Synthetic Metals (v.160, #5-6)
Structure and properties of solid-state synthesized poly(3′,4′-ethylenedioxy-2,2′:5′,2″-terthiophene)
by Tursun Abdiryim; Ruxangul Jamal; Chunbao Zhao; Tunsagul Awut; Ismayil Nurulla (pp. 325-332).
A polyterthiophene derivative: poly(3′,4′-ethylenedioxy-2,2′:5′,2″-terthiophene) was synthesized by solid-state oxidative-polymerization of 3′,4′-ethylenedioxy-2,2′:5′,2″-terthiophene (TET) in various ratios of oxidant (FeCl3) to the monomer (TET). The resulting polymers were characterized by FT-IR,1H NMR, TEM, SEM, UV–vis–NIR, GPC, X-ray diffraction, EDX, CV, galvanostatic charge–discharge, as well as TGA and conductivity measurements. The results showed that the as-made poly(TET)s were partially in doped state with a conductivity ranging from 2.1×10−3Scm−1 to 8.1×10−3Scm−1 at room temperature, and exhibited good thermal stability in nitrogen up to 337–356°C. The poly(TET)s showed a similar UV–vis absorption peak at 462nm in acetonitrile. In addition, as-made poly(TET)s had low molecular weight ranging from 3300 to 3500 with microstructured morphology including nanorodes and nanofibers, and presented one redox couple at 1.1–1.2V(ox) and 0.6–0.7V(re) in 0.1M Et4NBF4 acetonitrile solution. A moderate specific capacitance of 71Fg−1 for poly(TET) modified graft electrode was obtained within the potential range of −0.2V to 0.5V in 1M H2SO4 solution. X-ray diffraction results imply the enhanced crystallinity of poly(TET)s, indicating the existence of crystalline phase in polymer matrix. Furthermore, the comparison of results from every measurement indicated that the [FeCl3]/[TET] ratio strongly affects the morphology of the poly(TET), and the fibrillar growth tendency of poly(TET) was observed with the increase of the [FeCl3]/[TET] ratio, and long-length fibrillar morphology occurred in the highest [FeCl3]/[TET] ratio.
Keywords: Polyterthiophene; Derivative; 3,4-Ethylenedioxythiophene; Solid-state oxidative-polymerization
A novel poly(o-anisidine)/CoFe2O4 multifunctional nanocomposite: Preparation, characterization and properties
by Jing Jiang; Lun-Hong Ai; Ai-Hua Liu (pp. 333-336).
A novel poly(o-anisidine) (POA)/CoFe2O4 nanocomposite was synthesized by a facile in situ polymerization of o-anisidine in the presence of CoFe2O4 nanoparticles which were obtained by a simple refluxing process in ethylene glycol. The structures of the resulting nanocomposite were investigated by means of X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra. The optical, thermal and magnetic properties of the POA/CoFe2O4 nanocomposite were characterized by UV–visible spectrometer, thermogravimetry analyzer (TGA) and vibrating sample magnetometer (VSM). It was indicated the existence of CoFe2O4 in the POA/CoFe2O4 nanocomposite. The scanning electron microscopy (SEM) observation illustrated that POA layers were wrapped on the surface of CoFe2O4 nanoparticles appearing as small aggregated globules. The POA/CoFe2O4 nanocomposite exhibited a ferromagnetic behavior under applied magnetic field at room temperature. The saturation magnetization of POA/CoFe2O4 nanocomposite was lower than that of pure CoFe2O4 nanoparticles due to the contribution of non-magnetic POA layers.
Keywords: Conducting polymers; CoFe; 2; O; 4; Structural characterization; Properties
Effect of thermal annealing on the electrical conductivity of high-strength bicomponent polymer tapes containing carbon nanofillers
by Hua Deng; Emiliano Bilotti; Rui Zhang; Joachim Loos; Ton Peijs (pp. 337-344).
A new concept is described that creates highly oriented multifunctional polymer nanocomposite tapes (or fibres) that combine high stiffness and strength with good electrical properties and a low percolation threshold of conductive nanofillers. The concept is based on a bicomponent construction consisting of a highly oriented polymer core together with conductive polymer composite skins based on a polymer with lower melting temperature than the core. This construction allows for a thermal annealing process that can be applied selectively to the skins to improve their conductivity through a kinetic re-aggregation process while retaining the mechanical properties of the core and hence those of the overall tape or fibre. In the current study this generic concept was applied to bicomponent tapes based on a polypropylene homopolymer core and a multi-wall carbon nanotube or carbon black filled polypropylene copolymer skin. The conductivity of the bicomponent tape containing 5.3wt.% of MWNTs in its outer skins increased from 1.3E−6 to 1.5S/cm after annealing while the percolation threshold in the copolymer skins of highly drawn bicomponent tapes could be decreased from 5.3 to 1.1wt.%. To the best of the authors’ knowledge this is the lowest percolation threshold reported in literature for highly drawn polymer nanocomposites fibres or tapes. In fact, the percolation threshold is as low as 0.1wt.% when considered on the overall tape as the conductive skins account for only 10% of the total volume of these bicomponent tapes.
Keywords: Conductive polymer composites; Multifunctional fibre; Carbon nanotubes; Carbon black
Water-dispersed polypyrrole nanospheres via chemical oxidative polymerization in the presence of castor oil sulfate
by Chao Yang; Peng Liu (pp. 345-350).
The castor oil sulfate (COS), produced by the sulfonation of the castor oil (one of the most promising renewable sources), was used as both the surfactant and the dopant in the chemical oxidative polymerization of pyrrole. The resulting castor oil sulfate doped polypyrrole nanospheres (PPy/COS) were characterized with FTIR, UV–vis, TGA, zeta potentials and TEM techniques. It was found that their diameter decreased and their dispersing stabilities in water increased with the increasing of feeding ratio of COS. The PPy/COS nanospheres possess high electrical conductivity at room temperature and the weak temperature dependence of the conductivity.
Keywords: Polypyrrole; Castor oil sulfate; Electrical conductivity; Water-dispersed; Temperature dependence of the conductivity
Facile chemical synthesis of DNA-doped PEDOT
by Yogesh Ner; Michael A. Invernale; James G Grote; Jeffrey A. Stuart; Gregory A. Sotzing (pp. 351-353).
