaw Lapkowski; Sylwia Golba; Jadwiga Soloducho; Krzysztof Idzik (2202-2204).
A novel phenylamine substituted derivatives possessing different photochromic groups were investigated. Using the electrochemical and spectroelectrochemical measurements the electrochemical activity of the monomers and polymers have been studied. The results indicate good film forming properties most of the monomers and stability of the forming films. The polymeric films include diphenylamine or triphenylamine unit and five member heterocycle ring moieties.
Keywords: Electrochemical doping; Diphenylamine and triphenylamine derivatives; Electroconductivity; Electrochemical polymerisation;

Ferroelectricity in synthetic metals: Reality and hypotheses by Serguei Brazovskii; Natasha Kirova (2205-2207).
Ferroelectricity is one of the demanded effects in fundamental and applied solid state physics. Till now, the ferroelectrics were available mostly in the inorganic world. The breakthrough of 2000s was an unexpected discovery of the ferroelectricity related to the charge ordering in quasi-1D organic conductors (TMTTF)2X, and in some layered compounds. The achieved understanding of underlying mechanisms allows to speculate on synthesis of a would-be ferroelectric polymer: it must possess a combination of dimerizations of sites and bonds, one of which must be build-in and another spontaneous. The theory of these “combined Peierls states” predicts an existence of solitons (dimerization kinks) with non-integer variable charges—they are the walls separating domains with opposite electric polarization. The physics of these exotic solitons will serve to describe transient processes in ferroelectric polymers, linking optical- and low-frequency properties. The promising example of such an (AB) x conjugated polymer has already appeared but was not yet tested for ferroelectricity. A wide chemical search is necessary because of a problematic competition of an anti-ferroelectric phase, whose occurrence depends on complicated details of the interchain coupling.
Keywords: Ferroelectricity; Conjugated polymer; Charge ordering; Spontaneous dimerization; Soliton;

A statistical model of a resistor network is proposed to describe the electrical properties, real and imaginary components of ac conductivity, of natural rubber (NR) and poly(o-methoxyaniline) (POMA) blend. It takes into account the polydispersivity of the material as well as intrachain and interchain charge transport processes in the POMA phase and the interfacial processes between conducting islands and the insulating matrix. The model calculates the alternated conductivity of these structures by transfer matrix technique. The conductance between two neighboring sites of the natural rubber was determined by Dyre's Equation. The conductance between sites of the conductive polymer, using the resonance quantum-tunnelling model, is obtained by the equation generalized of Breit–Wigner. The interface conductance between both polymers was determined by means of the combination of these two equations assuming the resistances of them are linked in series. The model reproduced the measured conductivity in NR/POMA films in a large range of frequencies.
Keywords: Statistical model; Resistor network; Alternating conductivity; Resonance quantum tunnelling; Natural rubber;

Highly fluorescent oligomers with donor and acceptor groups: DFT calculations and experiments by Yukihiro Shimoi; Yoshihiro Yamaguchi; Zen-ichi Yoshida (2211-2214).
We investigate π -conjugated oligomers with donor and acceptor groups using the DFT method and compare the theoretical excited states with the observed photophysical properties. The oligophenylene ethynylenes substituted by methoxy and cyano groups in a block manner exhibit high fluorescence at longer wavelength region (Y. Yamaguchi, et al., J. Phys. Chem. A 112 (2008) 5074 [5]). We demonstrate that the S1 state of these highly fluorescent molecules has the character of intramolecular charge transfer and discuss the relevance of this character to the photophysical properties like bathochromic effects. We also examine substitution effects on the ring torsion around the triple bond.

A nanocomposite of poly(3-hexadecylthiophene) (PHDT) with montmorillonite (MMT) was prepared by in situ polymerization (PHDT/MMT) and nanocomposites of PHDT with organomontmorillonite clay (OrgMMT) were prepared by both in situ polymerization (PHDT/OrgMMT) and by the solvent casting method (PHDT/OrgMMT-sc). The nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). PHDT/OrgMMT was also characterized by transmission electron microscopy (TEM). FTIR spectra indicate the presence of the clay in the polymer matrices and show variations on the frequency of the Si–O–Si stretching vibration. The XRD diffractograms indicate that PHDT/MMT and PHDT/OrgMMT-sc are intercalated nanocomposites, while PHDT/OrgMMT is mostly exfoliated, but present also some intercalation, as confirmed by TEM.
Keywords: Poly(3-alkylthiophene); Montmorillonite clay; Polymer nanocomposite; Layered silicate nanocomposite; Montmorillonite nanocomposite;

The effect of lattice dynamics on electron localization in poly-(para-phenylenevinylene) by Mathieu Linares; Magnus Hultell; Sven Stafström (2219-2221).
The lattice dynamics in poly-(para-phenylenevinylene) and its effect on the electron localization properties have been investigated. The simulations were performed using a hybrid quantum mechanical/molecular dynamics approach including the Pariser–Parr–Pople Hamiltonian. It is found that the dynamic disorder that exists at room temperature induces electron localization. The most important lattice modes in the context of localization are the torsional modes of the phenylene rings, that are shown to couple strongly to the electronic system. Since these modes occur at low frequencies, they will also have a strong impact on intra-chain charge transport.
Keywords: Electron localization; Molecular dynamics; Torsional modes;

Effects of torsional disorder on poly-para-phenylene by L.M.M. Jorge; M.J. Caldas (2222-2224).
We study the effect of thermal disorder on the electronic structure of one-dimensional poly-para-phenylene (PPP). In a real chain the torsion angles between rings are bound to be distributed over a range of values, which depend on temperature, and thus the chain is intrinsically disordered. In this study we simulated this kind of thermally induced off-diagonal disorder through the simple Hückel method. We base our Hamiltonian on ab initio results for the effect of temperature on torsion angles, and the effect of torsion angles on the energy gap. We analyze the electronic structure of 200-monomer-long chains focusing on the density of states, and the associated localization character (measured by the inverse participation ratio). Our results contrast with the usually assumed Gaussian-shaped density of localized states for disordered systems.
Keywords: Poly-para-phenylene; Disorder; Anderson localization;

We have investigated effect of solvent on poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) nanometer-scaled thin films by means of a scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) in terms of thickness and PEDOT:PSS ratio of the films. As a result, the PEDOT:PSS ratio, surface roughness, number of highly conductive grain, and thickness of the PEDOT/PSS thin film coincidently increased with the addition of ethylene glycol (EG). It suggests that primary nanoparticles decrease in size but aggregate by removing excess PSS after the addition of the EG.
Keywords: PEDOT/PSS; Colloidal dispersion; Thin film; XPS; STEM/TEM; AFM;

Micrometer-scaled OFET channel patterns fabricated by using PEDOT/PSS microfibers by Hu Yan; Tsubasa Kagata; Hidenori Okuzaki (2229-2232).
We have easily fabricated channel patterns of organic field-effect transistors (OFETs), in which channel lengths were 5 μm, by using wet-spun poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) microfibers with diameters of ca. 5 μm. Pentacene-based FETs with a top-contacted configuration, showed a hole mobility of 0.13 cm2  V−1  s−1 and on/off current ratio of 9.4 × 104. The device also showed large current of ca. 160 μA (V D  = −50 V; V G  = −50 V), reflecting shorter channel length of the devices. We have evaluated self-assembled monolayer (SAM) through measurements of water contact angle and by Zisman plot. As a result, critical surface tension of the octadecyltrichlorosilane (OTS)-treated SiO2 surface is 17 mN m−1 which is consistent with that of well-known SAM. We also well analyzed the cross-sections of the device by a scanning transmission electron microscopic (STEM) technique. The results indicated that the thicknesses of the pentacene layer in the channel part and Au layer in the source/drain part were ca. 30 and 30 nm, respectively. Furthermore, it is also indicated that the 100-nm grains of the pentacene were well adhered on the surface of the SAM-formed SiO2 layer.
Keywords: PEDOT/PSS; Microfiber; OFET; Pentacene; SAM; STEM;

