Synthetic Metals (v.149, #2-3)

AFM and electrochemical studies of mono- and bis-anthracene derivatives of C60 deposited on gold electrodes by Marcela Rendón; Michael E. Hyde; Marco F. Suárez; Alvaro Duarte-Ruiz; Richard G. Compton (99-108).
Keywords: C60; Anthracene; Gold electrodes; Atomic force microscopy; Reductive dissolution;

Oxidative polymerization of N-vinylcarbazole (NVC) was achieved in bulk (65 °C) and in CHCl3 (70 °C) by MoVIO3 and by ‘molybdenum blues’ (MB) prepared by the reducing MoO3 with SnCl2. Formation of polyN-vinylcarbazole (PNVC) and its subsequent incorporation in these composite systems was endorsed by FTIR spectral analyses. Scanning electron micrographic analyses revealed the presence of very small spherical particles in MB and lumpy aggregates in PNVC–MB composite system, respectively. Thermogravimetric stability studies showed overall thermal stability trend as follows: MB > PNVC–MB > PNVC. The dc conductivity values (S/cm) of the PNVC–MB composite obtained in the present study were 10−2—a value 1012 fold improved compared to that of the unmodified PNVC (10−12 to 10−16).
Keywords: Molybdenum blues; Nanocomposite; Thermogravimetric stability; Conductivity;

A new chemical polymerization process for substituted anilines by A. Falcou; A. Duchêne; P. Hourquebie; D. Marsacq; A. Balland-Longeau (115-122).
A new chemical polymerization process has been developed for the synthesis of polyaniline derivatives. Various poly(N-alkylanilines) and poly(o-alkylanilines) bearing different alkyl chain lengths (3–18 carbons) can be prepared by oxidation with ammonium persulfate in a mixture comprising methanesulfonic acid, water, hexane and a cosolvent (THF). Using this general process and further purification procedures, we found that numerous polymers can be produced in their dedoped forms with very high purity and reproducibility. The physical, spectral and thermal properties of poly(N-alkylanilines) and poly(o-alkylanilines) were studied and compared. As expected, the solubility of these substituted polyanilines in their dedoped form increased with alkyl chain length, and doped polymers containing long alkyl chains were also totally soluble in the usual organic solvents.
Keywords: N-Alkylanilines; o-Alkylanilines; Polymerization; Properties of poly(N-alkylanilines) and poly(o-alkylanilines);

Effects of backbone modification on the linear and third order nonlinear optical properties in fluorene based copolymers by Franco D’Amore; Johann Osmond; Silvia Destri; Mariacecilia Pasini; Valerio Rossi; William Porzio (123-127).
Linear and third order nonlinear optical phenomena have been studied in two fluorene based copolymers having different polarisability. The materials synthesized and characterized show many of the properties necessary for device application. As a matter of fact they have been already used in the fabrication of both LED and FET. The complete linear and nonlinear optical characterization has been performed determining the real part of the refractive index n, its imaginary part k and the third order nonlinear value χ (3). The higher third order nonlinear susceptibility on very homogeneous spin coated film has been measured in the more planar copolymer containing thiophene, showing a value of 2 × 10−11  esu at 1650 nm.
Keywords: Fluorene-copolymer; Ellipsometry; Third order susceptibility; Films; Telecommunications;

Synthesis of phenyl-capped aniline heptamer and its UV–vis spectral study by Liang Chen; Youhai Yu; Huaping Mao; Xiaofeng Lu; Wanjin Zhang; Yen Wei (129-134).
Phenyl-capped aniline heptamer was synthesized by a simple oxidative coupling reaction. The method was accomplished by the reaction of parent aniline pentamer in the pernigraniline oxidation state with N,N′-diphenyl-p-phenylenediamine in the leucoemeraldine oxidation state. The mechanism probably involves the formation of cation radicals and their coupling. The heptamer has been characterized by IR, MALDI-TOF-MS, 1H NMR and elemental analysis. Its chemical oxidation process was studied by UV–vis spectra and the electrochemical analysis was studied by CV. It was found that the phenyl-capped aniline heptamer showed three oxidative waves in the cyclic voltammetry, different from polyaniline.
Keywords: Oxidative coupling; Phenyl-capped aniline heptamer; UV–vis spectra;