The preparation of a water-dispersible conducting polymer system comprised of a DNA-PEDOT bio-composite using DNA as a polyelectrolyte template for polymer growth is described. Optoelectronic properties, conductivity, and morphology are explored in this potentially bioactive and biocompatible system.Neutral and oxidized state of a solution of DNA-PEDOT in water.Herein we report the template polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) using a biomacromolecule, DNA, as the polyelectrolyte. The resultant bio-composite material formed a stable, aqueous-dispersible system. Higher conductivities than that of conventionally prepared PEDOT-PSS without conductivity enhancing additives were observed ( ca. 1.0S/cm versus ca. 0.15S/cm). The material was redox active in the dispersed state and in the solid state. The DNA double helix was found to undergo changes in conformation upon redox switching, resulting in controllable variance of its ability to polarize light. This non-acidic template is non-corrosive and is therefore an ideal candidate for use in device applications. The system described is potentially bioactive and biocompatible, as well, which would further extend its applicability.
Keywords: Conducting polymers; DNA; Template polymerization; PEDOT; Water-dispersible
Efficient electrophosphorescence based on 2-(9,9-diethylfluoren-2-yl)-5-trifluoromethylpyridine iridium complexes
by Wenguan Zhang; Yongsheng Wang; Zhiqun He; Linping Mu; Ye Zou; Chunjun Liang; Shengmin Zhao (pp. 354-360).
A novel cyclometalated ligand 2-(9,9-diethylfluoren-2-yl)-5-trifluoromethyl-pyridine (fl-5CF3-py), and its complexes bis[2-(9,9-diethylfluoren-2-yl)-5-trifluoromethyl-pyridinto-C3, N]iridium (acetylacetonate) (fl-5CF3-py)2Ir(acac) (5) and bis[2-(9,9-diethylfluoren-2-yl)-5-trifluoromethylpyridinto-C3, N] iridium (2-picolinic acid) (fl-5CF3-py)2Ir(pic) (6) were synthesized, respectively. Trifluoromethyl group and 2-picolinic acid were incorporated into iridium ligands to tune luminescent color. Emission spectra of5 and6 in THF solutions were 589 and 572nm. Decomposition temperatures (Td) of5 and6 were 326 and 360°C. Multilayer electrophosphorescent devices were fabricated using5 and6 as emitter dopants with electroluminescent spectra maximized at around 585 and 571nm, respectively. The relatively high efficiencies of the devices and their slow rate of decay against increases in current densities indicated that (fl-5CF3-py)2Ir(acac) or (fl-5CF3-py)2Ir(pic) was a promising emitter for practical device applications.
Keywords: Trifluoromethylpyridine; Fluorene; 2-Picolinic acid; Iridium(III) complex; Tune color; Electrophosphorescent
Preparations and characterizations of new series of TTF ligands containing a nitrogen aromatic heterocycle
by Sabrina Bouguessa; Abdelkrim K. Gouasmia; Lahcène Ouahab; Stéphane Golhen; Jean-Marc Fabre (pp. 361-367).
The detailed synthesis of a new series of conjugated TTF ligands with nitrogen-based aromatic heterocycle are presented. In all these molecules, trimethyl-TTF or TTF skeleton are bridged to the nitrogen aromatic ligand through a conjugated spacer such as ethenyl or phenylethenyl unit. Their electrochemical characterization as well as the crystal structure of one of these compounds is given.
Keywords: TTF derivative; Synthesis; X-ray structure; N aromatic heterocycle
Electrical and mechanical properties of novel polyaniline coated polycaprolactam fibers
by Xin Jin; Changfa Xiao; Wenyu Wang (pp. 368-372).
Polycaprolactam (PA6) fibers were coated with polyaniline (PANI) by a novel dissolving-coating method. In the dissolving-coating method, dissolution of PA6 fiber surface is the necessary condition for imparting conductivity to PA6 fiber. But the dissolution of fiber surface would cause the structural integrity of PA6 fiber being destroyed. In this research, the effect of solvent concentration and roller speed on the mechanical and electrical properties of PANI-coated PA6 fiber were discussed. The results showed that the optimum condition for PANI-coated PA6 fiber is 75% formic acid aqueous solution and 100rpm. The coating durability of PANI was tested by TG, FT-IR, water washing and heating to different temperatures. The experimental data indicate that PANI coating is difficult to peel off after the heating and washing treatment.
Keywords: Polyaniline; Polycaprolactam fiber; Coating; Electrically conductive fiber; Electrical and mechanical properties
High response organic ultraviolet photodetector based on bis (2-methyl-8-quinolinato)-4-phenylphenolate aluminum
by Yuncheng Cui; Lihui Liu; Chunbo Liu; Qingwei Wang; Wenlian Li; Guangbo Che; Chunhui Xu; Mei Liu (pp. 373-375).
We report highly efficient visible-blind ultraviolet photodetectors based on 1,3,5-tris(3-methylphenyl-phenylamino)-triphenyamine (m-MTDATA) as donor and bis(2-methyl-8-quinolinato)-4-phenylphenolate aluminum (BAlq) as acceptor. Strong photoluminescence quenching of m-MTDATA by BAlq is observed manifesting the efficient photoinduced charge transfer occurs between m-MTDATA and BAlq. The optimized device exhibits a photocurrent of 172μA/cm2 at −14V under an illumination of 365nm UV light irradiation with an intensity of 0.691mW/cm2, corresponding to a responsivity of 248mA/W. We attribute the high response to the efficient electron transfer from the donor to the acceptor, the feasible level alignment match and the high carrier mobility of photoresponsive materials.
Keywords: Organic ultraviolet photodetector; BAlq; Photoluminescence quenching; High response
MoO x interlayer to enhance performance of pentacene-TFTs with low-cost copper electrodes
by Jun Li; Xiao-Wen Zhang; Liang Zhang; Hao Zhang; Xue-Yin Jiang; Khizar-ul-Haq; Wen-Qing Zhu; Zhi-Lin Zhang (pp. 376-379).
