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Synthetic Metals (v.159, #15-16)

Editorial Board (pp. iii).

Solution processable organic electro-phosphorescent iridium complex based on a benzothiazole derivative by Jae-Ho Choi; Choong-Hwa Jung; Ji Young Kwon; Hoon-Je Cho; Jonghee Lee; Jeong-Ik Lee; Hye-Yong Chu; Do-Hoon Hwang (pp. 1517-1521).
We have synthesized a new solution processable iridium complex, di[2-(4′-octyloxyphenyl) benzothiazole]iridium(III)acetoacetone, [(OPBT)2Ir(acac)], based on benzothiazole derivative for organic electro-phosphorescent devices. The synthesized molecule was identified by1H NMR and13C NMR, and readily soluble in common organic solvents such as chlorobenzene. The UV–visible absorption and photoluminescence properties of pristine [(OPBT)2Ir(acac) thin film as well as poly( N-vinylcarbzole) (PVK) thin film doped with the iridium complex were studied. The maximum UV–visible absorption and photoluminescence (PL) spectra are found to be at 337nm and 547nm, respectively. We have fabricated phosphorescent organic light-emitting devices using the ITO/PEDOT:PSS (40nm)/PVK:(OPBT)2Ir(acac) (40nm)/Balq (40nm)/LiF (1nm)/Al (80nm) configuration with the iridium complex as a triplet emissive dopant in poly( N-vinylcarbazole) (PVK) host. The electroluminescence (EL) devices showed greenish yellow light emission with maximum peak at 551nm. Especially, the maximum external quantum and current efficiency of 1mol% doped device were 1.74% and 4.89cd/A, respectively.

Keywords: Electro-phosphorescence; Benzothiazole; Iridium complex; Solution processable

Morphology and properties of polypyrrole electrosynthesized onto iron from a surfactant solution by I.L. Lehr; S.B. Saidman (pp. 1522-1528).
The morphology of polypyrrole (PPy) deposits during electrosynthesis onto iron electrodes in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) solutions have been investigated using Scanning Electron Microscopy (SEM). At the early stages of electrosynthesis, fibrillar, toroidal and globular forms are observed while polymerization at longer times leads to a closely packed deposit. The effects of electropolymerization parameters on the obtained morphology are discussed. It is proposed that electropolymerization rate and polymer stiffness are important factors in controlling the morphology. Electrochemical investigations demonstrate that toroid-shaped deposits present electrochemical activity. The experimental results indicate that a gelatinous product, formed as a result of iron dissolution, grows simultaneously with PPy.

Keywords: Polypyrrole; AOT; Electrochemical polymerization; Iron electrode; Scanning electron microscopy

Novel conjugated polymers employing the binding of polyfluorene derivatives and C60 by Youngeup Jin; Jaesung Jee; Heejoo Kim; Suhee Song; Sung Heum Park; Jaehong Kim; Shin-Won Kang; Han Young Woo; Kwanghee Lee; Hongsuk Suh (pp. 1529-1537).
New polyfluorene (PF)-based conjugated polymers, PClBEHF, PClBEHF- co-PDEHF, PN3BEHF, PN3BEHF- co-PDEHF, PEHPBF, PC60BEHF, PC60BEHF- co-PDEHF, and PEHPBF+PCBA containing chloro, azido, piperidine, and fullerene (C60) groups as pendants, were synthesized. In the case of PC60BEHF and PC60BEHF- co-PDEHF, the C60 moiety was introduced by using covalent bond formation between the azido group and C60. PEHPBF+PCBA was synthesized by using ionic bond formation between the piperidinium cation of PEHPBF and carboxylate anion of PCBA. The PL and EL spectra of PClBEHF, PClBEHF- co-PDEHF, PN3BEHF, PN3BEHF- co-PDEHF, and PEHPBF exhibited red-shifted and broad peaks caused by the aggregation which was induced by the increasing interchain interaction due to the polar pendants. After binding with C60, covalently and ionically, the photovoltaic properties of PC60BEHF, PC60BEHF- co-PDEHF, and PEHPBF+PCBA were studied. PL was quenched completely, which indicates photo-induced charge transfer from PF to pendant C60. Even though photovoltaic effects did not occur in short circuit condition, blending with MEH-PPV as the ratio of 1:1 generated the photovoltaic effects.