Two new Zn(II) complexes of, 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine (L 1 ), 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridine (L 2 ) were synthesized. These two complexes have the formulas Zn(L1)Cl2 (1) and Zn(L2)Cl2·CH3CN (2), respectively. Crystal structures of complexes 1 and 2 were determined by single-crystal X-ray diffraction. Crystallographic studies on 1 and 2 reveal both complexes to be five-coordinate with geometries that can be best described as distorted trigonal bipyramidal. Complexes 1 and 2 have blue luminescence at room temperature in solution and the solid state. The blue luminescence of the complexes is due to π*  → π transition centered on the ligands. The Zn(II) centers play a key role in enhancing fluorescent emission of the ligands.
Keywords: Bis(imino)pyridyl ligands; Zinc complexes; Crystal structure; Blue luminescence;

Polyaniline (PAn) film can directly react with the concentrated sulfuric acid to form sulfonic acid ring-substituted polyaniline (SPAn). Based on the cyclic voltammograms, the electrochemical behavior of SPAn is the same as that of PAn in the acid solution at pH <1, but is quite different from that of PAn in the basic solution. The cyclic voltammograms of SPAn in 0.3 M Na2SO4 solution with various pH values indicate that there are an anodic peak and two cathodic peaks at pH 10.6 when the scan rate was set at 60 mV s−1. The electrochemical behavior of SPAn is affected by the potential scan rate. At the scan rate of 6 mV s−1, two pairs of redox peaks occur on the cyclic voltammogram of SPAn in the solution of pH 10.6. In this case, its usable potential range is between 0.0 and 0.65 V (versus SCE). Based on the area of the cyclic voltammogram, a 44.8% of the electrochemical activity of SPAn is still retained when the SPAn electrode moved from pH 5.0 to 10.6. SPAn has a conductivity of 4.3 S cm−1, which is slightly dependent on pH when equilibrated with water. SPAn can react with alcohol to form the ester followed by hydrolization, which gives a straightforward evidence for the sulfonation of polyaniline. The FTIR spectra reveal a fact that polyaniline immersed in the concentrated sulfuric acid can be sulfonated, and the sulfonic acid group can be removed from SPAn by the reaction of SPAn with alcohol.
Keywords: Polyaniline; Sulfonation; Electrochemical activity; Wide pH range; Conductivity; IR spectra;

Structural and electronic properties of 3,4-ethylenedioxythiophene, 3,4-ethylenedisulfanylfurane and thiophene oligomers: A theoretical investigation by Carlos Alemán; Elaine Armelin; José Ignacio Iribarren; Francisco Liesa; Manuel Laso; Jordi Casanovas (151-156).
We report the results of a series of ab initio and DFT quantum mechanical calculations on the structure and on the electronic spectral of 2,3-ethylenedioxythiophene-, thiophene- and 2,3-ethylenedithiafurane-containing oligomers. Calculations were performed on oligomers formed by n repeating units, where n ranges from 1 to 8. The bond-length alternation patterns in the π-system, the importance of long-range interactions in the stabilization of oligomer chains, the energies of the HOMO and LUMO orbitals and the values of the lowest transition energy have been examined allowing a systematic comparison among the three families of conducting polymers.
Keywords: 3,4-Ethylenedioxythiophene; Thiophene oligomers; Conducting polymer; PEDOT; Band gap;

Interfacial properties of photovoltaic TiO2/dye/PEDOT–PSS heterojunctions by E.M.J. Johansson; A. Sandell; H. Siegbahn; H. Rensmo; B. Mahrov; G. Boschloo; E. Figgemeier; A. Hagfeldt; S.K.M. Jönsson; M. Fahlman (157-167).
Systems comprising a dense TiO2 film electrode, a ruthenium polypyridine dye and a PEDOT–PSS (poly(3,4-ethylenedioxythiophene)–poly(4-styrenesulphonate)) film were prepared. The heterojunctions were shown to have photovoltaic properties, with the dye absorbing the light, the TiO2 acting as an electron conducting material and PEDOT–PSS acting as a hole transport material. A series of dyes was used to investigate their influence on the photocurrent and the photovoltage characteristics of the heterojunction. These results were compared to a photoelectrochemical system in which the PEDOT–PSS was replaced by a liquid electrolyte containing triiodide/iodide redox-couple.Photoelectron spectroscopy (PES) was used to monitor the interfacial properties of the heterojunction and the investigation points out effects of importance when assembling the materials together to a functional unit. Specifically, it was concluded that the interaction with the dye clearly affects the structure of PEDOT–PSS, both with respect to the surface composition of PSS relative to PEDOT and with respect to the chemical state of the sulphur in the polymers. Moreover, a comparison of the Ru3d and the valence band spectra of the two different interfaces (dye/TiO2 and dye/PEDOT–PSS) indicates that the energy level structure of the dyes compared to the substrate is different for the two surfaces. Thus, in the combined energy level picture under dark conditions, the energy levels in TiO2 relative to the energy levels in PEDOT–PSS depend on the dye.
Keywords: Electron spectroscopy; PEDOT–PSS; TiO2; Dye-sensitized; Solar cell; Photovoltaic;

