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Synthetic Metals (v.160, #23-24)

ICSM 2010 Awards (pp. i-iii).

Uniform dispersion of triplet emitters in multi-layer solution-processed organic light-emitting diodes by Sheng-Yang Huang; Hsin-Fei Meng; Heh-Lung Huang; Teng-Chih Chao; Mei-Rurng Tseng; Yu-Chiang Chao; Sheng-Fu Horng (pp. 2393-2396).
The influence of the iridium complex solubility on the efficiency of multi-layer solution-processed organic light-emitting diode is demonstrated by synthesized orange triplet iridium complexes with the same core. The solubility of the iridium(III) bis(4-phenylthieno[3,2- c]pyridinato- N, C2′) acetylacetonate is increased and uniform dispersion of iridium complex in polymer host poly(vinylcarbazole) is achieved by tert-butyl and n-hexyl group modification. Blade coating technique is utilized to achieve tri-layer structures with a polymer hole-transporting layer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-s-butylphenyl))diphenylamine)], a host–guest emissive layer, and small-molecule hole-blocking layer 1,3,5-tris(N-phenylbenzimidazol-2-yl) benzene. The efficiency as high as 20cd/A is achieved for orange-emitting device.

Keywords: Triplet emitters; Polymer light-emitting diodes

Structural characterization of poly- para-phenylenediamine–montmorillonite clay nanocomposites by Gustavo M. do Nascimento; Ricardo H. Sestrem; Marcia L.A. Temperini (pp. 2397-2403).
The structure of the poly-( para-phenylenediamine) (PpPD) formed by oxidative polymerization of 1,4-phenylenediamine ( p-PD) into the galleries of the Montmorillonite (MMT) clay was determined by different spectroscopic techniques. According to X-ray diffraction (XRD) pattern the polymer is formed between the clay layers. In addition, the composite morphology, visualized by electron microscopy (SEM), is similar to the pristine clay. The UV–vis–NIR data of PpPD–MMT sample shows strong absorption bands at 620 and 670nm, being related to groups with protonated phenazine-like rings. The resonance Raman spectrum of PpPD–MMT displays bands at 1179, 1201, 1347, 1412, and 1630cm−1, which are related to phenazine-like rings modes. X-ray absorption (XANES) at Nitrogen K edge of PpPD–MMT confirms the presence of azo, hydrazo and phenazinic nitrogens. The intercalated material is EPR silent, confirming that the charge carriers, responsible for the conductivity of ca. 10−4Scm−1, have diamagnetic behavior. Hence, the results confirm that when aniline or its derivates are polymerized in confined environments, it causes preferentially the formation of diamagnetic segments having protonated phenazine and azo segments.

Keywords: Polyaniline; Raman spectroscopy; Nanocomposites; para; -Phenylenediamine

Fabrication and characteristics of composite containing HCl-doped polyaniline and Ni nanoparticles by Rongcheng Liu; Hong Qiu; Hui Li; Hua Zong; Chunying Fang (pp. 2404-2408).
HCl-doped polyaniline powder (HCl-PANI) was synthesized using a polymerization procedure and then Ni nanoparticles were deposited on the HCl-PANI at room temperature by direct current magnetron sputtering. After this process the HCl-PANI–Ni composite was obtained. Ni nanoparticle size ranges from 5nm to 20nm in the composite. HCl-PANI structure is not influenced by the Ni nanoparticles. The composite pellet exhibits room temperature ferromagnetism and a conductivity of about 0.66S/cm. A temperature dependence of the conductivity from 160K to 290K reveals that a carrier transport mechanism in the composite is three-dimensional variable range hopping. Thermogravimetric analysis reveals that a weight loss of the HCl-PANI–Ni composite is larger than that of the HCl-PANI for the same heating temperature. The weight loss difference between the composite and the HCl-PANI increases with increasing the temperature.

Keywords: HCl-doped polyaniline; Ni nanoparticles; Composite; Structure; Ferromagnetism; Conductivity

Photoluminescence of MEH-PPV with ultraviolet excitation by Marcelo M. Faleiros; Paulo B. Miranda (pp. 2409-2412).
The basic optical properties of PPV-based polymers have been extensively studied due to their potential technological applications. However, a detailed investigation of electronic processes following photoexcitation in the ultraviolet is still lacking. We report photoluminescence measurements on poly(1-methoxy-4-ethylhexyloxy- paraphenylenevinylene) – MEH-PPV in the 2.0–5.6eV range, with excitation up to 5.6eV. The photoluminescence spectra lineshape is independent of excitation energy. The photoluminescence efficiency is high for energies well below the absorption maximum due to near-resonant excitation of the longest conjugated segments which are responsible for the PL. It decreases strongly for excitation energies in the range 2.1–2.5eV (up to the absorption maximum) and slightly from 2.5 to 5.6eV. The results indicate that states excited in the ultraviolet rapidly relax nonradiatively to the lowest state, from where the usual luminescence occurs.

Keywords: Photoluminescence; Ultraviolet; Conjugated polymers; Energy relaxation

Crystal structure and physical properties of a magnetic molecular conductor (EDO-TTFVODS)2FeCl4 by Xunwen Xiao; Jianghua Fang; Jin Zhou; Haoqi Gao; Hideki Fujiwara; Toyonari Sugimoto (pp. 2413-2416).
Crystal structure, and electrical conducting and magnetic properties of a radical cation salt of EDO-TTFVODS with magnetic FeCl4 ion, (EDO-TTFVODS)2FeCl4 (EDO-TTFVODS=ethylenedioxytetrathiafulvalenoquinone-1,3-diselenolemethide) are reported. In this salt, there are two independent donor molecules formed two different layers A and B, and the counter FeCl4 ions layer is sandwiched between two donor layers A and B along the b-axis. The donor molecules form the one-dimensional columns along the a-axis in both donor layers. This salt shows high conductivity at room temperature ( σRT=25Scm−1) and a metallic behavior down to ca. 80K, where a metal–insulator transition however occurs. The magnetic susceptibility obeys a Curie–Weiss law (Curie constant C=4.42emuKmol−1 and Weiss temperature Θ=−1.5K), without any magnetic ordering down to 1.8K. This result suggests the weak antiferromagnetic interaction between the d spins of FeCl4 ions.

Keywords: Keyword; Bent donor molecule; Magnetic molecular conductor; Metallic behavior; Antiferromagnetic interaction; π–d interaction

Field effect transistor behavior of organic light-emitting diodes with a modified configuration of ITO anode by Lin Lu; Fangfang Yu; Li Long; Jianning Yu; Bin Wei; Jianhua Zhang; Musubu Ichikawa (pp. 2417-2421).
We have developed the organic light-emitting diodes (OLEDs) with a modified configuration of ITO anode in which a thin channel was etched to form a bottom-contact field effect transistor (FET) using ITO and MgAg as a source/drain electrode and a gate electrode, respectively. The hole injection layer in OLEDs functioned as an active layer of FET and the other organic layers as insulator-like layer. The devices were found to exhibit a behavior of FET due to horizontal charge migration between source and drain, and an electro-optical transfer characteristic due to vertical charge transport and recombination. We have investigated the dependence of drain current on the channel length from 5 to 30μm and found that the modified channel length could change drain current directionally and quantitatively.

