Synthetic Metals (v.159, #13)

Thermal bath effect on soliton propagation in three-level atomic system by N. Boutabba; H. Eleuch; H. Bouchriha (1239-1243).
In a three-level media coupled to the thermal bath, an analytical expression of the soliton shapes have been derived. The velocity of these solitons depends mainly on the amplitude of the stationary control field, the coupling with the thermal bath and the detuning. Especially, we show that for a given value of the detuning, the soliton can be completely stopped.

Synthesis of highly conductive poly(3,4-ethylenedioxythiophene) fiber by simple chemical polymerization by Woonphil Baik; Wanquiang Luan; Ren He Zhao; Sangho Koo; Kyu-Sik Kim (1244-1246).
Poly(3,4-ethylenedioxythiophene) (PEDOT) fiber was chemically synthesized by the polymerization of 2,5-dihalo-3,4-ethylenedioxythiophene in the presence of BF3 without a template. The resulting conductive PEDOT fiber exhibited conductivity in the range of 150–250 S/cm (pressed powder pellet). The thermal stability of PEDOT was also improved and UV-spectroscopy analysis of a film exhibited a strong absorption band at 460 nm. The well-defined needle-shaped fibers of PEDOT were examined by SEM, and the average length and diameter of the fibers were 10 and 0.4 μm, respectively.
Keywords: PEDOT; Conductive polymer; Nanofiber; Chemical polymerization;

Electrochemical deposition of polypyrrole (PPy) on steel surface has been carried out from an aqueous polyphosphate medium using constant potential coulometry (CPC) and cyclic voltammeter (CV), and the adherence, anticorrosion property and thermal stability of the coated material have been studied.Open circuit potential (OCP) measurements were carried out in a 3.5% NaCl solution. The high OCPs maintained for a period of 40 days suggest that polyphosphate-doped PPy (PPy/PP) retains its oxidative state and provide good corrosion protection for SS-304. It seems that, the large polyphosphate counter-ion prevents the ingress of chloride ions much better than other dopants reported elsewhere. The amount of polypyrrole formed on the steel surface increased with electrodeposition time, monomer concentration and applied potential. However, the effect of potential was higher than the effects of either monomer concentration or deposition time. Also, the effect of electrolyte concentration on the polymer formation was insignificant. Scanning electron microscopy (SEM), however, showed that PPy surface morphology was affected by polyphosphate concentration. Very smooth, compact and adherent PPy films with significantly smaller globules were obtained from solutions with high concentration of polyphosphate. Thermogravimetric analysis of the coated material indicated that PPy/PP has excellent thermal stability at temperatures up to 700 °C, much higher than other conductive polymer coatings cited.
Keywords: Polypyrrole; Polyphosphate; Electrodeposition; Steel; Thermal stability; Composite;

A series of LiMn2O4 spinel was prepared by adipic acid-assisted sol–gel method at different temperatures. The structure and physicochemical properties of spinel LiMn2O4 synthesized by different temperatures were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron micrographs (SEM), inductively coupled plasma-mass spectroscopy (ICP-MS), galvanostatic charge–discharge test, and cyclic voltammetry (CV), respectively. TG–DTA shows that the weight loss occurs in four temperature regions during the synthesis of LiMn2O4. XRD indicates that the sintering temperature affects the formation of spinel phase, and prominent LiMn2O4 spinel powder with smaller atom location confusion forms about 800 °C. XPS reveals that the manganese oxidation state in spinel lithium manganese oxide synthesized at different temperatures is between +3 and +4. SEM shows that LiMn2O4 spinel synthesized at 800 °C has the uniform, nearly cubic structure morphology with narrow size distribution. ICP-MS indicates that the average chemical valence of Mn element of LiMn2O4 synthesized at 800 °C is the most close to 3.5 among the samples synthesized at different temperatures. CV illustrates that the LiMn2O4 synthesized at 800 °C has the best electrochemical activity. Charge–discharge test explains that the capacity retention sintered at 350, 700 and 800 °C over the first 50 cycles is 93.6%, 86.1% and 85.2%, respectively, but the discharge capacity at the 50th cycle is 82.2, 104.8 and 110.8 mAh g−1, respectively.
Keywords: Lithium ion battery; Cathode material; LiMn2O4; Synthesis temperature; Physicochemical properties;