The effects of organic solvent on the electronic, structural and chemical properties of tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-OTs) are investigated. The use of different organic solvents during the oxidative chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) with iron(III)-tosylate can greatly vary the electrical conductivity of PEDOT-OTs along with molecular structure and doping concentration. For example, PEDOT-OTs prepared from methanol shows the conductivity of 20.1 S/cm, which is an increase by a factor of 107 compared to PEDOT-OTs prepared from acetone. From the X-ray diffraction (XRD) experiments, it was found that PEDOT-OTs samples prepared from ketone solvents are amorphous state, whereas PEDOT-OTs samples prepared from alcoholic solvents show the better defined crystalline structure in which the charge transport along and between the PEDOT chains are promoted. Chemical analysis employing X-ray photoelectron spectroscopy (XPS) revealed that the doping concentration of PEDOT-OTs with alcoholic solvents is much higher than that of PEDOT-OTs with ketones. It is proposed that the interactions between the organic solvent and iron(III)-tosylate can cause the variation in doping concentration and, therefore, result in the PEDOT-OTs of different conductivities and chain structures.
Keywords: Poly(3,4-ethylenedioxythiophene); Tosylate (p-toluene sulfonate); Organic solvent; Electrical conductivity; Doping concentration;

Synthesis, characterization and optical non-linearities of gold nanoparticles stabilized by oligo-2-aminopyridine derivative by Junpeng Zhuang; Huibiao Liu; Yinglin Song; Xiaofang Li; Ning Wang; Xiaorong He; Yuliang Li; Daoben Zhu (175-179).
Oligo-2-aminopyridine derivative-protected gold nanoparticles (OAP-Au) with narrow size distribution have been prepared via reduction of HAuCl4 by NaBH4 using a two-phase method. TEM image shows that the diameters of these particles range from 2 to 5 nm and the average diameter is 3.5 nm. The optical non-linearities of OAP-Au in chloroform were determined by the Z-scan technique with a pulsed laser of 8 ns width at 532 nm. The results indicate that OAP-Au show strong non-linear absorption and self-focusing effects.
Keywords: Oligo-2-aminopyridine; Gold nanoparticles; Optical non-linearities; Z-scan technique;

Electrically conductive PANI-DBSA/Co-PAN composite fibers prepared by wet spinning by Jiang Jianming; Pan Wei; Yang Shenglin; Li Guang (181-186).
Conductive composite fibers of polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) and polyacrylonitrile containing methylacrylate (Co-PAN) were prepared via a conventional wet spinning process. The influences of PANI-DBSA content on the electrical conductivity, thermal stability and mechanical properties of the composite fibers were investigated. The fiber with 7 wt% PANI-DBSA showed its conductivity of an order of 10–3  S/cm. The tensile strength of the fibers was in the range of 2.5–3.5 cN/dtex. The thermal stability of the composite fiber was superior to both pure Co-PAN and PANI-DBSA. It was observed through scanning electron microscope (SEM) and transmission electron microscope (TEM) that nanosized dot-like PANI-DBSA was well dispersed within Co-PAN matrix.
Keywords: Polyaniline; Polyacrylonitrile; Conductivity; Composite fiber; Wet spinning;