Electrically driven PEDOT/PSS actuators by H. Okuzaki; H. Suzuki; T. Ito (2233-2236).
The film made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) was prepared by casting and electrical conductivity, tensile properties, electromechanical response, and moisture sorption isotherm of the PEDOT/PSS film were investigated. A linear expansion of the PEDOT/PSS film occurred with increasing ambient humidity, where the strain of the film in a RH range from 20 to 90%RH was 3.3%. Upon application of an electric field, the film underwent significant contraction in ambient air. The degree of contraction increased as the applied voltage became higher and the value attained 2% at 35 V, which was nearly twice as that of polypyrrole films. The principle lay in the desorption of water vapor due to local Joule heating, where the electric field controlled an equilibrium of water vapor sorption. The moisture sorption isotherm of the PEDOT/PSS film indicated that the interaction between water and PEDOT/PSS was superior to that between water molecules, in which isosteric heat of sorption decreased with an increase in the sorption degree and the value reached to the heat of water condensation.
Keywords: PEDOT/PSS; Actuator; Artificial muscle; Joule heating; Moisture sorption isotherm; Electro-active polymer;

PEDOT:PSS films—Effect of organic solvent additives and annealing on the film conductivity by O.P. Dimitriev; D.A. Grinko; Yu.V. Noskov; N.A. Ogurtsov; A.A. Pud (2237-2239).
We report results on conductivity of PEDOT:PSS films, which contain different amounts of organic solvents, i.e., dimethyl sulphoxide (DMSO) or ethylene glycol (EG), and annealed at different temperatures. The maximum of conductivity of the resulting films was reached at about 5wt.% of DMSO or EG in the solution. At the same time, the presence of the solvent residue in the film also resulted in the poor control of the film morphology and conductivity. It was found that conductivity of a film prepared with the same DMSO content is sensitive to the surface quality of the substrate used. It was also found that annealing substantially reduces conductivity of the films prepared with and without the additives. The higher the temperature of annealing, the smaller film conductivity was observed. Correlation in changes of the electronic absorption of the PEDOT:PSS film in the near-IR and the film conductivity induced by the solvent additive was also found. Exposure of PEDOT:PSS films to the solvent vapors has been employed as an alternative controlled method to increase film conductivity. This method, in combination with quartz microbalance measurements, showed a great capability of the film to absorb DMSO vapors and that a saturation limit for conductivity is reachable after more than 20 h of exposure. Swelling and interconnection of the polymer chains is suggested to be the main factor responsible for the conductivity increase.
Keywords: PEDOT:PSS; Conductivity; Solvent additive; Annealing;

Electrochemically synthesised polymers of long, 2-oxaalkyl chain derivatives of 3,4-ethylenedioxythiophene (EDOT) have been studied using in situ EPR spectroelectrochemistry. Originally developed as promising candidates for preparation of soluble PEDOT derivatives, their polymers themselves reveal interesting spectroelectrochemical properties, in some cases even superior to their family's parent. Our results indicate notable differences in potential dependencies of concentration of spins and ΔB pp width between the two polymers, indicating a major 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. Certain features of their spectroscopic response however, like the hysteresis of potential dependence of concentration of spins and ΔB pp widths, point to similarities of their doping - dedoping mechanism with the one of PEDOT.
Keywords: PEDOT derivatives; Electrochemical doping; Polarons; Bipolarons; Electron paramagnetic resonance; Polythiophenes;

The interaction of semiconducting single wall carbon nanotubes (SWCNT) and the conducting polymer poly(3,4-ethylendioxythiophene/polystyrenesulfonate) (PEDOT/PSS) was studied by Raman spectroscopy and in-situ Raman spectroelectrochemistry. The mixing of SWCNT with PEDOT/PSS caused a partial doping of SWCNT as indicated by the change of the relative intensity of the Raman features of SWCNT. The in situ Raman spectroelectrochemical measurements showed that semiconducting tubes could be doped even if they are embedded in PEDOT/PSS. However, in contrast to the neat SWCNT, the doping of SWCNT in composite is less efficient. For SWCNT in composite it is necessary to apply larger potential (by about 0.4–0.6 V) to achieve the same level of bleaching of Raman bands as in the case of neat SWCNT.
Keywords: PEDOT/PSS; Carbon nanotubes; Nanocomposites; Raman spectroscopy; Spectroelectrochemistry; Doping;

The polyanilines were synthesized via an inverse emulsion polymerization path at 0 °C or room temperature using ammonium peroxydisulfate (APS) as oxidant and dodecylbenzene sulfonic acid (DBSA) as surfactant and dopant simultaneously for the resulting polyanilines. The influence of polymerization temperature, organic continuous phase type (xylene or hexane) and APS/aniline molar ratio on the polyaniline properties was investigated. Polyaniline–DBSA precipitates prepared at 0 °C showed high conductivity in the range of 1.0–4.0 S/cm. Polyanilines in emeraldine base form prepared at 0 °C and APS/aniline molar ratio of 0.4 had high intrinsic viscosities of 191 and 202 ml/g using xylene and hexane as the organic continuous phase of emulsion system, respectively. The polyaniline–DBSA precipitates obtained from the polymerization system using xylene as the organic continuous phase possessed nice fibrillar morphology.
Keywords: Polyaniline; Inverse emulsion polymerization; Intrinsic viscosity; Morphology; Conductivity;

Formation and properties of nano- and micro-structured conducting polymer host–guest composites by A.A. Pud; Yu.V. Noskov; N.A. Ogurtsov; O.P. Dimitriev; Yu.P. Piryatinski; N.M. Osipyonok; P.S. Smertenko; A. Kassiba; K.Yu. Fatyeyeva; G.S. Shapoval (2253-2258).
Process of formation of polyaniline (PANI) at the surface of SiC and CdS nanoparticles or submicron- and micron-sized particles of poly(vinylidene fluoride) (PVDF), polycarbonate and polyamides-11, 12 and properties of the prepared composites are considered. Beginning of the formation of the PANI shell at the particle surface was evaluated. This important result opens the possibility to control properties of the final hybrid composite. In case of CdS nanoparticles PANI was synthesized in the form of nanofibers embedding these nanoparticles. Films of the PANI–polymer composites showed the conductivity of up to ∼0.4 S/cm. The planar heterojunction of the compression molded PVDF/PANI–DBSA film with bulk CdS displayed photovoltaic activity.
Keywords: Aniline; Polymerization; OCP monitoring; Polyaniline; Hybrid nanocomposites; Applications;

Conducting polymer embedded with nanoferrite and titanium dioxide nanoparticles for microwave absorption by S.K. Dhawan; Kuldeep Singh; A.K. Bakhshi; Anil Ohlan (2259-2262).
The present paper deals with the synthesis of conducting ferrimagnetic polyaniline nanocomposite embedded with γ-Fe2O3 (9–12 nm) and titanium dioxide (70–90 nm) nanoparticles via a micro-emulsion polymerization. The microwave absorption properties of nanocomposite in 12.4–18 GHz (Ku-band) frequency range shows shielding effectiveness due to absorption (SEA) value of −45 dB, which is much higher than polyaniline composite with iron oxide and polyaniline–TiO2 composites. The higher EMI shielding is mainly arising due to combined effect of γ-Fe2O3 and TiO2 that leads to more dielectric and magnetic losses which consequently contributed to higher values of shielding effectiveness. XRD analysis of the nanocomposite reveals the incorporation of nanoparticles in the conducting polymer matrix while the thermal gravimetric analysis (TGA) demonstrates that the nanocomposite is stable up to 250 °C.
Keywords: Polyaniline; Nanocomposite; Nanoparticles; Shielding effectiveness;