A thiophene/phenylene vinylene-based polymer (P1) was synthesized and its properties compared with those of a previously described analogous polymer (P2-CN) which contains CN substituents in the vinyl moieties. In solution, the P1 polymer absorbed in a range from UV to near 600 nm and, compared to P2-CN, exhibited a band gap energy that was larger, from 1.7 to 2.0 eV, and the energy levels of LUMO and HOMO lower, by 0.2 and 0.5 V, respectively. However, the power conversion efficiencies (PCE, 0.30%) of photovoltaic devices fabricated using a blend of P1 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) appeared to be slightly higher than the reported PCE (0.15%) for P2-CN devices fabricated in the same configuration.
Keywords: Conjugated polymer; Thiophene/phenylene vinylene-based polymer; Low band gap; Photovoltaic device;

Preparation and characterization of chemically synthesized poly(N-methylaniline) by Atul Kapil; Manish Taunk; Subhash Chand (1267-1271).
Poly(N-methylaniline) (PNMA), a electrically conductive derivative of polyaniline was synthesized by chemical polymerization of N-methylaniline (NmANI) using ammoniumpersulfate (APS) as an oxidizing agent and studied by electrical conductivity measurement, UV–vis and FTIR spectroscopy. The observed electrical conductivity was found to have a dependence on some synthesis parameters. The oxidant/monomer molar ratio ∼1 and p-toluenesulfonic acid (PTSA)/monomer molar ratio ∼4 showed higher values of electrical conductivity for the polymer. The d.c. conductivities of PTSA doped poly(N-methylaniline) have been measured in the temperature range 298–373 K. The conductivity of the samples has been observed to show an increasing trend with increasing temperature. However, on increasing temperature from 298 K to 373 K, the conductivity rise was found to be more for the samples having lower dopant/monomer ratio. The observed d.c. conductivity data was described by Mott's three-dimensional variable range hopping (VRH) model.
Keywords: Poly(N-methylaniline); Chemical polymerization; UV–vis absorption spectra; Electrical conductivity;

Synthesis, structures and properties of ternary rare earth complexes with m-methoxybenzoic acid and 1,10-phenanthroline by Rui-Xia Ma; Zhi-Min Chen; Zhi-Hua Gao; Shu-Ping Wang; Rui-Fen Wang; Jian-Jun Zhang (1272-1276).
Two dimeric rare earth complexes [Eu(m-MOBA)3(phen)]2 (I) and [Tb(m-MOBA)3(phen)]2·2C2H5OH (II) (where m-MOBA =  m-methoxybenzoate, phen = 1,10-phenanthroline) were synthesized and structurally characterized. Both complexes consist of neutral dimeric molecules. Complex I crystallizes in triclinic system, space group P 1 ¯ . Each Eu(III) ion is nine-coordinated with one 1,10-phenanthroline molecule, one bidentate chelating carboxylate group, two bridging bidentate carboxylate groups and two bridging tridentate chelating carboxylate groups. Complex II crystallizes in triclinic system, space group P 1 ¯ . Each Tb(III) is eight-coordinated with one 1,10-phenanthroline molecule, one bidentate chelating carboxylate group and four bridging bidentate carboxylate groups. Complex I shows bright red luminescence, II shows green luminescence under UV light at room temperature, respectively. The thermal analysis indicates that they are all quite stable to heat.
Keywords: m-Methoxybenzoic acid; Phenanthroline; Complex; Crystal structure; Luminescence;