We demonstrated that the electrical properties of pentacene-thin film transistors with low-cost Cu electrodes can be enhanced by inserting a thin MoO x interlayer layer between pentacene and Cu source/drain (S/D) electrodes. In comparison with the device having Cu-only electrodes, the performance of the device with MoO x/Cu electrodes was significantly improved. The saturation mobility increased from 0.13 to 0.61cm2/Vs, threshold voltage reduced from −14.5 to −7.3V, on/off ratio shifted from 8.9×105 to 1.6×106 and threshold swing varied from 1.92 to 1.33V/decade. The improvement was attributed to the reduction of contact resistance and the enhancement of hole-injection efficiency. The results suggest modification of Cu S/D electrodes is a simple and effective way to improve device performance and reduce the fabrication cost.
Keywords: Organic thin-film transistor; Pentacene; MoO; x; Cu
Synthesis of micromulti-prisms polypyrrole boxes in the presence of α-cyclodextrin
by Jiangtao Feng; Wei Yan (pp. 380-383).
Polypyrrole (PPy) boxes with micromulti-prisms have been synthesized in aqueous solution via a self-assembled method using α-cyclodextrin (α-CD) as a dopant and FeCl3 as an oxidant. The morphology and the micro-structure of the as-synthesized PPy boxes were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier-transform infrared (FTIR) spectrum. The formation mechanism of the PPy boxes structure was also discussed. And the congregated structure of dissociative pyrrole monomers with the inclusion complexes (between α-CD and pyrrole monomer) was proposed to play a significant role in forming the multi-prisms sectional PPy-CD boxes.
Keywords: Polypyrrole (PPy); Morphology; Micromulti-prisms; Boxes
The structure change-induced morphology transition of polyaniline in 1.6-hexanediol aqueous and acid-free solutions: From submicron-spheres to nanofibers
by Y.F. Huang; C.W. Lin (pp. 384-389).
This study shows that the polymerization of aniline monomers in 1.6-hexanediol aqueous and acid-free solutions can produce three-dimensional (3D) polyaniline submicron-spheres and one-dimensional (1D) nanofibers at different reaction stages through a morphology transition process. Fourier transform infrared spectra indicate that the aniline monomers form phenazine-like units in the initial reaction stage, producing polyaniline submicron-spheres with a diameter of ∼400nm. The hydrogen bonds between 1.6-hexanediol molecules and polyaniline chains serve as the driving force for the polyaniline chains to construct submicron-spheres. However, as the reaction proceeds, the solution acidity increases and the initially formed phenazine-like segments function as the nucleate for the free aniline monomers to polymerize through para-coupling linkage. This process forms polyaniline samples with a structure consisting of a core of phenazine-like units and a shell of para-linked units. In this stage, the newly formed para-linked aniline units exhibit an intrinsic tendency to transit the polyaniline morphology from submicron-spheres into nanofibers. These results indicate that a change in polyaniline structure during the polymerization process can produce different micro/nanostructures at different reaction stages. This finding provides a practical route for the further design and synthesis of different polyaniline micro/nanostructures.
Keywords: Polyaniline; 1.6-Hexanediol; Microspheres; Nanofibers; Self-assembly
Synthesis, photophysical and electrophosphorescent properties of a novel fluorinated rhenium(I) complex
by Xiao Li; Shuanghong Wu; Dongyu Zhang; Zisheng Su; Peng Lei; Zhiqiang Zhang; Zhizhi Hu; Wenlian Li (pp. 390-393).
A novel fluorinated rhenium complex, i.e., Re-BFPP (BFPP, 2, 3-bis(4-fluorophenyl)pyrazino[2,3- f][1,10]phenanthroline) was designed, synthesized and characterized by1H NMR and mass spectroscopy. The light-emitting and electrochemical properties of this complex were studied. The organic light-emitting diodes (OLEDs) employing Re-BFPP as a dopant emitter with the structures of ITO/m-MTDATA (10nm)/NPB (20nm)/CBP: Xwt.% Re-BFPP (30nm)/Bphen (10nm)/Alq3 (30nm)/LiF (1nm)/Al (100nm) were successfully fabricated and a broad electroluminescent peak at 553nm was observed. The 10wt.% Re-BFPP doped device exhibited the maximum luminance of 6342cd/m2 and a peak current efficiency of 17.9cd/A, corresponding to the power efficiency of 8.1lm/W.
Keywords: Rhenium complex; Synthesis; Electrophosphorescence; OLEDs
Polyaniline nanofibers synthesized in compressed CO2
by Quoc Minh Pham; Jae-Seong Kim; Sunwook Kim (pp. 394-399).
Polyaniline (PANI) nanofibers were synthesized in compressed liquid carbon dioxide without any template or surfactant. The polymerization of aniline took place at the interface between CO2 and aqueous solution in a high-pressure stirred reactor. The prepared PANI nanofibers were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), electrical conductivity (EC), Fourier-transform infrared (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses. The yield of polymerization was high enough to reach 63.04% while maintaining small diameters of the PANI nanofibers. This result is very important for the preparation of the PANI nanofibers because no other previous investigations have achieved both high yield and small diameter of fibers at the same time. Through SEM and TEM analyses, we observed that the PANI nanofibers had diameter range of 30–70nm and a length range of 0.3–1μm, which caused them to disperse well in various solvents such as water, ethanol, 2-propanol, m-cresol and toluene. The electrical conductivity of the PANI nanofibers was 4.34S/cm at 20°C. The XRD diffraction pattern showed that the PANI nanofibers had crystalline one-dimensional structures, which gave high thermal stabilities as confirmed by TGA.
Keywords: Polyaniline; Nanofiber; Carbon dioxide; High yield; Electrical conductivity
Synthesis and properties of novel electroactive polyamide containing crown ether in the main chain
by Lili Cui; Danming Chao; Junfeng Zhang; Hui Mao; Yongxin Li; Ce Wang (pp. 400-404).
A new electroactive polyamide with dibenzo-18-crown-6 and well-defined oligoaniline in the main chain was synthesized through oxidative coupling polymerization. The structure of the electroactive copolymer was confirmed by FTIR, NMR spectroscopy. And its electrochemical activity was tested in 0.5M H2SO4 aqueous solution and it shows three redox peaks. Moreover, the UV–vis absorption attenuation of the copolymer solution was found upon K+ binding, but the absorption had hardly change on Na+. We found the polymer has selectivity toward K+ ions. So it has a potential application in chemical sensors.
