Synthetic Metals (v.156, #2-4)

The in situ polymerization of aniline in nitrile rubber by Bluma G. Soares; Gabriel S. Amorim; Fernando G. Souza; Marcia G. Oliveira; J.E. Pereira da Silva (91-98).
Electrically conductive elastomer blends based on polyaniline-dodecylbenzene sulfonic acid (PAni.DBSA/nitrile rubber (NBR) was prepared by polymerization of aniline in the presence of NBR, using a direct, one-step in situ emulsion polymerization method in which DBSA played both roles of surfactant and dopant. At the same PAni content, the conductivity of the in situ emulsion-polymerized blends is higher than that of blends produced by mechanical mixing of both components. In addition, a more uniform morphology with the presence of PAni in the form of microtubules was achieved by the in situ process. Stronger interaction between the components were also confirmed by the presence of great amount of insoluble material in non-vulcanized blends, by Raman spectroscopy and rheological processing analysis (RPA).
Keywords: Polyaniline; Emulsion polymerization; Nitrile rubber; Electrical conductivity; Raman spectroscopy; Conductive composite; RPA;

The effects of surface treatment on device performance in pentacene-based thin film transistor by Jae Bon Koo; Seong Hyun Kim; Jung Hun Lee; Chan Hoe Ku; Sang Chul Lim; Taehyoung Zyung (99-103).
We report on the influence of surface treatment using hexamethyldisilazane (HMDS) on device performance of pentacene-based thin film transistor. The samples with surface treatment using HMDS show higher mobility, lower subthreshold slope, and lower off-current compared to the untreated samples. We have also investigated the effect of various coating methods of HMDS on device performance. In the case of post-baked samples after spin coating, the improvements of mobility and on-current are larger than those of spin-coated samples. Especially a dip-coated sample has threshold voltage of −4.11 V and turn-on voltage of −0.03 V, showing the enhancement mode characteristics, which is useful for the operation as a circuit and a switch device for active-matrix displays. However, the mobility of dip-coated sample is one order lower than that of spin-coated sample, and hysteresis is larger than that of spin-coated sample.
Keywords: Organic thin film transistor; Threshold voltage; Mobility; Pentacene; HMDS;

Electrochemical synthesis, characterization and photophysics of a poly(fluorenylene vinylene) derivative by Jonas Gruber; Rosamaria W.C. Li; Luis H.J.M.C. Aguiar; Tiago L. Garcia; Hueder P.M. de Oliveira; Teresa D.Z. Atvars; Ana F. Nogueira (104-109).
The electrosynthesis of a soluble poly(fluorenylene vinylene) derivative, namely poly(9,9-dioctyl-2,7-fluorenylene vinylene) (PDO27FV), its characterization, photophysical properties and electrochemistry are reported in this work. Photophysical studies indicate a strong dependence on the solvent employed, suggesting a highly polar excited state. The fluorescence quantum yield was estimated to be 0.52. Further, time-resolved photoluminescence exhibited two decays times, 0.68 and 1.31 ns, that are in agreement with a coupling deactivation process of the fluorenylene moiety, induced by the vinylene moiety. Electron affinity and ionization potential calculated from absorption and electrochemical data indicates that PDO27FV has potential to be applied as photoactive film in organic light emitting diodes and bulk heterojunction solar cells.
Keywords: Poly(fluorenylene vinylene); Photophysics; Electrosynthesis; Solvent effect; Time-resolved luminescence;

Photoluminescence and electroluminescence of oligoacetylenic silanes and germanes by Liming Ding; Wai-Yeung Wong; Hongqi Xiang; Suk-Yue Poon; Frank E. Karasz (110-116).
A series of light-emitting oligoacetylenic silanes and germanes containing fluorene units was investigated. It was found that the higher oligomers display lower band gaps and that the C―Si(Ge)―C bond permits π-electron delocalization. The π-dSi or π-dGe interactions aid the π-electrons in passing through the Si (Ge) atoms. The observed differences in fluorescence spectra may also result from a substituent effect of the silyl groups. The Si―Si σ bond also permits π-electron delocalization and thus there is a through-bond interaction between π orbitals and the Si―Si bond. The conjugation-interrupting Ge sp3 link aids π-electron delocalization along the oligomer backbone less efficiently than does a Si link, thus leading to relatively shorter effective conjugation lengths and higher band gaps. In the higher oligomers, multiple π-dSi or π-dGe interactions permit the vibrational levels of the excited state to split to form sublevels observable as new transitions in the respective absorption spectra. FWHM values of the PL spectra increase with increase of the oligomer backbone length which relates to the increase of the intermolecular interaction between the chromophore units. With increasing oligomer backbone length, the EL efficiency decreases, which can be attributed to the enhanced probability of interchain exciton annihilation in LEDs using higher oligomers.
Keywords: Oligoacetylenic silanes and germanes; Conjugation length; π-Electron delocalization; Photoluminescence; Electroluminescence; Light-emitting diodes;

This paper describes the effects of polyimide (PI) structure on electrical conductivity of blends of dodecylbenzene sulfonic acid-doped polyaniline (PANI-DBSA) and PI, as well as its thermal degradation behavior. Four types of PIs with different molecular architecture were synthesized and subsequently solution blended with PANI-DBSA. Of the four types of PIs, 4-4′-diaminodiphenyl sulfone (DADPS)-based PI provides the highest conductivity to the blends. It is attributed to the rigid nature of DADPS, which may induce more extended conformation of PANI chains, and hence result in a more ordered structure. The conductivity of the blends has significant higher thermal stability than that of PANI-DBSA. The thermal stability is, however, independent on the polyimide structure. TGA studies show that the PI matrix may have hindered the thermo-oxidative degradation and evaporation of the dopants and thus slowed down the process of thermal degradation of the conductivity.
Keywords: Polyaniline; Polyimide; Blend; Electrical conductivity; Thermal degradation;

