Synthetic Metals (v.151, #2)

Polyurethane latex modified with polyaniline by Irina Sapurina; Jaroslav Stejskal; Milena Špírková; Jiří Kotek; Jan Prokeš (93-99).
The strategy of the modification of polyurethane latex with a conducting polymer, polyaniline, is proposed. It is based on the introduction of the polymer steric stabilizer to the latex. The stabilizer prevents the macroscopic precipitation of a conducting polymer during the polymerization. Polyaniline has been prepared by the oxidative polymerization of aniline in the presence of polyurethane latex with average particle size of 36 nm and poly(N-vinylpyrrolidone). Thus, modified latex produces an aqueous colloidal dispersion having the particle size 100–200 nm. The presence of poly(N-vinylpyrrolidone) was needed to obtain a colloid. In its absence, a polyaniline–polyurethane composite precipitated. The composite coatings obtained after their drying contained 5–18 wt.% polyaniline in a protonated emeraldine form, had the conductivity up to 10−2  S cm−1, and mechanical properties typical of elastomers.
Keywords: Conducting polymer; Colloid; Colloidal dispersion; Coatings; Polyaniline; Polyurethane;

Electrochemical properties and conductivity of poly(3-methylpyrrole/ClO4) by M.J. González-Tejera; E. Sánchez de la Blanca; I. Carrillo; M.I. Redondo; M.A. Raso; J. Tortajada; M.V. García (100-105).
Electrosynthesis of conducting poly(3-methylpyrrole) has been carried out at fixed potentials of 0.5 and 0.6 V in a NaClO4 acetonitrile solution. The electrochemical behaviour of doped-polymer films has been analysed considering the influence of the negative and positive potential limits as well as the scan rate on the voltammograms recorded in acetonitrile. From these studies a mechanism for the redox processes is proposed. Polymer morphology has been examined by scanning electron microscopy, which reveals a cauliflower and compact texture depending on the potential of synthesis and deposition time. Kinetic of conductivity decay with aging time has been determined to be dependent of exp(−t 1/2) with a characteristic time of the degradation process around 20 days.
Keywords: Poly(3-methylpyrrole); Conducting polymers; Electroactivity; Conductivity;

Synthesis, spectroscopic and magnetic properties of mp aniline tetramers by R. Kaczorowski; J. Gosk; I. Kulszewicz-Bajer; A. Twardowski (106-113).
Alternating mp-N-hexylaniline and aniline tetramers have been synthesized via palladium-catalyzed amination reactions. The tetramers can be oxidized with m-chloroperbenzoic acid or NOBF4 and form radical cations stable in acidic media. The magnetization measurements of oxidized N-hexylaniline or p-aniline tetramers reveal the paramagnetic-type behaviour.
Keywords: Oligoanilines; Organic magnets; High-spin molecules; Magnetization;

Anodic oxidation of difluorenyls bridged through a dimethylsilyl group and of the 9-trimethylsilyl fluorene: Towards new three-dimensional polyfluorenes by Ioan Silaghi-Dumitrescu; Jean Escudie; Gabriela Cretiu-Nemes; Eugène Raoult; Joëlle Rault-Berthelot (114-119).
Anodic oxidation of difluorenes bridged by dimethylsilyl moieties leads to the formation of insoluble electroactive films. Compared to classical polyfluorenes and poly(9,9′-difluorenes), the polymer bridged through Si(CH3)2 or substituted by Si(CH3)3 units are more stable towards oxidation, their yield of polymerization are higher and the conjugation length deduced by their λ max UV–vis absorption bands under their neutral state are more important.
Keywords: Electroactive polymer; Anodic electrodeposition; Conducting polymer; Modified electrode;

The electronic structure of perylene was analyzed by using ultraviolet photoelectron spectroscopy to introduce the energy level alignment of perylene/Au interface. The energy level alignment was studied by the onset of the highest occupied molecular orbital level and the shift of the vacuum level of the perylene layer, which was deposited on Au surface by stages. The measured onset of the highest occupied molecular orbital energy level was 1.0 eV from the Fermi level of Au, and the vacuum level was shifted 0.2 eV toward higher binding energy side with additional perylene layer. Furthermore, the density functional theory calculation was performed to identify the valence band spectrum of perylene film. The good agreement between the experimental and theoretical valence band spectrum allows us to assign each peak of the valence band spectrum, which was obtained from the perylene/Au film. The representative molecular orbital shapes, which composed the valence band of perylene, are presented in this report.
Keywords: Perylene; Ultraviolet photoelectron spectroscopy; Density functional theory;