Keywords: Photovoltaic effect; Pendant fullerene; Polyfluorene

Development and characterization of ionic liquid doped solid polymer electrolyte membranes for better efficiency by Pramod K. Singh; Kang-Wook Kim; Hee-Woo Rhee (pp. 1538-1541).
Solid polymer electrolyte membranes based on poly(ethylene oxide) (PEO) polymer electrolyte incorporated with low viscosity ionic liquid (IL), 1-ethyl 3-methylimidazolium trifluoromethanesulfonate (EMImTFO) have been prepared and used in dye-sensitized solar cell (DSSC) application. Ionic conductivity ( σ) measurement shows improvement in σ due to reduced crystallinity and free charge carriers provided by IL which was further affirmed by our differential scanning calorimetry (DSC) and optical microscopy (OM) measurements. Surface feature of films was characterized by scanning electron microscopy (SEM) measurement. The photovoltaic characteristics of the fabricated DSSC are compared with those without IL, in which the low viscosity IL doped solid polymer electrolyte system shows excellent improvement in efficiency.

Keywords: Polymer electrolytes; Ionic liquid; SEM; Ionic conductivity; Dye-sensitized solar cell

Electrochemical polymerization of pyrrole in BMIMPF6 ionic liquid and its electrochemical response to dopamine in the presence of ascorbic acid by Aijian Zhang; Jun Chen; Dongfang Niu; Gordon G. Wallace; Jiaxing Lu (pp. 1542-1545).
Polypyrrole (PPy) film modified glassy carbon (GC) electrode was prepared by electrochemical polymerization in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) room temperature ionic liquid. The PPy film obtained in ionic liquid adhered on the electrode surface well and the properties of the PPy film have been characterized via UV–vis spectra and scanning electron microscopy (SEM). The electrochemical response of the PPy modified electrodes toward ascorbic acid (AA) and dopamine (DA) was investigated by differential pulse voltammetry (DPV). Well separated anodic peaks were observed at PPy electrode with peak separation (Δ E) of 200mV at pH 6.2. Compared with PPy electrode prepared in aqueous solution, DA has a higher oxidation currents at the modified electrode prepared in ionic liquid. The oxidation peak potentials and currents were affected by the pH valuation and the film thicknesses.

Keywords: Polymer; Modified electrode; Ionic liquid; Dopamine; Ascorbic acid

Synthesis, photophysics and photovoltaics of alternating vinylene-copolymer and model compound containing triphenylamine moieties along the backbone by John A. Mikroyannidis; Qingfeng Dong; Bin Xu; Wenjing Tian (pp. 1546-1551).
A soluble alternating vinylene-copolymerP and the corresponding model compoundM were synthesized by Heck coupling. They contained triphenylamine moieties and cyano-substituted olefinic bonds along the backbone. Both samples were stable up to about 300°C and afforded char yields of 76–89% at 800°C. Their glass transition temperature ( Tg) was 72–78°C and the absorption maximum was located at 307–366nm with optical band gaps of 2.19–2.35eV. They emitted yellow-orange light with photoluminescence (PL) maximum at 560–576nm. Bulk heterojunction photovoltaic cells with the configuration of ITO/PEDOT:PSS/Sample:PCBM(1:1, w/w)/LiF/Al were fabricated. The PCE of devices based onP andM reached 0.09% and 0.07%, respectively.

Keywords: Synthesis; Copolymerization; Vinylene-copolymer; Triphenylamine; Photophysics; Organic solar cells; Photovoltaic

Synthesis and photoelectric study of 6, 13-dibenzylpentacene by Zhong Huang; Yuansheng Jiang; Xiuying Yang; Yali Fu; Weiliang Cao; Jingchang Zhang (pp. 1552-1556).
6, 13-Dibenzylpentacene was first synthesized. The introduction of benzyl group largely improved the solubility. At the visible region, its maximum absorption in CHCl3 was found at 604.5nm. The fluorescence spectrum shows that its emitting peak is at 624nm. Cyclic voltammetry gave its forbidden-band gap of 2.02eV. Photooxidation test showed that 6, 13-dibenzylpentacene in CHCl3 is sensitive to ambient light, but sluggish to oxygen. Noticeably, 6, 13-dibenzylpentacene is stable in solid state.

Keywords: 6, 13-Dibenzylpentacene; Grignard reagent; Photoelectric performance; Synthesis

Synthesis and fluorescent properties of europium–polymer complexes containing 1,10-phenanthroline by Xingyu Liu; Yulin Hu; Baoyan Wang; Zhixing Su (pp. 1557-1562).
In this paper, 5-acrylamido-1,10-phenanthroline (AP) was synthesized, then the luminescence material containing Eu–polymer complexes were obtained by two methods. The polymer structure and properties were characterized by FT-IR, UV, fluorescence spectra, DSC, GPC, ICP and XRD. Compared with the two methods the rare earth ions-containing polymers, we obtained copolymer B by the second one that had high and stable fluorescence intensity with the Eu content 0.31%. Comparing the two results via different methods, we have set down the useful basement for the study of the luminescence material containing Eu–polymer complexes.