Keywords: Polyamide; Crown ether; Absorption attenuation
Effects of content of polyaniline doped with dodecylbenzene sulfonic acid on transparent PANI-SiO2 hybrid conducting films
by Li Wei; Qi Chen; Yingjun Gu (pp. 405-408).
Transparent PANI-SiO2 conducting films were prepared by hybrid of dodecylbenzene sulfonic acid-doped polyaniline (DBSA-PANI) and 3-glycidoxypropyltrimethoxysilane (GPTMS) through sol–gel route. The influence of content of DBSA-PANI on the structural, electrical and optical properties of the films was investigated. Sheet resistance of the hybrid films was 5.1kΩ/□ and visible light transmittance was 75%, when the content of DBSA-PANI was 30wt.%. Thermogravimetric analysis (TG) showed that the obtained films were thermally stable under 120°C and optical bandgap of the hybrid films was determined from Tauc plots.
Keywords: Sol–gel; DBSA-PANI; Hybrid film; Conductivity; Transparence
Effects of substituents on the third-order nonlinear optical properties of poly(3-alkoxythiophene) derivatives
by Dong Yanmao; Jianmei Lu; Qingfeng Xu; Feng Yan; Xuewei Xia; Lihua Wang; Li Hu (pp. 409-412).
Poly(3-alkoxythiophenes) (P3AOTs) have been synthesized with octoxyl, dodecaoxyl and 4-nitro-benzyloxyl as sidechains, respectively. The novel poly(3-octoxycthiophen)-co-poly(3-(4-nitro-benzyloxy)-thiophene) (P3OOT-co-P3NBOT) has also been prepared. The absorption spectra of samples indicate that the side groups affect the bandgap of P3AOTs. The nonlinear optical (NLO) properties of P3AOTs were investigated using Z-scan method. The third-order NLO susceptibility ( χ(3)) of the polymers shows a strong dependence on the length of the alkoxyl sidechains and polarity of polymers, which affect the intra- and intermolecular charge transfer. These polymers have potential application in optical limiting device.
Keywords: Substituent; Nonlinear optics; Poly(3-alkoxythiophene)
Synthesis, electrochemical, and spectroelectrochemical properties of conductive poly-[2,5-di-(2-thienyl)-1 H-pyrrole-1-( p-benzoic acid)]
by Yung Hyun Kim; Jaeyoung Hwang; Jung Ik Son; Yoon-Bo Shim (pp. 413-418).
Poly( ter-heteroaromatic( thiophene- pyrrole- thiophene)), PDPB, was electrochemically prepared from the 2,5-di(2-thienyl)-1 H-pyrrole-1-( p-benzoic acid) (DPB) monomer using the Paal-Knorr pyrrole condensation reaction. The structure of the monomer was confirmed using1H-,13C NMR, FT-IR and mass spectroscopy. The maximum UV–visible absorption and PL emission bands of DPB were observed at 330nm and 500nm, respectively. The cyclic voltammograms (CVs) recorded for the electrochemically polymerized DPB revealed a set of redox peaks at 0.65/0.53V. The conductivity monotonically increased with respect to the applied potential from 0.0V to 1.0V, exhibiting a maximum conductivity of 0.18S/cm at +0.80V. The in situ UV–visible spectroelectrochemical analysis of PDPB revealed electronic transitions at 420nm, 654nm, and 870nm corresponding to the π–π* transition, polaron, and bipolaron states, respectively. The optical band-gap ( Eg) of PDPB was 2.16eV. The color of the PDPB film transitioned yellow (at 0.0V) to blue (at 1.0V) when the potential was switched between the reduced and oxidized states with a good electrochromic response time (0.95s).
Keywords: Conducting polymer; Electrochemical polymerization; Electrochromism; Spectroelectrochemistry; Poly-(2,5-di(2-thienyl)-1; H; -pyrrole) derivative
Fabrication of high adhesive silver-coated PET electrode challenged by simulated body fluid (SBF) soaking
by Yinxiang Lu; Suhua Jiang; Yongming Huang (pp. 419-424).
Ultrasonic assisted electroless deposition of silver on poly(ethylene terephthalate) (PET) modified with silanes was investigated. Mercapto groups were linked to the PET film as an active layer, which was proved by Raman spectra and EDX analysis. The composition, structure, thermal decomposing behavior of silver-coated PET films after simulated body fluid (SBF) treatment were characterized by scanning electron scopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TG), and ATR-FTIR spectra respectively. Silver plating on modified PET films has good adherence stability (>40N/cm) and high electric conductivity (∼0.03Ω/□) before and after SBF soaking. The practical implication of these results is that this silver-coated polymer can be applied to the flexible conductive electrodes for interventional therapy because of its firmness and improved mechanical property.
Keywords: Poly(ethylene terephthalate); Silver; Adhesion strength; Modification; Simulated body fluid; Flexible electrode
Reactive polymer films
by T.F. Otero; J. Arias-Pardilla; E. Chermak (pp. 425-431).
The oxidation kinetics of electrogenerated polypyrrole films was studied in aqueous solution. The influence of reactant concentrations (LiClO4 in solution and active centres in the polymer film) and temperature on the kinetics has been studied. The usual procedure for any kinetic study was now repeated for different initial states, attained by electrochemical reduction at the same cathodic potential for different reduction times. For rising reduction times, lower kinetic coefficient ( k) and higher activation energies ( Ea) were obtained. The activation energy is assumed to include rising conformational energy for more packed conformations of the initial states. Both kinetic magnitudes become a way to quantify the initial packing conformational degree. So, kinetic magnitudes can include structural information opening a new window for the chemical kinetics of reactive macromolecules that could be extended to reactive biopolymers. When compared the evolutions of k and Ea experimental changes from aqueous and acetonitrile solutions of the same salt, important differences were found. Evolutions of k and Ea from different solvents could be used as tools to quantify the polymer–solvent interaction evolution along the reaction.
Keywords: Oxidation kinetics; Polypyrrole; Conformational energy; Activation energy; Kinetic coefficient
Synthesis and electrochromic properties of oligothiophene derivatives
by Binbin Yin; Chuanyu Jiang; Yongguang Wang; Ming La; Ping Liu; Wenji Deng (pp. 432-435).