Keywords: Field effect transistor; Organic light emitting diodes; Channel length

Synthesis and characterization of soluble narrow band gap conducting polymers based on diketopyrrolopyrrole and propylenedioxythiophenes by Sarada Prasad Mishra; Akshaya Kumar Palai; Manoranjan Patri (pp. 2422-2429).
The synthesis of high molecular weight polymers containing diketopyrrolopyrrole units and dialkylProDOT units has been carried out. The resultant polymers were found to be low band gap, highly stable and excellent film forming properties. A maximum conductivity of 0.2–6S/cm was obtained from this set of polymers.A series of novel electro-active conjugated polymers containing 2,5-dialkyl-3,6-di(thiophen-2-yl)pyrrolo[3,4- c]pyrrole-1,4(2 H,5 H)-diones (DPPs) and 3,4-dihydro-3,3-dialkyl-2 H-thieno[3,4- b][1,4]dioxepines (dialkyl-ProDOTs) were synthesized using Stille coupling reaction in presence of CuO. The molecular weights of the synthesized polymers were found to be in the range of 18,000–45,000. Incorporation of the electron deficient DPP units and the electron rich dialkyl-ProDOT units in the conjugated backbone leads to low band gap polymers. All the polymers were found to be highly soluble in most chlorinated organic solvents as well THF and toluene with excellent film forming properties. From the UV–vis spectra, the band gap of the polymers was determined as 1.40–1.42eV which is lower than the poly(dialkylProDOT)s. From the electrochemical study, highest occupied molecular orbital (HOMO) energy levels of the synthesized polymers were found to be in the range of 5.54–5.51eV. Because of such high HOMO level, the resulting polymers were found to be more oxidatively stable. Polymers are thermally stable till 325–346°C with only 5% weight loss which was confirmed from thermogravimetric analysis (TGA). The polymers were found to be moderately conducting with maximum conductivity up to 0.2–6.0S/cm.

Keywords: Low band gap polymers; Diketopyrrolopyrrole; Dialkyl-ProDOT; HOMO energy level

Enhanced stability of poly(3-hexylthiophene) transistors with optimally cured poly(methyl methacrylate) dielectric layers by S.W. Lin; Y.M. Sun; A.M. Song (pp. 2430-2434).
Poly(3-hexylthiophene)-based organic field-effect transistors (OFETs) have been fabricated on poly(methyl methacrylate) (PMMA) gate dielectric layers under different process conditions, resulting in very different device stability in ambient air. The dielectric layers were prepared by spin coating and subsequently curing at various temperatures (120, 150, and 180°C) or by ultraviolet light (UV) exposure. With respect to the variations of the on/off current ratio and the threshold voltage, dramatically enhanced stability of the OFETs with the PMMA layer cured at 150°C has been demonstrated when compared to those cured at different temperatures. The devices cured by UV exposure showed even more superior stability, with reliable performance in ambient air for more than 10 days. The differences in the film surface morphology were analyzed and possible mechanisms for the enhanced stability are discussed.

Keywords: Organic field-effect transistors; Air stability; Dielectrics; Polymers

Uniaxial-stress effects on electronic structures of monolayer and bilayer graphenes by S.H. Lee; C.W. Chiu; Y.H. Ho; M.F. Lin (pp. 2435-2441).
Band structures of deformed monolayer and bilayer graphenes are explored through the tight-binding model. The mechanical effects of the strain on graphene lattices are based on the elasticity theory. Electronic properties are dependent on the existence of uniaxial stress, interlayer interactions, and the stacking sequence. Uniaxial stress drastically changes the energy dispersions, band-edge states, Fermi momenta, state degeneracies, and density of states ( D( ω)). The interlayer interactions induce two pairs of band structures and double the number of the special structures in D( ω). Each prominent peak at the middle energy splits into two separate peaks in the presence of uniaxial stress. The analysis of the stacking sequence shows some important differences between the AA- and AB-bilayer graphenes, such as the relationship between the uniaxial stress and low-energy D( ω), and the zero-gap semimetal-semiconductor transition. The calculated results could be verified by experimental measurements.

Keywords: Deformation effect; Monolayer and bilayer graphenes; Electronic property; Zero-gap semimetal-semiconductor transition

Optical, mechanical and etch properties of amorphous carbon nitride films grown by plasma enhanced chemical vapor deposition at room temperature by Sang Hoon Kim; Cheol Min Choi; Kil Mok Lee; Yoon-Bong Hahn (pp. 2442-2446).
Amorphous carbon nitride (a-CN) films were grown on Si(100) and SiO2/Si(100) substrates by plasma enhanced chemical vapor deposition at room temperature using gas mixtures of CH4 and N2. The as-deposited films showed two bond structures of CN and CN, and with increasing the N2 content the bond structure changed to graphite-like structure. All the samples showed low optical absorption coefficient ( k<0.15) in the wavelength range of 300–800nm. The a-CN films exhibited a good resistance to etching (i.e. higher selectivity over SiO2), which indicates a potential use of a-CN films as a new hard mask material.

Keywords: Carbon nitride; PECVD; Hardness; Optical absorption; Etch behavior

2,9-Dibromopentacene: Synthesis and the role of substituent and symmetry on solid-state order by Toshihiro Okamoto; Colin Reese; Michelle L. Senatore; Ming L. Tang; Ying Jiang; Sean R. Parkin; Zhenan Bao (pp. 2447-2451).
We have developed an effective synthetic route for 2,9-dibromopentacene, opening up new possibilities for future derivatization of pentacene. We also present the fundamental properties. Thin-film and single-crystal field-effect transistor results demonstrate a decrease in apparent charge transport efficiency with decreasing symmetry. The trend in symmetry was further correlated to single-crystal structural analysis, which implied that reduction in symmetry also reduced solid-state order. It is likely that this reduction in order is responsible for the diminished performance in the solid-state films and crystal, despite a reduction in overall tilt angle of the molecules relative to one another. Combined with previous studies, this work provides a more complete perspective on the interplay of symmetry, energetic, and intermolecular interactions in the macroscopic properties of solid-state organic electronic materials.

Keywords: Substituted pentacene; Selective synthesis; OFETs; High hole mobility

NH3 and HCl sensing characteristics of polyaniline nanofibers deposited on commercial ceramic substrates using interfacial polymerization by Jiangtao Chen; Jie Yang; Xingbin Yan; Qunji Xue (pp. 2452-2458).
This paper reports the use of the interfacial polymerization method in a simple route for fabricating low-cost, highly sensitive NH3 and HCl gas sensors made of polyaniline (PANI) nanofiber coatings on commercially available ceramic substrates. The PANI coatings consisted of uniform nanofibers and formed emeraldine salt. NH3 gas-sensing properties of as-synthesized PANI nanofibers were also investigated in detail. The influence of PANI nanofiber acidification treatment at different HCl solutions (pH=0, 1, 2, and 3) on NH3-sensing properties was discussed as well. As-synthesized PANI nanofibers exhibited very low detection limit (1ppm) and high sensing response (response S) was above 2 when the sensor was exposed to 50ppm NH3 gas, though a limited drift of the response appeared in the reproducibility test. For acid-treated PANI sensors, the response time increased and response S decreased with increasing pH value of HCl solutions. Response S, especially after acid-treatment, increased as testing proceeded. This is possibly due to the creation of reaction sites on the surface and/or the bulk of the sensors. When PANI was used to detect gaseous HCl, an irreversible process occurred and response S became saturated when the concentration of gaseous HCl reached 200ppm.

