Synthetic Metals (v.160, #15-16)

Electrochemical polymerization and in situ FTIRS study of conducting polymers obtained from o-aminobenzoic with aniline at platinum electrodes by Abdelghani Benyoucef; Smain Boussalem; Mohamed I. Ferrahi; Mohamed Belbachir (1591-1597).
The electrochemical copolymerization of o-aminobenzoic acid with aniline (ANI) was carried out on platinum electrodes in perchloric acid aqueous medium by cyclic scanning of the potential. Electrochemical homopolymerization of o-aminobenzoic acid was also done. Experimental results showed that the polymers are formed in all cases and the presence of aniline promoted markedly the growth of the rate of copolymerization.The obtained polymer films have been characterized by cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroscopy. The mechanism of the electrochemical polymerization reaction has been discussed.
Keywords: o-Aminobenzoic acid; Aniline; Electropolymerization; Copolymerization; Cyclic voltammetry; In situ FTIR spectroscopy;

The polymerization of aniline in polystyrene latex particles by Natalia V. Blinova; Stéphanie Reynaud; François Roby; Miroslava Trchová; Jaroslav Stejskal (1598-1602).
Polystyrene latex particles were swollen with aniline and subsequently exposed to ammonium peroxydisulfate solution. The polyaniline membrane was produced at the particle interface and separated both reactants. The electrons from aniline monomer are transferred to oxidant molecules through conducting polyaniline membrane. The aniline and peroxydisulfate thus react without the need to physically meet. Polyaniline gradually penetrated inside latex particle, in contrast to core–shell morphology obtained in classical coating of latex particles with polyaniline.
Keywords: Polyaniline; Polystyrene latex; Polyaniline–polystyrene composite;

Electrospinning PVDF/PPy/MWCNTs conducting composites by Kriangsak Ketpang; Jun Seo Park (1603-1608).
Conducting PVDF/PPy composites (PPy composites) were prepared by using the highly porous electrospun (e-spun) nonwoven web as a host polymer. E-spun nonwoven web was made by electrospinning a solution of PVDF and CuCl2·2H2O in solvent of N,N-dimethylacetamide (DMAc). The PPy composites were fabricated by exposing a nonwoven web containing oxidant to pyrrole vapors. Field-emission scanning electron microscopy (FE-SEM) analysis was conducted to show the microstructure of the nonwoven webs and the uniform coating of PPy on the e-spun fiber surfaces of the PPy composite. The information of PPy on the e-spun fibers surface was confirmed by attenuated Fourier-transform infrared spectrometer (ATR FT-IR) and X-ray photoelectron spectroscope (XPS). The thermal property of PPy composites was also investigated by differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The electrical conductivity of the PPy composites was affected by the fabrication method and oxidant content in the nonwoven web. The electrical conductivity and mechanical strength of the PPy composites were improved when surface-modified multi-walled carbon nanotubes (MWCNTs) were added to the e-spun fibers. Energy-filtered transmission electron microscopy (EF-TEM) results confirmed that the MWCNTs were well arranged and embedded in the e-spun fibers. The observed conductivity of the conducting PPy-MWCNTs composite was 10−1  S/cm.
Keywords: PPy; Electrospinning; PVDF; MWCNT;

Effects of [SDS]/[H2O] molar ratio on the electromagnetic properties of polyaniline/maghemite nanocomposites by Tar-Hwa Hsieh; Ko-Shan Ho; Xiaotao Bi; Ching-Hung Huang; Yen-Zen Wang; Yu-Kai Han; Zhi-Long Chen; Chia-Hao Hsu; Po-Hsing. Li; Yu-Chen Chang (1609-1616).
Polyaniline (PANI)/maghemite (γ-Fe2O3) nanocomposites were prepared by using the reverse micelle polymerization, where aniline, ferrous and ferric salts and sodium dodecyl sulfate (SDS) act as monomer, precursor of γ-Fe2O3 and surfactant, respectively. The effect of the molar ratio of [SDS]/[H2O] on the electromagnetic properties of PANI/γ-Fe2O3 nanocomposites was investigated by Fourier transform spectroscopy (FTIR), UV–visible spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), wide angle X-ray diffraction diffractometer (WAXD), impedance analysis analyzer, micro-ohmetry and superconductor quantum interference device (SQUID). The nanostructure of the PANI/γ-Fe2O3 nanocomposites was characterized by micrographs of transmission electron microscopy (TEM). Results showed that both the γ-Fe2O3 content and particle size in the nanocomposites decreased with molar ratio of [SDS]/[H2O]. The γ-Fe2O3 phase is non-uniformly distributed in the PANI matrix, and exhibits a broader size distribution at higher [SDS]/[H2O] molar ratio due to the reduced strength of PANI–γ-Fe2O3 interactions. In the presence of γ-Fe2O3, the growth rate of quinoid ring is markedly retarded. The retard effect is significantly reduced by increasing the [SDS]/[H2O] molar ratio, leading to the improvement of crystallinity, conductivity and dielectric properties (i.e., permittivity and loss factor) of nanocomposites. Simultaneously, the ionic polarization relaxation time is shortened from 2.61 × 10−9 to 1.04 × 10−9  s. For SQUID analysis at room temperature, the typical superparamagnetic behavior is found with the saturation magnetization decreased with the [SDS]/[H2O] molar ratio, resulting from the reduced γ-Fe2O3 content, smaller γ-Fe2O3 particle size, and the wider particle size distribution.
Keywords: Polyaniline/γ-Fe2O3 nanocomposites; [SDS]/[H2O] molar ratio; Reverse micelle polymerization; Electromagnetic properties;