In order to develop novel organic electrochromic materials, oligothiophene derivatives, 5,5″-biformyl-2,2′:5′,2″-terthiophene (OHC-3T-CHO) and 2,3,4,5-tetrathiopenyl-thiophene (X-T), were synthesized. Three electrochromic devices have been fabricated using OHC-3T-CHO and XT, and the electrochromic properties of OHC-3T-CHO and X-T were studied. The indium-tin-oxide (ITO)/OHC-3T-CHO/electrolyte solution/ITO device exhibited reversible, clear colour change from yellow to bright bluish-green on electrochemical doping and dedoping, while ITO/OHC-3T-CHO/conducting gel/ITO device and ITO/OHC-3T-CHO/conducting filter paper/ITO device exhibited colour change from yellow to green. The ITO/XT/electrolyte solution/ITO device showed reversible, clear colour change between yellowish orange and silver-gray on electrochemical doping and dedoping.
Keywords: Oligothiophene derivative; Microwave irradiation reaction; Electrochromic property; Electrochromic device
Comparison of photophysicochemical properties of hexaphenoxycyclotriphosphazenyl-substituted metal-free, mono- and bis-lutetium phthalocyanines
by Mahmut Durmuş; Serkan Yeşilot; Bünyemin Çoşut; Ayşe Gül Gürek; Adem Kılıç; Vefa Ahsen (pp. 436-444).
The aim of this study is to compare the photophysicochemical properties of hexaphenoxycyclotriphosphazenyl-substituted metal-free (1), mono-(phthalocyaninato) lutetium(III) (2) [LuIII(AcO)(Pc)] (Pc=phthalocyaninato, AcO=acetate) and bis-(phthalocyaninato) lutetium(III) (3) [LuIIIPc2]. The synthesis and characterization (using the elemental analysis, mass spectrometry, IR,1H, and31P NMR and UV–vis spectroscopy) of new compounds (2,3) are described in this study. The electronic absorption and fluorescence spectral properties of compounds1–3 are investigated. Photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen and photodegradation quantum yields) measurements are also studied on hexaphenoxycyclotriphosphazenyl-appended metal-free, mono- and bis-lutetium phthalocyanines in dimethylsulfoxide (DMSO). Photophysical and photochemical properties of phthalocyanines are very useful for photodynamic therapy (PDT) applications. Singlet oxygen quantum yields ( ΦΔ) give an indication of the potential of the complexes as photosensitizers in PDT applications. Hexaphenoxycyclotriphosphazenyl-substituted mono-(phthalocyaninato) lutetium(III) complex (2) gave good singlet oxygen quantum yield (0.66) in DMSO. Thus, this complex shows potential as Type II photosensitizer for PDT of cancer.
Keywords: Rare-earth phthalocyanine; Bis-lutetium phthalocyanine; Mono-lutetium phthalocyanine; Phosphazene; Photosensitizer; Quantum yields; Photodynamic therapy
Investigation of annealing effects on microstructure of hybrid nanocrystal–polymer solar cells by impedance spectroscopy
by WenBo Huang; JunBiao Peng; Li Wang (pp. 445-449).
We have fabricated hybrid bulk heterojunction solar cells with blends of MEH-PPV (poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene]) and nano-CdS as electron donor and electron acceptor, respectively. The effect of thermal annealing was investigated with impedance spectroscopy (IS) and capacitance–voltage ( C– V) characteristic measurements on devices. The IS and C– V characteristic manifested very different before and after thermal annealing. We performed equivalent circuit to explain the effect of thermal annealing. The thermal treatment of nanocrystal–polymer films is seen to aid in the formation of a continuous network for electron transport between nanorods, and hence improves devices performance. The method based on the IS is available to probe the microstructure of hybrid bulk heterojunction solar cells before and after thermal annealing, and therefore detect the mechanism for the annealing improvements.
Keywords: Impedance spectroscopy; Hybrid bulk heterojunction solar cells; Nanocrystal–polymer films; Thermal annealing
Conversion of a green light emitting zinc-quinolate complex thin film to a stable and highly packed blue emitter film
by Vivek Kumar Shukla; Satyendra Kumar (pp. 450-454).
Tris-(8-hydroxyquinoline) metal complex Znq2, used as light-emitting layer in electroluminescent (EL) devices was synthesized and optical properties of as-deposited Znq2 in thin films were studied. Interesting phenomenon was observed while studying the ageing and degradation behavior of Znq2 films and consequently a stable form having strong blue photoluminescence (peak 465nm) was discovered. This converted (from green to blue emitting) film has higher molecular packing density and comparable photoluminescence intensity with Znq2 film. Here, we report on the production of this blue material under controlled conditions and its optical properties.The thin films have been deposited by thermal evaporation on quartz and silicon substrates. The optical constants ( n and k) of green Znq2 film and converted (to blue) thin films have been determined using spectroscopic ellipsometry. Environment induced effects on optical properties of films have been studied using ellipsometry, photoluminescence and UV–vis transmission measurements.
Keywords: Tris-(8-hydroxyquinoline) metal complex; Znq; 2; Spectroscopic ellipsometry (SE)
Water-soluble polyaniline and its composite with poly(vinyl alcohol) for humidity sensing
by Yang Li; Bangyu Ying; Lijie Hong; Mujie Yang (pp. 455-461).
Water-soluble polyaniline (PANi) was prepared by a “green” method with poly (stryrenesulfonic acid) (PSSA) as a template, and characterized by UV–vis spectroscopy, FT-IR spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). It was found that the films of PANi and its composite with poly(vinyl alcohol) (PVA) were composed of nanoparticles. The humidity sensitive properties of the both PANi and its composite with PVA were investigated at room temperature. The water-soluble PANi exhibited high sensitivity (impedance change over three orders of magnitude in the range of 15–97%RH) and good sensing linearity on a semi-logarithmic scale, but a relatively large hysteresis of ∼8%RH. In contrast, the composite of PANi and PVA showed a very small hysteresis of ∼2%RH. Moreover, the response was fast and highly reversible. The humidity sensing mechanism of the composite of PANi with PVA was explored by measuring its complex impedance spectra under different humidities.