Keywords: Polyaniline nanofiber; Interfacial polymerization; Gas sensor; NH; 3; HCl

Dendrites and pillars in spin cast blends of polyaniline or its oligomeric analogue by J. Haberko; A. Bernasik; W. Łużny; J. Raczkowska; J. Rysz; A. Budkowski (pp. 2459-2466).
In the present work morphological structures were examined which are formed spontaneously during the spin-casting of polymer blends. Mixtures of polyaniline (PANI) (doped with camphorsulfonic acid, CSA) or its oligomeric counterpart (N,N′-diphenyl-p-phenylenediimine, DPI) and a conventional polymer (polystyrene, PS or poly(methyl methacrylate), PMMA) were studied. The samples were manufactured in controlled humidity conditions (relative humidity, RH=10%, 60% or 95%). In case of PANI(CSA)/PS (or PMMA) blends, hierarchic structures arise. They are built of large (>10μm) PS-rich (or PMMA-rich) dendrites and sub-micron PANI-rich pillars in the pores of PS (PMMA) host. In analogous PS/DPI films, DPI dendrites embedded in the PS film are observed. This microstructure formation route, based on solution blend processing, is an alternative to chemical synthesis of fibres and columns. Film structures were determined with microscopic (optical, Atomic Force Microscopy) and spectroscopic techniques (dynamic Secondary Ion Mass Spectroscopy and X-ray Photoelectron Spectroscopy). Structure formation models are presented. Diffusion-Limited Aggregation is postulated for solution droplets agglomerating as PS-rich fractals (with low attachment probability P) and for crystallizing DPI dendrites (with higher P value and hence larger and less compact fractals, as observed).

Keywords: Polymer thin films; Polymer blends; Polyaniline; Dendrites; Diffusion-Limited Aggregation

Quantum interference and Shubnikov–de Haas oscillations in β″-(ET)4(H3O)[Fe(C2O4)3]·C6H4Cl2 under pressure by David Vignolles; Alain Audouard; Vladimir N. Laukhin; Enric Canadell; Tatyana G. Prokhorova; Eduard B. Yagubskii (pp. 2467-2470).
Magnetoresistance oscillations of the quasi-two dimensional charge transfer salt β″-(ET)4(H3O)[Fe(C2O4)3]·C6H4Cl2 are investigated in pulsed magnetic fields of up to 55T, under an applied pressure of 0.5GPa. As it is the case at ambient pressure, data are in agreement with the coexistence of a Shubnikov–de Haas orbit and a quantum interference path with the same cross section. As a result, oscillations are observed at temperatures as high as 25K.

Keywords: PACS; 71.18.+y; 71.20.Rv; 72.15.GdOrganic metals; High magnetic fields; Quantum oscillations; Fermi surface

Synthesis, characterization and self-assembled film of poly(3-((2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy)propane-1-thiol) (PEDTMSHA) by Wenqiong Su; Ha Tran Nguyen; Misuk Cho; Yongkeun Son; Youngkwan Lee (pp. 2471-2475).
An alkylthiol functionalized monomer based on 3,4-ethylenedioxythiophene methanol (EDTM), namely 3-((2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy)propane-1-thiol (EDTMSHA), was synthesized and confirmed by1H NMR,13C NMR, and gas chromatography mass spectroscopy (GC/MS). The new monomer successfully produced a self-assembled monolayer (SAM), which was deposited on a gold disc electrode and then electrochemically polymerized. The SAM formation of the new conducting polymer films exhibited relatively low oxidation potentials with a well defined reversible and stable electrochemical behavior compared to conventional electropolymerized film.

Keywords: EDTM; EDTMSHA; Functionalized 3,4-ethylenedioxythiophene; Self-assembled monolayer

Yellow–green organic light-emitting diode based on tris(2-methyl-8-quinolinolate) scandium by Marina A. Katkova; Tatyana V. Balashova; Alexander A. Maleev; Vasilii A. Ilichev; Alexey N. Konev; Georgy K. Fukin; Alexander S. Mitin; Sergey Yu. Ketkov; Mikhail N. Bochkarev (pp. 2476-2480).
Efficient yellow–green electroluminescence emission at λmax=530nm with CIE coordinates x=0.3913, y=0.4947 was obtained with organic light-emitting devices based on tris(2-methyl-8-quinolinolate) scandium (1). The device with the configuration of indium tin oxide/ N,N′-bis(3-methylphenyl)- N,N′-diphenylbenzidine/1/Yb exhibits current efficiency of 3.1cd/A and power efficiency of 1.8lm/W at a luminance of 100cd/m2. The DFT calculations demonstrate that structural changes of the scandium complex1 influence the electroluminescence spectrum, the better agreement with experimental data being achieved when monodentate ligands are taken into consideration.

Keywords: Scandium complex; 2-Methyl-8-quinolinolate; amidine; Electroluminescence; Non-doped OLED; Hole-transporting; DFT calculations

Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) films with improved thermoelectric performances by Congcong Liu; Baoyang Lu; Jun Yan; Jingkun Xu; Ruirui Yue; Zhaojin Zhu; Shuyun Zhou; Xiujie Hu; Zhuo Zhang; Ping Chen (pp. 2481-2485).
Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films with room-temperature electrical conductivity of about 300Scm−1 were successfully prepared from PEDOT/PSS solution containing additives (DMSO or EG) on the smooth and flexible polypropylene (PP) film substrate with contact angle of 87°. As formed free-standing PEDOT/PSS films possess good flexibility and can be easily cut into various shapes with a knife. The contact angle of substrate has significant effect on the preparation of free-standing PEDOT/PSS films. Additionally, the process of adding DMSO or EG did not result in the change of carrier concentration but the increase of carrier mobility. The free-standing PEDOT/PSS film showed high electrical conductivity and stable Seebeck coefficient and its figure of merit (ZT) with high environment stability can be up to 10−2, one order of magnitude higher than that of pressed PEDOT/PSS pellets (10−3).

Keywords: PEDOT/PSS; Free-standing film; Contact angle; Thermoelectric performances

Thermal aging of single-layer polymer light-emitting diodes composed of a carbazole and oxadiazole containing copolymer doped with singlet or triplet emitters by Parul Rungta; Volodymyr Tsyalkovsky; Christopher F. Huebner; Yuriy P. Bandera; Stephen H. Foulger (pp. 2486-2493).
An electron-transporting monomer was synthesized that was structurally and energetically similar to the small molecule 2-biphenyl-4-yl-5-(4- tert-butylphenyl)-1,3,4-oxadiazole (tBu-PBD). The monomer was copolymerized with 2-(9 H-carbazol-9-yl)ethyl 2-methylacrylate and the resulting copolymer was utilized in organic light emitting devices which employed fluorescent coumarin 6 (C6) or phosphorescent tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] emitters. The copolymer devices exhibited a mean luminance of ca. 400 and 3552cd/m2 with the C6 and Ir(ppy)3 emitters, respectively, that was stable with thermal aging at temperatures ranging from 23°C to 130°C. Comparable poly(9-vinyl-9 H-carbazole)/tBu-PBD blend devices exhibited more pronounced variations in performance with thermal aging.

Keywords: Organic light emitting device; Copolymer; Electroluminescence; Phase separation; Density functional theory; Cyclovoltammetry

Composition and annealing effects in solution-processable functionalized graphene oxide/P3HT based solar cells by Jigang Wang; Yongsheng Wang; Dawei He; Zhiyong Liu; Hongpeng Wu; Haiteng Wang; Yu Zhao; Hui Zhang; Bingyang Yang (pp. 2494-2500).
Characterization of a solution-processable functionalized graphene oxide (SPFGraphene oxide) was investigated by FT-IR spectroscopy and the result of elemental analysis showed that the isocyanate treatment results in the functionalization groups in SPFGraphene oxide. Doping SPFGraphene oxide to P3HT based solar cells induces absorbing spectra more strongly and a great quenching of the photoluminescence of the P3HT. With an increase in the SPFGraphene oxide content, the overall performances of the hybrid devices increases first, reaching the peak efficiency for the 10wt% SPFGraphene oxide content, and then decreases. After annealing at 160°C for different time durations, the device containing 10wt% of SPFGraphene oxide for 10min shows the best performance with a power conversion efficiency of 1.046%, an open-circuit voltage of 0.73V, a short-circuit current density of 3.98mAcm−2 and a fill factor of 0.36 under simulated AM1.5G conditions at 100mWcm−2; The similar content one for 20min shows η value of 1.013%, which is lower than the former one to a small extent for longer annealing duration. The graphene has the potential to act as the next-generation material in the photovoltaic devices and other applications for ease of preparation, low price, large surface area, high conductivity and excellent transparency.