Effect of pressure on the morphology of polyaniline nanostructures by O.O. Adetunji; N.-R. Chiou; A.J. Epstein (2263-2265).
We present experimental results regarding the effects of applied pressure on the morphology and electrical conductivity of polyaniline/HClO4 nanostructures synthesized via dilute polymerization. By applying a local pressure of 4000 psi (28 MPa) to the nanostructured network, the morphology of the network was transformed to that of a continuous film. The conductivity shows a concomitant increase for the temperature range of 250–300 K. We assign this enhancement of room temperature conductivity to an increase in the effective contact areas between the previously fibrous structures leading to a shorter charge transport path length as the morphology of the film is transformed from a nanostructured network to a continuous film.
Keywords: Polyaniline; Nanostructure; Dilute polymerization; Pressure; Interfiber contacts;

Nanofibres from polyaniline/polyhydroxybutyrate blends by R. Fryczkowski; T. Kowalczyk (2266-2268).
Three-dimensional nanofibres nonwoven webs were obtained from solution of poly(3-hydroxybutyric acid) (PHB) and dodecylbenzene sulfonic acid (DBSA) doped polyaniline in chlorophorm/trifluoroethanol mixture, using electrospinning method. The morphology, electro-active properties and supermolecular structure of nanofibres webs have been analyzed and discussed. Obtained nanofibres are potentially applicable as scaffolds for tissue engineering.
Keywords: Polyaniline; Poly(3-hydroxybutyric acid); Electrospinning; Scaffold;

Electrochemical and morphological characterization of poly(12-pyrrol-1′-yl dodecanoic acid) by Ana Júlia C. da Silva; Fred A.R. Nogueira; Odilon A.S. Araújo; José Ginaldo da Silva Junior; Marcelo Navarro; Josealdo Tonholo; Adriana S. Ribeiro (2269-2272).
12-Pyrrol-1′-yl dodecanoic acid was prepared and electrochemically polymerized on ITO electrodes by three different methods. The electrochemical and morphological properties of poly(12-pyrrol-1′-yl dodecanoic acid) films were investigated by cyclic voltammetry, galvanostatic charge–discharge curves and AFM, which characteristics varied as function of deposition method. Films deposited by potentiodynamic and galvanostatic methods showed capacitive properties and are promising for application in polymeric capacitors.
Keywords: Substituted polypyrrole; Electropolymerization; Atomic force microscopy;

Non-woven fabric of poly(N-isopropylacrylamide) nanofibers fabricated by electrospinning by Hidenori Okuzaki; Keiko Kobayashi; Hu Yan (2273-2276).
We have succeeded in fabricating non-woven fabric of a typical thermo-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM) with a low critical solution temperature (LCST) in water at 32 °C, by the electrospinning, a simple and facile method which enables to form a mat of nanofibers directly deposited on the grounded target. The PNIPAM nanofibers electrospun at concentration and applied voltage of 15 wt% and 20 kV, respectively, had an average diameter of 165 nm. The moisture sorption isotherms of the PNIPAM nanofibers belonged to the type II of IUPAC classification, in which the interaction between polymer and water molecule was stronger than that between water molecules.
Keywords: Electrospinning; Nanofiber; Poly(N-isopropylacrylamide); Non-woven fabric; Moisture sorption isotherm; Isosteric heat of sorption;

Unimolecular electronics and rectifiers by Robert M. Metzger (2277-2281).
Unimolecular or molecular-scale electronics has made huge progress towards unimolecular resistors, switches, rectifiers, negative differential resistance devices, and gain-less single-electron transistors. Twelve unimolecular rectifiers have been found in Tuscaloosa, and many others elsewhere. The challenges are to understand the “metal|molecule” interface and to make reliable unimolecular electronic devices.
Keywords: Rectifiers; Unimolecular electronic devices; Single-molecule electronics; IETS; Monolayers; Langmuir–Blodgett; Langmuir–Schaefer; Self-assembled monolayers; Break junctions; Moore's law; Aviram–Ratner rectifier;

Molecular rectification: Confirmation of its molecular origin by chemical suppression of the electrical asymmetry by Geoffrey J. Ashwell; Abdul Mohib; Christopher J. Collins; Amirreza Aref (2282-2285).
Bis[N-(ω-decyl)-5-(4-dimethylaminonaphthalen-1-yl-methylene)]-5,6,7,8-tetrahydroisoquin-olinium]-disulfide diiodide forms self-assembled monolayers (SAMs) on gold substrates in which the acceptor–(π-bridge)–donor moieties are aligned: Au|Au–S–C10H20–A+–π–D (I). These diode-like molecules exhibit rectification ratios of 30–80 at ±1 V but display symmetrical current–voltage (IV) characteristics when exposed to HCl and rectify again when exposed to NH3. This reversible switching is explained by protonation/deprotonation of the amino group which disrupts/restores the donor–acceptor combination and provides evidence of the molecular origin of the electrical asymmetry.
Keywords: Molecular diode; Molecular rectification; Molecular electronics;

Effects of applied stress and long-term stability on PPy(CF3SO3) linear actuators by Shu Yi Chu; Paul A. Kilmartin; Jadranka Travas-Sejdic (2286-2288).
The actuation performance of PPy(CF3SO3) films, in the free-standing form, has been characterized in aqueous NaPF6 electrolytes during potential step experiments. Actuation strains of up to 7.5% were observed due to anion insertion at more positive potentials. The actuation strain decreased as the applied stress was increased up to 12 MPa, and then remained constant at above 4% up to the maximum applied stress of 28.8 MPa. A relatively large creep was observed in the case of an applied stress of 28.8 MPa. The film could be cycled more than 1500 times with the retention of 18% of the initial strain level.
Keywords: Polypyrrole; Actuator; ECMD; NaPF6;

Molecular relaxations in polyfluorene based cast films by Gregório C. Faria; Rafael F. Cossiello; Teresa D.Z. Atvars; Eduardo R. deAzevedo (2289-2292).
This article reports a study of the thermal relaxation in cast films of two polyfluorene based polymers, poly{9,9-dioctylfluorenyl-2,7-diyl} (BE329) and poly{(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene]} (GE108). The relaxation processes were identified by Dynamical Mechanical Thermal Analysis (DMTA), which revealed three processes in both samples: β process at lower temperatures and two relaxations at higher temperatures (named as α A and α B). The relaxations mechanics were elucidated by Solid-State Nuclear Magnetic Resonance (NMR) methods. The results revealed that the β relaxation is related to molecular motions in the side-groups, while the second and third relaxations can be attributed to local rotations in the backbone and to a glass transition. The molecular relaxations were also identified by the temperature dependence of the fluorescence spectra, which were also associated with their molecular nature.
Keywords: Polyfluorene; Thermal relaxation; Molecular dynamics; Photoluminescence; Nuclear Magnetic Resonance;