In this study poly(dithieno[3,4-b,3′,4′-e]-[1,4]-dithiine) (PDTH) was synthesized potentiodynamically in both p- and n-doping domains in 0.1 M tetrabutylammonium tetrafluoroborate/acetonitrile/borontrifluoride ethylether (8:2, v/v). Resulting homopolymer was characterized via cyclic voltammetry, FTIR and UV–vis Spectroscopy. PDTH revealed both anodically and cathodically coloring electrochromic behavior, upon p- and n-doping, respectively. Spectroelectrochemistry analysis of p-doped polymer, reflected electronic transitions at 450–486, 766 and ∼900 nm, revealing π–π* transition, polaron and bipolaron band formation, respectively. As an anodically coloring material, polymer revealed multi-color electrochromism, exhibiting brick, green and light gray colors. As the cathodically coloring material, color varied between highly transmissive and brown, as such this material exhibits potential controllable states. Switching ability of the polymer was also investigated by a kinetic study upon measuring the %T at the maximum contrast point. Results showed that PDTH is a potential material for electrochromic devices both as anodically and cathodically coloring material.
Keywords: Electrochemical polymerization; Conducting copolymers; Electrochromic properties;

Results are reported of an investigation into the effects of UV irradiation on the electrical conductivity of poly(3-hexylthiophene) films and on the field-effect mobility in transistors formed from this semiconducting polymer. The UV source used was a pulsed excimer-laser (KrF, 248 nm) in a commercial, excimer-laser micromachining workstation. By limiting the fluence in the pulse to ∼50 mJ/cm2 controlled reductions of up to 2 orders of magnitude in both the bulk conductivity and field-effect mobility were achieved before significant ablation took place. Changes in the UV–vis spectrum of the P3HT show that reduced electrical transport is accompanied by an increase in the optical bandgap which is attributed to a reduction in π-conjugation either by chain scission or photo-oxidation of the polymer. It is argued that photobleaching of selected regions of the semiconducting polymer film is a viable technique for isolating individual transistors in a polymer electronic circuit.
Keywords: Polymer field-effect-transistor; Poly(silsesquioxane); Poly(3-hexylthiophene); Photobleaching; Conductivity; Field-effect mobility; Excimer-laser micromachining;

A novel low band gap polymer with an electron deficient oxadiazole side chain, poly[(α-bithiophene-5,5′-diyl) (5′-(2′′-phenyl-1′′,3′′,4′′-oxadiazole-5′′-phenylidene))-block-(α-bithiophene (2′′-phenyl-1″,3″,4″-oxadiazole-5″-phenylidene)quinodimethane-5, 5′-dily)] (PBTBQ-Oid), was synthesized. The polymer was soluble in common organic solvents, such as THF, chloroform and xylene. The structure of the polymer was confirmed by FT-IR, 1H NMR. The optical spectrum revealed that it had maximum absorption among 600–700 nm. The electrochemical analysis showed that it had good electron-transporting properties and a low band gap of ∼1.10 eV.
Keywords: Conjugated polymer; Low band gap; Oxadiazole;

Synthesis and properties of a new two-photon absorbing chromophore by Lei Wang; Xu-Tang Tao; Jia-Xiang Yang; Gui-Bao Xu; Yan Ren; Yang Liu; Yun-Xing Yan; Zhi Liu; Min-Hua Jiang (141-145).
This paper presents of a new, conjugated and symmetric multi-branched two-photon absorption chromophore 1,2,4,5-tetrakis(4-N-methyl-N-hydroxyethylamino)vinylphenyl benzene (TKAVPB) with D-π-D structure. The new dye built on 1,2,4,5-benzene core with four amino-branching units, which allows efficient π-electron delocalization, exhibits moderate two-photon absorption (TPA) value in the femtoseconds regime (TPA cross-section as 97 × 10−50  cm4  s photon−1  molecule−1 with 200 fs laser pulses). Linear absorption, single and two-photon fluorescence spectra were experimentally studied. When pumped with 760 nm laser irradiation, TKAVPB shows strong two-photon up-conversion fluorescence with peak at 527 nm.
Keywords: Two-photon absorption; Multi-branched compound; TKAVPB;

Composites of polypyrrole (PPy) and porous cross-linked polystyrene (PCPS) were prepared using a two-step batch method proposed by Ruckenstein and Park. However, the solvent employed by Ruckenstein and Park (methanol) in the polymerization step of their method was replaced with supercritical CO2. For comparison purposes, PPy/PCPS composites were also prepared using no solvent in the polymerization step. Conductivities as high as 10−2  S cm−1 were obtained, with or without the use of supercritical CO2. Uniformity of conductivity was determined via surface and bulk conductivity measurements, as well as by a new volume conductivity measurement that provides a measure of spatial (three-dimensional) distribution of the conducting component in the composite.The conductivity of composites prepared with or without the use of supercritical CO2 conformed to the same percolation behavior with respect to the amount of PPy formed. The percolation threshold in all cases was as low as 4 wt.%. The mechanical strength of the composites was found to be about the same as that of the host PCPS, as was the thermal stability. Therefore, the conductive component did not appear to adversely affect these properties of the host. Finally, the temperature behavior of the conductivity could be correlated with Mott's variable-range hopping (VRH) model for three-dimensional electronic transport.
Keywords: Conductive composite; Polypyrrole; Polystyrene; Supercritical carbon dioxide;