Keywords: Graphene; FT-IR; Photovoltaic cells; Performance

Interface-controlled pulsed-laser deposited polymer films in organic devices by D. Adil; N.B. Ukah; R.K. Gupta; K. Ghosh; S. Guha (pp. 2501-2504).
Matrix assisted pulsed laser evaporation (MAPLE) allows homogeneous film coverage of organic materials for layer-by-layer growth providing a tighter control of the polymer–dielectric interface in field-effect transistors (FETs) and metal–insulator–semiconductor (MIS) diodes. Electrical characteristics of FETs and MIS diodes using MAPLE and spin-coated grown fluorene copolymer films are compared. Current–voltage characteristics of MAPLE grown FETs without any surface modification show a better performance compared to the spin-coated FETs. Capacitance–voltage and conductance–voltage investigations of the MIS structures show that loss as well as accumulation capacitance and time constant dispersions are less in the MAPLE grown film compared to the spin-coated film.

Keywords: Pulsed laser evaporation; Polyfluorene; Field-effect transistor; Metal–insulator–semiconductor

Different solvents effect on the performance of the solar cells based on poly(3-hexylthiophene):methanofullerenes by Huangzhong Yu (pp. 2505-2509).
This paper reports the effect on the performance of the solar cells based on poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) with different casting solvents. These blend films are characterized by UV–vis absorption spectra, photoluminescence spectra, charge-transport dark JV curve, X-ray diffraction pattern curve, and AFM images. The results indicate that high boiling point solvent leads to an enhanced self-organization of P3HT in the active layer, which causes an increased charge transport. Increased incident light absorption and higher carrier mobility in the active layer contribute to the enhancement in the device performance, the power conversion efficiency of 3.69% and fill factor up to 65.3% are achieved with 1,2,4-trichlorobenzene as casting solvent without further heat treatment under Air Mass 1.5, 100mW/cm2.

Keywords: Solar cell; Polymer; Different solvents; Performance

Fabrication and characterization of flexible and high capacitance supercapacitors based on MnO2/CNT/papers by Yu Jin Kang; Byungwoo Kim; Haegeun Chung; Woong Kim (pp. 2510-2514).
Flexible paper-based supercapacitors were fabricated using carbon nanotubes (CNTs) and manganese oxides (MnO2), and their electrochemical properties were characterized in a three-electrode system. CNTs were synthesized via water-assisted chemical vapor deposition (CVD) and dispersed in water using the surfactant sodium dodecylbenzenesulfonate (SDBS). The solution containing dispersed CNTs was simply coated on papers by drop-dry method. MnO2 was then electrochemically deposited on the CNT-coated papers. The MnO2/CNT/paper supercapacitors showed high specific capacitance of 540F/g. Specific energy and specific power were 20Wh/kg and 1.5kW/kg, respectively, at current density of 5A/g in 0.1M sodium sulfate (Na2SO4) aqueous solution. Demonstrated high capacitance of the paper-based electrochemical capacitor makes it a promising candidate for flexible and low-cost energy storage device applications.

Keywords: Carbon nanotubes; Manganese oxides; Papers; Supercapacitors; Flexible

Electronic structure evolution of neutral and dicationic states of conjugated polymers with their band gap by Manuel Garcia; Lioudmila Fomina; Serguei Fomine (pp. 2515-2519).
The electronic structures of neutral and dicationic states of 8 conjugated oligomers were studied at UB3LYP/6-31G* level as models of conjugated polymers with different band gaps ( Eg). The evolution of the electronic structure for polymers with experimental Eg ranging from 3.0 to 0.0eV has been investigated for both neutral and dicationic species. For polymers with Eg>1.1eV the ground state of neutral oligomers was found to be a closed shell singlet (S0) while the dicationic state was a polaron pair open shell singlet (OSS) state. For polymers with lower Eg, OSS becomes the ground state for both dicationic and neutral states. The energy difference between OSS and S0 state increases with closure of Eg for neutral oligomers. However, in dications the S0–OSS energy difference becomes less than 1kcal/mol for the low band gap polymers. Both, the charge distribution and the bond length alternation pattern suggest that bipolaronic state and not polaron pair state dominates in dications of the low band gap polymers ( Eg<1.1eV).

Keywords: Low band gap conjugated polymers; Broken symmetry DFT; Dications

Synthesis and third order optical nonlinearity studies of the donor–acceptor conjugated polymer, poly(2-[3,4-didodecyloxy-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-5-phenyl-1,3,4-oxadiazole) and a polymer/TiO2 nanocomposite by M.G. Murali; M.G. Ramya; D. Udayakumar; N.B. Lakshmi; Reji Philip (pp. 2520-2525).
▶ 1,3,4-Oxadiazole unit increases the electron affinity of poly(alkoxythiophene). ▶ TiO2nanoparticles improve the thermal stability of the polymer. ▶ Polymer and nanocomposite films show a strong optical limiting behavior. ▶ TiO2nanoparticles enhance the nonlinear absorption coefficient value of the polymer.A donor–acceptor conjugated polymer (PDOThPOD) containing 3,4-didodecyloxythiophene and (1,3,4-oxadiazolyl)benzene units is synthesized by using precursor polyhydrazide route. Cyclic voltammetry studies reveal that the polymer possesses a low-lying LUMO energy level (−3.57eV). A nanocomposite of polymer PDOThPOD and nano TiO2 is also prepared. The linear optical properties of PDOThPOD and the nanocomposite are studied using UV–vis absorption spectroscopy and fluorescence emission spectroscopy. z-scan technique is used to study the third order nonlinear optical properties of the polymer and nanocomposite films. Both polymer and nanocomposite films show a strong optical limiting behavior. The value of nonlinear absorption coefficient ( β) is found to be of the order of 10−7m/W, indicating that these materials are potentially suited for fabricating optical limiters.

Keywords: Conjugated polymers; Nanocomposite; Cyclic voltammetry; Nonlinear optics; z-Scan; Optical limiting

Electron transport properties of some newly synthesized nonsymmetrical bisindolizines in thin films by L. Leontie; R. Danac; I. Druta; A. Carlescu; G.I. Rusu (pp. 2526-2533).
In this work, temperature dependences of electrical conductivity and thermoelectric power, for some recently synthesized nonsymmetrical bisindolizines, are studied. Thin-film samples ( d=0.10–0.30μm) spin-coated from dichloromethane solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are subjected to a heat treatment within the temperature range of 301–541K.The studied organic compounds show typical p-type semiconductor behavior. The activation energy of electrical conduction was found in the range 1.00–1.26eV, while the ratio of charge carrier mobilities ranged between 0.90 and 0.97.The correlations between determined semiconducting parameters and specific features of molecular structure of the compounds have been discussed.In the higher temperature range (363–541K), the electronic transport in actual compounds can be interpreted by using the band gap representation model, while for lower temperatures, Mott's variable-range hopping conduction model was found to be appropriate.