Keywords: 5-Acrylamido-1,10-phenanthroline; Rare earth; Fluorescence; Polymer complex

Synthesis, photophysical and photochemical properties of crown ether substituted zinc phthalocyanines by Mahmut Durmuş; Zekeriya Bıyıklıoğlu; Halit Kantekin (pp. 1563-1571).
The photophysical and photochemical properties of the tetra- and octa-12-crown-4-substituted zinc (II) phthalocyanines are reported for the first time in the scope of this work. The new compounds have been characterized by elemental analysis, IR,1H and13C NMR spectroscopy, electronic spectroscopy and mass spectra. General trends are described for photodegradation, singlet oxygen and fluorescence quantum yields, and fluorescence lifetimes of these compounds in dimethylsulphoxide (DMSO). Photophysical and photochemical properties of phthalocyanine complexes are very useful for photodynamic therapy (PDT) applications. The effects of the substituents on the photophysical and photochemical parameters of the zinc (II) phthalocyanines (5,6 and7) are also reported. The singlet oxygen quantum yields ( ΦΔ) ranged from 0.48 to 0.78 are indicating the potential of the complexes as photosensitizers in applications of PDT. The fluorescences of the substitutedZnPc complexes are effectively quenched by benzoquinone (BQ).

Keywords: Phthalocyanine; Crown ether; Zinc; Singlet oxygen; Photodynamic therapy

Synthesis and characterization of graft copolymers of melamine: Thermal stability, electrical conductivity, and optical properties by İsmet Kaya; Mehmet Yıldırım (pp. 1572-1582).
In this study, novel three Schiff bases of melamine were synthesized via condensation reaction of melamine with salicylaldehyde, 3-hydroxybenzaldehyde, and 4-hydroxybenzaldehyde namely N,N′,N′′,-tris[(2-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (2-HPMTT), N,N′,N′′-tris[(3-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (3-HPMTT), N,N′,N′′-tris[(4-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (4-HPMTT), respectively. Then, oligo/polyphenol derivatives of these Schiff bases were obtained by grafting melamine onto oligosalicylaldehyde (OSA), oligo-3-hydroxybenzaldehyde, and oligo-4-hydroxybenzaldehyde that have generate names of poly-N,N′,N′′-tris[(2-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (P-2-HPMTT), poly-N, N′,N′′-tris[(3-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (P-3-HPMTT), and oligo-N,N′,N′′-tris[(4-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (O-4-HPMTT), respectively. The structures of the synthesized compounds were confirmed by FT-IR, UV–vis,1H NMR, and13C NMR techniques. The characterization was made by TG-DTA, DSC, size exclusion chromatography (SEC), and solubility tests. Electrical conductivities of the synthesized materials were measured by four-point probe technique using a Keithley 2400 electrometer showing that the synthesized oligo/polyphenols have higher electrical conductivities than the monomeric Schiff bases. Also considerable increases in the conductivities were observed when they were doped with iodine as a doping agent. The order of increase rates of the conductivities were found as follows: 2-HPMTT>P-2-HPMTT>P-3-HPMTT>3-HPMTT>4-HPMTT>P-4-HPMTT. Additionally, the optical band gaps ( E g) were calculated by using the absorption spectra and found to be 2.78, 2.17, 3.58, 3.30, 4.03, and 2.82eV for 2-HPMTT, P-2-HPMTT, 3-HPMTT, P-3-HPMTT, 4-HPMTT, and O-4-HPMTT, respectively.

Keywords: Melamine; Polyazomethine; Oligophenol; Graft copolymer; Schiff base oligomer or polymers; Conjugated polymers; Thermal analysis; Differential scanning calorimetry; Conductivity and band gap

Preparation of polyaniline microplates via a novel template-free method by Junsheng Wang; Jixiao Wang; Zhongde Dai; Zhi Wang; Fengbao Zhang (pp. 1583-1588).
Two-dimensional plate-like PANI are successfully synthesized by a self-assembly process using benzoyl peroxide as oxidant. The micelles formed by aniline/ p-TSA salt serves as ‘soft template’ to form PANI micro/nanostructures and proper [An]/[acid] ratios are required for the formation of plate-like PANI. It is found that at high [An]/[ p-TSA] ratios (5:1 to 2:1) plate-like PANI are obtained, while at low [An]/[ p-TSA] ratios ranging from 1:1 to 1:3 PANI nanoparticles are obtained. The influence of the other synthetic parameters, such as temperature, the concentration of benzoyl peroxide and stirring, on the morphologies of the PANI micro/nanostructures has also been investigated. Fourier transform infrared (FTIR), UV–vis spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), as well as X-ray diffraction (XRD) and cyclic voltammeter method (CV) are applied to characterize the products.