Layered nanostructures of polyaniline with graphene oxide as the dopant and template by Nailiang Yang; Jin Zhai; Meixiang Wan; Dan Wang; Lei Jiang (1617-1622).
Novel layered structures of polyaniline (PANI) doped with graphene oxide (GO) were directly prepared by adding GO aqueous solution into the emeraldine base form of PANI (PANI-EB) dissolved in a mixture solution of m-cresol and ethanol. The method is simple and inexpensive because of saving inorganic or organic acids as the dopant, opening a new way to prepare hybrid materials of PANI with GO. It was proposed that the π–π planar structure of GO and the carboxyl groups on the surface of GO are served as the template and dopant, respectively that results in the formation of the layered structures. The doping function of GO in the PANI-GO has been proved by structural characterizations and conductivity measured by a four-probe method.
Keywords: Dopant; Modified graphene; Layered polyaniline;

Development of efficient solution-processed red phosphorescent organic light-emitting diodes using carrier transport materials by Myungkwan Song; Jin Su Park; Chul-Hyun Kim; Jang Soo Kim; Yeong-Soon Gal; Jae Wook Lee; Sung-Ho Jin (1623-1626).
We report on efficient solution-processed red emissive phosphorescent organic light-emitting diodes (PhOLEDs) employing bis[9-ethyl-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C 2′]iridium acetylacetonate (Et-Cvz-PhQ)2Ir(acac) and bis[9-(2-(2-methoxyethoxy)ethyl)-3-(4-phenylquinolin-2-yl)-9H-carbazolato-N,C 2′]iridium acetylacetonate (EO-Cvz-PhQ)2Ir(acac) doped into polymer host PVK, blended with electron transporting material OXD-7, and optimized concentration of carrier-transporting material TPD. The optimized PhOLEDs doped with 16 wt% carrier-transporting material shows a maximum luminance efficiency and power efficiency of 4.66 cd/A and 1.22 lm/W, which were increased by 40% and 20%, respectively, compared with that of reference device. The electroluminescence (EL) spectra exhibited the characteristic spectrum of (Et-Cvz-PhQ)2Ir(acac) and (EO-Cvz-PhQ)2Ir(acac) with its maximum at 630 nm and CIE (Commission International de L’Eclairage) coordinate of (0.66, 0.33).
Keywords: Solution-process; PhOLEDs; Phosphorescent; Red; Carrier-transporting material;

Spectrophotometric investigation of co-solvent induced doping of PCA-protonated polyaniline solutions by Rama Dubey; Dhiraj Dutta; Vinay Kumar Yadav; T.C. Shami; K.U. Bhasker Rao (1627-1630).
Protonation of polyaniline emeraldine base (PANI EB) was carried out by using different molar concentrations (0.1–0.5 M) of 2-pyrrolidone-5-carboxylic acid (PCA) in dimethylformamide (DMF) solvent. A dedoping effect was observed by UV–vis spectroscopic analysis when doped PANI solutions were diluted with DMF. This effect is due to interaction between the dopant and the solvent which leads to dedoping. It was observed that the dedoping effect was minimized on diluting with methanol. Further on methanol addition a dilution-induced partial doping effect was observed. It is assumed that this may be due to hydrogen bonding interactions between the two solvents.
Keywords: Polyaniline; Dedoping; UV–vis absorption; 2-Pyrrolidone-5-carboxylic acid;

Structure and phase stability of hydrogenated first-stage alkali- and alkaline-earth metal–graphite intercalation compounds by G. Srinivas; A. Lovell; C.A. Howard; N.T. Skipper; M. Ellerby; S.M. Bennington (1631-1635).
We report the hydrogenation temperature and pressure dependence of hydrogen absorption capacity in CaC6. In addition, the structure and phase stability of hydrogenated CaC6, LiC6 and KC8 has been investigated using X-ray diffraction and Raman spectroscopy. It is found that the hydrogen chemisorption in both CaC6 and LiC6 leads to either metastable or higher stage intermediate compounds but eventually leaves completely deintercalated graphite by forming stable metal hydrides. In contrast hydrogenation of KC8 generates a restaged ternary hydride compound. The phase stability of hydrogenated compounds is discussed in the text based on the observed experimental results and correlated to the thermodynamic and kinetic aspects of intercalated metal.
Keywords: Graphite intercalation compounds; Hydrogen absorption; X-ray diffraction; Raman spectroscopy;

Electrodeposited PEDOT films on ITO with a flower-like hierarchical structure by Cuifeng Zhou; Zongwen Liu; Xusheng Du; Simon P. Ringer (1636-1641).
Poly(3,4-ethylenedioxythiophene) (PEDOT) films with a flower-like nanostructure have been electrochemically deposited on indium tin oxide (ITO) electrode simply by a one-step cyclic voltammetry (CV) method in an aqueous media in the absence of any surfactant. The PEDOT films deposited on the substrates were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The results indicate that the flower-like hierarchical structure of the PEDOT film is composed of nanosheets with a thickness of even less than 2 nm at the edge. The resulted porous structure of the PEDOT coating leads to a two-order increase of magnitude in the electrochemical capacitance-current. The growth process of the electrodeposited PEDOT as well as the effect of polymerization potential on the properties of products was studied.
Keywords: PEDOT; Conductive polymer; SEM; Electro-polymerization; Nanostructure;