Effect of structural modifications in the laser properties of polymer films doped with perylenebisimide derivatives by M.A. Díaz-García; E.M. Calzado; J.M. Villalvilla; P.G. Boj; J.A. Quintana; F.J. Céspedes-Guirao; F. Fernández-Lázaro; Á. Sastre-Santos (2293-2295).
In this work we study the effect of different types of modifications of the chemical structure of perylenebisimide derivatives (PBIs) in the laser properties of PBI-doped polystyrene films at various concentrations. In particular, we focus on controlling the wavelength of emission, in order to tune the laser wavelength, as well as on increasing the amount of PBI in the films, aiming to decrease the laser thresholds, while keeping a good photostability. Amplified spontaneous emission (ASE) was observed for all compounds, the best performance being obtained for films doped with PBIs symmetrically substituted at the imide positions, that emitted at 580 nm with a threshold of 20 kW/cm2 and a photostability half-life of 30,000 pump pulses. Substitution at the bay positions of the PBI core and replacement of imide functions by anhydride groups allow to red-shift the emission wavelength up to 645 nm, but the thresholds increase considerably and the photostability is reduced. PBIs are among the most photostable materials reported in the literature and show very reasonable thresholds. In addition they have a great potential for their application in the field of data communications based on poly(methyl methacrylate) optical fibers, with low-loss transmission windows between 530 and 590 nm and at 650 nm.
Keywords: Perylenebisimides; Amplified spontaneous emission; Solid-state lasers; Photostability;

Initiation of fabrication of neuron-type conducting polymer by Sachiko Matsumoto; Haruo Ihori; Masaharu Fujii (2296-2298).
Conducting polymers has been polymerized on a bottom of the vessel/cell under certain conditions, and the patterns of two-dimensional (2-D) conducting polymer have become fractal. A neuron-like conducting polymer can be fabricated by changing the polymerization conditions under polymerization. The pattern of conducting polymer network depends on the polymerization/environment conditions. The conducting polymer has many functional properties. If conductivity at paths in the network depends on signals that flow the paths, a neuron-like device can be prepared. In this process, it is hard to control the transition of the polymerized points from the surface of the electrode to the vessel. The pattern depends on the time of transition because the concentrations of monomer and electrolyte decrease with time. In some conditions, transition never occurs. In this paper, the initiation conditions of neuron-type conducting polymer have been investigated. It is found that concentrations of oligomer/polymer that did not attach myself to the electrode is the important factor for the transition of polymerized points from on the electrode to on the surface of the vessel.
Keywords: Neuron device; Conducting polymer; Polypyrrole;

New tunable thieno[3,4-b]pyrazine-based materials by Li Wen; Jon P. Nietfeld; Chad M. Amb; Seth C. Rasmussen (2299-2301).
The effect of electron-donating and electron-withdrawing side chains on the electronic properties of thieno[3,4-b]pyrazines and their corresponding homopolymers have been investigated. Contrary to common trends in polythiophene materials, the addition of electron-donating groups results in higher HOMO–LUMO energies in the monomers and higher E g values in the resulting polymers. The use of electron-withdrawing groups, however, provides reduced HOMO–LUMO energies and lower E g values. The application of electron-withdrawing functionalized thieno[3,4-b]pyrazines appears to be a promising new approach for the production of low E g materials.
Keywords: Low band gap conjugated polymers; Poly(thieno[3,4-b]pyrazine)s; Electropolymerization; Functional group effects;

We performed classical molecular dynamics simulations of the vapor-deposition of α -T4 oligomers on the TiO2-anatase (1 0 1) surface, comparing different sets of charges associated with the atoms of the model. The potential energy surfaces for α -T4 and TiO2 were described by re-parametrizations of the Universal force field with charges given by the charge equilibration (QEq) scheme, or with fixed charges obtained by an ab initio method using the Hirshfeld partition. The two sets of charges lead to completely different results for the interface formation, and for the characteristics of the organic film, with a clearly defined α -T4 contact layer in the QEq case, and a more homogeneous molecular distribution when using Hirshfeld charges. The main reason for the discrepancy was found to be the incorrect charge assignment given by QEq to the sulfur and α -carbon atoms in thiophenes, and highlight the relevance of long-range interactions in the organization of molecular films.
Keywords: Thiophene; Conjugated polymers; TiO2; Classical molecular dynamics; Charge equilibration; Hirshfeld partition;

Electroluminescence of phenylene–vinylene random copolymers with different conjugation lengths by Tunísia Eufrausino Schuler; Shu Hui Wang; Roberto Koji Onmori; Gerson Santos; Emerson Roberto Santos; Elvo Calixto Burini; Adnei Melges de Andrade (2306-2308).
PPV random derivates were synthesized and characterized. Polymer light emitting diodes (PLEDs) were assembled using the random copolymers as emissive layer and showed EL in the blue-green region in function of the method of preparation. The increase in the average conjugation degree in the polymer chain led to the reduction of the turn-on voltage of the device. The addition of Alq3 as ETL increased tenfold the luminescence efficiency.
Keywords: PPV; Random copolymer; Conjugation confinement;

Polyphosphate based electrochemical capacitors by E. Skovroinski; R.J. de Oliveira; A.J.G. Zarbin; A. Galembeck (2309-2311).
Environmentally friendly electrochemical capacitors (ECs) were assembled using hybrid materials formed by a polyphosphate gel matrix in which carbon-based materials were inserted and polyaniline were formed in a single-step synthesis. The hybrid materials were deposited on FTO glasses and symmetric ECs were assembled using a cellulose membrane soaked with an aqueous NaH2PO4 solution as a separator. The capacitance values were calculated from impedance spectroscopy and galvanostatic charge/discharge measurements. The devices showed capacitances ranging from 4.0 to 27.0 F cm−3, which are comparable to some commercial devices. Better results were achieved in samples with polyaniline, which were ascribed to the pseudocapacitance impaired to the samples by the conducting polymer.
Keywords: Polyphosphate; Electrochemical capacitors; Polyaniline; Hybrid materials;

The role of the TiO2 layer in hybrid organic–inorganic light-emitting diodes (HOILEDs) was discussed. A TiO2 layer was fabricated using a process that formed an “oxygen-rich” and “porous” TiO2 layer in an HOILED. The importance of the surface state on the TiO2 and the hole injection scheme in the HOILED was confirmed. All the data support the idea that HOILEDs are strongly hole-dominated LEDs, and that the TiO2 in HOILEDs plays a supporting role. The TiO2 seems to act as a hole-blocking layer.
Keywords: OLED; Metal oxide; Hybrid; Titanium oxide;

On the energy transfer from a polymer host to the rhenium(I) complex in OLEDs by Sergio Kenji Mizoguchi; Antonio Otávio Toledo Patrocínio; Neyde Yukie Murakami Iha (2315-2317).
Photoluminescence and electroluminescence of PVK films doped with fac-[ClRe(CO)3(bpy)], bpy = 2,2′-bipyridine, are investigated. Photoluminescence spectra of spin-coated PVK films (λ exc  = 290 nm) exhibit a broad band centered at 405 nm. As the concentration of dopant increases, the polymer emission is quenched and a band at 555 nm appears (isosbestic point at 475 nm). In OLEDs with ITO/PEDOT:PSS/PVK/butylPBD/Al architecture doped with fac-[ClRe(CO)3(bpy)], the polymer host emission is completely quenched even at the lowest concentration of dopant. The electroluminescence spectra of the devices show that there is an efficient energy transfer from the host to the dopant, which exhibits a very intense emission at 580 nm.
Keywords: Photoluminescence; Electroluminescence; Re(I) complex; Light-emitting diodes (LED); Energy transfer;