Keywords: Conducting polymers; Polyaniline; Benzoyl peroxide; Plate; Microstructure

Synthesis and characterization of a series of bis(dimethyl- n-octylsilyl)oligothiophenes for organic thin film transistor applications by Jung Hei Choi; Dae Won Cho; Hea Jung Park; Sung-Ho Jin; Sukmo Jung; Moonsuk Yi; Chung Kun Song; Ung Chan Yoon (pp. 1589-1596).
Synthesis and characterization of a series of bis(dimethyl- n-octylsilyl) oligothiophenes for organic thin film transistor applications.A series of bis-dimethyl- n-octylsilyl end-capped oligothiophenes consisting of two to six thiophene units has been synthesized and characterized to develop novel organic semiconductor materials. The UV–vis spectral data indicate that these silyl end-capped oligothiophenes have longer conjugation lengths as evidenced by the higher λmax values than the corresponding unsubstituted thiophene oligomers. The thermal analyses indicate that the bis-silylated oligothiophenes show lower melting point (DSi-4T=80°C;DSi-5T=115°C;DSi-6T=182°C) than the corresponding dialkylated thiophene oligomers by 100°C and hexamerDSi-6T exhibits a liquid crystalline mesophase at 143°C. The α,ω-bis(dimethyl- n-octylsilyl)oligothiophenes (DSi-6T) have a remarkably high solubility in chloroform which are comparable to the corresponding α,ω-dihexyloligothiophenes. The remarkably increased solubility by these silyl end groups leads bis-silylated oligothiophenes to be applicable to solution processable devices for thin film transisitor (TFT) by utilizing a spin-coating technique. α,ω-Bis(dimethyl- n-octylsilyl)sexithiophene can be deposited as active semiconducting layer in thin film transistors, either by vacuum evaporation or by spin-coating. A high charge-carrier mobility has been obtained for both deposition techniques, μ=4.6×10−2 and 1.4×10−2cm2V−1s−1, respectively.

Keywords: Sexithiophene; Bis(; n; -octylsilyl)oligothiophenes; Stille cross-coupling reaction; Organic thin film transistors

Chiral polyaniline with flaky, spherical and urchin-like morphologies synthesized in thel-phenylalanine saturated solutions by Yu Li; Bichen Wang; Wei Feng (pp. 1597-1602).
Chiral polyaniline (PANI), of flaky, spherical and urchin-like morphologies, was synthesized in the saturatedl-phenylalanine solution by adjusting the molar ratio ofl-phenylalanine to aniline from 0.25 to 40. The concentration ofl-phenylalanine solution was constant, which was different from the conventional synthesis. The morphologies of PANI were observed by scanning electron microscopy. The molar ratio ofl-phenylalanine to aniline and the amount of aniline were proposed to be crucial to the morphologies. Circular dichroism spectra confirmed thatl-phenylalanine endowed predominately one type of chirality to polyaniline by hydrogen bonding. The optical, structural and electrochemical properties of these synthesized PANI were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy and cyclic voltammetry, respectively. There were some insulating structures, such as oligomers, in the PANI chains, which were caused by the weak acid circumstance during the polymerization.

Keywords: Conjugated polymer; Polyaniline; Chirality; Morphology

Current–voltage and capacitance–voltage characteristics of a Sn/Methylene Blue/p-Si Schottky diode by Y.S. Ocak; M. Kulakci; T. Kılıçoğlu; R. Turan; K. Akkılıç (pp. 1603-1607).
Electrical and interfacial properties of Sn/Methylene Blue (MB)/p-Si Schottky diode have been determined by using current–voltage ( IV) and capacitance–voltage ( CV) measurements of the device at room temperature. Cheung functions and modified Norde functions have been used to obtain the electrical characteristics such as barrier height and series resistance of the diode. It has been seen that the MB layer modifies the effective barrier height of the structure because the layer creates the physical barrier between the metal and the semiconductor. Electrical properties of the device obtained from CV characteristics have been compared with the ones obtained from its IV characteristics. It has been seen that at sufficiently high frequencies, the charge at the interface cannot follow an ac signal. The interface state density of the diode has been also calculated.