A series of thiophene-based oligomers are investigated by electroabsorption spectroscopy in terms of influence of chain length and peripheral substitution for the first time. Polycrystalline thin films of nonsubstituted oligomers, 8T, 6T and 4T, and of oligothiophenes with electron-withdrawing cyano substituents, 4T-V(CN)2 and CN-TET-CN, are measured and analyzed to determine the character of optical transitions. The results of the nonsubstituted oligomers suggest that the transitions at 500–600 nm present a neutral (Frenkel exciton) character, while those of oligothiophenes with electron-withdrawing substituents suggest that the transitions present a polar (charge-transfer exciton) one, indicating significant contribution of noncentrosymmetric substitution. Third-order nonlinear susceptibilitiy χ (3) (−ω; ω, 0, 0) is also evaluated, and it is shown that the longest unsubstituted oligomer 8T presents a high value of χ (3)  ∼ 45 × 10−12  esu, and substituted one CN-TET-CN presents further higher value of χ (3)  ∼ 250 × 10−12  esu. These investigations indicate multiple significance of electron-withdrawal substitution in molecular design of an oligothiophene-based nonlinear optical material.
Keywords: Oligothiophene; Electroabsorption spectroscopy; Third-order nonlinearlity; Chain length effect; Substitution effect;

Field-induced SDW phase and superconductivity of (DMET)2CuCl2 by H. Ito; Y. Yokochi; D. Suzuki; H. Tanaka; S. Kuroda; K. Enomoto; S. Uji; M. Umemiya; H. Miyasaka; K.-i. Sugiura; M. Yamashita (162-165).
We report low temperature electronic properties of a newly synthesized organic conductor (DMET)2CuCl2, consisting of stacks of DMET molecules constructing a quasi-one-dimensional Fermi surface. Superconductivity transition below 0.8 K is found, which is suppressed by a small magnetic field of 0.1 T. Under magnetic fields, successive step-like anomalies of magnetoresistance and plateau-like Hall resistance with sign reversals are found, indicating the occurrence of field-induced spin density wave (FISDW) transitions. The angular-dependent magnetoresistance and thermopower are measured in order to clarify the quasi-one-dimensional electronic structure.
Keywords: Organic superconductors; Magnetic phase transitions; Magnetotransport; Thermopower;

Design and electropolymerization of new chiral thiophene–salen complexes by Arnaud Voituriez; Mohamed Mellah; Emmanuelle Schulz (166-175).
New chiral thiophene-containing salen ligands have been synthesized. The corresponding metal complexes (Co, Cu, Cr and Ni) were prepared and electropolymerized at a platinum electrode by cyclic voltammetry. The resulting polymers exhibited stable and quasi-reversible redox processes when submitted to voltammetric repeated scans, whatever the nature of the metal or the structure of the ligand. Preliminary catalytic tests have been performed to examine the efficiency of these new chiral polymeric complexes as asymmetric heterogeneous catalysts.
Keywords: Chiral thiophene–salen ligands and complexes; Electropolymerization; Cyclic voltammetry;

Electrical conductivity in solution cast (using chloroform as well as mixture of chloroform and benzene as solvents) ferrocene-doped poly(methyl methacrylate) (PMMA) thin films were studied under photoexcitation in air by using surface-type sample cells at room temperature (300 K). The changes in current were measured in the films upon photoexcitation and after turning it off for repeated photoexcitations after a sufficient interval of time. Such studies were carried out as a function of the amount of chloroform in the PMMA film as well as the amount of ferrocene in the film prepared from chloroform. Ferrocene-doped PMMA thin films prepared from solution in chloroform and modified under photoexcitation in air have exhibited interesting photoswitching property monitored by photoconductivity measurements in air. The rise and decay of the photocurrent were studied. The results on photoconductivity have been discussed on the basis of formation of photoinduced charge-transfer complexes of ferrocene with chloroform molecules confined in the PMMA thin films, dissociation of the complexes, secondary thermal reaction and photodegradation of PMMA. Photodegradation of PMMA was studied by FTIR spectroscopy. The possible application of the modified ferrocene-doped PMMA films (containing chloroform molecules) upon photoexcitation in air has been mentioned.
Keywords: Polymer; Organic semiconductor; Thin films; Photoconductivity; FTIR spectra;

Photoluminescence and electroluminescence of 3-methyl-8-dimethylaminophenazine by Siewling Chew; Pengfei Wang; Oiyan Wong; Zirou Hong; Maoxia He; Ruiqin Zhang; Hoilun Kwong; Jianxin Tang; Shiling Sun; Chun Sing Lee; Shuit-Tong Lee (185-189).
A new phenazine dye—3-methyl-8-dimethylaminophenazine (MDAP) with intramolecular charge transfer (ICT) property was synthesized. The photoluminescence and electroluminescence of were investigated. The device with a configuration of ITO/TPD (30 nm)/TPD:MDAP (30 nm)/Alq3:MDAP (35 nm)/Alq3 (30 nm)/Mg:Ag (200 nm) showed a good performance with a brightness of 21650 cd/m2 at 250 mA/cm2, a maximum luminous efficiency of 9.97 cd/A and a yellow emission peaked at about 564–586 nm.
Keywords: Electroluminescence; Yellow emitting materials; Phenazine;

Conducting polymers of succinic acid bis-(2-thiophen-3-yl-ethyl)ester and their electrochromic properties by Lale Sacan; Ali Cirpan; Pinar Camurlu; Levent Toppare (190-195).
The homopolymer and copolymer of succinic acid bis-(2-thiophen-3-yl-ethyl)ester with thiophene were achieved via constant potential electrolysis in the presence of tetrabutylammonium tetrafluoroborate as the supporting electrolyte, and acetonitrile/borontrifluoride ethylether (ACN/BFEE) (10:2 v/v) solvent mixture. The characterizations of both homopolymer (PSATE) and copolymer P(SATE-co-Th) were achieved by various techniques including cyclic voltammetry (CV), FT-IR, scanning electron microscopy (SEM) and UV–vis spectroscopy. The four-probe technique was used to measure the conductivities of the polymers. Investigation of the electrochromic properties via spectroelectrochemistry, colorimetry and switching studies revealed that both polymers may serve as anodically coloring materials for use in ECD applications.
Keywords: Conducting polymers; Electrochemical polymerization; Electrochromic properties;