Using the copper selenide as hole injector electrode in MeH-PPV polymer light emitting diodes by Adriano César Rabelo; Alexandre Marletta; Raigna A. Silva; Newton M. Barbosa Neto; Otávio Luiz Bottecchia (2318-2319).
This work addresses the electrical characterization of the junction copper selenide (Cu2−x Se) and poly-[2-metoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MeH-PPV). The Cu2−x Se film was produced on copper (Cu) substrate using the chemical bath deposition technique. The polymer light emitting diodes were processed using the following layers: Cu/Cu2−x Se or ITO (indium tin oxide), MeH-PPV and aluminum (Al). The barrier height (ϕ) of Cu/Cu2−x Se/MeH-PPV was estimated using the Fowler–Nordheim field-emission tunneling theory. We observed that ϕ decreases from 180 meV, for conventional ITO/MeH-PPV/Al device, to 10 meV for Cu/Cu2−x Se/MeH-PPV/al diode.
Keywords: Copper selenide; Cu2−x Se; MeH-PPV; PLED; Photovoltaic;

A new kind of polyfluorene copolymers, poly(2,7-(9,9-dioctyl-fluorene)-alt-5,5 -(4′,7′-di-2-thienyl-2′,1′,3′,-benzothiadiazole) (PFDTBT), was prepared. The introduction of ZnO nanoparticles with perfect wurtzite crystal character into PFDTBT makes the resulted single-layer photovoltaic device to perform a significant photovoltaic response. Among the tested devices, the best performance is observed for that containing 60 wt% of ZnO nanoparticles, which has a photocurrent density of 1.17 μA/cm2, an open circuit voltage of 0.81 V, a fill factor of 0.09 and a power conversion efficiency of 0.009%. The results show that the polyfluorene derivatives/ZnO nanoparticles hybrid composites are excellent fluorescence and photovoltaic materials.
Keywords: Polyfluorene derivatives; PFDTBT; ZnO; Photovoltaic devices;

Positive and negative magnetic field effects in organic semiconducting materials by Liang Yan; Yue Wu; Zhihua Xu; Bin Hu (2323-2325).
It has been found that non-magnetic organic semiconducting materials can exhibit magnetic responses in electrical current, electroluminescence, photoluminescence, and photocurrent when an external magnetic field is applied. These intrinsic magnetic responses can be naturally attributed to (i) magnetic field-dependent singlet/triplet ratio and (ii) singlet/triplet ratio-dependent excited processes. We observe that inter-molecular and intra-molecular excited states are sensitive and insensitive, respectively, to external magnetic field in magnetic field dependences of electroluminescence, photocurrent, and photoluminescence. This experimental phenomenon suggests that the electron–hole separation distance essentially determines whether magnetic field effects can be activated through the competition between spin-exchange interaction-induced singlet–triplet energy difference and magnetic Zeeman splitting when applied magnetic field is stronger than spin–orbital coupling. Furthermore, the dissociation in inter-molecular excited states and exciton–charge reaction in intra-molecular excited states have positive and negative responses to external magnetic field. As a result, controlling the dissociation in inter-molecular excited states and the exciton–charge reaction in intra-molecular excited states provide an effective methodology to tune the magnetic field effects between positive and negative values in organic semiconducting materials.
Keywords: Magnetic field effects; Organic electroluminescence; Organic photovoltaic;

Semitransparent organic photovoltaic cell with carbon nanotube-sheet anodes and Ga-doped ZnO cathodes by S. Tanaka; A.A. Zakhidov; R. Ovalle-Robles; Y. Yoshida; I. Hiromitsu; Y. Fujita; K. Yoshino (2326-2328).
We demonstrate a semitransparent organic photovoltaic (OPV) cell with two transparent electrodes: a multi-wall carbon nanotube (MWCNT) sheet and a Ga-doped ZnO (GZO) are used as a transparent anode and cathode, respectively. As an active layer, we used a bulk heterojunction structure with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The photovoltaic cell has a GZO/P3HT:PCBM/poly(3,4-ethylene-dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/MWCNT/PEDOT:PSS structure. For comparison, an OPV cell with a MWCNT-sheet anode and an indium tin oxide (ITO) cathode were also fabricated. The OPV cell with the GZO cathode showed better performance than that with the ITO cathode, owing to the lower work function of the former. The semitransparent OPV cell with GZO cathode demonstrated a short-circuit current of 3.4 mA/cm2, open-circuit voltage of 0.51 V, and efficiency of 0.45%.
Keywords: Organic photovoltaic cell; Carbon nanotube; ZnO;

Low-cost sensors developed on paper by line patterning with graphite and polyaniline coating with supercritical CO2 by C. Steffens; A. Manzoli; E. Francheschi; M.L. Corazza; F.C. Corazza; J. Vladimir Oliveira; P.S.P. Herrmann (2329-2332).
Low-cost sensors were developed in two steps: (i) using a negative template to print graphite electrodes on vellum paper and (ii) coating with conductive polymers. Thin films of polyaniline (PANI) in the emeraldine oxidation state were investigated as active layers, after being synthesized by two routes: (a) polyaniline doped with dodecylbenzenesulfonic acid (DBSA) deposited by supercritical fluid (SC CO2) and (b) PANI doped with hydrochloric acid (HCl) by the in situ polymerization method. The electrical response (mV) was measured with dedicated circuitry, both in static laboratory air and with a flow of dry nitrogen gas (N2) at room pressure and temperature in a closed chamber, to assess the sensors for their sensitivity and reversibility. The phase morphology (microfiber structure) was characterized by FE-SEM. Results showed a difference in behavior between the sensors obtained by SC CO2 coating with PANI and by in situ polymerization. The voltage in the SC CO2 sensor decreased when it was exposed to the flow of dry nitrogen, whereas the opposite effect was observed in the other sensor.
Keywords: Polyaniline; Gas sensor; Supercritical fluid; In situ polymerization; Reversibility; Sensitivity;

Sensor arrays to detect humic substances and Cu(II) in waters by Fabio L. Leite; Alessandra Firmino; Carlos E. Borato; Luiz H.C. Mattoso; Wilson T.L. da Silva; Osvaldo N. Oliveira (2333-2337).
The interaction between poly(o-ethoxyaniline) (POEA) adsorbed onto solid substrates and humic substances (HS) and Cu2+ ions has been investigated using UV–vis spectroscopy and atomic force microscopy (AFM). Both HS and Cu2+ are able to dope POEA and change film morphology. This interaction was exploited in a sensor array made with nanostructured films of POEA, sulfonated lignin and HS, which could detect small concentrations of HS and Cu2+ in water.
Keywords: Humic substances; AFM; Metal complexes; Water; Sensors; Heavy metals;

Triplet excitons in a ladder-type conjugated polymer: Application in solar cells by K. Yang; M. Arif; M. Förster; U. Scherf; S. Guha (2338-2341).
Inclusion of trace quantities of heavy metal atoms (Pd) in a ladder-type polymer (PhLPPP) backbone allows transitions between the singlet and the triplet manifolds. Temperature-dependent photoinduced absorption studies of PhLPPP show the triplet–triplet absorption peak (T 1  →  T N) at 1.3 eV to blue-shift with increasing temperatures, suggesting a localization of the excitons on smaller chain segments with large exchange splitting energy. Furthermore, solar cells were fabricated using PhLPPP as the donor material; on an average the power conversion efficiencies of PhLPPP-based solar cells were 3–10 times greater compared to the ladder-type polymer with no incorporation of Pd atoms.
Keywords: Conjugated polymers; Triplet excitons; Photoinduced absorption; Solar cells;