We report the results of a systematic investigation of the electrical and physical modifications to pentacene organic thin-film transistors (OTFT) that result from postfabrication thermal annealing. The thermally induced electrical modifications of the performance of the pentacene OTFTs were explored, and the morphology and structure of the pentacene films were investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. We found that postfabrication thermal annealing at 50 °C significantly improved the mobility, from 0.19 to 0.36 cm2/Vs, and increased the on/off ratio to almost twice that of the non-annealed device. We also found that annealing increased the pentacene grain size and enhanced the 0 0 1 peak intensity in the XRD pattern, indicating greater molecular ordering. At postfabrication thermal annealing temperatures of 70 °C and above, the pentacene films lose their crystallinity and the OTFT performance is decreased.
Keywords: Organic thin-film transistor; Pentacene; Thermal annealing; Crystallinity;

Synthesis and third-order nonlinear optical studies of a novel four-coordinated organoboron derivative and a bidentate ligand by Mario Rodríguez; Rigoberto Castro-Beltrán; Gabriel Ramos-Ortiz; José Luis Maldonado; Norberto Farfán; Oscar Domínguez; Jesús Rodríguez; Rosa Santillan; Marco Antonio Meneses-Nava; Oracio Barbosa-García; Jorge Peon (1281-1287).
The third-order nonlinear optical characterization of a new boronate (2) derived from 4-dimethylaminocinnamaldehyde was performed by third-harmonic generation (THG) at the infrared wavelength of 1550 nm. Compound 2 was prepared from the reaction of diphenylboronic acid and the bidentate ligand (1) and characterization was made through UV, IR, 1H, 11B, and 13C NMR and X-ray diffraction. The THG experiments showed that the N → B coordinative bond in 2 enhanced the second molecular hyperpolarizability of the type γ (3)(−3ω, ω, ω, ω) by a factor of three with respect to the value exhibited by the ligand 1. On the other hand, Z-scan studies at 800 nm (femtosecond (fs) pulses) also showed that such coordinative bond increased the nonlinear absorption (two-photon absorption (TPA)) in 2 with respect to 1. These studies demonstrate that the N → B coordinative bond facilitates the polarization of the electronic π-system, a situation that optimizes the third-order NLO response. Results on the excited state absorptions in these compounds are also presented.
Keywords: Boronates; NLO; Z-scan; 11B NMR; X-ray;

Organic thin film transistors (OTFTs) for low-voltage operation have been realized with very thin organic–inorganic hybrid gate dielectrics. Organic–inorganic hybrid thin films have good electrical properties, including high dielectric strength and low leakage current density down to 40 nm thickness. In addition, organic–inorganic hybrid thin films have smooth and hydrophobic surface. OTFTs with 40-nm-thick organic–inorganic hybrid dielectrics are operating within −5 V and exhibit a mobility of 0.3 cm2/(V s), a threshold voltage of −2.6 V, and a small subthreshold swing of 0.43 V/decade. In addition, OTFTs with 40-nm-thick organic–inorganic hybrid dielectrics have low hysteresis.
Keywords: Organic thin film transistors (OTFTs); Organic–inorganic hybrid materials; Gate dielectrics; Low-voltage operation;

A lithium quinolate-based electron injection structure was developed to improve luminance efficiency and lifetime of organic light-emitting diodes (OLEDs). A electron injection material based on Li complex, 8-hydroxyquinolinato lithium (Liq), was introduced as an electron injection material for OLEDs and the efficiency and lifetime of OLEDs were investigated according to the structure of the electron injection layer. A bilayer electron injection structure, a mixed layer of tris(8-hydroxyquinoline) aluminium (Alq3) and Liq and a Liq layer, showed high efficiency of 11.6 cd/A compared with 9.8 cd/A for lithium fluoride (LiF). In addition, the extrapolated lifetime of OLED with the bilayer electron injection structure was improved by 40% at 1000 cd/m2.
Keywords: Electron injection layer; Lithium quinolate; High efficiency; Long lifetime;