Keywords: Organic compounds; Thin films; Chemical synthesis; Electrical conductivity

Benzyl substituted benzotriazole containing conjugated polymers: Effect of position of the substituent on electrochromic properties by Basak Yigitsoy; S.M. Abdul Karim; Abidin Balan; Derya Baran; Levent Toppare (pp. 2534-2539).
New classes of EDOT coupled-benzotriazole bearing π-conjugated monomers containing benzyl units on electron-withdrawing benzotriazole moiety were synthesized. The effect of structural differences on electrochemical and optoelectronic properties of the resulting polymers (PBBTES and PBBTEA) was investigated. The results showed that the insertion of benzyl substituent to benzotriazole from different positions changes the electronic structure of polymer which results in completely different electrochemical and optical properties. PBBTES has a very low oxidation potential (0.13V) compared to the oxidation potential of PBBTEA (0.98V). Spectroelectrochemical analyses revealed that PBBTES is blue in its neutral state with a π–π* transition at 625nm whereas PBBTEA is orange in its neutral state with a π–π* transition at 477nm. The band gap ( Eg) values for PBBTES and PBBTEA were calculated as 1.48eV and 1.57eV, respectively. PBBTEA can be switched between blue neutral state and light blue oxidized state while PBBTEA reveals orange color at the neutral state and gray color at oxidized state.

Keywords: Electrochemical polymerization; Conducting polymer; Low band gap; Electrochromism; Benzotriazole

Morphological and adhesive properties of polypyrrole films synthesized by sonoelectrochemical technique by Jérôme Dejeu; Abdeslam Et Taouil; Patrick Rougeot; Sophie Lakard; Fabrice Lallemand; Boris Lakard (pp. 2540-2545).
This paper presents electrochemical synthesis of polypyrrole films under high frequency sonication. The films are characterized in terms of adhesion and surface morphology. Comparison to classical electrosynthesized polypyrrole films is made. In particular, the use of high frequency sonication (500kHz) during electrodeposition of polypyrrole on Si was reported for the first time. Chronocoulometry was used for polymer films electrosynthesis on Si substrates. Influence of polymer thickness on the rugosity, morphology and adhesion force properties was studied. Scanning Electron Microscopy and mechanical probe profiling showed that sonication led to less rough and more homogeneous surface structure. Adhesion force properties of polypyrrole films were also studied by means of force–distance curves obtained by atomic force microscopy. For polymer films obtained in the absence of sonication, adhesion forces decreases with increase in polymer thickness. On the contrary, for polymer films obtained under sonication, the adhesion of the films decreased when the polymer thickness decreased.

Keywords: Polypyrrole; Sonochemistry; Electrochemistry; Atomic force microscopy; Adhesion force or pull-off force

Redox behaviour of polyaniline–palladium catalytic system in the presence of formic acid by Wadia Dhaoui; Magdalena Hasik; David Djurado; Andrzej Bernasik; Adam Pron (pp. 2546-2551).
Redox behaviour of polyaniline (PANI) films containing chemically incorporated palladium particles in the presence of formic acid was studied. Two types of PANI–Pd hybrids were prepared: PANI-PdHA and PANI-PdLA, depending on the acidity of the PdCl2 solution used for the introduction of palladium into the polymer matrix. UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to examine the nature of processes involved upon the decomposition of formic acid on polyaniline–palladium hybrids. In particular, UV–vis changes of both kinds of films were followed in situ (in 1M aqueous HCOOH solution) as a function of time. Rather unexpectedly, the redox properties of polyaniline films are found to be significantly altered in the presence of palladium particles. Particles of Pd0 promote the reduction of PANI from the most oxidized and semi-oxidized states to the most reduced one with simultaneous decomposition of formic acid.

Keywords: Polyaniline; Palladium; Formic acid; Redox conversion; Optical properties

The role of solvent on the doping of polyaniline with Fe(III) ions by Celly M.S. Izumi; Daniel C. Rodrigues; Marcia L.A. Temperini (pp. 2552-2558).
The products formed from the reaction of emeraldine base polyaniline (EB-PANI) with Fe(III) ions in N-methyl-pyrrolidone (NMP), dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol media have been investigated using UV–VIS–NIR and resonance Raman ( λ0=632.8 and 1064nm) spectroscopies. Through these results it was verified that the different PANI forms in solution can be formed by the suitable choice of the solvent. The behavior of Fe(III)/EB-PANI in different solvents was rationalized in terms of the interactions among Fe(III) ions, EB-PANI and solvent. In basic NMP, DMA and DMF media, the reaction of Fe(III) with EB-PANI yields EB-PANI doping giving ES-PANI and/or the EB-PANI oxidation to PB-PANI. The formation of ES-PANI is favored in DMF while PB-PANI is formed in a greater extension in NMP and DMA. In acidic m-cresol, only ES-PANI is produced in Fe(III)/EB-PANI solutions indicating the important role played by the solvent in the nature of the product.

Keywords: Polyaniline; Resonance Raman; Doping; Iron; Conducting polymer

Controlling of electrical characteristics of Al/p-Si Schottky diode by tris(8-hydroxyquinolinato) aluminum organic film by A.A.M. Farag; B. Gunduz; Fahrettin Yakuphanoglu; W.A. Farooq (pp. 2559-2563).
We study how tris(8-hydroxyquinolinato) aluminum organic semiconductor layer at p-silicon/Al interface can affect electrical transport across this interface. Al/Alq3/p-Si device shows a good rectifying behavior with an ideality factor value of 1.95. The barrier height values obtained from IV and Norde method were found to be 0.84 and 0.82eV, respectively. This indicates that the barrier height obtained from Norde method is lower than that of barrier height value obtained from IV due to the series resistance effect. The modification of the interfacial potential barrier for Al/p-Si diode was achieved using an interlayer of the Alq3 organic semiconductor and this is ascribed to the fact that the Alq3 interlayer increases the effective barrier height, because of the interface dipole induced by passivation of the organic layer. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance and interface state density values. The series resistance of the diode was changed from 9kΩ to 1kΩ with increasing frequency. The distribution profile of R sV gives a peak at low frequencies in the depletion region and disappears with increasing frequency.

Keywords: Organic–inorganic diode; Alq3 organic semiconductor

Properties of composite films of titania nanofibers and Safranin O dye by M. Drabik; J. Touskova; J. Hanus; H. Kobayashi; H. Biederman (pp. 2564-2572).
Titania (TiO2) nanofibers and composite thin films of titania nanofibers and Safranin O dye (SAF) were studied. TiO2 nanofibers were prepared by electrospinning technique from titanium tetra-isopropoxide precursor solution in ethanol. Surface topology of the nanofibers was observed using scanning electron microscopy (SEM), their crystal structure was studied by X-ray diffraction (XRD) and the chemical composition by X-ray photoelectron spectroscopy (XPS). Properties of the TiO2 nanofibers were studied in dependence on the values of relative air humidity in the range from 15% to 55%. It was necessary to maintain the relative humidity lower than 30% during electrospinning in order to obtain high quality nanofiber films. The average minimum diameter of the as-prepared TiO2 nanofibers was found to be around 100nm. Nanofiber diameter diminishes to about 50nm after annealing at 420°C for 1h. The as-prepared titania nanofiber films were completely amorphous while anatase crystal phase was detected in the films after annealing. In order to prepare the composite films, solution of SAF dye with poly(vinylpyrrolidone) in ethanol/water was dropped off on the prepared titania nanofibers surface. Opto-electrical properties of SAF dye and the resulting nanocomposite films were studied by UV–Vis spectroscopy and current–voltage characteristics. Safranin O is characterized by two strong absorption peaks; one at 274nm and a wide band with splitting between 420nm and 600nm. The optical energy band gap of titania nanofibers was estimated from the UV–Vis measurements to be 3.4eV. The charge transport in the composite films is influenced by the space charge limited currents due to the very high resistance of the materials.