Keywords: Water-soluble polyaniline; Humidity sensitivity; Polymeric humidity sensor; Composite; Poly(vinyl alcohol)
Structure–property relationship in mechanochemically prepared polyaniline
by O. Yu. Posudievsky; O.A. Goncharuk; R. Barillé; V.D. Pokhodenko (pp. 462-467).
High conductivity of mechanochemically prepared polyaniline is analyzed in respect of structure–property relationship.The comparative analysis of the physicochemical properties of polyaniline prepared in the conditions of solventless mechanochemical treatment in the ball mill (PAni|mch) and polyaniline synthesized by the usual oxidative polymerization in the solvent (PAni|c) is carried out. Conductivity of PAni|mch substantially exceeds that of PAni|c. As molecular weights of PAni|mch and PAni|c are comparable, the observed difference could be connected with the influence of mechanical stress which affects the polymer during its mechanochemical preparation. The increased conductivity of polyaniline obtained by post-synthesis mechanochemical treatment of PAni|c (PAni|mt) confirms such explanation. It could be concluded from the results of the structural investigations as well as of spectral and electrochemical studies that the shear stress which exerts influence on the polymer during mechanochemical synthesis or mechanochemical treatment leads to the increase of the interchain π–π interaction and, consequently, to the efficient improvement of conductivity.
Keywords: Polyaniline; Mechanochemical preparation; Conductivity; Structure–property relationship
Synthesis, characterization and comparative OFET behaviour of indenofluorene–bithiophene and terthiophene alternating copolymers
by Prashant Sonar; Luke Oldridge; Andrew C. Grimsdale; Klaus Müllen; Mathieu Surin; Roberto Lazzaroni; Philippe Leclère; Jason Pinto; Lay-Lay Chua; Henning Sirringhaus; Richard H. Friend (pp. 468-474).
The synthesis of alternating copolymers of tetraalkylindenofluorene with bithiophene and terthiophene using Suzuki polycondensation route is reported. We report on the optical and electrochemical properties of these copolymers. AFM analysis of the microscopic morphology of thin deposits showed that the copolymer with terthiophene units produced the more ordered films, with well-defined fibrillar structures, resulting from highly-regular dense packing due to strong π–π interchain interactions, in contrast to the amorphous bithiophene copolymer. Upon testing these materials in FETs the terthienyl copolymers displayed the higher charge mobilities among the studied compounds, with values of over 10−4cm2V−1s−1 being obtained.
Keywords: Indenofluorene copolymers; Semiconducting Materials; Microscopic Morphology; Charge; Carrier Mobility
Depletion- and ambipolar-mode field-effect transistors based on the organic heterojunction composed of pentacene and hexadecafluorophtholocyaninatocopper
by Fei Hong; Feifei Xing; Wen Gu; Weipeng Jin; Jianhua Zhang; Jun Wang (pp. 475-478).
We investigated heterojunction organic field-effect transistors (OFETs) using pentacene and hexadecafluorophtholocyaninatocopper (F16CuPc) as double active layers. Two operation modes including depletion- and ambipolar-type were observed depending on the deposition order of two organic films. Depletion-mode was firstly observed from that devices with pentacene as the bottom layer and F16CuPc as the top layer, which was attributed to dipole effects originated from the pentacene/F16CuPc interface. Then improved device performances were obtained with mobility from 0.87 to 1.06cm2/Vs, and threshold voltage shifted from −20 to +25V as compared with conventional pentacene-based devices. Furthermore, the heterojunction OFETs exhibited typical ambipolar transport when alternating the deposition order of two films, which exhibited ambipolar mobilities with 0.06cm2/Vs for electron and 0.0025cm2/Vs for hole, respectively. All results implied the utilization of heterojunction can effectively improve the device performances of OFET, and operation mode strongly on the deposition order of two films.
Keywords: Organic heterojunction; Threshold voltage; Depletion; Ambipolar
Synthesis, characterization and spectroscopic studies of CdS/polyaniline core/shell nanocomposite
by R. Seoudi; M. Kamal; A.A. Shabaka; E.M. Abdelrazek; W. Eisa (pp. 479-484).
In this work, CdS/polyaniline (PANI) nanocomposite was synthesized by a novel method. Transmission electron microscope (TEM) images showed that the CdS/PANI nanocomposite had a core/shell structure. The crystal structure was studied using X-ray diffraction (XRD) and the obtained results showed that CdS had cubic structure. Fourier transform infrared (FTIR) spectroscopic measurements confirmed the formation of PANI at the surface of CdS nanoparticle. The prepared samples were further characterized using UV–visible (UV–vis) and fluorescence spectroscopy.
Keywords: CdS/polyaniline nanocomposite; Core/shell; TEM; XRD; FTIR; UV–visible; Fluorescence
Photo-induced charge separation process in (PCBM-C120O)/(M3EH-PPV) blend solid film studied by means of X and K-bands ESR at 77 and 120K
by A. Konkin; U. Ritter; P. Scharff; H.-K. Roth; A. Aganov; N.S. Sariciftci; D.A.M. Egbe (pp. 485-489).
The new fullerene dimer adduct PCBM-C120O was studied as an electron acceptor by light-induced ESR (LESR) when blended with the electron donor-conjugated polymer M3EH-PPV in a thin solid film. ESR parameters for the PCBM-C120O anion radical and the M3EH-PPV polaron (triaxial g x, y, z factors) were determined by X- and K-band ESR techniques at temperatures of 77 and 120K. It was found that isotropic g0 of PCBM-C120O anion radical ESR spectra obtained in this blend under illumination is close to g-factors of electrochemically reduced (C120-O)− and does not coincide with the analogous parameter of (C120-O)2− (reported in literature). Spin relaxation parameters ( T1 and T2) of the PCBM-C120O anion radical and M3EH-PPV positive polaron are similar to T1, T2 for light-induced ion radicals in the P3HT/PCBM blend.
Keywords: LESR; Fullerene dimer (PCBM-C; 120; O); M3EH-PPV; Charge separation
Multifunctional polyconjugated molecules with carbazolyl and pyrazolyl moieties for optoelectronic applications
by E. Arbačiauskienė; K. Kazlauskas; A. Miasojedovas; S. Juršėnas; V. Jankauskas; W. Holzer; V. Getautis; A. Šačkus (pp. 490-498).