Effect of doping concentration on device performances of triplet mixed host devices by Sung Hyun Kim; Jyongsik Jang; Jun Yeob Lee (1295-1297).
Device performances of triplet mixed host devices were correlated with host composition and doping concentration. A mixed host of (4,4′-N,N′-dicarbazole)biphenyl (CBP) and spirobifluorene type host (PH1) was used and quantum efficiency of mixed host devices was optimized in CBP:PH1 (90:10) devices at all doping concentration. Quantum efficiency was not greatly affected by host composition at high doping concentration, while host composition was critical to quantum efficiency at low doping concentration. In addition, doping concentration had no influence on quantum efficiency of CBP:PH1 (90:10) devices.
Keywords: Triplet mixed host; Doping concentration;

Syntheses and properties of cyano and dicyanovinyl-substituted oligomers as organic semiconductors by Erjing Wang; Qing Meng; Chengliang Wang; Liqiang Li; Hongxiang Li; Wenping Hu (1298-1301).
Thiophene-phenylene co-oligomers with cyano and dicyanovinyl substituents at different positions were synthesized. Their stability and energy levels were estimated through thermal gravimetric analysis, UV–vis absorption spectra and electrochemistry. Interestingly, the absorption of BTCV covered the range of 430–610 nm, and thin film transistors of BTCV exhibited p-type behavior with high stability, suggesting BTCV a good candidate for solar cell.
Keywords: Organic semiconductor; Oligomer; Electro-withdrawing group; Transistor;

Solid phase mechanochemical synthesis of polyaniline branched nanofibers by C.-F. Zhou; X.-S. Du; Z. Liu; S.P. Ringer; Y.-W. Mai (1302-1307).
A polyaniline supramolecular structure composed of polyaniline nanofibers, has been prepared by a simple solid-state mechanochemical reaction and template-free method. XRD analysis confirmed the good crystallinity of the product, and FTIR and UV–vis analysis indicated that the product was a highly doped emeraldine salt. Electrochemical cyclic voltammetry confirmed the electrocatalytic effect of the branched nanofiber to dopamine and hydroquinone. The growth mechanism of the unique supramolecular structure in mechanochemical reaction was discussed, together with the effect of the crystalline water of the oxidant.
Keywords: Polyaniline; Solid-state polymerization; Nanofiber; Nanomaterial; Mechanochemical synthesis;

A picolinic acid derivative bearing an 1,3,4-oxadiazole unit and its bicyclometalated iridium complex (PhOXD)2Ir(BuPhOXD-Pic) were synthesized and characterized, in which BuPhOXD-Pic is 5-(4′-(5″-(4-tert-butylphenyl)-1″,3″,4″-oxadiazol-2″-yl) phenyl) picolinic acid and PhOXD is 2,5-diphenyl-1,3,4-oxadiazole. The optoelectronic properties of this iridium complex were studied in the double-layer polymer light-emitting devices using a blend of poly (9,9-dioctylfluorene) and 5-biphenyl-2-(4-tert-butyl) phenyl-1,3,4-oxadiazole as a host matrix. This complex exhibited a maximum luminance efficiency of 7.7 cd/A at 5.6 mA/cm2 and a peak brightness of 5288 cd/m2 at 153.7 mA/cm2 in the devices. Compared to the (PhOXD)2Ir(Pic) complex, the (PhOXD)2Ir(BuPhOXD-Pic) complex displays better optoelectronic properties in the devices. This study provides a convenient way to improve the optoelectronic properties of iridium complexes by modifying an ancillary ligand of picolinic acid (Pic) with an 1,3,4-oxadiazole unit.
Keywords: Iridium complex; 1,3,4-Oxadiazole; Polymer light-emitting device; Photoluminescence; Electrophosphorescence;