Synthesis, crystal structure, photo- and electro-luminescence of 3-(4-(anthracen-10-yl)phenyl)-7-(N,N′-diethylamino)coumarin by Hui Zhang; Tianzhi Yu; Yuling Zhao; Duowang Fan; Yangjun Xia; Peng Zhang (1642-1647).
A new coumarin derivative, 3-(4-(anthracen-10-yl)phenyl)-7-(N,N′-diethylamino)coumarin, was synthesized and characterized by FT-IR, 1H NMR, element analysis and single crystal X-ray crystallography. The dihedral angle of coumarin ring and phenyl group is 30.83°, and the dihedral angle of phenyl group and anthracene skeleton is 76.99°. The photoluminescent (PL) and electroluminescent (EL) properties of the compound were investigated. The results show that the compound exhibits high fluorescence quantum yield (0.83), large Stokes shift and strong blue emission (466 nm). The electroluminescence devices comprised of vacuum vapor-deposited films using the compound as dopant were fabricated, showing blue emission that is identical to its photoluminescent spectrum in chloroform solutions. The electroluminescence device of indium tin oxide (ITO)/4,4′,4″-tris[2-naphthyl (phenyl)-amino]triphenylamine (2-TNATA) (5 nm)/N,N-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) (40 nm)/4,4-N,N-dicarbazole-biphenyl (CBP): dopant (1.0 wt%, 30 nm)/2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) (30 nm)/LiF (1 nm)/Al (100 nm) gives a maximum luminous efficiency of 3.3 cd/A at the current density of 20 mA/cm2, and maximum luminance of 5070 cd/m2 at 16 V.
Keywords: Coumarin; Anthracene; Synthesis; Photoluminescence; Electroluminescence;

Two new solution processable organic molecules based on carbazole and triphenylamine (TPA) substituted fluorene were synthesized by Suzuki coupling reaction. The bandgap of the molecules can be controlled by the 3,6-linkage of the carbazole. The propeller-shaped TPA moieties endow the molecules with good thermal stability and perfect solution processability. Smooth films of both molecules could be readily obtained by spin-coating and n-type ZnO nanoparticles were further incorporated to construct bulk-heterojunction. Under the excitation of 1 mW/cm2 ultraviolet light at 365 nm, devices with those hybrid films as active layers show a relative quick response with photo-to-dark current ratio of about three orders of magnitude. The current decay time (decay to 1% of the value before removing of the light) is less than 200 ms. Moreover, the spectral response of the devices covers 300–400 nm and can be well tuned by the conjugation length of the organic molecules. Those results indicate that the synthesized molecules might be candidates for solution processable low cost UV photodetectors.
Keywords: Solution processability; Organic–inorganic hybrid; Heterojunction; UV photoresponse;

Investigation of new PPV-type polymeric materials containing fluorene and thiophene units and their application in organic solar cells by Jilian Nei de Freitas; Almantas Pivrikas; Bruno F. Nowacki; Leni C. Akcelrud; N. Serdar Sariciftci; Ana Flávia Nogueira (1654-1661).
New poly(p-phenylenevinylene) (PPV)-type conducting polymers containing different concentrations of thiophene and fluorene functional units were investigated in this work and the photophysical and electrochemical properties were evaluated. We observed a dependence of these properties on the concentration of thiophene units in the polymer backbone. The hole mobilities were estimated to be on the order of 10−6  cm2  V−1  s−1. The polymers were combined with different concentrations of a soluble fullerene derivative (PCBM) and applied in bulk-heterojunction photovoltaic cells. The effects of PCBM concentration and of annealing (post-production treatment) on these devices were investigated. The best results were obtained for the materials containing higher concentrations of thiophene units.
Keywords: Conducting polymers; PPV; Polyfluorene; Polythiophene; Organic solar cells;

Synthesis and structure of a novel mixed-ligand electroluminescence-relevant complex of gallium(III) with 2-(2′-hydroxylphenyl)benzothiazole and acetate, and a theoretical investigation on effect of ancillary ligand on solid stacking structure, electroluminescent wavelength shift and other changes in photophysical properties compared to its conventional tris-chelate electroluminescence-relevant counterpart have been reported.One novel mixed-ligand electroluminescence-relevant ML2X-type Ga(III) complex (L: main ligand; X: ancillary ligand), [Ga(pbt)2(Ac)] (1) (Hpbt = 2-(2′-hydroxylphenyl)benzothiazole, main ligand; HAc = acetic acid, ancillary ligand), has been prepared, structurally characterized and investigated theoretically. The reason for forming novel mixed-ligand electroluminescence-relevant ML2X-type complex of 1, but not conventional tris-chelate electroluminescence-relevant ML3-type complex ([Ga(pbt)3]) is ascribed to the steric hindrance from bulky N,O-donor main ligand (pbt). The effect of ancillary ligand (Ac) on the supramolecular π–π stacking interactions, the electron transport ability and electroluminescent wavelength shift and other changes in photophysical properties of important optical transitions in crystalline 1 with respect to its tris-chelate electroluminescence-relevant counterpart [Ga(pbt)3] have been analyzed in detail. The important electroluminescent/photoluminescent transition is only mainly related to the main ligands (pbt) with π → π* ligand-to-ligand charge transfer (LLCT) transition nature based on the density functional theory (DFT) and time-dependent density functional theory (TDDFT) results.
Keywords: X-ray structure; DFT; TDDFT; Calculation; 2-(2′-Hydroxylphenyl)benzothiazole; Gallium(III) complex;

New analytical approach to the insulator–metal transition in conductive polyaniline by P. Fedorko; M. Trznadel; A. Pron; D. Djurado; J. Planès; J.P. Travers (1668-1671).
A new empirical formula describing the temperature dependence of the conductivity of polyaniline films in the metallic regime close to the insulator–metal transition at temperature below 30 K is deduced from the analysis of the temperature dependence of the reduced activation energy. Its elaboration is based on a careful study of electrical transport properties of camphorsulfonic acid-doped polyaniline (PANI(CSA)0.5) films, containing increasing amounts of triphenyl phosphate (TPP) plasticizer. The use of this three component system (polymer, protonating agent, plasticizer) and control of the amount of adsorbed water enable precise tuning of the electrical transport properties in the solution cast films, in this manner providing the set of experimental data, covering the insulating, critical and metallic regimes, necessary for the elaboration of the proposed new empirical formula.
Keywords: Conducting polymers; Insulator–metal transition; Polyaniline; Plasticizer; Conductivity; Metallic state;