The influence of thermal activation on polaron interactions of poly(3-dodecylthiophene) (PDDT) was studied. It was found that when an undoped PDDT sample was heated above 450 K and subsequently cooled to under the glass transition temperature, there were strong spin–spin interactions. When the polaron concentration was increased by FeCl3 doping, all polarons including the immobile ones started to interact mutually. Changes in its internal microstructure, caused by thermal activation of the sample, followed by its freezing can generate an amplification of polaron interactions, giving rise to diamagnetic inter- and intra-chain bipolarons. As a result of strong spin–spin interactions the doped polymeric sample of PDDT displays diamagnetism even at room temperature. The diamagnetic properties depend on the consecutive structural relaxation of PDDT, caused either by immediate temperature changes, or by long-term standing at room temperature.
Keywords: Conducting polymers; Polyalkylthiohenes; Poly(3-dodecylthiophene); Polarons; Diamagnetism;

SWNTs coated by conducting polyaniline: Synthesis and modified properties by Mohammad Rezaul Karim; Chul Jae Lee; Yong-Tae Park; Mu Sang Lee (131-135).
Conducting polyaniline (PaN) was synthesized onto single-wall carbon nanotubes (SWNTs) by using the in situ polymerization method. Elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), field emission scanning electron microscope (FE-SEM), thermal gravimetric analysis (TGA), electron spin resonance (ESR), X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize the resulting complex nanotubes (SWNTs–PaN) structure. We observed no significant interaction chemically between the PaN and SWNTs. The physical properties of the complex nanotubes were measured and also showed that the SWNTs were modified by conducting polyaniline.
Keywords: Conducting polyaniline; Single-wall carbon nanotubes; In situ polymerization;

Polypyrrole nanoparticles and dye absorption properties by Hongxia Wang; Tong Lin; Akif Kaynak (136-140).
Polypyrrole (PPy) nanoparticles were prepared by using microemulsion polymerization processes at 3 °C. Particle characterization was performed by using FTIR, elementary analysis, UV–vis spectra and scanning electron microscope (SEM). The size of the nanoparticles varied from about 50 to 100 to 100 to 200 nm with the change in concentration of surfactant from 0.8 to 0.44 M. Polypyrrole nanoparticles were dedoped by a 10% NaOH solution, followed by a redoping process using a nuclear fast red kernechtrot dye, which has a sulfonate group. Dedoping changed the optical absorption properties of the nanoparticles.
Keywords: Polypyrrole; Nanoparticles; Absorption; Surfactant;

Enhanced performance of organic light emitting device by insertion of conducting/insulating WO3 anodic buffer layer by Jingze Li; Masayuki Yahiro; Kenji Ishida; Hirofumi Yamada; Kazumi Matsushige (141-146).
Tungsten oxide (WO3) ultrathin film with high optical transparency is deposited on indium–tin oxide glass as hole injection layer of organic light emitting device (OLED). As-deposited WO3 film is amorphous and insulating, wherein the buffer thickness of 0.5 nm shows enhancement of hole injection in OLED. The device performance is further enhanced after the as-deposited WO3 film is thermally treated, which is ascribed to lowering of the effective energy barrier height for hole injection. The annealed buffer layer is identified to be a semiconductor with crystalline structure. Although the thickness of the annealed WO3 buffer layer is up to 1.5 nm, the device performance is still better than that of unmodified OLED. The difference in anodic buffer thickness dependent device performance for both types of WO3 films is determined by the electrical property.
Keywords: OLED; Tungsten oxide; Hole injection layer; Thermal annealing;

White, phosphorescent, wet-processed, organic light-emitting diode, on a window-glass substrate by V. Maiorano; E. Perrone; S. Carallo; A. Biasco; P.P. Pompa; R. Cingolani; A. Croce; R.I.R. Blyth; J. Thompson (147-151).
A substrate is presented as an alternative to indium tin oxide as the anode material for organic light-emitting diodes. We show that float glass, the material most commonly used in window glass, with a thin transparent evaporated gold layer, provides a cheap, and readily available alternative. Bright organic light-emitting diodes emitting in the white, and near white, are demonstrated, using a spin coated blend of phosphorescent iridium complexes doped into a suitable polymer host, as the emissive layer. The emission colour of these blends is shown to be tunable from the blue to the red, dependant on the relative concentrations of the two phosphorescent molecules.
Keywords: Glass surfaces; Metal/insulator surfaces; OLEDs; Phosphorescence; Large area;