Biocompatible composites of polyaniline nanofibers and collagen by Hooi-Sung Kim; Hugh L. Hobbs; Lian Wang; Michael J. Rutten; Carl C. Wamser (1313-1318).
A new hybrid composite material composed of polyaniline nanofibers and collagen was fabricated with various ratios of polyaniline nanofibers in a collagen matrix. The nanofibers were well dispersed in the composite matrix, as confirmed by scanning electron microscopy. The polyaniline nanofiber–collagen composite film remained electronically conductive, although conductivity decreased significantly with decreasing polyaniline in the composite. Conductivity could also be adjusted by dedoping in neutral water and redoping in acid, easily monitored with UV–vis spectroscopy. Flash welding, a technique to fuse polyaniline nanofibers with a pulse of light, did not significantly affect the composite, presumably due to the discontinuous nanofiber population in the composite matrix; only minor structural changes were observed. Contact angles are relatively high (around 80°) and independent of the amount of polyaniline in the composite, suggesting that the dominant surface material in the composite is collagen. Porcine skeletal muscle cells cultured as well on the composite films as they did on collagen reference samples, suggesting that the composite material is suitable for biomedical applications.
Keywords: Polyaniline; Nanofibers; Collagen; Composite material; Conductive polymer;

Mesomorphism of dialkylterthiophene homologues by Nicolas Boucher; Julie Leroy; Sergey Sergeyev; Eric Pouzet; Vincent Lemaur; Roberto Lazzaroni; Jérôme Cornil; Yves Henri Geerts; Michele Sferrazza (1319-1324).
New dialkylterthiophene liquid crystalline compounds were synthesised and characterised using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarized optical microscopy (POM). Upon cooling from the isotropic state to the crystalline phase, these dialkylterthiophenes present different types of smectic mesophases. For the highest ordered smectic phase, XRD analyses have revealed a molecular organisation within the smectic layers and the key structural parameters are determined by molecular modelling simulations. The structural properties of these smectic phases are discussed in relation to the alkyl chain length.
Keywords: Dialkyterthiophenes; Organic semiconductors; Liquid crystals; Transition temperatures; Smectic mesophases;

An iron phthalocyanine with tetra-sulphonated substituents (FeTsPc) was used as photosentizer for the development of dye sensitized nanostructured TiO2 solar cells. The influence of surface modification (TiO2 film treated with HCl and HNO3) and thermal annealing of TiO2 photo-electrode on the performance of dye sensitized solar cell (DSSC) having structure FTO/TiO2–FeTsPc/electrolyte/PEDOT:PSS (carbon added)/FTO was investigated through the analysis of current–voltage characteristics under illumination and electrochemical impedance spectra (EIS). The improvement in crystallinity of TiO2, decrease in the internal surface area and adsorbed amount of dye and increase in the lifetime of injected electrons upon thermal annealing of TiO2 photo-electrode affects the photovoltaic properties of DSSC. The increase in power conversion efficiency of DSSC based on nitric acid treatment for the photo-electrode is mainly attributed to the increase in photocurrent. A comparative photovoltaic investigation of DSSCs using HCl-treated TiO2 photo-electrode, indicates that the HNO3-treated photo-electrode retards back electron transfer at the interface with electrolyte and increases the amount of dye.
Keywords: Sulphonated iron phthalocyanine; Dye sensitized solar cell; Acid treatment; Photovoltaic effect; Electrochemical impedance spectroscopy;

A facile method to prepare silver–polypyrrole composite (Ag–PPy) by a modified silver mirror reaction is reported. PPy films pretreated by Al(NO3)3 solution were immersed into the silver ammonia with glucose. Silver ammonia ions were reduced to two-dimensional staggered silver nanosheets which immobilized on the surface of polypyrrole. The silver nanosheets with different morphologies and sizes can serve as active-substrates for surface-enhanced Raman spectroscopy (SERS). Using 4-mercaptopyridine (4-Mpy) as probe molecules, the as-prepared composites exhibited excellent surface-enhanced Raman scattering.
Keywords: Silver–polypyrrole composite; 4-Mercaptopyridine; Surface-enhanced Raman spectroscopy;