Polyaniline–transition metal salt complexes: insight into formation mechanisms by O.P. Dimitriev; P.S. Smertenko; B. Stiller; L. Brehmer (187-192).
Two basic morphologies of emeraldine base of polyaniline–transition metal salt complex films cast from N-methylpyrrolidinone solutions are described. The first morphology consists of grains and the other consists of loose aggregates, respectively. The correlation of the film morphology with formation of precipitate in the complex solution, kinetics of solvent evaporation from the cast film, amount of solvent entrapped in the film, film conductivity, and IR absorption spectra is shown. Two different mechanisms of the complex formation as a result of competition in the polymer–inorganic salt–solvent trio interactions are discussed; the first mechanism results in folding of macromolecules into compact coils being then a core of grains in the complex films, and the second mechanism leads to blending of the polymer chains with solvent giving rise to formation of loose aggregates.
Keywords: Polyaniline; Solvation; Transition metal salt; Morphology;

Two novel compounds based on aluminum and zinc metallo-8-hydroxyquinolates were prepared as electroluminescent (EL) materials and their absorbance, photoluminescence (PL), and EL properties were investigated. The structures of the compounds were characterized by 1H NMR, FT-IR and element analysis techniques. The luminescence centers of the two compounds, evidenced by absorbance and PL spectra, were from Alq3 and Znq2 units, respectively. The electron-donating substituents increased the solubility of the corresponding metal quinolate complexes in nonpolar solvents and caused a red-shift in the emission wavelength. The end groups of two compounds facilitated polymerization to form the metalloquinolate-containing polymers. The polymerization temperature was conformed by differential scanning calorimetry (DSC). EL data showed the two-layer devices fabricated using the two compounds exhibit diode-like electrical behavior. EL spectra mimic the PL spectra for the two compounds.
Keywords: Organic light-emitting diodes (OLEDs); Photoluminescence; Electroluminescence; 8-Hydroxyquinoline;

Free-standing polypyrrole actuators with response rate of 10.8% s−1 by Susumu Hara; Tetsuji Zama; Wataru Takashima; Keiichi Kaneto (199-201).
A free-standing polypyrrole film doped with bis(trifluoromethanesulfonyl)imide (TFSI) exhibited large electrochemical strains with fast response rate up to 10% s−1 in H2O/propylene carbonate solutions of LiTFSI. ▪A free-standing polypyrrole (PPy) film actuator without any additional electrode or metal backing, prepared electrochemically from an aromatic ester solution of tetra-n-butylammonium bis(trifluoromethanesulfonyl)imide (TBATFSI), exhibited up to 29% electrochemical strain, and a peak response rate of 10.8% s−1 in an H2O/propylene carbonate (PC) solution of LiTFSI. This is the very first time both large electrochemical strains and fast response rates were achieved in the conducting polymer actuators. The large and fast electrochemical deformation resulted from the fact that the PPy film doped with large TFSI anions swelled in PC such that TFSI can insert and expel the PPy film easily, and that a high ionic conductivity in H2O/PC solution enabled to move TFSI quickly.
Keywords: Fast response rate; Polypyrrole actuator; Artificial muscle; Conducting polymer; Bis(trifluoromethanesulfonyl)imide;

4-Bromocynnamic acid (1) was condensed with hydrazine hydrate in polyphosphoric acid to afford 2,5-di(p-bromostyryl)-1,3,4-oxadiazole (2). Two new series of soluble distyryloxadiazole-containing polyfluorenes (PF-OXD) and poly-p-phenylenes (PP-OXD) with various compositions were synthesized by Suzuki coupling utilizing 2 as a comonomer. These polymers showed optical band gaps of 2.85–2.90 eV and photoluminescence (PL) quantum yields in solution of 0.30–0.62. The solutions of polymers PF-OXD emitted blue light with PL maximum at 434–462 nm that was red shifted with the increase of the distyryloxadiazole content in the polymer. Thin films of polymers PF-OXD emitted intense green light with PL maximum around 520 nm as a result of the efficient energy transfer from the fluorene to the distyryloxadiazole segments even though the content of the latter in the polymer was 2 mol%. Polymers PP-OXD behaved as blue light emitting materials both in solution and solid state with PL maximum at 450–473 nm. Thin films of PF-OXD displayed excellent color stability even after being annealed at 100 °C for 24 h. The PL maximum of PP-OXD thin films was slightly blue shifted by 5 nm following this annealing.
Keywords: Poly(fluorene)s; Poly(p-phenylene)s; Distyryloxadiazole; Suzuki coupling; Energy transfer; Photoluminescence;