Grain size effects on contact resistance of top-contact pentacene TFTs by Sung Hun Jin; Keum Dong Jung; Hyungcheol Shin; Byung-Gook Park; Jong Duk Lee (196-201).
Multiple top-contact OTFTs with various channel lengths (L c) were successfully scaled-down to the L c of 1.8 μm by using the membrane shadow mask and the interface between the evaporated Au and pentacene was analyzed based on the channel resistance method. For large grain pentacene (S-80) deposited at 80 °C, the parasitic resistance (R p) at V GS  = −20 V has 1.8 ± 0.2 kΩ cm, whereas for small grain pentacene (S-20) deposited at 20 °C has 4.2 ± 0.2 kΩ cm, which means that R p depends on the grain size of pentacene. The grain size and grain boundary trap density for pentacene can be possibly origins to determine R p, which is critically correlated with bulk transport in pentacene. The grain boundary trap density (N t) for S-80 and S-20 was extracted as (5.6 ± 0.5) × 1011 and (1.2 ± 0.3) × 1012  cm−2 from the Levinson plots, respectively. In addition, activation energy of R p for S-80 is in the range from 42 to 48 meV, whereas for S-20 is from 72 to 108 meV.
Keywords: OTFTs; Shadow mask; Parasitic resistance; Grain boundary trap density; Activation energy;

Polyaniline nanofibers coated with polycatechol, FcPAn/polycatechol, have been prepared with two steps by using repeated potential cycling. First, aniline in a solution containing ferrocenesulfonic acid (Fc) was polymerized on a platinum electrode to form polyaniline nanofibers (FcPAn); second, catechol was polymerized on the polyaniline nanofibers to form FcPAn/polycatechol. The scanning electron microscopy (SEM) images show that the diameters of FcPAn and FcPAn/polycatechol fibers are in the range of 40–60 and 70–90 nm, respectively. The IR and XPS spectra of FcPAn/polycatechol indicate that ―OH groups and ferrocenesulfonic acid are contained in FcPAn/polycatechol. FcPAn/polycatechol has a good electrochemical activity in the wide pH range. The cyclic voltammogram identifies that FcPAn/polycatechol in the Na2SO4 solution with pH 11.0 still has the electrochemical activity at the scan rate of 60 mV s−1. The conductivity of FcPAn/polycatechol is 0.48 S cm−1, which is slightly affected by water. FcPAn/polycatechol nanofibers with the diameter of 70–90 nm have a higher catalytic activity to the electrochemical oxidation of ascorbic acid, compared with FcPAn/polycatechol fibers with the diameter of 140–210 nm.
Keywords: Polyaniline nanofibers; Coated with polycatechol; Ferrocenesulfonic acid; Catalytic activity; XPS and IR spectra; Conductivity;

Synthesis and characterization of light-emitting materials composed of carbazole, pyrene and fluorene by Zujin Zhao; Xinjun Xu; Fang Wang; Gui Yu; Ping Lu; Yunqi Liu; Daoben Zhu (209-214).
A series of ethynyl-linked π-conjugated light-emitting molecules with good photoluminescence properties were designed and synthesized through Pd/Cu-catalyzed Sonogashira coupling reaction. The main structure comprised of different fluorophors (pyrene, carbazole, and fluorene), which were linked with triple bonds in order to be screened for high emission efficiency. Optical properties of these synthesized compounds (I a I f ) were examined in solutions, thin films and solid states, respectively. All of them showed relative high quantum yields both in solutions (Φ s: 0.70–0.83) and in films (Φ f: 0.17–0.34). Light-emitting diode using I e as an emissive layer was fabricated in the ITO/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS)/I e/2, 2′, 2″-(1, 3, 5)-benzene-triyl)tris[1-phenyl-1H-benzimidazole] (TPBI)/Al configuration. The maximum emission wavelength of the device was 496 nm. The maximum luminance and electroluminescence efficiency was 1000 cd/m2 and 0.41%, respectively.
Keywords: Sonogashira coupling reaction; Photoluminescence; Electroluminescence; Quantum yields; Light-emitting materials;

In this work, we describe the use of electrical impedance spectroscopy to investigate not only the process of absorption of monomers of pyrrole in films of conventional polymers, but also the kinetics of their subsequent polymerization in the interior of dielectric matrices of this kind. By exposing the matrix to pyrrole vapor and monitoring the in situ dielectric response of the composite system, as the polymerization proceeds we can observe the gradual increase in the number of percolation pathways for the electrical current by following the associated shift in the frequency of the dielectric relaxation of the polymeric blend formed. By comparing the different rates in which these mechanisms occur, we can estimate how easily the polypyrrole (PPY) chains are formed in the interior of distinct dielectric matrices, establishing in this manner the relative feasibility of use of these polymeric blends as convenient materials in molecular electronic devices.
Keywords: Polypyrrole; Impedance; Dielectrics; Polymeric blends;

We found that the luminescence profile of poly[2,5-di(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (OC10C10-PPV), which originally is an orange-emitting polymer, can red-shift significantly by ca. 30 nm (λ max: from 585 to 614 nm) and become very narrow (full width at half maximum: 30 nm) when doped into poly{2-[m-(3′,7′-dimethyloctyloxy)phenyl]-1,4-phenylene vinylene} (m-Ph-PPV). Due to the ordered structure of the host polymer, the effective conjugation length of the guest polymer is extended as if the chains were frozen. Surprisingly, the OC10C10-PPV chains can even be more tightly locked in the ordered m-Ph-PPV matrix than in the cooled neat OC10C10-PPV film at 5 K.
Keywords: Conjugated polymers; Poly(phenylene vinylene); Polymer blends; Electroluminescence; Red light emitting diodes;