In this paper, temperature-dependent current–voltage (IV) characteristics of poly-N-epoxipropyl carbazole (PEPC) are evaluated. The PEPC is doped with anthracene (An) and deposited on nickel (Ni) substrate with a centrifugal machine. The films are grown at room temperature but at varying gravity conditions, such as 1g, 123g, 277g and 1107g, where g is acceleration due to gravity. It is demonstrated that the space charge created by the trapped charges controls the device's characteristics. Thus, by employing trapped space charge limited current model, charge transport parameters are estimated and discussed as a function of ambient temperatures. It is learned that the trap factor, free carrier density, effective mobility and trap density are quasi-linear functions of temperatures. It is shown that devices fabricated at 277g exhibit superior electrical properties compared to 1g, 123g and 1107g devices. It has been demonstrated that an organic semiconductor device performance could be enhanced by optimizing its fabrication parameters.
Keywords: High gravity thin film; TSCLC; Organic semiconductor; PEPC; Charge transport;

New rhenium complexes containing 4,5-diazafluorene ligand for high-efficiency green electrophosphorescence by Xiao Li; Dongyu Zhang; Wenlian Li; Bei Chu; Liangliang Han; Tianle Li; Zisheng Su; Jianzhuo Zhu; Shuanghong Wu; Yiren Chen; Peng Lei; Zhizhi Hu; Zhiqiang Zhang (1340-1344).
Two novel tricarbonyl rhenium complexes featuring 4,5-diazafluorene (DF)-based ligand, i.e., Re-DF and Re-EPDF (EPDF, 9,9-di-(4-ethoxyphenyl)-9-H-4,5-diazafluorene), were designed, synthesized and characterized by 1H NMR and mass spectroscopy. The green organic light-emitting diodes (OLEDs) based on these complexes with the configuration of ITO/m-MTDATA (10 nm)/NPB (20 nm)/CBP: Re-complex (30 nm)/Bphen (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The devices based on Re-DF showed a maximum current efficiency of 20.7 cd/A and a peak luminance of 2506 cd/cm2, respectively. And the Re-EPDF doped devices exhibited a maximum current efficiency of 13.5 cd/A and a luminance of 3208 cd/cm2. Moreover, the 20 wt.% Re-EPDF doped device still provided a maximum current efficiency of 13.2 cd/A.
Keywords: Rhenium complex; 4,5-Diazafluorene; Phosphorescence; OLEDs;

Formation and characterization of copper tetrakis (4-cumylphenoxy) phthalocyanine:perylene solar cells by Ryosuke Motoyoshi; Atsushi Suzuki; Kenji Kikuchi; Takeo Oku (1345-1348).
Perylene-based bulk heterojunction solar cells with copper tetrakis (4-cumylphenoxy) phthalocyanine (Tc-CuPc) and heterojunction solar cells with copper phthalocyanine (CuPc) were produced and characterized. A device based on CuPc and perylene provided better efficiency, fill factor, short-circuit current and open-circuit voltage compared to those of a device based on Tc-CuPc and perylene. The Tc-CuPc:perylene structure was examined by transmission electron microscopy, which indicated mixtured microstructure. Energy levels of the molecules were calculated and discussed.
Keywords: Bulk heterojunction solar cells; Copper tetrakis (4-cumylphenoxy) phthalocyanine; Perylene;

Electrochemical and photoelectrochemical study of gallium arsenide–polybithiophene composite by F. Hab Elhames; B. Nessark; N. Boumaza; A. Bahloul; D. Bouhafs; A. Cheriet (1349-1352).
Bithiophene (BiTh) was galvanostatically polymerized in the presence of gallium arsenide (GaAs) particles at different concentration. The properties of the composite layers were studied by electrochemical method (cyclic voltammetry), UV–vis spectroscopy and photocurrent measurements. From UV–vis spectroscopy studies, the absorbance of the composites is larger than the polybithiophene absorbance in the UV region. The p-type semiconducting behaviour of the reduced polybithiophene was studied by photocurrent measurements. It was observed that the photocurrents of the composites was higher than that of the PBiTh without GaAs, and increased with GaAs concentration.
Keywords: Organic–inorganic composite; Photocurrent; Conjugated organic polymers; Gallium arsenide;