Highly electrically conductive poly(3,4-ethylenedioxythiophene) prepared via high-concentration emulsion polymerization by Yong Lei; Hideki Oohata; Shin-ichi Kuroda; Shintaro Sasaki; Takakazu Yamamoto (211-217).
Poly(3,4-ethylenedioxythiophene) (PEDOTh) with high electrical conductivity was prepared by oxidative polymerization of 3,4-ethylenedioxythiophene under high-concentration emulsion conditions in the presence of 2-naphthalenesulfonic acid sodium salt acting as an emulsifier and a doping agent and Fe2(SO4)3 as an oxidant. PEDOTh with electrical conductivity as high as 165 S cm−1 was obtained with good yield. XRD analysis indicated that the PEDOTh had a face-to-face stacking distance of 3.3 Å between the polythiophene planes in the solid. The SEM image revealed that the PEDOTh particles formed a layered structure. The packing structure, morphology, and electrical conductivity of the obtained PEDOTh were compared with those of PEDOTh synthesized via a usual emulsion polymerization.
Keywords: Poly(3,4-ethylenedioxythiophene); High electrical conductivity; High-concentration emulsion polymerization; Naphthalenesulfonate;

Organic field-effect transistors based on new TTF-based liquid crystalline materials by Mao Katsuhara; Isao Aoyagi; Hideyasu Nakajima; Takehiko Mori; Takuya Kambayashi; Masato Ofuji; Yoichi Takanishi; Ken Ishikawa; Hideo Takezoe; Hideo Hosono (219-223).
Tetrathiafulvalene (TTF)-based new organic semiconductors with a long alkyl chain and electron withdrawing substituents are prepared. Among them, cyano-substituted TTF (C n EDT-DC) shows a liquid crystalline phase (Smectic A) at 110–120 °C. This compound forms a good thin film on a SiO2 substrate on account of the good affinity of the polar cyano groups to the inorganic substrate, and the field-effect transistor fabricated on SiO2 shows mobility up to 0.02 cm2  V−1  s−1.
Keywords: Organic transistor; Organic FET; Tetrathiafulvalene; Liquid crystal;

Self-assembled colloidal crystalline arrays using hollow colloidal spheres by Hongyu Li; Bo Meng; Yawei Di; Xiaoyu Li (225-230).
Well-defined mesoporous colloidal crystals are generally prepared using templates, but these procedures are often very complicated. In this paper, we report a simple one-step method for forming three-dimensionally (3-D) ordered mesoporous polymer colloidal crystalline arrays (CCA). The CCA were formed by self-assembly of monodispersed hollow colloidal spheres obtained by classification of polydispersed hollow colloidal spheres in gravitational field, combined with separation using membrane technology. Four different methods have been employed to self-assemble polymer colloidal crystals, which were then experimentally evaluated. The polymer CCA formed by this method should be useful for preparing photonic band-gap materials and other applications.
Keywords: Colloidal crystalline arrays; Hollow colloidal beads; Self-assembly; Mesoporous materials; Photonic band-gap materials;

1,4-bis(5-decyl-2,2′-bithien-5-yl)benzene as new stable organic semiconductor for high performance thin film transistors by Sergei A. Ponomarenko; Stephan Kirchmeyer; Marcus Halik; Hagen Klauk; Ute Zschieschang; Günter Schmid; Alexander Karbach; Doris Drechsler; Ninel M. Alpatova (231-235).
The efficient synthesis of 1,4-bis(5-decyl-2,2′-bithien-5-yl)benzene, leading to “electronic-grade” pure semiconducting organic material, was elaborated. Cyclovoltamperometry measurements showed high oxidation stability of the thiophene-phenylene oligomer as compared to corresponding oligothiophenes. OTFT and integrated circuits, based on the synthesized oligomer, showed the mobilities as large as 0.3 cm2/Vs, on/off current ratios as large as 105, and signal delays as low as 300 μs (measured with ring oscillators). AFM measurements confirmed improved morphology of the oligomer films obtained by vacuum evaporation on room temperature substrates.
Keywords: Thiophene-phenylene oligomers; Organic semiconductors; Oxidative stability; Organic field-effect transistors;