Synthetic Metals (v.159, #17-18)
Synthesis of new hole-transporting molecular glasses with pendant carbazolyl-based hydrazone moieties
by Giedre Bubniene; Tadas Malinauskas; Albina Stanisauskaite; Vygintas Jankauskas; Vytautas Getautis (pp. 1695-1700).
Synthesis, thermal, optical and photoelectrical properties of new hole-transporting molecular glasses with pendant carbazolyl-based hydrazone moieties, linked by aliphatic linking fragments, are reported. Electron photoemission spectra of the synthesized derivatives have been recorded and the ionization potentials have been established. The hole drift mobility values in compositions of the designed structures with bisphenol Z polycarbonate exceed 10−5cm2V−1s−1 at an electric field 106V/cm.
Keywords: Charge transport; Carbazole; Hydrazone; Ionization potential
Enhanced optical and electrical properties of PEDOT: PSS films by the addition of MWCNT-sorbitol
by Y. Chen; K.S. Kang; K.J. Han; K.H. Yoo; Jaehwan Kim (pp. 1701-1704).
A thin layer of carbon nanotubes (CNTs) presents a strong candidate for application as a transparent conducting electrode and a high frequency Schottky diode. Multiwalled carbon nanotubes (MWCNTs) were modified using nitric acid to form –OH and –COOH groups on the MWCNT surface. Functionalized MWCNTs (FMWCNTs) were further modified using sorbitol molecules. N, N′-carbonyldiimidazole (CDI) was utilized as an activating agent for carboxylic acids in a homogeneous one-pot reaction of FMWCNTs in N, N-dimethylacetamide (DMAc). The activated FMWCNTs were mixed with sorbitol and heated up to 60°C with stirring. Due to the mild conditions and efficiency of the reaction, a large amount of sorbitol molecules were covalently attached with increasing reaction time. The FMWCNTs with sorbitol (FMWCNTSORs) were mixed with poly(3,4-ethylene dioxythiophene):poly(styrene sulphonate) (PEDOT:PSS). The FMWCNTSORs were homogeneously dispersed into PEDOT:PSS solution without any precipitation. The FMWCNTSORs/PEDOT:PSS film showed stronger FTIR absorption peaks in the case of samples reacted for longer time. The UV–vis transmittance and the conductivity of the FMWCNTSORs/PEDOT:PSS film was increased as the reaction time increased. Although the field emission scanning electron microscope (FESEM) surface image of the 2h reacted FMWCNTSORs/PEDOT:PSS film showed large number of small aggregated particles, only a small number of aggregated particles was found for the sample reacted for 6h. These results indicate that the appropriate amount of sorbitol molecules on the MWCNT can increase the conductivity and transmittance of the PEDOT:PSS film.
Keywords: Carbon nanotubes; Conducting electrode; Sorbitol; Functionalized carbon nanotube
Impact of donor, acceptor, and blocking layer thickness on power conversion efficiency for small-molecular organic solar cells
by Su-Hwan Lee; Dal-Ho Kim; Ji-Heon Kim; Tae-Hun shim; Jea-Gun Park (pp. 1705-1709).
We investigated the dependency of the power conversion efficiency on the thickness of donor (copper phthalocyanine; CuPc), acceptor (fullerene; C60), and hole/exciton blocking (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline; BCP) layers in the OPV devices fabricated with double small-molecular layers. The power conversion efficiency peaked at a specific layer thickness, ∼12.7nm for the donor layer, ∼17.5nm for the acceptor layer, and ∼8.0nm for the hole/exciton blocking layer. This trend of power conversion efficiency was determined by short-circuit-current rather than open-circuit-voltage after light absorption. In addition, the donor layer thickness was more sensitive than the thickness of the acceptor or hole/exciton blocking layers in improving power conversion efficiency; i.e., ∼330% for the donor layer, ∼118% for the acceptor layer, and ∼112% for the hole/exciton blocking layers.
Keywords: Organic solar cell; Donor layer; Acceptor layer; Small-molecular; Photovoltaic cell
Multiwalled carbon nanotube/polyaniline thermoreversible gel composites
by Ashesh Garai; Arun K. Nandi (pp. 1710-1716).
Composites of multiwalled carbon nanotubes (MWCNTs) in a dinonylnaphthalene disulphonic acid (DNNDSA)-doped polyaniline (PANI) thermoreversible gel were prepared from a formic acid medium. A three-dimensional fibrillar network and a reversible first order phase transition characterize the systems as thermoreversible gels. Transmission electron micrographs indicate that the MWCNTs are well dispersed in the gel and PANI-DNNDSA wraps the MWCNT surface unevenly. π–π, CH–π and acid–base interactions are evident from Fourier transform infrared spectroscopy. Thermal stability increases with increasing MWCNT content and the storage modulus of the composites increases dramatically. Photoluminescence increases significantly in the composites showing a red shift of the emission peak with increasing MWCNT content. The π band-polaron band transitions show a red shift and the dc conductivity increases two orders of magnitude over that of the PANI-DNNDSA gel with the addition of MWCNTs. The current–voltage characteristic curves are Ohmic in nature and the current increases appreciably with increasing MWCNT concentration.