Polypyrrole microstructure deposited by chemical and electrochemical methods on cotton fabrics by K. Firoz Babu; R. Senthilkumar; M. Noel; M. Anbu Kulandainathan (1353-1358).
Electrochemically and chemically coated cotton fabrics with polypyrrole are comparatively evaluated and characterized in order to produce the conducting fabrics/textiles. The polypyrrole coated fabric is obtained electrochemically by constant current electrolysis (2 mA cm−2) at room temperature for 4 h. The stability, electrical conductivity and electrochemical behaviour of such composite coating are evaluated by means of SEM, FTIR, TGA, DSC, four-probe conductivity, impedance spectroscopy and cyclic voltammetry. When compared to chemical method thicker films of polypyrrole with globular microstructure could be obtained by electrochemical technique and the conductivity of the polypyrrole film was also high (1.9 × 10−2 to 3.3 × 10−1  S cm−1). The weight uptake and the electrical conductivity of the coated fabric increase with concentration of pyrrole and time of electrolysis. Many other physico-chemical properties of the polypyrrole films obtained by the two methods were found to be qualitatively similar.
Keywords: Conducting textiles; Polypyrrole; Electrochemical oxidation; Constant current electrolysis; Cotton; Electrical conductivity;

High efficient organic light emitting diodes using new 9,10-diphenylanthracene derivatives containing bulky substituents on 2,6-positon by Woo Jong Jo; Kwon-Hyeon Kim; Hyeon Chang No; Dong-Yun Shin; Se-Jin Oh; Joo-Hwan Son; Yun-Hi Kim; Yong-Kuk Cho; Qing-Hwa Zhao; Kyeong-Hoon Lee; Hyeong-Yun Oh; Soon-Ki Kwon (1359-1364).
Novel blue emitters with two bulky substituents on the 2,6-position of 9,10-diphenylanthracene (DPAN), which can provide effective hindrance to the intermolecular packing, were synthesized, characterized, and used in the fabrication of organic light emitting diodes (OLEDs). DSC thermograms and theoretical calculations of 3-dimensional structures of Ph-DPAN, Flu-DPAN and TPA-DPAN, support that they have an amorphous and non-coplanar structure. With application of these newly non-doped, blue emitting materials in a multilayer device structure, it is possible to achieve a current efficiency of 4.6–5.8 cd/A for DPAN derivatives.
Keywords: OLED; Blue; Anthracene;

The influence of the growth of Aspergillus niger Tiegh. fungi on the morphological, chemical and electrochemical properties of the polyaniline (PANI) modified Ni surface has been investigated. The strain of Aspergillus niger Tiegh. L-10 was cultivated on the malt extract agar (DIFCO OXOID). A PANI film was synthesized by potentiodynamic polymerization in an aqueous 0.3 M H2C2O4 solution containing 0.1 M aniline on the Ni electrode. The electrochemical behaviour of polymer films was determined in a 0.05 M H2SO4 solution by the cyclic voltammetry method. The composition of PANI and Aspergillus niger Tiegh. treated PANI surfaces have been characterized using X-ray photoelectron spectroscopy (XPS). The morphology has been studied using scanning electron microscopy (SEM). The attachment of a polymer film via the metabolic product resulted in oxidation of the surface. It was estimated that at the PANI/microorganism interface, a Ca-complexed carboxylate interfacial reaction product was formed.
Keywords: Polyaniline; Oxalate; Electrochemistry; Aspergillus niger; XPS; Chemical and morphological properties;

In situ template polymerization of aniline on the surface of negatively charged TiO2 nanoparticles by Bong-Soo Kim; Ki-Tae Lee; Pil-Ho Huh; Dong-Han Lee; Nam-Ju Jo; Jang-Oo Lee (1369-1372).
The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO2) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO2 composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO2 composites were quite different from those of pure PANI or TiO2, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO2 composite was estimated to be 0.91 × 10−1  S/cm at 25 °C in the range of semiconductor.
Keywords: Hybrid PANI/TiO2; Negatively charged TiO2; In situ oxidative template polymerization;