Synthesis and light-emitting properties of fluorene-based copolymers by Qiang Peng; Guanwen Fu; Dan Su (1672-1678).
New type of alternating fluorene-based copolymers containing electron-deficient aryl-substituted imidazole units in the main chains were designed, synthesized and characterized. The resulting copolymers were amorphous and showed excellent solubility in common organic solvents, such as dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene, toluene, and THF. These polymers also possessed good thermal stability with glass transition temperatures of 96 and 82 °C and decomposition onset temperatures of 365 and 379 °C, respectively. They exhibited good blue photoluminescence properties with high photoluminescence efficiencies. The long-wavelength emission of polyfluorenes had been effectively reduced by introduction of nonlinear structure aryl-substituted imidazole units. Light-emitting devices with an ITO/PEDOT/PVK/copolymer/LiF/Al configuration could emit strong blue light with high external quantum efficiencies of 1.49 and 2.05%.New type of fluorene-based copolymers containing electron-deficient aryl-substituted imidazole units were successfully synthesized and characterized. The resulting copolymers have good thermal stability, improved electron affinity and high PL efficiencies. The long-wavelength emission of polyfluorenes had been effectively reduced in these copolymers. Light-emitting devices based on these copolymers could emit strong blue light with high external quantum efficiencies of 1.49 and 2.05%, indicating these copolymers are promising candidates for efficient light-emitting materials.
Keywords: Conjugated polymers; Photoluminescence; Light-emitting diodes;

Charge transporting block copolymer for morphological control in light emitting device based on polymer blends by Kousuke Tsuchiya; Kota Sakaguchi; Akira Kawakami; Hideo Taka; Hiroshi Kita; Takeshi Shimomura; Kenji Ogino (1679-1682).
Bipolar charge transporting block copolymer composing of carbazole and oxadiazole monomers as hole and electron transporting units, respectively, was synthesized by nitroxide mediated radical polymerization. It is found that the current efficiency significantly increased with the addition of the block copolymer in the device based on polymer blend system. AFM measurement revealed that a phase-separated structure in the polymer blend layer changed to suitable morphology in the presence of block copolymer.
Keywords: Block copolymer; Polymer light emitting diode; Microphase separation;

Electrically conducting-adhesive coating on polyamide fabrics by Alessio Varesano; Barbara Antognozzi; Claudio Tonin (1683-1687).
Solvent-based preliminary treatments were carried out on polyamide fabrics to be coated with a thin layer of electrically conducting doped polypyrrole, with the aim of improving the adhesion of the conducting layer to the fibre substrate. Polyamide fabrics were treated with dilute formic acid, pure tetrachloroethylene and ethanol/water at different temperatures and times. After the treatments, the fabrics were coated with polypyrrole by in situ chemical oxidative polymerisation. The adhesion of the PPy layer was evaluated by means of surface resistivity measurements, SEM investigation and ATR FT-IR analysis after Martindale abrasion tests. The adhesion of PPy layer on the fibre surface was strongly improved by the solvent treatments, in particular with ethanol and tetrachloroethylene. The surface resistivity of the ethanol-treated fabrics did not change after more than 200 abrasion cycles and the PPy layer linked to the fibre surface was observed by SEM and ATR FT-IR also after 4000 abrasion cycles.
Keywords: Electrically conductive textiles; Polypyrrole; Polyamide; Adhesion;

Hierarchical polypyrrole microspheres, which have nanofibers as building blocks, the size of several microns and a conductivity of 0.8 S cm−1, were prepared simply and directly via a one-step self-assembly approach in the presence of (NH4)2S2O8 (APS), cetyltrimethylammonium bromide (CTAB) and sulfonated polyaniline (SPANI). It was found that the formation probability of hierarchical polypyrrole microspheres depended on the (NH4)2S2O8/CTAB and SPANI/CTAB molar ratio. Bulk quantities of hierarchical polypyrrole microspheres can be obtained readily under the optimal conditions such as (NH4)2S2O8/CTAB molar ratio >2.8 and SPANI/CTAB molar ratio >4.7 × 10−3. The precipitate [(CTA)2S2O8] of CTAB and (NH4)2S2O8 was proposed to act as a “template” to promote the formation of PPY nanofibers, while the dopant SPANI was suggested to play a “rope-like” or “bridge-like” role in the subsequent self-assembly of nanofibers into PPY hierarchical microspheres. The experimental results and our investigation for the formation of PPY hierarchical microspheres may shed some light on preparing of other conductive hierarchically materials by proper molecular design and experimental condition optimization.
Keywords: Hierarchical microsphere; Polypyrrole; Cetyltrimethylammonium bromide; Sulfonated polyaniline; One-step;