Keywords: PACS; 73.30.+; y; 73.40.Ei; 73.40.NsSchottky diode; Organic–inorganic heterojunction; Barrier height; Interface layer; Methylene Blue

An amperometric enzyme biosensor based on in situ electrosynthesized core–shell nanoparticles by Nian-Feng Li; Ting Lei; Chun Ouyang; Yue-Hui He; Yong Liu (pp. 1608-1611).
This work describes a new approach to the construction of an amperometric biosensor for hydrogen peroxide detection based on in situ electrosynthesized gold/polyaniline core–shell nanocomposites on conducting ITO electrode. The immobilization of the enzyme, horseradish peroxidase (HRP), on the polyaniline nanofilm was carried out by electrostatic attachment approach. Results showed that the immobilized HRP exhibited enhanced performance toward the reduction of H2O2, in comparison with other bulk polyaniline (PANI)-based H2O2 biosensor and metallic nanoparticles incorporated PANI systems. The resulting biosensor shows a fast amperometric response (<2s) to H2O2. A linear range from 0.2 to 80μM for the detection of H2O2 was observed with a sensitivity of 20.5μA/mM and a detection limit of 0.16μM at a signal-to-noise ratio of 3. Moreover, the biosensor has a good reproducibility, and long-term stability.

Keywords: Core–shell nanocomposites; Polyaniline; Gold nanoparticle; Horseradish peroxidase; Biosensor

Synthesis and characterization of Ag nanoparticles–polyaniline composite powder material by Sofiane Bouazza; Véronique Alonzo; Didier Hauchard (pp. 1612-1619).
The chemical deposition of silver particles in polyaniline (PANI) powder has been carried out via the reduction of Ag+ ions by PANI in various concentrations of AgNO3 aqueous solutions. It is found that the rate of Ag(I) reduction and the size of the metal particles incorporated were strongly dependent on the reaction medium, the PANI redox form and the stirring method used. Homogeneous distribution of silver nanoparticles into PANI matrix was obtained at low Ag(I) concentration, PANI in emeraldine base form and short reaction time under ultrasonic stirring. The presence of silver particles dispersed into porous polyaniline structures was confirmed using X-ray diffraction, scanning electron microscopy and cavity microelectrode (CME) technique in acidic aqueous electrolyte. The electrochemical study of Ag-PANI composite by CME showed that the redox system of silver depends on the size and the distribution of metal particles incorporated into PANI.

Keywords: Silver nanoparticles; Polyaniline-matrix composites; Powder processing; Scanning electron microscopy (SEM); X-ray diffraction (XRD); CME (Cavity microelectrode)

Polystyrene functionalized carbazole and electrochromic device application by Ayhan Oral; Sermet Koyuncu; İsmet Kaya (pp. 1620-1627).
Polystyrene (PS) functionalized carbazole macromonomer was synthesized and polymerized by electrochemical oxidative polymerization on the ITO-glass surface. The structure of the macromonomer was elucidated by1H NMR, FT-IR, UV–Vis and cyclic voltammetry (CV). The spectro-electrochemical and electrochromic properties of the polymer film were investigated. Also the greenish blue colored film converted to dark blue color by the applying potential. Polystyrene-carbazole/polyethylenedioxythiophene (PS-Carb/PEDOT) electrochromic device was assembled in sandwich configuration: ITO-coated glass/anodically coloring polymer (PS-Carb)//gel electrolyte//cathodically coloring polymer (PEDOT)/ITO-coated glass. According to kinetic studies of this device, the optical contrast Δ T% at 640nm between −1.0 and +2.0V with a residence time of 10s was found to be 38% and switching time was measured as 1.1s.

Keywords: Carbazole; Electrochemical polymerization; Electrochromic devices; Conducting polymers

Synthesis, structure, and electrochemistry of N-(3-thenoyl)fluorosulfonimide and bis(2-thenoic)imide. Preparation of polymers containing the fluorosulfonimide group by Christopher M. MacNeill; Jian Dai; Cynthia S. Day; Stephen P. Lazar; S. Jarrett Howell; Ronald E. Noftle (pp. 1628-1635).
N-(3-Thenoyl)fluorosulfonimide, (1), C4H3SC(O)N(H)SO2F, was prepared by the reaction of 3-thenoic acid with fluorosulfuryl isocyanate in acetonitrile solution. The new compound is a moderately strong nitrogen acid having a pKa of 2.4. Single-crystal X-ray structural analysis of (1) shows a pattern of strong intermolecular hydrogen-bonding, resulting in the formation of linear chains. (1) is electroinactive over a range of 2V but undergoes hydrogen reduction (Ep/2c=−0.28V). The salt of (1) with TBA+,2, has been prepared and its crystal structure determined. The new dithienyl compound, bis(2-thienyl)imide,3, has been prepared and crystallographically characterized. The polymers of1,3, and a polymer containing the fluorosulfonimide group formed from a copolymer of 3-methylthiophene/3-thiophene carboxylic acid are also reported.