Keywords: Electrospinning; Nanocomposite; Nanofiber; Safranin O; Titania

I2-doped and pyrrole ring-iodinated semi-conducting oligomers of N-vinyl-3-alkyl-2-phenylpyrroles by Boris A. Trofimov; Marina V. Markova; Inna V. Tatarinova; Al’bina I. Mikhaleva; Lyudmila V. Morozova; Ol’ga V. Petrova; Lyubov’ N. Sobenina; Konstantin B. Petrushenko; Tamara I. Vakul'skaya; Spartak S. Khutsishvili; Galina F. Prozorova (pp. 2573-2580).
I2-doped and pyrrole ring-iodinated semi-conducting oligomers of N-vinyl-3-alkyl-2-phenylpyrroles have been synthesized by free-radical polymerization of the above monomers (AIBN, 2–5wt%, 60–80°C) and further exposure of the oligomers obtained to I2 vapor. The parent oligomers exhibit paramagnetic and fluorescent properties and stable up to 300–370°C.

Keywords: N-vinyl-2-phenylpyrrole; N-vinyl-3-alkyl-2-phenylpyrroles; Free-radical polymerization; Electoconducting oligomers; Paramagnetism; Fluorescence

Insights into the physical basis of metal(II) hydrazone complexes with isoxazole and barbituric acid moieties for recordable blu-ray media by Zhimin Chen; Yiqun Wu; Chunying He; Bin Wang; Donghong Gu; Fuxi Gan (pp. 2581-2586).
Tetrafluoropropanol soluble, metal(II) hydrazone complexes derived from alkyl substituted isoxazole and barbituric acid were synthesized and evaluated as suitable optical recording materials for the recordable blu-ray disc system. The behaviour and relationships of the absorption, reflectivity and optical constants (complex refractive indices N= n+ ik) for different metal(II) complexes in spin-coated films were discussed. In addition, the important thermal decomposition data of these metal(II) complexes from simultaneous TG–DSC analyses were presented as well. As an example of the utility of dye-based blu-ray recording media, we used the nickel(II) hydrazone complex thin film as recording layer for static optical recording performance test. Results showed that high reflectivity contrast over 45% and durable information marks (after repeatedly reading 20,000 times) could be achieved under optimum laser writing power and pulse width conditions, indicative of producing a very promising optical recording medium for blu-ray disc-recordable system.

Keywords: Optical recording material; Metal(II) hydrazone complexes; Spin-coated film; Optical properties; Blu-ray disc-recordable

Unique structural features and electrical properties of electrospun conjugated polymer poly(3-hexylthiophene) (P3HT) fibers by Kok Ho Kent Chan; Takeshi Yamao; Masaya Kotaki; Shu Hotta (pp. 2587-2595).
This study examines and compares the internal structure conjugated polymeric fibers fabricated by electrospinning with cast films. Despite rigidity of polymer chain and the inability of its molecular chains to entangle to form viscoelastic jets, regioregular poly(hexyl-3-thiophene) (P3HT) exhibited the remarkable capability to be electrospun when the solution was subjected to gelation. In order to investigate the influence of additional mechanical stretching on the fibers, P3HT was electrospun with the aid of a rotating disc collector. Structure of electrospun fibers was probed via characterization techniques such as differential scanning calorimetry (DSC), Fourier transform infrared and photoluminescence (PL) spectroscopies. The findings indicated internal structural modifications developed within P3HT fibers, as a consequence of additional mechanical stretching induced by the rotating collector. Polarized FTIR and PL spectroscopies suggested that the molecular chains were aligned along the fiber axis. Electrical conductivity of iodine doped P3HT electrospun fibers was between 3×103S/m and 6×103S/m.

Keywords: Electrospinning; Molecular orientation; Single fiber; Electrical property; Poly(hexyl-3-thiophene)

Conducting polyaniline–montmorillonite composites by Patrycja Bober; Jaroslav Stejskal; Milena Špírková; Miroslava Trchová; Martin Varga; Jan Prokeš (pp. 2596-2604).
Polyaniline (PANI)–montmorillonite (MMT) composites were prepared in two ways: (a) by the polymerization of aniline hydrochloride with ammonium peroxydisulfate (APS) in aqueous suspensions of MMT, (b) by the intercalation of aniline hydrochloride into MMT in aqueous suspension followed by the oxidation with APS, i.e. by the surface and intercalative polymerizations of aniline. The products were analyzed by SEM, XRD, TGA, FTIR and Raman spectroscopies. The formation of red coloration after interaction of MMT with aniline is discussed. The conductivity of PANI–MMT composites increased to units Scm−1 as the content of PANI reached 50–60wt.%. The intercalation of aniline into MMT before the polymerization had no marked effect on the conductivity of resulting composites, which was determined mainly by the PANI present at the MMT particles surfaces.

Keywords: Polyaniline; Montmorillonite; Nanocomposites

Chemical synthesis of poly(aniline-co-o/m-toluidine)/V2O5 nano composites and their characterizations by J. Juliet Latha Jeyakumari; A. Yelilarasi; B. Sundaresan; V. Dhanalakshmi; R. Anbarasan (pp. 2605-2612).
Chemical oxidative polymerization of aniline (ANI) and o/m-toluidine (OT or MT) and their nano composites at different experimental conditions were performed using peroxydisulfate (PDS) as a lone chemical initiator and V2O5 as a host material in an aqueous HCl medium at 45°C under nitrogen atmosphere. The nano composites were synthesized under different experimental conditions and were characterized by Fourier transform infra red (FTIR) spectroscopy, conductivity measurements, high resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TGA) like analytical tools. The effect of methyl substituent in the phenyl ring of ANI derivatives on the structure and property relationship of copolymer was studied.

Keywords: Copolymer; Nano composites; TGA; FTIR; HRTEM; Conductivity

Characterization of graphene-based supercapacitors fabricated on Al foils using Au or Pd thin films as interlayers by Kahoe Ku; Byungwoo Kim; Haegeun Chung; Woong Kim (pp. 2613-2617).
We demonstrate that an Au or Pd interlayer between graphene and an Al-foil current collector plays an important role in enhancing supercapacitor performance. Graphene was prepared by scalable chemical exfoliation and mild thermal reduction (∼150°C) processes. Working electrodes were prepared by coating the graphene on Au/Al or Pd/Al by drop-dry method. The graphene deposited on the noble metals Au and Pd demonstrated excellent supercapacitor performance. Estimated specific energy and specific power of supercapacitors were ∼40Wh/kg and ∼40kW/kg at the current density of ∼33A/g, when operated in organic solution. Altogether, we demonstrate that employing noble metals in the fabrication of graphene-based supercapacitors can lead to excellent performance, and this could be a critical basis for further development of graphene-based supercapacitors.

Keywords: Graphene; Supercapacitor; Interface; Current collector; Gold; Palladium

Synthesis and characterization of low-bandgap copolymers based on dihexyl-2 H-benzimidazole and terthiophene by Suhee Song; Sung Heum Park; Youngeup Jin; Youngran Goo; Il Kim; Heesoo Lee; Kwanghee Lee; Hongsuk Suh (pp. 2618-2622).
A series of new semiconducting polymers with 3-(hexyloxy)thiophene, 2,2-dihexyl-2 H-benzimidazole (HBI) and thiophene units was synthesized using Stille polymerization. These random copolymers show good solubility at room temperature in organic solvents owing to the long alkyl chain in new acceptor, 2,2-dihexyl-2 H-benzimidazole. InHBI, the sulfur at 2-position of 2,1,3-benzothiadiazole (BT) unit was replaced with the carbon to make a highly soluble electron deficient moiety while keeping the 1,2-quinoid form ofBT unit. The spectra of the solid films show absorption bands with maximum peaks at about 408–526nm and the absorption onsets at 550–692nm, corresponding to band gaps of 1.79–2.25eV. The onset wavelengths of the absorption spectra in thin films exhibit a gradual red-shift with decreased amount of dihexyl-2 H-benzimidazol unit, that is, from 550nm withPHOTDTHBI-9 to 692nm withPHOTDTHBI-1. Under white light illumination (AM 1.5 G, 100mW/cm2), the device withPHOTDTHBI-3:PCBM blend demonstrated a VOC value of 0.36V, a JSC value of 1.20mA/cm2, and a FF of 0.37, leading to the efficiency of 0.16%.