Diethylene derivative possessing carbazolyl and pyrazolyl moieties and its analogue containing additional cyano groups were synthesized and investigated as potential multifunctional materials for organic light emitting diodes. The influence of the electron affinitive cyano groups on the ionization potential ( I p) of the films as well as on the photoluminescence (PL) spectrum, PL quantum yield ( η) and PL decay time of the dilute solutions and thin films of the diethylene derivatives was studied. PL measurements revealed that highly luminescent ( η=0.80) cyano-free pyrazole–carbazole derivative in solution became weakly emissive ( η=0.04) by attaching cyano groups as a result of these groups-induced torsional deactivation. However in the solid state, the steric and electrostatic effects of the bulky and polar cyano groups prevented close packing of the molecules, thus significantly reducing migration-induced quenching of the excitons at the defects. Incorporation of the cyano groups resulted in the 3-fold enhancement of the PL quantum yield in the neat film of the polyconjugated derivative as compared to that of the cyano-free film. The I p of 5.50eV estimated for the cyano groups-containing compound was found to be higher as compared to the I p of 5.35eV for the cyano-free analogue, which in conjunction with the PL data for the films indicated increased electron affinity (by 0.40eV) in the cyano groups-containing diethylene derivative.
Keywords: Pyrazole; Carbazole; Diethylene derivatives; Fluorescence; Ionization potential; Charge carrier mobility
I– V characteristics of the p–n junction between vertically aligned ZnO nanorods and polyaniline thin film
by Yinhua Li; Jian Gong; Mallarie McCune; Gaohong He; Yulin Deng (pp. 499-503).
The characteristics of the p–n junction between vertically aligned ZnO nanorods and polyaniline (PANI) thin film were investigated. The rectifying behavior of the I– V curve of ZnO/PANI diode was verified with assembled ZnO/PANI structures. The cut-in voltage of the p–n junction was found to be around 0.5V and the reverse breakdown voltage was about −27V. In addition, the effects of UV illumination and NH3 exposure on the I– V characteristics of ZnO/PANI configuration were also investigated.
Keywords: p–n junction; ZnO nanorods; Polyaniline
Investigation of organic n-type field-effect transistor performance on the polymeric gate dielectrics
by Moumita Mukherjee; Biswanath Mukherjee; Youngill Choi; Kyoseung Sim; Junghwan Do; Seungmoon Pyo (pp. 504-509).
We report a copper hexadecafluorophthalocyanine (F16CuPc) based n-type organic field-effect transistor (OFET) with polymeric gate dielectrics with different physical/electrical properties. The gate dielectrics are four types of cross-linked poly(4-vinylphenol) and newly prepared poly(4-phenoxy methyl styrene) and those are characterized based on surface tension, leakage current and capacitance. The performance of F16CuPc OFETs with those gate dielectrics was compared. We found that the composition of the gate dielectrics and the interfacial interaction of F16CuPc with the gate dielectric play a decisive role in the performance of OFETs. The effect of physical/electrical properties, composition and processing condition of the gate dielectrics on the device performance was investigated.
Keywords: Organic field-effect transistors; Gate dielectric; Surface properties; Organic semiconductor
Organic field effect transistors based on 5,10,15,20-tetrakis(4-pentyloxyphenyl)porphyrin single crystal
by Pan Ma; Yanli Chen; Xue Cai; Hailong Wang; Yuexing Zhang; Yingning Gao; Jianzhuang Jiang (pp. 510-515).
OFET devices fabricated from single crystal of metal free tetrakis(4-pentyloxyphenyl)porphyrin exhibit relatively high carrier mobility for hole of 1.8×10−3cm2V−1s−1 in the direction parallel to the aromatic porphyrin ring and high current modulation value of 104.Diffusion of methanol into the chloroform solution of metal free 5,10,15,20-tetrakis(4-pentyloxyphenyl)porphyrin H2TPOPP yields large single crystals with length as long as 1.5mm, which allow the fabrication of single crystal-based organic field effect transistors (OFETs). These single crystal-based devices were revealed to exhibit relatively good OFET performance with the carrier mobility for hole of 0.0018cm2V−1s−1 and current modulation of 104. In addition to confirming the tetrappyrole nature, single crystal X-ray diffraction analysis also reveals the planar two-dimensional supramolecular structures formed via porphyrin molecules in the head-to-tail manner through C–H⋯O interaction between oxygen atom and pyrrole hydrogen atom as well as p(O)–π(phenyl) interaction between the meso-attached phenyloxy groups of neighboring porphyrin molecules in the single crystal. This results in effective intermolecular interaction due to the significant participation of phenyloxy groups to the HOMO of the central porphyrin core as revealed by density functional theory (DFT) analysis and in turn is responsible for the relatively good OFET performance in terms of carrier mobility for hole in the direction parallel to the aromatic porphyrin ring. Density functional theory (DFT) calculation also reproduces the experimentally revealed carrier mobility for hole in the single crystal of H2TPOPP. The present work, representing our continuous efforts in understanding the relationship between molecular structure, crystal packing, and OFET performance of tetrapyrrole organic semiconductors, will be helpful for attracting further research interest over the semiconducting properties of tetra(aryl)porphyrin compounds for OFET applications.
Keywords: Porphyrin; Single crystal; Organic field effect transistor; Density functional theory
Improved electrical and thermal properties of polypyrrole prepared by the repetition of a combination of chemical polymerization and 2-naphthalenesulfonic acid treatment
by Sadamu Toita; Kenzo Inoue (pp. 516-518).