Keywords: Sulfonimide; Sulfur heterocycle; Thiopheneimide; Crystal structure; Cyclic voltammetry; Polythiophene; Proton conductor

Efficiency improvement of blue phosphorescent organic light emitting diodes by using a stacked emitting structure by Kyoung Soo Yook; Jun Yeob Lee (pp. 1636-1639).
Quantum efficiency of blue phosphorescent organic light emitting diodes (PHOLEDs) was improved by using a stacked emitting structure which can balance holes and electrons in light emitting layer. N,N′-dicarbazolyl-3,5-benzene (mCP) doped with iridium(III) bis(4,6-(di-fluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) was used as an emitting layer with good hole injection properties near hole transport layer and 1,3-bis(triphenylsilyl)-benzene (TSB) doped with FIrpic was used as an emitting layer with good electron injection properties near electron transport layer. High quantum efficiency of 10.2% was obtained at 500cd/m2 compared with 7.5% and 7.6% of mCP and TSB reference devices.

Keywords: Blue phosphorescent device; Recombination zone; Double emitting layer

Effect of electron- and hole-transporting materials on the performance of FIrpic-doped PVK phosphorescent devices by D.-H. Lee; Z. Xun; H. Chae; S.M. Cho (pp. 1640-1643).
PVK-based phosphorescent FIrpic-doped devices have been fabricated and the effect of carrier transporting materials on the device performance has been investigated. We have fabricated the single-layer and double-layer devices to investigate the role of electron- and hole-transporting materials both when they are mixed in the single- and separated from the emissive layer. We have studied NPB as a hole-transporting material, OXD-7 and PBD as electron-transporting materials. Even though PBD had been well known to be unsuitable as an electron-transporting material for FIrpic-doped PVK devices, it was found in this study that the separate utilization of PBD from PVK:FIrpic layer instead of mixing it with the emissive layer could enhance the device performance significantly. Nevertheless, the OXD-7 was found not only superior to PBD as the electron-transporting material for FIrpic-doped PVK devices but also suitable as an electron-transporting material for the single-layer devices.

Keywords: Organic light-emitting diode; Electrophosphorescence; Electron-transporting material; Hole-transporting material

Synthesis and properties of polyaniline–cobalt coordination polymer by Li Tang; Tao Wu; Jinqing Kan (pp. 1644-1648).
Polyaniline–cobalt coordination polymer (abbreviated as PANI-Co) was synthesized using peroxydisulphate as an oxidant in the solution containing 0.1moldm−3 aniline, 0.5moldm−3 HCl and an adequate content of CoCl2·6H2O at room temperature. The conductivity of PANI-Co was 0.5Scm−1. The cyclic voltammogram results indicated that the PANI-Co film was of electrochemical activity, and the EPR spectrum showed that there were unpaired electrons in the PANI-Co. The relationship between magnetization ( M) and the applied magnetic field ( H) suggests that PANI-Co was soft ferromagnetic material at room temperature. Thus, the PANI-Co was both conductive and ferromagnetic. Moreover, UV–vis and FTIR spectra showed that there existed a strong interaction between Co2+ and PANI chains.

Keywords: Ferromagnetic; Polyaniline; Conductivity; Cobalt

Synthesis and properties of polyacetylenes containing bis(4-alkylphenyl)terephthalate as pendant and methyleneoxy as spacer by Yiwang Chen; Lie Chen; Weihua Zhou; Daijun Zha; Dan Zhou; Fenglian Bai; Meixiang Wan (pp. 1649-1656).
Monosubstituted polyacetylenes containing lateral pendants of bis(p-alkylphenyl)terephthalate with spacer and alkyl tails [R, where R is H, CH3 and C3H7] were synthesized, and the effects of the backbone structure and alkyl tails on the properties were investigated. The monomer with alkyl tails (p-methyl and p-propyl) formed a smectic mesophase upon heating above the melting temperature, but the other one without tails could not exhibit liquid crystallinity at elevated temperatures. The lower melting temperature and wider mesomorphic temperature range of 2-propargyloxy-bis(p-propylphenyl)terephthalate (k 91.6 SmB 102.6 i) than 2-propargyloxy-bis(p-methylphenyl)terephthalate (k 134.3 SmB 143.7 i) indicated that the long tail in mesogen played an important role in the packing order and stability of their liquid crystalline phase. The polymerization of acetylene monomers were carried out with [Rh(nbd)Cl]2 as a catalyst in toluene. The structures and properties of the monosubstituted polyacetylenes were characterized by the means of nuclear magnetic resonance, polarized optical microscopy, infrared spectroscopy, ultraviolet spectroscopy, photoluminescence, thermogravimetry and differential scanning calorimetry. The molecular weights of the polymers were measured by gel permeation chromatograph. The polymers could not exhibit liquid crystallinity at elevated temperatures. The steric effect of bulky liquid-crystallinity mesogens prevented the coplanar conformation of the polyene backbone, and thus, led to the lower absorption and emission of the polymers.