The synthesis and the study of temperature dependence of the electrical conductivity, σ, and Seebeck coefficient, S, for some new organic salts, N-(p-R-phenacyl)-4,5-diazafluorenium-9-one bromides, in thin films, is reported.The dependences ln  σ(103/T) and S(103/T) are typical for p-type semiconducting compounds. The values of some characteristic parameters for the examined compounds (the thermal activation energy of electrical conduction, ΔE, the ratio of carrier mobilities, b, etc.) have been determined. The obtained values of ΔE ranged from 1.71 and 2.01 eV, while those of b lay in the range 0.70–0.87. The analysis of the absorption edge evidenced direct energy gaps, ranged between 3.31 and 3.39 eV, as well the presence of Urbach absorption tails.Some correlations between respective values and molecular configurations of the present organic salts are established. The model based on band gap representation is suitable for the explanation of the electronic transfer mechanism in the investigated compounds.
Keywords: Heterocycle synthesis; Optical absorption and emission spectroscopy; Atomic force microscopy; Transport measurements (conductivity); Polycrystalline thin films; Organic semiconductors based on conjugated molecules;

Preparation and characterization of polyaniline (PANI) doped with anions containing phosphorus was investigated with the help of various technique. The chemical polymerization of aniline was carried out in acid media containing different anions of organic phosphorus acid with the use of ammonium peroxidisulfate as oxidant agent. The highest yield was observed in the case of styrilphosphonic acid. The conductivity increased in the following order: phenylphosphinic acid < 2chloroethylphosphonic acid < styrilphosphonic acid. The solubility tests carried out in DMF, DMSO and NMP showed that the presence of voluminous anions improves the solubility of doped PANI. The synthesized PANI was characterized by density, intrinsic viscosity, solubility, FTIR, UV–vis, NMR, conductivity and TGA measurements. The hardness, elasticity, resistance and protective behavior of acrylic films were determined. The acrylic dispersion based on PANI doped with anions containing phosphorus provides improved corrosion protection of carbon steel.
Keywords: Conductive polymers; Polyaniline; Solubility; Thermal stability;

An intramolecular cyclic disulfide-containing polypyrrole was prepared by the chemical-oxidative polymerization of 4,6-dihydro-1H-[1,2]dithiino[4,5-c]pyrrole (MPY), and the electrical properties were investigated as the cathode active material in lithium secondary batteries. Oxidizing agents and solvents for the chemical-oxidative polymerization were examined to prevent over-oxidation of the polypyrrole backbone. The conductivity of poly(MPY), the polymer prepared using FeCl3 in ethylene glycol, was around 10−4  S/cm. Poly(MPY) showed very little over-oxidation, good redox properties, and a high discharge capacity of 398 mAh/g based on the redox response of the disulfide.
Keywords: Polypyrrole; Disulfide; Chemical-oxidative polymerization; Lithium battery; Conductivity;

The specific capacitance of polyaniline (PANI) deposited potentiodynamically on a stainless steel (SS) substrate, in the presence of p-toluene sulphonic acid (PTS) is estimated. Cyclic voltammetric experiments, galvanostatic charge–discharge studies and impedance analysis are carried out in order to investigate the applicability of the system as an electrochemical supercapacitor. Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are employed for characterization of the electrode.
Keywords: Capacitance; Polyaniline; Potentiodynamic deposition; p-Toluene sulphonic acid; Stainless steel;

Conductive complexes of [Ni(dmid)2] with TTF, TMTTF, and ET by O.N. Kazheva; G.G. Alexandrov; O.A. Dyachenko; T.N. Zinenko; A.V. Kravchenko; V.A. Starodub; A.V. Khotkevich (251-255).
Three charge-transfer salts of [Ni(dmid)2] (dmid: 1,3-dithiol-2-one-4,5-dithiolate)—TMTTF[Ni(dmid)2], TTF x [Ni(dmid)2] and ET x [Ni(dmid)2] (TMTTF: tetramethyl-tetrathifulvalene, TTF: tetrathifulvalene, ET: bis(ethylenedithio)-tetrathiafulvalene) are prepared and characterized. The TMTTF[Ni(dmid)2] complex has a structure with mixed packs is formed by cations and anions, which alternate each other with subsequent shift. This compound is semiconductor with the room-temperature conductivity of 2.2 × 10−3  Ω−1  cm−1. The TTF x [Ni(dmid)2] and ET x [Ni(dmid)2] complexes have a highest conductivity: σ RT 1.86 and 0.54 Ω−1  cm−1, respectively.
Keywords: Charge-transfer salts; 1,3-Dithiol-2-one-4,5-dithiolate; Crystal structure; Electrical conductivity;

Poly[1-(thiophene-2-yl)benzothieno[3,2-b]benzothiophene] (poly-TBTBT) was electrosynthesized on a Pt electrode by anodic oxidation of TBTBT in 0.1 M LiClO4 acetonitrile solution and in a micellar medium (water/methanol, 9/91, v/v) containing 0.39 M perchloric acid and 0.1 M sodium dodecylsulfate (SDS). Films prepared in acetonitrile were thick and electroactive, whereas in micellar medium they were very thin. Poly-TBTBT was characterized by cyclic voltammetry, MALDI-TOF mass spectrometry, IR, and scanning electron microscopy (SEM). Poly-TBTBT films were essentially constituted of short-chain oligomers (dimer to octamer). The molecular orbital (MO) calculations, carried out on the basis of a radical–cation electropolymerization mechanism, confirmed the spectral results The optical properties, including the electronic absorption and fluorescence spectra, were also examined.
Keywords: 1-(Thiophene-2-yl)benzothieno[3,2-b]benzothiophene; Electropolymerization; Conducting oligomers; Optical properties; Fluorescence; Micellar media;