Efficient and low cost devices for solar energy conversion: Efficiency and stability of some natural-dye-sensitized solar cells by A.O.T. Patrocínio; S.K. Mizoguchi; L.G. Paterno; C.G. Garcia; N.Y. Murakami Iha (2342-2344).
Dye-sensitized solar cells, named by us Dye-Cells, are one of the most promising devices for solar energy conversion due to their reduced production cost and low environmental impact, especially those sensitized by natural dyes. The efficiency and stability of devices based on natural sensitizers such as mulberry (Morus alba Lam), blueberry (Vaccinium myrtillus Lam), and jaboticaba's skin (Mirtus cauliflora Mart) were investigated. Dye-Cells prepared with aqueous mulberry extract presented the highest P max value (1.6 mW cm−2) with J sc  = 6.14 mA cm−2 and V oc  = 0.49 V. Photoelectrochemical parameters of 16 cm2 active area devices sensitized by mulberry dye were constant for 14 weeks of continuous evaluation. Moreover, the cell remained stable even after 36 weeks with a fairly good efficiency. Therefore, mulberry dye opens up a perspective of commercial feasibility for inexpensive and environmentally friendly Dye-Cells.
Keywords: Dye-sensitized solar cells; Energy conversion; Natural sensitizers;

Polaron recombination in pristine and annealed bulk heterojunction solar cells by C. Deibel; A. Baumann; A. Wagenpfahl; V. Dyakonov (2345-2347).
The major loss mechanism of photogenerated polarons was investigated in P3HT:PCBM solar cells by the photo-CELIV technique. For pristine and annealed devices, we find that the experimental data can be explained by a bimolecular recombination rate reduced by a factor of about 10 (pristine) and 25 (annealed) as compared to Langevin theory. Aided by a macroscopic device model, we discuss the implications of the lowered loss rate on the characteristics of polymer:fullerene solar cells.
Keywords: Organic semiconductors; Polymers; Photovoltaic effect; Charge carrier recombination;

Synthesis and characterization of aniline copolymers containing carboxylic groups and their application as sensitizer and hole conductor in solar cells by Júlia C. Fatuch; Mauro A. Soto-Oviedo; César O. Avellaneda; Marcos F. Franco; Wanderson Romão; Marco-A. De Paoli; Ana Flávia Nogueira (2348-2354).
Copolymers of m-aminobenzoic acid and o-anisidine doped with p-toluenesulphonic acid in different proportions were successfully synthesized by oxidative polymerization. The copolymers were characterized by FT-IR, UV–vis, 1H NMR and EPR spectroscopies, cyclic voltammetry, conductivity and SEM. The copolymer with equivalent amounts of the monomers o-anisidine and m-aminobenzoic acid presented the highest conductivity, The EPR analyses and SEM images show that this copolymer provides more homogeneous films with particle size distribution of approximately 1–2 μm. The copolymer with a high fraction of o-anisidine gives rises to films with larger particle sizes and a more defined electrochemical process. The m-aminobenzoic acid monomer was intentionally chosen in order to promote a better electronic coupling between the conducting copolymer and the TiO2 surface. The copolymers were tested as both sensitizers and hole conducting materials in dye-sensitized solar cells. The device assembled using the copolymer with the highest proportion of m-aminobenzoic acid units as sensitizer produced the highest photocurrent (I sc  = 0.254 mA cm−2) and photovoltage (V oc  = 0.252 V) at 100 mW cm−2. The energy diagram shows that although the electronic injection from the conducting polymer excited state is an allowed process the regeneration of the positive charges created after the electron transfer process is forbidden, thus explaining the low efficiency of solar energy conversion. When this copolymer was applied as a hole conducting material, an improvement in the V oc to 0.4 V, was observed, indicating that this material is more suitable for charge transport when applied in this type of solar cells.
Keywords: o-Anisidine; o-Methoxyaniline; m-Aminobenzoic acid; Copolymers; Dye-sensitized solar cells; TiO2; Hole transport;

Development of large size dye-sensitized solar cell modules with high temperature durability by Shuji Noda; Kazuhide Nagano; Eiji Inoue; Toshio Egi; Takeshi Nakashima; Naoto Imawaka; Masahiro Kanayama; Shiro Iwata; Kunihiro Toshima; Keiko Nakada; Katsumi Yoshino (2355-2357).
The DSSC sub-module of 120 mm2 which has high temperature durability was fabricated. The durability was tested under 85 °C for 1000 h; at the end of the test the conversion efficiency was retained over 95% of the initial one. The high temperature durability was realized using the improved sealant, protective material of collecting grids and the new ruthenium-complex dye J2 which was developed by SIIT. By the same way the larger size module was developed.
Keywords: Dye-sensitized; Solar cells; High temperature; Durability; Module; Titania; Catalyst; Platinum; Screen-print;

Efficient polymer solar cell modules by Burhan Muhsin; Joachim Renz; K.-H. Drüe; Gerhard Gobsch; Harald Hoppe (2358-2361).
Polymer solar cell modules based on the standard polymer–fullerene system of to-date, P3HT–PCBM, have been prepared and characterized. We have observed a loss of only 20% when up-scaling the active area of the solar cell by a factor somewhat larger than 10. An average solar cell efficiency of 3% and a module efficiency of 1.9% for three serially interconnected solar cells of 5.4 cm2 each are reported. The route for further optimization of module performance is discussed based on analyzing the existing loss factors within this design.
Keywords: Polymer solar cell; Polymer–fullerene bulk heterojunction; Solar module; Organic photovoltaics; Laser ablation;

Low-voltage organic n-channel thin-film transistors based on a core-cyanated perylene tetracarboxylic diimide derivative by Ute Zschieschang; Konstantin Amsharov; R. Thomas Weitz; Martin Jansen; Hagen Klauk (2362-2364).
Using the small-molecule organic semiconductor bis(1H,1H-perfluorobutyl)-dicyano-perylene tetracarboxylic diimide, C3F7CH2-PTCDI-(CN)2, and a low-temperature-processed, high-capacitance gate dielectric based on a phosphonic acid self-assembled monolayer, we have manufactured n-channel thin-film transistors on glass substrates. The transistors operate with low voltages (2 V) and have an electron mobility of 0.04 cm2/Vs and an on/off ratio of 105. By combining C3F7CH2-PTCDI-(CN)2 n-channel transistors with pentacene p-channel transistors, we have also manufactured low-voltage, low-power organic complementary inverters with good static and dynamic performance.
Keywords: Organic thin-film transistors; Organic complementary circuits;

High mobility p-channel organic field effect transistors on flexible substrates using a polymer-small molecule blend by Jeremy Smith; Richard Hamilton; Iain McCulloch; Martin Heeney; John E. Anthony; Donal D.C. Bradley; Thomas D. Anthopoulos (2365-2367).
Organic field effect transistors have been fabricated on poly(ethylene terephthalate) film substrates with excellent operating characteristics and maximum mobilities of 1.1 cm2/(V s). The semiconductor was a solution processible blend of 6,13-bis(triisopropyl silylethynyl) pentacene and a poly(triaryl amine) used to combine the favourable properties of small molecules and polymers. We have demonstrated that such systems are a good candidate for flexible organic electronics and that the surface energy of the substrate plays a key role in controlling the morphology of the semiconductor film.
Keywords: TIPS pentacene; Solution processing; Plastic substrate; Thin film transistors; Surface energy; Semiconductor blends;

Complementary circuits based on solution processed low-voltage organic field-effect transistors by James M. Ball; Paul H. Wöbkenberg; Floris B. Kooistra; Jan C. Hummelen; Dago M. de Leeuw; Donal D.C. Bradley; Thomas D. Anthopoulos (2368-2370).
The field of organic electronics is advancing quickly towards ultra low-cost, low-end applications and is expected to provide the necessary technology required for flexible/printed electronics. Here we address the need for solution processed low-voltage complementary logic in order to reduce power consumption of organic circuits and hence enable their use in portable, i.e. battery-powered applications. We demonstrate both p- and n-channel solution processed high performance organic field-effect transistors that operate at voltages below |1.5| V. The reduction in operating voltage is achieved by implementing ultra-thin gate dielectrics based on solution processed self-assembled monolayers. This work demonstrates the feasibility of fabricating low-voltage complementary organic circuits by means of solution processing.
Keywords: OFET; Organic field-effect transistor; Low-voltage; Fullerene; P3HT; Self-assembled monolayer dielectric; Phosphonic acid; Organic complementary logic; Inverter;