Keywords: Polymer; Photovoltaic cells; Thiophene; 2; H; -benzimidazole

Effect of wetting solvent on poly(3-hexylthiophene) (P3HT) nanotubles fabricated via template wetting by Joseph P. Cannon; Steven D. Bearden; Scott A. Gold (pp. 2623-2627).
Template wetting is a simple, solution based nanofabrication method that has been shown effective for a wide range of polymers. Like other solution based polymer processing methods, it is reasonable to expect that the choice of solvent will have a significant impact on the chain orientation in the final solid structure. Here we examine the impact of wetting solvent on the properties of 100nm diameter poly(3-hexylthiophene) (P3HT) nanotubules made via template wetting. The degree of alignment of the P3HT backbone with the nanotubule axis as observed through dichroism in the FTIR spectrum was observed to depend on the strength of polymer–solvent interaction forces, observed experimentally through thermogravimetric analysis experiments. This solvent effect was not observed in other properties as neither the UV–Vis absorbance nor the hole mobility was observed to depend significantly on the wetting solvent. It is believed that the rigid rod structure and large side chain limited the degree of increase in the effective conjugation length and preventing even the aligned chains from being more tightly packed as would be necessary for an increase in inter-chain π-bond interactions sufficient to impact these performance characteristics of the material.

Keywords: Poly(3-hexylthiopehene) (P3HT); Template wetting nanofabrication; Solvent effects; Thermogravimetric analysis; Polarized FTIR spectroscopy

Leakage conduction mechanism of top-contact organic thin film transistors by Yow-Jon Lin (pp. 2628-2630).
This paper presents an analysis of the leakage conduction mechanism of top-contact organic thin film transistors. According to the experimental result, the author found that the dominant leakage conduction mechanism of top-contact devices is the Schottky emission and the gate leakage current dramatically increases with an increase in applied voltage. It is important to identify the gate leakage effect for understanding the actual device operation mechanism and enhancing the device performance.

Keywords: Organic semiconductor; Leakage conduction; Schottky emission; Organic thin film transistors

Synthesis and characterization of polypyrrole by cyclic voltammetry at different scan rate and its use in electrochemical reduction of the simulant of nerve agents by Pushpendra K. Sharma; Garima Gupta; Virendra V. Singh; B.K. Tripathi; P. Pandey; M. Boopathi; Beer Singh; R. Vijayaraghavan (pp. 2631-2637).
In this study, polypyrrole (pPy) was in-situ electrosynthesized on gold electrode surface using four different scan rate variations such as 5, 10, 25 and 50mV/s with the help of cyclic voltammetry. Scanning electron microscopy (SEM) characterization revealed a scan rate dependent surface morphology for the pPy modified electrodes. The surface functional groups and elemental composition of the modified electrodes were deduced using Raman spectroscopy and energy dispersive X-ray spectroscopy (EDS), respectively. These pPy modified electrodes were utilized to study the electrochemical behavior of the nerve agents’ simulant dimethyl methyl phosphonate (DMMP) in aqueous medium. These modified electrodes exhibited electrochemical parameters with DMMP depending on the scan rate used for the in-situ synthesis of pPy conducting polymer.

Keywords: Simulant of nerve agents; Cyclic voltammetry; Electrocatalysis; DMMP

Two new nickel(II) complexes: Synthesis and third-order optical nonlinearity by Zhibin Cai; Mao Zhou; Jianrong Gao (pp. 2638-2642).
▶ The two nickel(II) complexes synthesized are new. ▶ A one-pot synthesis method adopted is simple and feasible. ▶ The third-order nonlinear optical properties of these complexes have not been reported.Two new nickel(II) complexes were synthesized and characterized by UV, MS and elemental analysis. Their off-resonant third-order nonlinear optical properties were measured using femtosecond laser and degenerate four-wave mixing technique. The third-order nonlinear optical susceptibilities χ(3) are 3.38×10−13esu and 3.64×10−13esu. The nonlinear refractive index n2 are 6.22×10−12esu and 6.70×10−12esu. The second-order hyperpolarizabilities γ of the molecules are 3.38×10−31esu and 3.65×10−31esu. The response times are 61fs and 74fs. The results show that the two complexes have potential nonlinear optical applications.

Keywords: Nonlinear optics; DFWM technique; Nickel(II) complex; Synthesis

Optimization of the active-layer morphology with a non-halogenic solvent for bulk-heterojunction polymer solar cells by Ching Lin; Wen-Chueh Pan; Feng-Yu Tsai (pp. 2643-2647).
Polymer solar cells (PSC) based on blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were fabricated with a non-halogenic solvent—tetralin—as the casting solvent for the active layer, and the morphology of the active layer was optimized by varying the casting conditions to obtain high efficiency and thermal stability from the PSCs. Tetralin as the casting solvent caused excessive P3HT and PCBM aggregations and hence dismal performance [power conversion efficiency (PCE)=0.5%] due to its low volatility and high dissolution power, which enhanced the plasticizing effect of residual solvent during the formation of the active layer. Accelerated removal of the residual solvent by a vacuum drying treatment greatly reduced the aggregations and improved the PCE to 2.4%, but the improvement was limited because the rapid drying inhibited full developments of continuous charge-transport pathways and of P3HT crystallinity, both of which are critical for charge transport through the device. The desirable morphology—minimal aggregations but high phase continuity and P3HT crystallinity—was obtained with a low-temperature drying process, which limited P3HT/PCBM aggregations and enhanced nucleation of P3HT crystallites, resulting in a finely interconnected P3HT crystal network that provided both large bulk-heterojunction area and facile hole-transport pathways. The resultant PSCs obtained a high PCE of 3.7%, and because of the morphological rigidity of the P3HT crystal network, showed excellent stability for extended duration at elevated temperature.

Keywords: Organic photovoltaic; Conjugated polymer; Organic electronics; Organic semiconductors

The study of new p–n mixed semiconductors: 6,13-Bis(4-propylphenyl)pentacene–ZnO nano-sized composites films by Zhong Huang; Jingchang Zhang; XiuyingYang; Weiliang Cao (pp. 2648-2652).
A series of 6,13-bis(4-propylphenyl)pentacene(BPP)–ZnO nano-sized composites were successfully constructed and characterized by UV–vis spectra, infrared spectra, X-ray diffraction spectra, cyclic voltammetry, X-ray photoelectric spectra, etc. These characterizations proved that an interaction between the BPP and ZnO happened, leading to the generation of p–n mixed semiconductors with many new properties. The forbidden band gaps of prepared semiconductors are among 1.09–1.29eV, which are much smaller than that of BPP and ZnO. From the comparison of BPP–ZnO nano-sized composites with some other related composites, it was found that the forbidden band gap of p–n mixed semiconductor becomes smaller as the forbidden band gap of pentacene derivative decreases.