Synthesis of 2-phenylquinoline-based ambipolar molecules containing multiple 1,3,4-oxadiazole spacer groups by Neng Jun Xiang; Tik H. Lee; Meng Lian Gong; K.L. Tong; S.K. So; Louis M. Leung (270-275).
A series of donor–acceptor type ambipolar electroluminescence dyes with the general structure PQ(OXD) n T (where n  = 1, 2 and 3) were prepared, in which PQ is 2-phenylquinoline, T is diphenylamine which constituted the hole transporting triphenylamine moiety with an adjacent phenyl ring, and OXD is an electron transporting 2-phenyl-1,3,4-oxadiazole repeating unit. The compounds fluoresced bluish green to green hue in solid-state, exhibited a positive solvatochromism in solution and their quantum efficiency decreased rapidly with increase in n. The materials are thermally stable with glass transition temperature (T g) ranging from 83 °C (n  = 1) to 130 °C (n  = 3). Cyclic voltammetry studies indicated the HOMO remained relatively unchanged with n while the LUMO decreased (away from the vacuum level) with an increase in the number of OXD. For single layer homojunction OLEDs, highest efficiency was obtained when n  = 1 (max luminous 3300 cd/m2 and current efficiency 0.9 cd/A), whereas for multilayer heterojunction OLEDs, best results was achieved for compounds with n  = 1 or 2 assuming the role of the HT layer (over 8200 cd/m2 max and 2.0 cd/A). Formation of exciplexes led to significant red-shift and lower emission efficiency for the compound with n  = 3.
Keywords: 1,3,4-Oxadiazole; 2-Phenylquinoline; Triphenylamine; Ambipolar fluorescence dyes;

A new conjugated polymer, poly{[1′,4′-bis-(thienyl-vinyl)]-2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene} (PTVMEH-PPV) was synthesized via Grim polymerization. The polymer is soluble in common organic solvents such as chloroform and tetrahydrofuran, and possesses adequate thermal stability (T d  > 246 °C). The absorption spectrum of PTVMEH-PPV film shows a broader absorption peak covering the wavelength range from 380 nm to 620 nm, which is red-shifted and broadened in comparison with that of MEH-PPV. The onset oxidation potential of the polymer is 0.12 V versus Ag/Ag+, ca. 0.2 V lower than that of MEH-PPV. The band gap of the polymer measured by cyclic voltammetry is 1.82 eV, which basically agrees with that obtained from the onset wavelength of the absorption spectra. Polymer solar cell was fabricated based on the blend of PTVMEH-PPV and PCBM with a weight ratio of 1:1. The device shows the maximum external quantum efficiency of 14% at ca. 520 nm, an open circuit voltage of 0.67 V and a power conversion efficiency of 0.32% under the illumination of AM1.5, 80 mW/cm2.
Keywords: Conjugated polymers; Copolymers; Absorption spectra; Polymer photovoltaic cells;

New conjugated materials containing cyano substituents for light-emitting diodes by Ali Cirpan; Hemali P. Rathnayake; Gorkem Gunbas; Paul M. Lahti; Frank E. Karasz (282-286).
New electroluminescent cyano-substituted phenylenevinylene (PV) monomeric and oligomeric chromophores, 13, were synthesized by Knoevenagel condensation and investigated in terms of their photoluminescence (PL) and electroluminescence (EL) behavior. All show PL emission maxima between 463 and 471 nm in solution with quantum efficiencies of 0.65, 0.46 and 0.68, respectively. EL maxima in an LED configuration ITO/PEDOT–PSS/13/Ca–Al were 507, 518 and 551 nm with luminance efficiencies 0.01, 0.05 and 0.02 cd/A, respectively.
Keywords: Light-emitting diode; Electroluminescence;

Aiming to investigate the influence of the growth potential on the properties of poly(3-methylthiophene), electrochemical and ellipsometric signals, simultaneously recorded during the potentiostatic polymer formation on platinum electrodes, are analysed. The experimental data is contrasted to that obtainable with the use of the three-layers model for the growth of homogeneous films. The results reveal that the polymer prepared at 1.36 V (versus SCE) shall be regarded as a multilayered material, whereas the polymer synthesized at 1.38 V (or higher potentials) can be modelled as a two layered system. For all studied growth potentials, the outer layers are less dense. Differences in the growth process imparted by small variations in the applied potential are also clearly retrieved from the calculated complex refractive indices: the inner layers of the films obtained at low growth potentials are thicker, less absorbing and displaying higher optical density. These features correlated with the amount of charge spent prior the polymer deposition at each potential support the precipitation of oligomers of distinct length originating differently ordered polymer structures. The analysis of the redox behaviour displayed by the films prepared under different controlled potentials is also consistent with the interpretation of the ellipsometric results.
Keywords: Poly(3-methylthiophene); Electropolymerization; Ellipsometry; Structure; Multilayered polymer film;