Synthesis and characterization of the core–shell Au covered LSMO manganite magnetic nanoparticles by O. Pana; R. Turcu; M.L. Soran; C. Leostean; E. Gautron; C. Payen; O. Chauvet (1692-1698).
In this work we report the synthesis and characterization of the nanomagnetic perovskite Sr manganites covered with Au shells having different thickness. La2/3Sr1/3MnO3 (LSMO) manganite nanoparticles were first prepared by a sol–gel procedure. The LSMO manganite nanoparticles were chemically covered with gold to produce the core–shell samples. TEM, HRTEM and atomic emission spectroscopy techniques were used to determine the morphology and structure of the LSMO@Au nanoparticles. The bare LSMO nanoparticles have a mean diameter of around 4.4 nm while LSMO@Au nanoparticles have mean diameters between 7.15 and 4.8 nm depending on the gold quantity involved in the capping process. XRD studies show that both core and shell systems have the expected crystalline structure. The formation of the core–shell structure is sustained by the shift of the plasmon resonance wavelength maximum observed in the UV–vis absorbtion spectra of the LSMO@Au samples depending on the gold concentration. The magnetization versus applied magnetic field of the bare LSMO nanoparticles and LSMO@Au samples shows no hysteresis loop indicating the superparamagnetic behavior of these systems. The analysis of the temperature dependences of FC and ZFC magnetizations shows that for all the samples the axial anisotropy energy barriers are increased due to the magnetic dipolar interactions between neighbor nanoparticles.
Keywords: Nanoparticles; Core–shell; Sr manganites; Superparamagnetic particles; Au coated nanoparticles;

Polypyrrole/TiO2 composite is prepared by in situ polymerization of pyrrole on the TiO2 template. The TiO2 microbelts are prepared by sol–gel method using the absorbent cotton template for the first time. Then the TiO2 microbelts are used as template for the preparation of polypyrrole/TiO2 composites. The structure, morphology and properties of the composites are characterized with scanning electron microscope (SEM), IR and Network Analyzer. A possible formation mechanism of TiO2 microbelts and polypyrrole/TiO2 composites has been proposed. The effect of the molar ratio of pyrrole/TiO2 on the photocatalysis properties and microwave loss properties of the composites is investigated.
Keywords: TiO2; Polypyrrole; Microwave absorbing; Photocatalysis;

Studies on the nonlinear optical properties of rf plasma polymerized aniline thin films by open aperture z-scan technique by U.S. Sajeev; Vinu V. Nambuthiri; Anwar Salah; V.P.N. Nampoori; M.R. Anantharaman (1704-1707).
Plasma polymerized polyaniline (PANI) thin films in their pristine and iodine doped forms were subjected to open aperture z-scan studies in order to investigate the nonlinear optical (NLO) properties of these materials. The investigations were carried out using a Q-switched resonant Nd:YAG laser at a wavelength of 532 nm for various fluences. The z-scan studies revealed that RF PANI thin films exhibit a saturable absorption (SA). Iodine doping modifies the NLO characteristics of these films substantially. These results qualify PANI thin films as potential materials for NLO materials. Investigations on the NLO properties of pristine (PANI) and iodine doped polyaniline (dPANI) thin films in its plasma polymerized form are reported for the first time.
Keywords: Plasma polymer; Polyaniline; Nonlinear optical; z-Scan; Saturable absorption;

Polypyrrole (PPy) and WO3 were prepared by chemical oxidation polymerization and emulsion method, respectively. PPy/WO3 hybrid materials with different PPy mass percent were prepared by mechanical mixing. WO3 and PPy/WO3 hybrids were characterized by XRD, SEM and HRTEM, and the sensitivity studies of PPy, WO3 and PPy/WO3 to toxic gases NH3, H2S, NOx were also carried out. It was found that the particle size of WO3 was about 29 nm, and PPy/WO3 was about 50–100 nm. Gas sensitivity tests showed that when operated at 90 °C, PPy/WO3 hybrids had better reversibility to H2S than PPy higher sensitivity and selectivity to H2S than WO3. PPy/WO3 materials had short response–recovery time to H2S and their sensitivities had linear relationship with the concentration of H2S. The sensitive mechanism of PPy/WO3 materials to H2S may be the co-effect of proton doping process and the n-type semiconductor's effect.
Keywords: Sensitivity; Polypyrrole; WO3; Hybrid materials; H2S;

A new donor–acceptor type conjugative poly{2-[4-(1-cyanoethenyl)phenyl]-3-(3,4-didodecyloxythiophen-2-yl)prop-2-enenitrile}: Synthesis and NLO studies by Pramod Kumar Hegde; A. Vasudeva Adhikari; M.G. Manjunatha; C.S. Suchand Sandeep; Reji Philip (1712-1717).
This research article describes a technique to synthesize a new donor–acceptor type conjugated polymer carrying cyanophenylenevinylene and 3,4-didodecyloxy thiophene moieties, as an effective optical limiting material. It also includes the evaluation of its linear and nonlinear optical properties and electrochemical studies. The new polymer, viz., poly{2-[4-(1-cyanoethenyl)phenyl]-3-(3,4-didodecyloxythiophen-2-yl)prop-2-enenitrile} (P1) has been synthesized starting from 2,2′-sulfanediyldiacetic acid and diethyl ethanedioate through multistep reactions. In the final step, the polymerization was brought about by Knovenagel condensation. The newly synthesized intermediate, monomer and the polymer (P1) have been characterized by different spectroscopic techniques followed by elemental analysis. Its optical and electrochemical properties are investigated by UV–vis, fluorescence spectroscopy and cyclic voltammetric studies, respectively. The red colored polymer has a well defined structure, good thermal stability and a band gap of 1.78 eV. It emits green fluorescence both in solution and in film state. The third-order nonlinear optical property (NLO) of the polymer was studied by the Z-scan technique. The measurements were performed at 532 nm with 5 ns laser pulses using samples in solution form. An absorptive nonlinearity of the optical limiting type was found in this polymer, which is due to the combined action of saturable absorption and excited state absorption processes. These studies revealed that polymer P1 is a promising material for optical limiting applications.
Keywords: Conjugated polymer; Cyanophenylenevinylene; 3,4-Didodecyloxythiophene; NLO; Saturable absorption;