Electrical property and thermal stability of acid-treated polypyrrole (Ppy) film, which was prepared by the repetition of chemical polymerization of pyrrole (Py) followed by dipping in an aqueous solution of citric acid/boric acid (MCB), p-toluenesulfonic acid (p-TS), 2-naphthalenesulfonic acid (2-NS), and 1,3,6-naphthalenetrisulfonic acid (NTS) were investigated. The normalized capacitance, the Cp/ C0 value of capacitor fabricated with Ppy film (Ppy-II-2-NS) treated with 2-NS increased with increasing the number of times of polymerization and acid treatment, and reached 0.8 after 18 times repetition, whereas for the capacitor fabricated with Ppy film (Ppy-I) without acid treatment the Cp/ C0 value stayed at a poor level of 0.4. A similar Cp/ C0=0.8 was obtained for Ppy films treated with p-TS and NTS. The equivalent series resistance (ESR) value at 100kHz of Ppy-II-2-NS showed a low value of 2mΩ being about one-fifth of Ppy-I film. The normalized resistance ( Rt/ R0) at 150°C indicates that the conductivity decay of the Ppy-II-2-NS/Al2O3/Al capacitor was significantly suppressed compared to the Ppy-I/Al2O3/Al capacitor. These results indicate that 2-NS treatment in the chemical polymerization process is highly effective to improve the electrical properties of Ppy/Al2O3/Al capacitor at elevated temperatures.
Keywords: Polypyrrole; Acid treatment; Electronic materials; Thermal properties; Capacitor
Fuzzy nanofibrous network of polyaniline electrode for supercapacitor application
by D.S. Dhawale; D.P. Dubal; V.S. Jamadade; R.R. Salunkhe; C.D. Lokhande (pp. 519-522).
Fuzzy nanofibrous network of polyaniline electrode is successfully electrosynthesized for supercapacitor application. The nanofibre network of polyaniline electrode is characterized using Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM) and optical absorption studies. Network of polyaniline is highly porous with interconnected fuzzy nanofibres having diameter typically between 120 and 125nm. The supercapacitive performance of polyaniline electrode is tested using cyclic voltammetry (C-V) technique in H2SO4 electrolyte within potential range of −100 to 800mV. The effect of scan rate on the capacitance of polyaniline electrode is studied. The highest specific capacitance of 839Fg−1 at the voltage scan rate of 10mVs−1 is achieved. Additionally stability and charging–discharging of polyaniline electrode are studied.
Keywords: Fuzzy nanofibrous network; Polyaniline; Electrodeposition; Supercapacitor
Interfacial polymerization of carbazole: Morphology controlled synthesis
by Bhavana Gupta; Rajiv Prakash (pp. 523-528).
One-dimensional nanotube and three-dimensional hollow spheres of conducting polymers have attracted immense attention due to their unique properties and potential applications. There are two routes of synthesizing these systems—electrochemical and chemical. However, chemical polymerization has incurred a particular interest because of two major advantages—possibility of bulk synthesis and control of morphology. In this article, we have reported for the first time chemical synthesis of unsubstituted polycarbazole and formation of its hollow microspheres. Carbazole is polymerized with controlled morphology using interfacial polymerization; however, so far it is known to synthesize using electrochemical technique only. Upon comparative analysis with polymer synthesized through electrochemical route, it is observed that polymer synthesized through interfacial polymerization has higher crystallinity with spherical morphology. Formation and growth of microspheres are observed with AFM and SEM micrographs.
Keywords: Conducting polymer Synthesis; Polycarbazole; Controlled morphology; Microsphere
Study of chemiresistor type CNT doped polyaniline gas sensor
by Subodh Srivastava; S.S. Sharma; Shweta Agrawal; Sumit Kumar; M. Singh; Y.K. Vijay (pp. 529-534).
The composite thin films of polyaniline (Pani) with multiwall carbon nanotube (MWNT) and single wall carbon nanotube (SWNT) for hydrogen gas sensing application are presented in this paper. Polyaniline (Pani) was synthesized by chemical oxidative polymerization of aniline using ammonium persulfate in acidic medium. The SWNT and MWNT were doped in Pani in presence of champhor sulfonic acid (CSA) by solution mixing method. Thin films of CNT/Pani composites were prepared by spin coating method. Finally, the response of these composite films for hydrogen gas was evaluated by monitering the change in electrical resistance at room tempeature. It is observed that the SWNT/Pani and MWNT/Pani composite films show a higher response as compare to pure Pani. The structural and optical properties of these composite films have been characterised by X-ray diffraction (XRD) and UV–visible spectroscopy respectively. Surface morphology of these films has also been characterised by optical microscopy.
Keywords: CNT/polyaniline composite; Interdigited electrodes; Hydrogen gas sensing; XRD; UV–vis spectroscopy
Synthesis and study of nonlinear optical properties of 4-substituted benzylidene-2-phenyl oxazol-5-ones by Z-scan technique
by Y.L.N. Murthy; V. Christopher; U. Viplava Prasad; P.B. Bisht; D.V. Ramanaih; B.S. Kalanoor; S. Akbar Ali (pp. 535-539).
4-substituted benzylidene-2-pheny-5-oxazolones (5 new compounds) were synthesized by both conventional and microwave assisted synthesis and were characterized by gas chromatography-mass spectrometry (GCMS), Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy, and Fourier-transform infrared (FT-IR) spectroscopy. The synthetic methodology of these new compounds is presented. The results of nonlinear optical study of 4-(4′- N, N-dimethyl benzylidene)-2-phenyl oxazol-5-(4H)-one by using Z-scan techniques are discussed here. The ultrafast fluorescence decay of the molecule has been explained to be due to the electron transfer from the dimethyl group to the carbonyl group.
Keywords: 5(4H)-Oxazolone; Nonlinear optics; Picosecond laser
Analysing space charge limited currents in organic light emitting diodes
by A.R. Buckley (pp. 540-543).
The error in making a mean field approximation when analysing space charge limited currents in organic light emitting diodes has been assessed. Using a Poole Frenkel-like,exp(γE), field dependent mobility, space charge limited currents have been simulated using zero field mobilities from 10−10m2/Vs to 10−4m2/Vs and field dependent parameter γ from 10−7(m/V)0.5 to 10−2(m/V)0.5. The simulated current–voltage data has been fitted using a mean field approximation to a modified Mott–Gurney equation and the deviation of zero field mobility and γ from the real values has been calculated. It was found that for a significant range of the simulations the error in both the zero field mobility and the γ factor was invariant, but systematically underestimated by 2% and 15% respectively. We conclude that the mean field approximation is a useful method with which to assess mobility using space charge limited currents in organic semiconductor devices, but the accuracy of such an analysis can be improved by accounting for the systematic error.
Keywords: Conjugated polymer; Space charge limited currents; PFB; SCLC