Photoconductivity in fullerene-doped polysilane thin films by Anjali Acharya; Shu Seki; Akinori Saeki; Seiichi Tagawa (293-297).
Flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements have been performed to study the transport properties of charge carriers in the polysilane films. The effect of C60 concentrations on photoconductivity of poly(methylphenylsilane) (PMPS) and poly(n-hexylphenylsilane) (PHPS) films has been studied using a variety of excitation light sources. The value of ϕ ∑ μ , which is the product of quantum efficiency of photocarrier generation (ϕ) and sum of moibilities of the carriers ( ∑ μ ), depends strongly on C60 concentration upon exposure of 532 nm. The quantum efficiency reaches ∼0.06 with C60 concentration at 5.7 mol%, and saturates at the higher concentrations. The ϕ ∑ μ value increases considerably upon exposure of 193 nm up to 1.22 × 10−3  cm2/Vs without significant dependence on C60 concentration, suggesting the direct formation of electron-hole pair by 6.39 eV photon absorption with the higher ϕ value at ∼0.12. The present technique gave the estimates of intra-chain mobility of charge carriers in PMPS and PHPS, and one-order magnitude higher intra-chain mobility was observed in PHPS than that in PMPS. This is suggestive of a highly ordered Si backbone conformation in PHPS. The intra-chain mobility in PMPS, however, is at least two orders of magnitude higher than the mobility values estimated by conventional time-of-flight techniques. Thus we conclude that the higher mobility than ∼10−3  cm2/Vs (E  ∼ 0) is realizable even with PMPS by precise synthesis and device fabrication free from disordering, defects, impurities, etc.
Keywords: TRMC; Polysilane; Flash photolysis; Mobility; Charge separation;

Current–voltage (IV) characteristics of the molecular electronic devices using various organic molecules by J.R. Koo; S.W. Pyo; J.H. Kim; S.Y. Jung; S.S. Yoon; T.W. Kim; Y.H. Choi; Y.K. Kim (298-301).
Organic molecules have many properties that make them attractive for electronic applications. We have been examining the progress of memory cell by using molecular-scale switch to give an example of the application using both nano scale components and Si-technology. In this study, molecular electronic devices were fabricated with amino style derivatives as redox-active component. This molecule is amphiphilic to allow monolayer formation by the Langmuir–Blodgett (LB) method, and then this LB monolayer is inserted between two metal electrodes. According to the current–voltage (IV) characteristics, it was found that the devices show remarkable hysteresis behavior and can be used as memory devices at ambient conditions, when aluminum oxide layer was existed on bottom electrode. The diode-like characteristics were measured only, when Pt layer was existed as bottom electrode. It was also found that this metal layer interacts with organic molecules and acts as a protecting layer, when thin Ti layer was inserted between the organic molecular layer and Al top electrode. These electrical properties of the devices may be applicable to active components for the memory and/or logic gates in the future.
Keywords: Langmuir–Blodgett techniques; Metal/insulator interfaces; Switches;

Charge carrier transport in layers of discotic liquid crystals as studied by transient photocurrents by A. Rybak; J. Pfleger; J. Jung; M. Pavlik; I. Glowacki; J. Ulanski; Z. Tomovic; K. Müllen; Y. Geerts (302-309).
Transient photocurrent measurements were performed for a series of layers of discotic liquid crystals and of perylene derivative prepared in different ways with an aim to characterize the charge carrier transport in configurations corresponding to photovoltaic devices and field effect transistors. The course of the transient photocurrent was found to be strongly dependent on the layer preparation procedure: the non-dispersive transport, and well defined transit times, were found only for “squeezed” sandwich-type sample of triphenylene derivative in which homeotropic orientation of the discotic columns was induced assuring formation of continuous paths connecting the opposite electrodes. In all other cases dispersive transport of charge carriers was observed, due to the spatial and/or energy disorder of hopping states and fast trapping by localized states. From the asymmetry of the transient photocurrents for different polarity of the illuminated electrode it was concluded, that holes are more mobile in the hexabenzocoronene derivatives and in the triphenylene derivative, while electron transport dominates in the perylene derivative.
Keywords: Organic semiconductors; Discotic liquid crystals; Photoconductivity; Electrical properties and measurements;

The paper presents results of studies on composites made from polypropylene (PP) modified with polyaniline (PANI) doped with phenylophosphonic acid (PPA). For better miscibility of the components, lauryl gallate (LG) was added. Obtained results show that the amount of PPA and LG affect the thermal and structural properties of the composites. Changes of thermal properties, and particularly of structure, caused by addition of PPA and LG, affect the conductivity of the composites. The results discussed in the paper were obtained using differential scanning calorimetry (DSC) and optical microscopy as well as wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS).
Keywords: Polypropylene; Polyaniline; Composites; Crystal structures; Conducting polymers;

Spectroscopic investigations of copolymers incorporating various thiophene and phenylene monomers by S. Ayachi; K. Alimi; M. Bouachrine; M. Hamidi; J.Y Mevellec; J.P. Lère-Porte (318-326).
Experimental and theoretical studies are combined in order to describe copolymers involving various thiophene and phenylene monomers (TBT). The copolymers structures are confirmed and their optical properties are examined. The incorporation of a block unit, such as biphenylene, bipyridine or anthracene into the full conjugated backbone has a significant effect not only on the structural and vibrational properties of the compound but also on its optical behavior, resulting in different electronic transitions and emission colors from blue to blue-greenish and green. Therefore, a better correlation between photoluminescence and Raman vibrational modes assigned to the phonon emission is established. Theoretical studies, based mainly on density functional theory (DFT) calculations, are performed to explain the effect of the block unit incorporation in the optical property modifications. As a result, the blue shift is related to a less planar structure of the copolymer.
Keywords: Conjugated polymers; Raman scattering; Optical properties; DFT calculations;

Physical properties and field-effect transistors based on novel thiazolothiazole/heterocyclic and thiazolothiazole/phenylene co-oligomers by S. Ando; J. Nishida; E. Fujiwara; H. Tada; Y. Inoue; S. Tokito; Y. Yamashita (327-331).
Novel five-membered heterocyclic or phenylene oligomers containing a thiazolothiazole ring system have been investigated as active materials of organic field-effect transistors (OFETs). The cyclic voltammetry and X-ray diffractogram studies revealed the relationship between the molecular structures of these co-oligomers and FET performance. The field-effect mobilities of 10−4 to 10−3  cm2/Vs were obtained for the furyl derivatives and their FET performances as p-type semiconductors are presented as the first examples of FET behavior of oligomers including furan rings.
Keywords: Organic semiconductors; Organic field-effect transistors; Heterocyclic synthesis; Co-oligomers; Thermal, optical and electrochemical measurement;