Double-walled carbon nanotube/polymer nanocomposites: Electrical properties under dc and ac fields by F. Yakuphanoglu; I.S. Yahia; G. Barim; B. Filiz Senkal (1718-1726).
The electrical properties of the poly(methyl methacrylate:carbon nanotubes nanocomposites) have been investigated by direct current conductivity and complex impedance spectroscopy methods. The direct current conductivity results of the poly(methyl methacrylate):carbon nanotube as a nanocomposites show that the electrical conductivity property of the poly(methyl methacrylate) changes from insulating state to semiconducting state with incorporation of double wall carbon nanotube DWCNTs into insulating polymer matrix. The alternating current conductivity mechanism of the nanocomposites is controlled by the correlated barrier hopping mechanism. The correlated barrier hopping CBH model for intimate valence alternation pairs IVAP's describes the conduction mechanism of PMMA doped with (1%) DWCNTs, while correlated barrier hopping CBH model for non-intimate valence alternation pairs describes the conduction mechanism of PMMA doped with (5% and 8%) DWCNTs. The real part of the complex impedance decreases with the increase of the applied frequency which revealed that the PMMA:DWCNT nanocomposites behaves like semiconducting materials. The complex impedance Nyquist plots for PMMA doped with different concentration DWCNTs over are characterized by the appearance of a single semicircular arc whose radii of curvature decreases with increasing the temperature. Cole and Cole plots show the presence of temperature dependent electrical relaxation phenomena in the PMMA:DWCNT nanocomposites. The obtained electronic parameters confirm that PMMA:DWCNTs exhibit organic semiconductor behavior.
Keywords: PMMA; Double wall carbon nanotubes (DWCNTs); Nanocomposites; Electrical properties (dc and ac);

Polyaniline nanofibers were synthesized by interfacial polymerization of aniline. Polyaniline so formed was studied using transmission electron microscopy, scanning electron microscopy, UV–vis and Raman spectroscopy. TEM of polymer dispersion shows the presence of fibers having diameter around 30–80 nm. Strikingly different Raman spectra were observed from the polyaniline film, which were related to two dissimilar areas on the film. SEM of polyaniline films shows fibrous as well as flake like structures scattered in fiber matrix. Raman spectra of the films heat treated from 25 °C to 300 °C were taken to study the structural variations induced by the change of temperature at these two regions. Many applications of polymer films are dependent on the homogeneity of the systems. In this work we intend to employ Raman Spectroscopy as an indispensable tool for looking into the non-uniformities of the polyaniline films.
Keywords: Polyaniline nanofibers; Interfacial polymerization; Raman spectroscopy; Temperature variation;

Viscoelastic and conductivity properties of thermoreversible polyaniline–DNNSA gel in m-cresol by Ashesh Garai; Shreyam Chatterjee; Arun K. Nandi (1733-1739).
The rheological behavior of polyaniline (PANI)–dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI–DNNSA0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI–DNNSA0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV–vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI–DNNSA0.5 in m-cresol showing a jump at ∼4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI–DNNSA0.5 concentration studied here for each frequency. At lower frequency (<105  Hz) ac-conductivity increase slowly with frequency but at higher frequency (>105  Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ∼5 orders and also an increase of ∼3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (RC) circuits in the gel and the increase of PANI–DNNSA0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.
Keywords: Polyaniline; DNNSA; Gel; Nanofiber conductivity; Rheology; Impedance spectroscopy;

Charge transport and microstructure in PFO:MEH-PPV polymer blend thin films by Manisha Bajpai; Ritu Srivastava; M.N. Kamalasanan; R.S. Tiwari; Suresh Chand (1740-1744).
Current density–voltage characteristics of poly(9,9′-dihexyl fluorenyl-2,7-diyl) (PFO) thin films (∼120 nm) have been studied in hole only device configuration at different temperatures (100–290 K) in pure form and with blending (∼0.25–50 wt%) of poly(2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV). It has been found that in the case of pure PFO the charge transport at low fields show an ohmic region which is followed by space charge limited conduction region. Blending of PFO with MEH-PPV at low ratio (up to 2 wt%) increases the current density. As the ratio is increased further, the current density decreases. Analysis show that there is a change in conduction mechanism up to 6 V from SCLC to thermally activated ohmic conduction upon blending indicating the creation of new energy level near the transport states of PFO. Morphology of the polymer blended thin films was obtained by atomic force microscopy (AFM) technique. It has been found that the surface roughness of the investigated films is significantly increased upon blending indicating aggregation as well as phase separation at high blending ratios. The decrease in conductivity at high blending ratio can be related to the change in morphology of the films.
Keywords: Polymer; Charge transport; Hole mobility;

Gold (Au) and copper (Cu) alloy catalysts were deposited on the defect sites of carbon nanotubes by spontaneous reduction among AuCl4 , Cu2+ and oxygen-containing functional groups. Compared with AuCu alloy catalysts prepared by adsorption methods and electrochemical deposition methods, AuCu alloy catalysts show excellent catalytic ability to glucose by spontaneous reduction. The linear range of nonenzymatic sensors that were prepared by spontaneous reduction for glucose detection is 0.08–9.26 mM, and detection limit is 4 μM. In addition, there are high sensitivity (22 μA mM−1), reproducibility (96%) and stability (95% after 60 days). Selectivity of this nonenzymatic sensor for ascorbic, uric acid and acetaminophen was also obtained.
Keywords: Glucose detection; Functional carbon nanotubes; Spontaneous reduction; Catalysis;