Keywords: Polyaniline; Carbon nanotube; Gel composite; Photoluminescence; Mechanical property and conductivity
Electrochemical investigations of self-doped polyaniline nanofibers as a new electroactive material for high performance redox supercapacitor
by H.R. Ghenaatian; M.F. Mousavi; S.H. Kazemi; M. Shamsipur (pp. 1717-1722).
Self-doped polyaniline (SDPA) nanofibers were deposited on platinum (Pt) electrode by reverse pulse voltammetric (RPV) method and their electrochemical performance was evaluated in an aqueous redox supercapacitor constituted as a two electrode cell in a weak acidic medium. Scanning electron micrographs clearly revealed the formation of nanofiber structures with diameters in range of 60–90nm under optimum experimental conditions. Different electrochemical methods including galvanostatic charge–discharge (CD) experiments, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out in order to investigate the applicability of the system as a redox supercapacitor. Based on the charge–discharge results obtained, the SDPA represented high specific capacitance, specific power and specific energy values of 480Fg−1, 436Wkg−1 and 9.40Whkg−1, respectively, at a current density of 5mAcm−2. The present study introduces new nanofiber materials for electrochemical redox capacitors with advantages including low cost, long cycle-life and stable at low acidic solutions of pH 3.
Keywords: Supercapacitor; Self-doped polyaniline nanofiber; Specific capacitance; Reverse pulse voltammetry (RPV)
Electrochemical and chemical characterization of polypyrrole/phosphotungstate coatings electrosynthesized on carbon steel electrodes in acetonitrile medium
by J. Bonastre; R. Lapuente; P. Garcés; F. Cases (pp. 1723-1730).
Hybrid material polypyrrole/PW12O403− was potentiostatically electrosynthesized on carbon steel electrodes in acetonitrile medium. The obtained coatings were characterized by cyclic voltammetry, FTIR-ATR, XPS, SEM and EDX techniques. Phosphotungstate as dopant agent, Fe oxides and polypyrrole chains are the compounds that form the hybrid material structure. The influence of the electrosynthesis potential was analysed. Oxidized and reduced state of the coatings was also studied. When the electrosynthesis potential is increased up to 2.00V and the polymeric coatings are in reduced state, the covering degree is very high and the coatings present a very homogenous and uniform surface.
Keywords: Polypyrrole; Phosphotungstate; Carbon steel; Polymer coating; Electrosynthesis; Chemical characterization
Encapsulation of laccase in a conducting polymer matrix: A simple route towards polypyrrole microcontainers
by Maciej Mazur; Agata Krywko-Cendrowska; Paweł Krysiński; Jerzy Rogalski (pp. 1731-1738).
The encapsulation of laccase dissolved in aqueous droplets adsorbed on glass or gold was studied. When the droplet-decorated substrate is placed in an organic solution containing a monomer (pyrrole), the enzymatic polymerization occurs at the droplet/solution interface yielding a polypyrrole shell. Due to the shape of the droplets, the polymeric hemispherical microcontainers that encapsulate the enzyme are produced on the substrate surface.The polymeric structures were investigated with several microscopy techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), conducting AFM and near-field scanning optical microscopy (NSOM). The chemical nature of the microcontainers was studied with infrared spectroscopy and cyclic voltammetry. The activity of the encapsulated laccase was probed spectrophotometrically. It was shown that the enzyme retains relatively high level of activity after encapsulation.
Keywords: Encapsulation; Microcontainers; Conducting polymers; Enzymatic polymerization; Micro- and nanostructures
Polymer-induced generation and characterization of electrophoretic properties of hollow TiO X nanospheres for electronic paper
by Tingfeng Tan; Shirong Wang; Shuguang Bian; Xianggao Li (pp. 1739-1743).
Hollow TiO X nanospheres have been successfully prepared using hollow core–double shell latex particles (poly(styrene-co-methyl methacrylate-co-butyl acrylate-co-methacrylic acid) (abbreviated in poly(St-co-MMA-co-BA-co-MAA)) as template, which involves the deposition of inorganic coating on the surface of hollow core–shell latex particles and subsequent removal of the latex by calcinations in air or ammonia gas. Ti(OBu)4 was used as precursor for the preparation of hollow TiO X nanospheres. TEM of white hollow core–double shell polymers particles with an aperture of approximately 225nm displays the perfect characteristic hollow nanospheres structure of primary core–double shell particles. The formation of TiO X was confirmed by XRD analysis and hollow structure of the particles was revealed by transmission electron microscopy (TEM). When the calcined temperature was at 800°C, hollow TiO2 nanospheres were arranged regularly with the diameter range of 130–170nm. The electrophoretic properties were characterized by JS94J micro-electrophoresis apparatus. The electrophoretic mobility of white TiO2 and black TiO hollow spheres in tetrachloroethylene were 1.09×10−5 and 3.12×10−5cm2/Vs, and the zeta potentials were 7.10 and 20.24mV, respectively. The results show that white TiO2 particles and black TiO hollow nanoparticles are suitable as electrophoretic particles and possess the application potential in the future electrophoretic display.