Multiwalled carbon nanotube nucleated crystallization and reinforcement in poly (vinyl alcohol) composites by K.P. Ryan; M. Cadek; V. Nicolosi; S. Walker; M. Ruether; A. Fonseca; J.B. Nagy; W.J. Blau; J.N. Coleman (332-335).
One of the fastest growing areas of nanotube research is the study of polymer-nanotube composite materials. These materials utilize the excellent strength of carbon nanotubes that has been evident but difficult to harness in the past and show impressive increases in strength relative to the polymer. It is suspected that many of the physical properties observed in these composites are related to the formation of crystalline polymer coatings around the nanotubes in solution. The work presented here addresses this issue by doping a semi-crystalline polymer, poly (vinyl alcohol), with multiwalled carbon nanotubes. Dynamic mechanical analyzer (DMA) measurements of thin films identified a three- to five-fold increase in the Young's modulus of the polymer depending on nanotube type. Dynamic differential scanning calorimetry (DSC) of thin films shows that the increase in modulus is accompanied by an increase in polymer crystallinity. In addition, the results verify that multiwalled carbon nanotubes nucleate crystallization of the polymer and a link between polymer crystallinity and composite reinforcement is established. Furthermore, transmission electron microscopy (TEM) images confirm an excellent dispersion and wetting of the nanotubes in the polymer solution providing visual evidence of matrix reinforcement.
Keywords: Solution processing; Crystalline/amorphous interfaces; Polycrystalline thin films;

The low energy onset of the optically accessible density of electronic states (OADOS) of the conjugated polymer MEH-PPV has been investigated by low temperature fluorescence single molecule spectroscopy (SMS). The first extensive set of high signal-to-noise SMS data have been acquired for MEH-PPV samples as a function of molecular weight confirming the previously reported bimodal energy gap distribution. These data have been acquired under sample and radiation conditions that inhibit photophysical dynamics that have distorted previous SMS studies. A molecule by molecule vibronic analysis has yielded an experimentally determined spectral density of the S0–S1 energy gaps for the individual chromophores for MEH-PPV. The SMS data has also led to new insights on the energy transfer pathways for conjugated polymers, and on the molecular nature of the “blue” and “red” sites of conjugated polymers. Finally, a combined analysis of the new SMS data with the previously obtained bulk absorption and emission data for MEH-PPV has offered clear evidence that the low energy onset of the OADOS for MEH-PPV, in analogy to the emission spectral density, confirms the existence of a bimodal energy gap distribution.
Keywords: MEH-PPV; Single molecule spectroscopy; Bimodal energy gap distribution;

Fabrication of Ag/polypyrrole coaxial nanocables through common ions adsorption effect by Aihua Chen; Huxiao Xie; Haiqiao Wang; Hongyu Li; Xiaoyu Li (346-350).
According to the common ions adsorption effect, Ag+ ions will be adsorbed onto the closest surface of silver nanowires after being immersed in AgNO3 solution. This makes the surface of silver nanowires become the active sites to oxidize pyrrole monomer to form PPy sheath without adding other oxidizing agent. The results of FT-IR and UV–vis spectra show the formation of PPy chain when pyrrole monomer was added to the reaction mixture containing the disposed silver nanowires. TEM images further prove that the Ag/polypyrrole (PPy) coaxial nanocables have been fabricated. The thickness of PPy sheath can be controlled by adjusting the concentration of AgNO3 aqueous solution, which used to dispose silver nanowires. To some extent, the thickness of PPy layer would increase with the increasing of the concentration of AgNO3 solution. After the adsorbed Ag+ ions on the surface of silver nanowires reach to the saturation, the thickness of PPy layer would not change greatly with continuously increasing of AgNO3 concentration.
Keywords: Common ions adsorption effect; Ag/polypyrrole; Coaxial nanocables;

A free-standing polypyrrole (PPy) film actuator, prepared electrochemically from a methyl benzoate solution of 1,2-dimethyl-3-propylimidazolium tris(trifluoromethylsulfonyl)methide (DMPIMe), exhibited up to 36.7% electrochemical strain in a propylene carbonate (PC)/water solution of lithium bis(nonafluorobutylsulfonyl)imide, Li(C4F9SO2)2N (LiNFSI). The maximum electrochemical strain of Me-doped PPy film depended on the electrolyte used for driving the Me-doped PPy actuator. When a PC/water mixed solution of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was used as the driving electrolyte, the maximum electrochemical strain, measured by cycling between −0.9 and +0.7 V versus Ag/Ag+ at 2 mV s−1, was 24.2%, smaller than that (30.0%) driven with LiNFSI. When a PC/water suspension of DMPIMe was used as the driving electrolyte, the maximum electrochemical strain was 31.9%. However, the response speed of Me-doped PPy actuator driven with DMPIMe was slower than those driven with Li(C n F2n+1SO2)2N, due presumably to the size and shape of the anions. The addition of CF3COOH in electrolytic solutions for electropolymerization increased the maximum electrochemical strains (36.7% and 36.6%) of Me-doped PPy actuator driven by using a PC/water solution of LiNFSI and a PC solution of DMPIMe, respectively.A polypyrrole tube doped with tris(trifluoromethylsulfonyl)methide (Me) prepared on a carbon rod at +1.2 V versus Ag/AgCl from a methyl benzoate solution of DMPIMe with CF3COOH. ▪
Keywords: Polypyrrole actuator; Artificial muscle; Conducting polymer; Tris(trifluoromethylsulfonyl)methide;