Improved electron injection into Alq3 based OLEDs using a thin lithium carbonate buffer layer by Po-Ching Kao; Jie-Han Lin; Jing-Yuan Wang; Cheng-Hsien Yang; Sy-Hann Chen (1749-1753).
A cathode buffer layer of lithium carbonate (Li2CO3) we used to improve the electro-optical properties of organic light-emitting diodes (OLEDs). Li2CO3 layers with various thicknesses were prepared by thermally evaporating Li2CO3 powders. When a 1-nm-thick Li2CO3 layer was inserted between the aluminum (Al) cathodes and tris(8-hydroxyquinolinato)aluminum (Alq3) electron-transporting layers, device properties such as the turn-on voltage, the maximum luminance, and the device efficiency were improved, becoming better than and comparable to those of devices with LiF and Cs2CO3 buffer layers. The surface of the Alq3 film became smoother after the Li2CO3 layer was deposited. The reaction mechanisms between Li2CO3 and Alq3 were also investigated. X-ray and ultraviolet photoelectron spectroscopy results show that some electrons transfer from Li2CO3 into Alq3, which increases the electron concentration in Alq3 films and moves the Fermi level close to the lowest unoccupied molecular orbital (LUMO) of Alq3. Thus, the electron injection efficiency was enhanced due to a lower electron injection barrier, which improves the charge carrier balance in OLEDs and leads to better device efficiency.
Keywords: Organic light-emitting diodes; Electron injection; Buffer layer;

Molecular design of donor–acceptor-type cruciform dyes for efficient dyes-sensitized solar cells by Min Ju Cho; Sung Soo Park; Yu Seok Yang; Jae Hong Kim; Dong Hoon Choi (1754-1760).
Novel donor–acceptor (D–A) type cruciform dyes were synthesized for use in a dye-sensitized solar cell. The geometries and electronic structures of the dyes were designed by the results of density functional theory (DFT) calculations. Two phenothiazine units in these dyes act as electron donors, while two cyanoacrylic acid groups act as electron acceptors. The solubility of these compounds is increased because of the presence of the hexyl groups in the phenothiazine rings. The photovoltaic properties of 14D-25A and 12A-45D were measured to identify the effects of the dye having two electron donors and two electron acceptors on the DSSC performance. The 12A-45D dye showed a power conversion efficiency of 4.5% under AM 1.5 illumination (100 mW cm−2) in an photoactive area of 0.42 cm2, short circuit current density of 10.8 mA cm−2, open circuit photovoltage of 0.65 V and a fill factor of 64%.
Keywords: Dyes-sensitized solar cells; Cruciform dye; Phenothiazine; Power conversion efficiency;

Nanostructured polyanilines (PANIs) with a variety of morphologies were synthesized in acidic aqueous solutions with an added ionic liquid, 1-butyl-3-methylimidazolium chloride. The influence of various reaction conditions, i.e., the molar ratio of aniline to ionic liquid and initial aniline concentration, on the morphology and properties of the synthesized PANIs were investigated. The morphologies of the PANIs, as studied by scanning electron microscopy (SEM), range from nanowires to complex three-dimensional structures and were influenced particularly by the molar ratio of aniline to ionic liquid. The chemical structure and molecular-weight characteristics, as determined by Fourier-transform infrared spectroscopy (FTIR), UV–Vis spectroscopy and size-exclusion chromatography (SEC), were not affected by the reaction conditions, indicating that the aniline polymerization mechanism did not change in the presence of the ionic liquid, which acted as a soft template. The conductivities of the prepared PANI samples, as measured by impedance spectroscopy, were of the order of 10−2  S/cm.
Keywords: Polyaniline; Conductive polymers; Nanostructures; Ionic liquids;

Synthesis and photovoltaic performance of new diketopyrrolopyrrole (DPP) dyes for dye-sensitized solar cells by Fuling Guo; Sanyin Qu; Wenjun Wu; Jing Li; Weijiang Ying; Jianli Hua (1767-1773).
Two new metal-free organic dyes (DPP-I and DPP-II) with diketopyrrolopyrrole (DPP) core were designed and synthesized, in which triphenylamine or N,N-bis(4-methoxyphenyl)benzenamine moieties was used as the electron donor, DPP units as the π-conjugated bridge, and carboxylic acid group as the electron acceptor. Photophysical and electrochemical properties of two dyes were investigated by UV–vis spectrometry and cyclic voltammetry. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels can be conveniently accomplished by alternating the donor moiety. The DSSC based on dye DPP-I showed better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 80.6% corresponding to an overall conversion efficiency of 2.68%. Although the power conversion efficiencies are not so high, this work explores new donor–π-accepter–π-donor models and the effects of molecular design on optical properties.
Keywords: Dye-sensitized solar cells; Diketopyrrolopyrrole; Synthesis; Triphenylamine; Donor–π-accepter–π-donor; Chenodeoxycholic acid;

Morphology and electrical properties of hybrid and sulphonated oxalic acid-doped polyaniline by Mona Abdel Rehim; Ahmed Youssef; Ebtesam Hassan; Nagwa Khatab; Gamal Turky (1774-1779).
Polyaniline–polyethylene glycol2000 (PAni–PEG2000) hybrid and sulphonated polyaniline (SPAni) were prepared using oxalic acid as dopant and potassium permanganate as oxidant. The properties of these two conductive polymers were studied in comparison with pure polyaniline (PAni) prepared using the same conditions. The investigated polymers were characterized using FTIR, UV–vis, TGA, TEM, SEM, XRD and their electrical conductivities were also investigated. The morphology of pure polymer was found to be flat ribbon-like form, while presence of polyethylene glycol led to the formation of separate nanospheres. The three polymer samples have different degrees of crystallinity, the highest degree is for SPAni. Unexpectedly, electrical conductivity is in the order SPAni > PAni–PEG2000 > PAni, aging of PAni increases gradually the conductivity of the polymer from 0.0056 to 0.023 S cm−1 and the increase of temperature gradually decreases the conductivity.
Keywords: Conductive polymers; Morphology; Crystallinity;