Temperature changes in conducting polypyrrole/para-toluene-2-sulphonic acid (PPy/pTSA) coated nylon textiles due to microwave absorption in the 8–9 GHz and 15–16 GHz frequency ranges were obtained by a thermography station during simultaneous irradiation of the samples. The temperature values are compared and related to the amounts of reflection, transmission and absorption obtained with a non-contact free space transmission technique, indicating a relationship between microwave absorption and temperature increase. Non-conductive samples showed no temperature increase upon irradiation irrespective of frequency range. The maximum temperature difference of around 4 °C in the conducting fabrics relative to ambient temperature was observed in samples having 48% absorption and 26.5 ± 4% reflection. Samples polymerized for 60 or 120 min with a dopant concentration of 0.018 mol/l or polymerized for 180 min with a dopant concentration of 0.009 mol/l yielded optimum absorption levels. As the surface resistivity decreased and the reflection levels increased, the temperature increase upon irradiation reduced.
Keywords: Conducting textiles; Polypyrrole (PPy); Thermal imaging; Microwave absorption;

We have investigated the influence of solvent chemistry on ink-jet printed semiconductor patterns. Our research focuses on improving the uniformity of an ink-jet printed single dot semiconductor by adjusting the solvent mixture combination. Use of a solvent mixture with one solvent of a lower boiling point and a higher solubility with respect to the semiconductor molecules and another of a higher boiling point and a lower solubility allows us to produce a uniform single dot pattern by ink-jet printing. It was observed that the film uniformity of the semiconductor layer plays an important role in determining the electrical parameters of the transistor. In comparison with uncontrolled ink composition, the OTFT fabricated from the well-controlled ink exhibited better device performance, including a carrier mobility of 8.5 × 10−3  cm2  V−1  s−1 in the saturation regime, an on/off current ratio of 103, and a threshold voltage of 0.39 V with subthreshold slopes of 0.95 V dec−1.
Keywords: Ink-jet printing; Organic thin-film transistor; Ink; Organic semiconductor;

Variable emissivity infrared electrochromic device based on polyaniline conducting polymer by Hua Li; Kai Xie; Yi Pan; Meng Yao; Cong Xin (1386-1388).
The use of polyaniline (PANI) as active layer in the electrochromic (EC) devices operating in the mid-infrared (mid-IR) ranges (3–5 μm, 8–12 μm) was investigated. The optical properties of the device were characterized by spectrophotometry in the wavelength range from 0.4 μm to 15 μm. Results show that upon reversible doping and undoping, the devices yield an average emissivity dynamic range of ca. 0.24 in the 8–12 μm region. The lowest emissivity of the devices in this region can be adjusted from 0.4 to 0.68 according to the preparation conditions. The average reflectance dynamic range is 18% in the 3–5 μm and 34% in the 8–12 μm regions.
Keywords: Infrared; Electrochromic device; Polyaniline; Emissivity;

Capacitive properties of RuO2 and Ru–Co mixed oxide deposited on single-walled carbon nanotubes for high-performance supercapacitors by Byung Chul Kim; Gordon G. Wallace; Y.I. Yoon; Jang Myoun Ko; Chee O. Too (1389-1392).
Composite electrodes for use in redox supercapacitors were prepared by electrochemical deposition of RuO2 or the co-deposition of Ru–Co mixed oxides on the surface of single-walled carbon nanotubes. Electrodes coated with the Ru–Co mixed oxide [Ru (13.13 wt%) and Co (2.89 wt%)] or RuO2, exhibited a similar specific capacitance (∼620 F g−1) at low potential scan rates (10 mV s−1). However, at higher scan rates (500 mV s−1) the mixed metal oxide electrode showed superior performance (570 F g−1) when compared to the RuO2 electrode (475 F g−1). This increase in capacitance at high scan rates is attributed to the role of the Co in providing enhanced electronic conduction.
Keywords: Supercapacitor; Single-walled carbon nanotubes; Ruthenium oxide; Ruthenium–cobalt mixed oxide;