Apatite/polypyrrole composite prepared by a biomimetic process by Zhizhong Jiang; Dongtao Ge; Wei Shi; Qiqing Zhang (152-155).
Apatite coatings were fabricated on polypyrrole (PPy) substrate by a biomimetic process using simulated body fluid (SBF). PPy was chemically synthesized with heparin sodium salt and toluene-4-sulfonic acid (P-TSA) as dopants. But apatite coatings were not induced when PPy was prepared without dopants, which suggests that heparin sodium salt and P-TSA play an important role in the formation of the apatite coatings. The possible mechanism responsible for the formation of apatite coatings was discussed. It is expected that this apatite/polypyrrole composite can be used as bioactive coatings on metal implants and tissue engineering scaffolds.
Keywords: Polypyrrole (PPy); Apatite; Biomimetic process; Simulated body fluid (SBF);

Synthesis, structure and conducting properties of two new multi-component radical cation ET salts with the (NO3) counterion: (ET)2(NO3)·C2H4(OH)2 (I) and (ET)2(NO3)·0.5[C2H4(OH)2]·H2O (II) are described. Both salts have layered structures with the distinguishing feature of hydrogen bonds being present between the radical cation layers and anion sheets. It was found that introduction of glycol molecules to compositions of I and II significantly affects the structure of their cation and anion layers and, as a result, their conducting properties. I is a semiconductor, while II demonstrates metallic conductivity down to 4.2 K.
Keywords: ET radical cation salts; Electrocrystallization; Structure; Conductivity;

New polyaniline/Ni(0) nanocomposites: Synthesis, characterization and evaluation of their catalytic activity in Heck couplings by Axel Houdayer; Raphaël Schneider; Denis Billaud; Jaafar Ghanbaja; Jacques Lambert (165-174).
Development of simple and reliable protocols for the immobilization of catalytically active metal nanoparticles is an important aspect of the nanomaterials field. This paper describes the synthesis and characterization of new organic/inorganic hybrid materials constituted of Ni(0) nanoparticles and polyaniline (PANI). Nanosized Ni(0) particles were prepared by reduction of Ni(OAc)2 using t-BuONa activated sodium hydride in refluxing THF. A ligand exchange with aniline on t-BuONa-stabilized Ni(0) particles yielded aniline-stabilized particles. Ni(0)/PANI nanocomposites were finally obtained by polymerising aniline-stabilized Ni(0) particles by using ammonium persulfate. Samples were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Results show that this “one-pot” experimental route is successful in producing hybrids constituted of Ni(0) nanoparticles stabilized by PANI due to the strong binding of PANI amine groups to Ni(0) particles. TEM images of the nanohybrids show that metal particles with diameters of ca. 6 nm are homogeneously dispersed on PANI. The catalytic activity of these novel nanocomposites was finally evaluated in Heck reactions. The rate of coupling between aryl iodides and olefins using Ni/PANI catalysts was much higher than those obtained using Ni catalysts reported to date.
Keywords: Polyaniline; Nickel; Nanocomposite; Heck coupling;

In this communication, we demonstrate high capacitance, low-voltage organic field-effect transistors (OFETs) built on extremely cheap, flexible, commercially available aluminized Mylar® films covered by ultrathin (∼3.5 nm) SiO2 layers, which were modified via application of n-octadecytrichlorosilane (OTS) self-assembled monolayer. The modified SiO2 was tested as gate insulator in OFETs using pentacene and regioregular poly(3-hexylthiophene) (rr-P3HT) as active materials. The characteristics of the fabricated devices display low threshold (<−1 V) assuring normally “off” transistor operation, very low inverse subthreshold slopes (pentacene: 255 mV/dec, rr-P3HT: 375 mV/dec), good carrier mobility (pentacene: 0.12 cm2/(V s), rr-P3HT: 0.01 cm2/(V s)) and a very small hysteresis. The performance of the presented OFETs is high enough for many commercial applications significantly reducing costs of their production.
Keywords: Organic field-effect transistor (OFET); Low voltage; Self-assembled monolayer (SAM); Gate insulator;