Keywords: Polyacetylene; Liquid crystals; Conjugated polymers

Synthesis and optical properties of poly(2,11-triphenyleneethynylene- alt-m-phenyleneethynylene)s by Chingen Chou; Degang Wang; Jeffrey F. Hsu; Yi Liu; Zhonghua Peng (pp. 1657-1663).
Triphenylene units are introduced into the backbone of a poly(m-phenyleneethynylene) (mPE). The new polymer, mPPET, exhibits strong intra-chain folding in good solvents in which the polymer is soluble, such as chloroform, benzene, and THF. In poor solvents, where the polymer is insoluble, such as acetonitrile, hexane, or DMSO, interchain aggregation dominates. In a solvent mixture of a good solvent and a poor solvent with appropriate ratios, mPPET appears to adopt a random coil conformation. Among the three conformations (intra-chain folding, interchain aggregation, and random coil chain), the intra-chain polymeric foldamer exhibits the highest fluorescence quantum yield. These results indicate that introducing a planar polynuclear aromatic compound into mPE not only increases its intra-chain folding propensity, but also may enhance its fluorescent properties. This approach may be applied to synthesize a variety of conjugated foldamers containing planar polynuclear aromatic hydrocarbons with interesting photophysical properties.

Keywords: Conjugated polymers; Folding; Fluorescence

Air stable and low temperature evaporable Li3N as a n type dopant in organic light-emitting diodes by Kyoung Soo Yook; Soon Ok Jeon; Chul Woong Joo; Jun Yeob Lee; Tae-Woo Lee; Taeyong Noh; Haa-Jin Yang; Sung-Kee Kang (pp. 1664-1666).
N doped organic light-emitting diodes were developed by using Li3N as a n type dopant in electron transport layer. Driving voltage was greatly lowered by using Li3N doped electron transport layer and combination of MoO3 doped hole transport layer with Li3N doped electron transport layer gave high quantum efficiency of 15% and low driving voltage of 4V at 1000cd/m2 in green phosphorescent organic light-emitting diodes. Decomposition of Li3N during evaporation into Li and N2 was found to be responsible for n doping effect of Li3N.

Keywords: n doping; High efficiency; Low driving voltage; LiN; 3

The spectroelectrochemical, magnetic, and structural characterization of reduced hexaazatriphenylenehexacarbonitrile, HAT(CN)6 by Joseph R. Gallegos; Anthony H. Francis; Nathan W. Ockwig; Paul G. Rasmussen; Raphael G. Raptis; Paul R. Challen; Issouf Ouedraogo (pp. 1667-1671).
The cyanoazacarbon, hexaazatriphenylenehexacarbonitrile, or HAT(CN)6, is readily reduced and the spectroelectrochemical properties associated with the multiple reductions are described. The singly reduced radical monoanion forms stable salts and we report the crystal structure and magnetic properties for the tetrabutylammonium salt. [Tetra- n-butylammonium] [HAT(CN)6] behaves ferromagnetically below 3K and follows Curie Law behavior at higher temperatures after correction for Pauli-type susceptibility. The room temperature conductivity of the powdered salt is 3.8×10−8S/cm. The crystal structure shows closely bound pairs of radical anions with slip-stacking of these pairs to form a staircase, features that elucidate the observed properties. Thin films of HAT(CN)6 were found to support negative charge transport by electron time-of-flight measurements, yielding electron mobilities of 10−4cm2/Vs at room temperature.