A study of the influence of the deposition rate of top-contact Au source and drain electrodes deposited by electron-beam evaporation on the electrical performance of pentacene organic field-effect transistors (OFETs) is presented. By adjusting the deposition rate of the Au electrodes to minimize metal diffusion into the semiconductor pentacene layer, the source/drain contact resistance could be reduced. At a Au deposition rate of 10 Å/s, high-performance pentacene p-channel OFETs were obtained with a field-effect mobility of 0.9 cm2/Vs and a normalized channel width resistance of 23 kΩ cm in a device with a channel length of 25 μm.
Keywords: Organic field-effect transistor; Pentacene; Au diffusion;

Crystal structure and properties of charge-transfer complex of N-butylguanine and FTCNQ by Tsuyoshi Murata; Kenji Nakamura; Hideki Yamochi; Gunzi Saito (2375-2377).
Charge-transfer complex formation between N-butyl guanine and FTCNQ yielded an ionic product composed of neutral and protonated N-butyl guanines and fully ionized FTCNQ molecules in a 1:1:1 ratio. Neutral and protonated N-butyl guanines were alternately connected by complementary hydrogen-bonds to form a one-dimensional ribbon, which stacked to establish a two-dimensional cation layer. FTCNQ formed a face-to-face dimer, which was separated from adjacent dimers because of the butyl group of N-butyl guanine. This salt was an insulator, and exhibited a strong antiferromagnetic interaction within the FTCNQ dimer.
Keywords: Charge-transfer complex; Complementary hydrogen-bond; Guanine; FTCNQ;

Preparation and characterization of Langmuir–Blodgett films of 16-membered azobenzocrown ether with naphthalene residue by Flávio M. Shimizu; José A. Giacometti; Elżbieta Luboch; Jan F. Biernat; Marystela Ferreira (2378-2380).
Langmuir and Langmuir–Blodgett films of 16-membered azobenzocrown ether with naphthalene residue were prepared and characterized. The Langmuir monolayers were successfully transferred to form LB films onto solid substrates. The films deposited onto ITO electrodes were also used as electrodes in cyclic voltammetry and the results showed that the films had a distinct response to metal ions.
Keywords: Azocrown ether; Cyclic voltammetry; Langmuir–Blodgett film; FTIR spectroscopy;

Charge ordering state of mixed-valence (TP-EDTT)3(PF6)2 by Yoshiaki Nakano; Motonobu Takahashi; Masafumi Sakata; Hideki Yamochi; Gunzi Saito; Koichiro Tanaka (2381-2383).
4,5-Ethylenedithio-2-(thiopyran-4-ylidene)-1,3-dithiole (TP-EDTT) and its radical cation salts were prepared. Conventional galvanostatic electrocrystallization gave (TP-EDTT)2SbF6, (TP-EDTT)GaCl4, (TP-EDTT)ReO4, and (TP-EDTT)3(PF6)2. The variation of bond lengths upon the charge of each molecule was examined based on 0, +0.5, and +1.0-charged TP-EDTT molecules. Applying the relationship between the charge and the bond lengths to the donor molecules, (TP-EDTT)3(PF6)2 was proved to be a charge ordering system.
Keywords: Molecular conductor; Bond length analysis; Charge ordering;

Theoretical study of fluorescence of self-assembling helical supramolecular aggregates by Leon van Dijk; Paul van der Schoot; Peter A. Bobbert (2384-2386).
The helical self-assembly of MOPV4 oligomers dissolved in dodecane solution has a large effect on the experimental fluorescence spectra. To describe the change in fluorescence upon aggregation, we combine a statistical mechanical theory describing the helical self-assembly with a tight-binding model to account for the delocalization of the exciton. We find our combined model to describe the red-shift of the main fluorescence peak upon aggregation qualitatively.
Keywords: Supramolecular electronics; Helical self-assembly; Exciton dynamics; Photoluminescence; Oligophenylenevinylene;

Thermoelectric figure of merit of τ -(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y , ( y ≤ 0.875 ) and (TMTSF)2PF6 by Harukazu Yoshino; George C. Papavassiliou; Keizo Murata (2387-2389).
Electrical resistivity, thermopower and thermal conductivity were measured simultaneously for τ -(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y , ( y ≤ 0.875 ) and (TMTSF)2PF6, respectively. The thermoelectric figure of merit Z of the materials is determined by combining these transport coefficients. It was found that the dimensionless figure of merit Z T of τ -(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y , ( y ≤ 0.875 ) amounts to 0.042 at 130 K. This relatively large Z T is due to large thermopower and small thermal conductivity measured by an improved method as compared with that previously reported by the present authors.
Keywords: Thermoelectric figure of merit; Organic conductor; Thermopower; Thermal conductivity; Electrical resistivity;

A new nickel complex consisting of extended thiophenedithiolene ligands has been synthesized. The complex has been characterized by UV–vis–NIR spectroscopy, mass spectrometry, cyclic voltammetry, and X-ray crystallography. The complex exhibits significant electron delocalization into the peripheral thiophene rings. The −1 complex displays diamagnetic behavior in the solid state, but is paramagnetic (S  = 1/2) in solution. X-ray analysis shows a number of close contacts which could explain the diamagnetism.
Keywords: Nickel dithiolenes; Oligothiophenes; Molecular conductors; NIR dyes;

Quantum critical behavior in the organic conductor κ-(DHDA-TTP)2SbF6 by Yufeng Weng; Harukazu Yoshino; Narumi Hiratani; Hiroki Akutsu; Jun-ichi Yamada; Koichi Kikuchi; Keizo Murata (2394-2396).
Temperature–pressure phase diagram of the 2-D organic conductor, κ-(DHDA-TTP)2SbF6 (DHDA-TTP = 2-(1,3-dithiolan-2-ylidene)-5-(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene) is presented. This phase diagram exhibits a pressure boundary between insulator and Fermi liquid (FL). This boundary is considered as a critical pressure of quantum fluctuation between probable charge ordering and FL ground states. In the vicinity of the specific pressure, divergence of the prefactor A in ρ  =  ρ 0  +  AT 2, is observed, where ρ is the in-plane resistivity and T is the temperature. Following the similar phase diagram to κ-(MeDH-TTP)2AsF6 by Yasuzuka et al., this is the second example in the two-dimensional 1/4-filled organic conductors, showing the temperature–pressure phase diagram of quantum critical behavior. It is remarkable that this kind of divergence of A at certain critical point is rather general phenomena at least in these 1/4-filled 2-D organic conductors, in contrast to the other 1/2-filled κ-type organic conductors, which show Kanoda's phase diagram with Mott insulator and superconductor.
Keywords: Strong correlation; Metal–insulator transition; Quantum critical behavior; High pressure;

Fluctuation of charge density wave of TTF–TCNQ under extreme pressure by Keizo Murata; Yufeng Weng; Yuki Seno; Natarajan Rani Tamilselvan; Kensuke Kobayashi; Sonachalam Arumugam; Yusaku Takashima; Harukazu Yoshino; Reizo Kato (2397-2398).
We have presented that the charge density wave (CDW) in TTF–TCNQ is suppressed by extremely high hydrostatic pressure (8 GPa). To understand the nature of CDW under pressure, we shed light on the fluctuation of CDW under pressure, by examining the resistance anisotropy and their temperature dependence along the b-axis (1D) and a-axis. It turned that the fluctuation of CDW above T CDW continues to be present in the whole pressure range where CDW is present, but is gradually suppressed as CDW is suppressed. Also remarkable is that this behavior is only observed in the resistance behavior along the b-axis (1D) but not along the a-axis.
Keywords: Charge density wave (CDW); TTF–TCNQ; Metal–insulator transition; Fluctuation; High pressure;