Keywords: 6,13-Bis(4-propylphenyl)pentacene; Nano-sized composite; p–n Mixed semiconductor; Photoelectric property

Development of an electrochemical sulfite biosensor by immobilization of sulfite oxidase on conducting polyaniline film by Baharak Bahmani; Fathollah Moztarzadeh; Mohammad Rabiee; Mohammadreza Tahriri (pp. 2653-2657).
▶ Aluminum electrode is a suitable substrate electrode for the preparation of enzyme-modified electrodes. ▶ Aluminum electrode improves the stability of the film growth on it. ▶ The nature of sulfite oxidase into polyaniline aluminum modified electrode allows the enhancement of the sensitivity for the detection of sulfite, and it exhibits linear response to sulfite ion over a wide concentration range (3 decades) with low detection limit of 2×10−6M.In this work, a biosensor was developed for the determination of sulfite. The bioelectrochemical response of the enzyme-modified electrode based on electrochemical incorporation of sulfite oxidase into polyaniline aluminum modified electrode was investigated. Electropolymerization of polyaniline and simultaneous immobilization of sulfite oxidase on the aluminum were performed in an aqueous solution containing sulfite oxidase. The sulfite biosensor constructed by cycling the potential scan between +1.2 and −0.5V vs. saturated calomel electrode (SCE) that showed a sensitive response to sulfite with a linear calibration graph in the concentration ranges of 0.006–5mM sulfite and detection limit 0.002mM sulfite (S/N=3). The obtained results from the stability tests of the biosensor show that the sulfite biosensor can be used for two different applications, for immediate usage and long term usage. Also, the bioelectrochemical response of the enzyme-modified electrode as a sulfite biosensor was evaluated at different experimental conditions. The optimum pH when using phosphate buffer and temperature were 8.5 and 35°C, respectively. Finally, the apparent Michaelis–Menten constant was determined which has value of 0.365mM which is really close to the magnitude of the Michaelis–Menten constant of free sulfite oxidase that shows the enzyme was not chemically modified and has its usual kinetic reaction.

Keywords: Sulfite biosensor; Polyaniline; Sulfite oxidase; Enzyme

Highly crystalline and soluble dodecylbenzene sulfonic acid doped poly(o-toluidine) by Sh. M. Ebrahim; A. Gad; A. Morsy (pp. 2658-2663).
Dodecylbenzene sulfonic acid (DBSA) doped poly(o-toluidine) (POT) was synthesized by oxidative polymerization technique. The optical, structural, morphological, thermal and electrical properties of the POT-DBSA have been investigated. It was found that conducting emeraldine salt of POT-DBSA is stable in chloroform. X-ray diffraction showed that the POT-DBSA is a highly crystalline polymer due to formation of H-bonding across chains. The scanning electron micrograph reveals a flaky like feature with few globular structures and the size of the grain was about 3μm. The highest conductivity of POT-DBSA was found to be 1.88×10−3S/cm at 1:1 molar ratio of oxidant to o-toludine and at 0.18M of DBSA. Schottky diode based on POT-DBSA was fabricated using Al as Schottky contact and Cu as an Ohmic contact. The junction parameters including ideality factor and barrier height of the diode was 3.0 and 0.989eV, respectively.

Keywords: Conducting polymers; Poly(o-toluidine); Dodecylbenzene sulfonic acid; Schottky diode

MWCNT–OH adsorbed electrospun nylon 6,6 nanofibers chemiresistor and their application in low molecular weight alcohol vapours sensing by Jaewon Choi; Eun Joo Park; Dong Wha Park; Sang Eun Shim (pp. 2664-2669).
Herein, we fabricated MWCNT–OH adsorbed electrospun nylon 6,6 nanofibers by electrospinning and dip coating method. The amount of MWCNT–OH adsorbed to the pure electrospun nylon 6,6 nanofibers was 0.056wt%. The electrical conductivity of MWCNT–OH adsorbed electrospun nylon 6,6 nanofibers was 5.24×10−3Scm−1. We also investigated the sensing properties of MWCNT–OH adsorbed electrospun nylon 6,6 nanofibers by measuring its response upon exposure to low molecular weight alcohol vapours such as methanol, ethanol, 1-propanol, and 1-butanol. The changes of the electrical resistance of MWCNT–OH adsorbed electrospun nylon 6,6 nanofibers were demonstrated on the basis of hydrogen bonds among the alcohol vapours and hydroxyl groups (–OH) on MWCNT–OH, and amide groups (–NHCO–) in nylon 6,6. The fabricated sensor showed good reversible and reproducible responses upon the cyclic test.

Keywords: Chemical vapour sensor; Nylon 6,6; MWCNT; Electrospinning; Nanofiber

Electrical properties of TiO2-filled polyimide nanocomposite films prepared via an in situ polymerization process by Jun-Wei Zha; Zhi-Min Dang; Tao Zhou; Hong-Tao Song; George Chen (pp. 2670-2674).
To fully understand the reliable electrical properties of the nanocomposite films, their physical and chemical behaviors as well as dielectric properties were analyzed. Polyimide/TiO2 (PI/TiO2) nanocomposite films were prepared using in situ dispersion polymerization process. Influences of frequency, temperature and the nano-TiO2 particles loading concentration on dielectric permittivities of the PI/TiO2 nanocomposite films were studied. The dielectric relaxation behavior of the PI/TiO2 nanocomposite films has been investigated with dielectric relaxation spectrum. It was found that interfacial polarization, namely Maxwell–Wagner–Sillars, existed in the PI/TiO2 nanocomposite films with different loading concentration of the nano-TiO2 particles. Dielectric permittivities of the PI/TiO2 nanocomposite films fluctuation with temperature (−50–150°C) were attributed to the mobility and thermal expansion of the polymer matrix, for which the Cole–Davidson model, or modified Cole–Cole model, was brought to account.

Keywords: Polyimide; Nanocomposite films; Electrical properties; Cole–Cole model; Interfacial polarization

Semiconducting properties of thin films with embedded nanoparticles by Mouhssine Benlarbi; Carole Farre; Carole Chaix; Marcus F. Lawrence; Loïc J. Blum; Volodymyr Lysenko; Christophe A. Marquette (pp. 2675-2680).
We demonstrate here the possibility of designing semiconducting thin films with controlled electrochemical properties. The thin films are composed of (i) an insulating binder and (ii) a semiconductor nanopowder which enables the fine tuning of the semiconducting properties of the layers. Thus, p- and n-type silicon particles (obtained from a top-down technique), or metal-oxide ZnO, SnO2 and NiO nanoparticles (synthesized using a bottom-up protocol) are successfully integrated into spin-coated or screen-printed thin films and used as semiconducting materials. The flat band potential (Vfb) of the films is then easily tuned from 0V to −1.138V.

Keywords: Impedance; Nanoparticles; Semiconductor; Spin-coating; Thin-film

Synthesis, characterization and electrochemical properties of new functional polythiophenes by E. Salatelli; L. Angiolini; A. Brazzi; M. Lanzi; E. Scavetta; D. Tonelli (pp. 2681-2686).
Novel fully soluble polythiophene derivatives containing halogen or ester moieties at the end of a tetramethylenic side chain were synthesized using either the direct oxidative polymerization procedure of functionalized thiophene or the post polymerization functionalization of the preformed polymeric precursor. The structures of the polymers were characterized and their physical properties carefully investigated. High average molecular weights (M¯n up to 30,550g/mol) and thermostable products were obtained. The absorption wavelength of the polymers in different solvents can be tuned up by varying the composition of solvent mixtures. Cyclic voltammetry measurements displayed good charge transport properties, strongly related to the kind of substituent linked to the side chain.

Keywords: Conducting polymers; Cyclic voltammetry; Functional polythiophenes

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