Keywords: n-Carrier; Radical anion solid; Stacked conducting solid

Synthesis and light-emitting properties of copolymers composed of fluorene and N-alkoxyphenylphenothiazine by Suk-Kyung Kim; Jae-Hoon Eom; Dongbo Mi; Choong-Hwa Jung; Ji-Hoon Lee; In-Nam Kang; Jae-Hoon Kim; Do-Hoon Hwang (pp. 1672-1676).
Poly[10-(4′-octyloxyphenyl)-phenothiazine-3,7-diyl] (POPPTZ), poly[9,9-bis(4′-octyloxyphenyl)fluorene-2,7-diyl] (PBOPF), and their random copolymers, poly(BOPF- co-OPPTZ), were synthesized through Ni(0) mediated polymerization. Light-emitting devices were fabricated using these polymers in an ITO (indium-tin oxide)/PEDOT:PSS/polymer/Ca/Al configuration. Each EL device constructed with a poly(BOPF- co-OPPTZ) copolymer exhibited significantly enhanced efficiency and brightness compared to devices constructed from the POPPTZ and PBOPF homopolymers. The EL device constructed with poly(83BOPF- co-17OPPTZ) exhibited the highest power efficiency and brightness (8,610cd/m2 and 2.831cd/A, respectively). This enhanced efficiency of the copolymer devices results from their improved hole injection and more efficient charge carrier balance, which arise due to the HOMO levels (∼5.42eV) of the poly(BOPF- co-OPPTZ) copolymers, which are lower than that of the PBOPF homopolymer (∼5.79eV).

Keywords: Polyfluorene; N; -Alkoxyphenylphenothiazine; Light-emitting diodes; Organic semiconductor

Direct observation of the energy gap in lutetium bisphthalocyanine thin films by R. Murdey; M. Bouvet; M. Sumimoto; S. Sakaki; N. Sato (pp. 1677-1681).
The energies of the frontier electronic states of neutral radical lutetium bisphthalocyanine (LuPc2) thin films are reported based on direct observation by a combination of ultraviolet photoemission spectroscopy (UPS) and inversion photoemission spectroscopy (IPES) techniques. Quantum chemical calculations are used to identify the states derived from the singly occupied molecular orbitals (SOMO) and singly unoccupied molecular orbitals (SUMO). The energy gap defined by the threshold onset values of the broadened SOMO and SUMO states is found to be 0.4±0.1eV.

Keywords: Lutetium; Phthalocyanine; UPS; IPES; Bandgap; Transport gap; Energy gap; Unpaired spin; Organic radical semiconductor

Influence of dopant ions on properties of conducting polypyrrole and its electrocatalytic activity towards methanol oxidation by Arindam Adhikari; S. Radhakrishnan; Rahul Patil (pp. 1682-1688).
The polypyrrole (PPy) films were deposited on vacuum metallized substrates by electro-oxidation of pyrrole monomer. These electrodes were then modified with a range of metal halides having different electronegativities. The modified polypyrrole electrodes were employed to investigate electrocatalytic activity towards methanol electrochemical oxidation by means of cyclic voltammetry in 0.1M HClO4 as supporting electrolyte. It was found that the electronegativity of the dopant ion incorporated in the PPy film governs the electrocatalytic activity towards methanol oxidation. Among different dopant anions used in the present work, the PPy doped with zirconium chloride gave the highest anodic current of 10mAcm−2 at the oxidation potential of methanol. Electrical property and the charge created due to doping in the polymers were measured using X-ray photoelectron spectroscopy (XPS) and Electron spin resonance spectroscopy (ESR). Electrocatalytic activity of the modified electrodes was correlated with various factors obtained from different polymer characterization experiments. The results were explained on the basis of the charge-transfer efficiency at the electrodeǀelectrolyte interface, which was associated with the acceptor state created by the dopant in the semi-conducting polymer.

Keywords: Polypyrrole; Methanol oxidation; Metal halide dopant; XPS; ESR; Charge transfer; Electrocatalyst

Correlation between the interface states and ultraviolet treatment for low-voltage pentacene thin-film transistors by Jeong-M. Choi; Seongil Im (pp. 1689-1693).
We report a comparative study on the interface states of pentacene thin-film transistors (TFTs) with ultraviolet (UV) illumination. The trap density (negative fixed charge) at the pentacene/poly-4-vynylphenol (PVP) interface of the TFT adopting UV-treated poly-4-vynylphenol (PVP) layers (prior to pentacene deposition) can be estimated at 1.75×1012/cm2 while another UV-treated TFT (after pentacene deposition) displays higher trap density of 2.40×1012/cm2 due to the additional negative charges at the interface generated from pentacene channel layers through UV treatment. It can lead to the formation of more conductive channels and thus effectively modulate the threshold voltage ( VT). In addition, we fabricated the resistance-load inverter showing improved performance through UV treatment using load-line analysis.

Keywords: Organic thin-film transistor; Ultraviolet treatment; Interface trap density

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