We investigate charge transport in disordered organic host–guest systems with a bimodal Gaussian density of states. The energy difference between the peaks of the two Gaussians defines the trap depth. By solving the Pauli master equation for the hopping of charge carriers on a regular lattice we obtain the dependence of the charge-carrier mobility on the relative guest concentration, the trap depth, the energetic disorder, the charge-carrier density, and the electric field. Our results for the zero-field mobility are generally in a good agreement with recent semi-analytical model results. However, in the regime where the mobility attains a minimum our results can be almost one order of magnitude larger than as predicted semi-analytically. Furthermore, it is shown that field-induced detrapping can contribute strongly to the electric-field dependence of the mobility.
Keywords: Organic semiconductors; Hopping conduction; Traps; Percolation;

Exploring low-energy landscape of quasi-one-dimensional conductors by heat relaxation and magnetic field by K. Biljaković; J.C. Lasjaunias; R. Mélin; P. Monceau; G. Reményi; S. Sahling; D. Starešinić (2402-2405).
Modulated charge or spin superstructures of organic quasi-one-dimensional conductors exhibit specific low-energy excitations (LEE) at very low temperatures due to metastable states caused by strong pinning centers. These phase excitations (soliton-like topological defects) demonstrate rich and unexpected properties in a magnetic field, due to their magnetic moments. We discuss mainly on the dynamical aspects related to the non-equilibrium phenomena measured in heat relaxation below 1 K.
Keywords: Density waves; Thermodynamics; Glassy dynamics; Relaxation; Magnetic field;

Theoretical study on the second-order nonlinear optical properties of gold (III) alkyl complexes by Chunsheng Qin; Guochun Yang; Liang Zhao; Shiling Sun; Yongqing Qiu; Zhongmin Su; Yulan Zhu (2406-2409).
The equilibrium geometries of gold (III) alkyl complexes are optimized by DFT/B3LYP method. On the basis of the optimized structures, the electronic structures and second-order nonlinear optical properties are calculated by using time-dependent density-functional theory (TDDFT) combined with the sum-over-states (SOS) method. The results show that these complexes possess remarkably larger molecular second-order polarizabilities compared with the typical organometallic and organic complexes. The analysis suggests that charge transfer from the z-axis directions plays a key role in the second-order nonlinear optical response. Moreover, different ancillary ligands can substantially adjust the second-order nonlinear optical response. Thus, it can be concluded that these complexes will be hopeful candidates for the second-order nonlinear optical materials from the standpoint of high transparency, relatively large β values and small dispersion behaviors.
Keywords: Gold (III) alkyl complex; Electronic structure; Nonlinear optical property; TDDFT-SOS method;

Anharmonic overtones quenching in Er3+ complexes by A. Monguzzi; M.I. Trioni; R. Tubino; A. Milani; L. Brambilla; C. Castiglioni (2410-2412).
The organic complexes of the erbium ion Er3+ emitting in the near-infrared at 1.5 μm are widely investigated as potential active materials for a new generation of low-cost optical amplifiers for telecommunications. The limiting factor in these systems is the very low quantum yield of the lanthanide ion, generally ascribed to the presence of nearby high-energy vibrational centers as OH and CH bonds which are present as residual coordination water and as functional groups of the organic ligands. To make a quantitative prediction of the extent of the non-radiative decay originating from Förster transfer, the transition moments of the vibrational overtones in resonance with the ion emission have been evaluated from first principle calculations to compute the intensity of the fundamental normal modes; the overtone transitions intensities with energy falling in the 1.5 μm region have been evaluated by recursive analytical expressions obtained by using the Morse oscillator approximation.
Keywords: Lanthanides complexes; Near infrared emission quenching; Vibrational intensities;

Third-order nonlinear optical properties of open-shell singlet molecular aggregates composed of diphenalenyl diradicals by M. Nakano; H. Fukui; H. Nagai; T. Minami; R. Kishi; H. Takahashi (2413-2415).
The longitudinal static second hyperpolarizabilities (γ) of one-dimensional open-shell singlet diphenalenyl radical clusters (up to trimer) are investigated using the spin-unrestricted hybrid density functional theory, UBHandHLYP, method. The longitudinal γ values per monomer for these clusters are found to significantly increase with increasing the number of monomers: the increase ratio [γ/n(n-mer)/γ(monomer)] is 2.0 (dimer) and 3.1 (trimer). The significant enhancement is predicted to be caused by the field-induced intermolecular virtual charge transfer between the both-end-phenalenyl rings, originating in the strong covalent interaction between the unpaired electrons of the cofacial phenalenyl rings.
Keywords: Nonlinear optics; Hyperpolarizability; Open-shell system; Spin multiplicity; Radical;

We investigate the longitudinal static second hyperpolarizabilities (γ) of several square planar nickel, palladium and platinum complexes involving two bidentate o-semiquinonato type ligands. It turns out that the diradical character and γ value of this type of complex can be controlled by modifying the donor atoms and the metal core.
Keywords: Nonlinear optics; Hyperpolarizability; Open-shell system; Transition metal complex;

We show that superconductivity is absent within the 1 2 -filled band triangular lattice repulsive Hubbard model that has been proposed for organic charge-transfer solids. We posit that organic superconductivity is rather reached from a bond-charge density wave that either constitutes the insulating state proximate to superconductivity, or is extremely close in energy to the antiferromagnetic state, and replaces the latter under pressure. The bond-charge density wave can be described within an effective attractive U extended Hubbard Hamiltonian with repulsive nearest neighbor interaction V. A first-order transition from the insulating to the superconducting state occurs within the model with increasing frustration.
Keywords: Organic superconductors; Unconventional superconductivity; Correlated electrons;

Superconducting and magnetic phases in quenched perchlorate Bechgaard salts by Noomen Belmechri; Gilles Abramovici; Michel Héritier; Sonia Haddad; Samia Charfi-Kaddour (2422-2424).
(TMTSF)2ClO4 is a quasi-1D organic conductor, in which the non-centrosymetric anion ClO4 undergoes an orientational order at 24 K. Structural studies have shown that in (TMTSF)2ClO4, samples cooled down through the anion ordering transition at 24 K, a certain amount of disorder is quenched: there appear, in the low T state, domains in which the anions are orientationaly ordered and domains in which they are disordered, with concentrations and sizes can be varied by varying the cooling rate. Such a structure is essential for the stability of the various phases which can appear. Here, the relevant parameter is not the mean anion potential, but the real values of the anion potential within each domain. When the sizes of the domains are larger than the coherence lengths, a functional renormalization group analysis shows that a d-wave superconducting order is more stable in the ordered domains, because of the gap opened on the Fermi surface by the periodic anion potential, while in the disordered domains, a SDW order is the stable one. There is a large range of cooling rates, in which these two kinds of domains coexist. In that case, in the low T state, a superconducting order and a SDW order exist together. These phases do not really coexist, but are indeed spatially segregated. When the sizes of the disordered domains are much smaller than the superconducting coherence length, they behave as non-magnetic impurities in the superconducting phase, which decrease the superconducting critical temperature, according to the Abrikosov–Gorkov law. Our results are in good agreement with recent experimental.
Keywords: Quenched disorder; Phase segregation; Superconducting domains; SDW domains; Quasi-1D Bechgaard salts;