Lanthanide tris(2-thenoyltrifluoroacetonate) complex based on 2-(3,5-difluorophenyl)imidazo [4,5-f]-1,10-phenanthroline (1) with red luminescence acted as effective receptors for F and AcO anions. Spectroscopic studies of UV–vis, fluorescence and NMR present that the sensor exhibits striking emission changes to fluoride (green) and acetate anions (yellow-red to green) respectively due to hydrogen binding interactions. More importantly, transparent hybrid thick films composed by europium complex and poly-methyl methacrylate (PMMA) matrix were successfully prepared. All the films exhibit intense red emissions of europium ions and the optimized composing concentration of luminescent species is 0.5 mg/5 ml MMA. The derived film could give rise to luminescence change in fluoride anion containing DMSO solution. The micro-structure and size of the hybrid films were characterized by dynamic light scattering (DLS), the results reflect that granule size has the average diameter of 300 nm.
Keywords: Europium; Emission; Fluoride; Polymer films;

Modeling of mobility in organic thin-film transistor based octithiophene (8T) by S. Mansouri; G. Horowitz; R. Bourguiga (1787-1792).
Thin-film organic field-effect transistor was made with vapor-deposited polycrystalline octithiophene on silicon oxide insulator layers. In conventional field-effect transistors, the extracted mobility does not take into account the distribution of charge carriers. However, in disordered organic field-effect transistors, the local charge carrier mobility decreases from the semiconductors/insulator interface in to the bulk, due to its dependence on the charge carrier density. It is demonstrated that the conventional field-effect mobility is a good approximation for the local mobility of the charge carriers at the interface. In this paper we present a new approach to the mobility in organic thin-film transistor (OTFTs), and with a new procedure we extract the electrical parameters of organic TFTs that possible to reproduce very well the device characteristic and mobility.
Keywords: Octithiophene TFTs; Charge carrier mobility; Output characteristic;

Polyethers containing 2-phenylindol-1-yl moieties as host materials for light emitting diodes by S. Lengvinaite; J.V. Grazulevicius; S. Grigalevicius; Y.M. Lai; W.B. Wang; J.H. Jou (1793-1796).
Oxetane monomers and polyethers containing electroactive 2-phenylindol-1-yl or 3-(2-phenylindol-1-yl)carbazol-9-yl fragments were synthesized and characterized by NMR spectroscopy and elemental analysis. The polymers represent amorphous materials of high thermal stability with glass transition temperatures of 94–179 °C and thermal decomposition starting at temperatures above 400 °C. The electron photoemission spectra of layers of the synthesized polymers showed ionization potentials of 5.7–5.8 eV. The polymers were tested as host materials in phosphorescent OLEDs with iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate as the guest. The device based on polymer containing 2-phenylindol-1-yl fragments exhibited the best overall performance with a driving voltage of 5.9 V, maximum power efficiency of 8.46 lm/W and maximum brightness of 718 cd/m2.
Keywords: Electroactive oxetane monomer; Polyether; Ionization potential; Host; Light emitting diode;

Synthesis of brominated tetrathiafulvalenes via phosphite-mediated cross-coupling by Antonio Alberola; Concha Bosch-Navarro; Pablo Gaviña; Sergio Tatay (1797-1799).
The synthesis of polybrominated tetrathiafulvalenes (TTF–Br n , 24) containing 2–4 bromine atoms via phosphite-mediated cross-coupling of bromo-substituted 1,3-dithiole-2-thiones and 1,3-dithiole-2-ones is reported.
Keywords: Brominated tetrathiafulvalenes; Lithiation; Halogenation; Phosphite cross-coupling;

The role of anthraquinone sulfonate dopants in promoting performance of polypyrrole composites as pseudo-capacitive electrode materials by Xuemei Lang; Qunyi Wan; Chunhua Feng; Xianjun Yue; Wendong Xu; Jing Li; Shuanshi Fan (1800-1804).
We report the role of anthraquinone sulfonate dopants in promoting performance of electro-synthesized polypyrrole (PPy) composites for use in electrochemical supercapacitors. The incorporation of anthraquinone sulfonate species into the polymer matrix can significantly improve the surface area of PPy composites that are composed of submicron-/nano-sized particles, as evidenced from scanning electron microscopy (SEM) results. Cyclic voltammetry and galvanostatic charge–discharge measurements in 1 M KCl solution reveal that these dopants result in an improved specific capacitance, a wide working potential range and enhanced long-cycle stability as compared to ClO4 dopant. Among the samples investigated, the resulting PPy/AQS (9,10-anthraquinone-2-sulfonic acid sodium salt) composite exhibits the highest specific capacitance of 608 F g−1 at a scan rate of 5 mV s−1 within a potential range between −0.9 and 0.5 V (vs. saturated calomel electrode, SCE).
Keywords: Electrochemical supercapacitor; Anthraquinone sulfonate; Polypyrrole; Specific capacitance; Electropolymerization;

Functionalization of multiwalled carbon nanotubes and related polyimide/carbon nanotubes composites by Fengchun Yang; Yanfeng Li; Shujiang Zhang; Ma Tao; Jiujiang Zhao; Congshu Hang (1805-1808).
A low molecular weight tree-type polyimide was used to modify the surface of multiwalled carbon nanotubes. The modified carbon nanotubes exhibited excellent dispersion in organic solvent; and the polyimide/carbon nanotubes composite film basic on such carbon nanotubes shows enlarged combination property compared with the composite film from acid-carbon nanotubes. Meanwhile, an electric conductivity was introduced to the composite film, and the thermal properties have also been developed.
Keywords: Polyimides; Multiwalled carbon nanotubes; Composites films; Resistivity;