Keywords: TiO; X; nanospheres; Core–double shell polymer; Chemical synthesis; Electrophoretic property
Self-assembly of polystyrene sphere colloidal crystals by in situ solvent evaporation method
by Yanan Fu; Zhengguo Jin; Guoqi Liu; Yuxin Yin (pp. 1744-1750).
The three-dimensional (3D) ordered colloidal crystals were fabricated on the surface of polystyrene (PS) emulsion through an in situ solvent evaporation, which was controlled by altering both emulsion temperature and environmental pressure. The evaporation rate serves as an important role in intensifying the sphere transfer through solution flux and the capillary force between spheres for assembly, as well as supporting a stable close packing of colloidal crystals. The self-assembly process behaves a multi-nucleus site evolution, and the plane packing undergoes a transformation from square to hexagonal arrangement. The colloidal crystal array achieves an ordered close packing with multi-layer structure at evaporation temperature of 50°C at normal pressure or proper pressure range of 160–500mmHg at room temperature. The in situ solvent evaporation by decreasing the environmental pressure at room temperature could reduce disturbing effect of Brownian diffusion for an ordered PS colloidal crystal arrangement. The relationship between layer thickness and in situ evaporation time is a linear trend in time range of 20–75min.
Keywords: Colloidal crystals; Polystyrene spheres; Self-assembly; In situ evaporation
Ultrafast real-time vibronic coupling dynamics of a breather soliton in trans-polyacetylene with a few-optical-cycle-pulse laser
by Takayoshi Kobayashi; Takahiro Teramoto; Valerii M. Kobryanskii; Takashi Taneichi (pp. 1751-1756).
The dynamics preceding the spatial separation of a charged soliton pair after photoexcitation in trans-polyacetylene was successfully investigated by using ultrafast spectroscopy with a 6.2fs pulse laser. It was directly verified that after photoexcitation, the electron–hole pair relaxes with a breather mode (i.e. multi-quanta vibronic states), as theory predicts, with an electron–hole pair lifetime of 33–50fs. By applying spectrogram analysis to the time trace of the absorbance change, the ultrafast amplitude and frequency modulations of CC and CC stretching modes, induced by breathers and lasting no longer than 100fs, can be observed simultaneously for the first time. The frequency shifts of both modes were in good agreement with a simulation based on the Su–Schrieffer–Heeger model. It was found that the intensities of transition dipoles changed due to breathers, whereas transition energies were dominantly modulated by CC stretching modes as recent theoretical work predicted.
Keywords: Ultrafast spectroscopy; Coherent vibration; Nuclear wave packets; Polymers
Synthesis and properties of high performance nanostructured polyaniline: Effect of initiator dosage and molecular oxygen
by Chan Woo Lee; Ki-Whan Chi; Ho Yun Hwang; Han Mo Jeong (pp. 1757-1760).
The effects of ammonium persulfate (APS)/aniline feed molar ratio or O2 bubbling on the polymerization of polyaniline (PANI) in self-stabilized dispersion polymerization (SSDP) were examined. As the APS/aniline feed molar ratio was increased from 0.25/1.00 to 1.50/2.00, the polymerization yield was enhanced from 20% to 80%. However the molecular weight reduction with increased feed ratio, that is normally observed when PANI was polymerized in aqueous medium, was little. The O2 bubbling during polymerization made the nanostructure of PANI to be finer, and this improved the solubility of PANI in solvent. The FT-IR spectra showed that the PANI prepared by SSDP, which have high conductivity in the range of 600–800S/cm, contained less amount of the structures by ortho-coupling or Michael reductive addition of aniline compared to that synthesized by the standard method in an aqueous medium.
Keywords: Polyaniline; Synthesis; Ammonium persulfate; Oxygen; Yield; Molecular weight
Structural investigation of lignosulfonate doped polyaniline
by L. Shao; J.H. Qiu; H.X. Feng; M.Z. Liu; G.H. Zhang; J.B. An; C.M. Gao; H.L. Liu (pp. 1761-1766).
Lignosulfonate doped polyaniline (LGS-PANI) was prepared in the presence of sulfamic acid as a novel conducting filler. The room temperature conductivity of LGS-PANI increases more than two-fold with LGS at a mass fraction of 11.4wt% and these conductivities (0.73–5.00S/cm) exceed the highest reported for polymer acid-doped PANI systems. The conductivity stability and thermal stability are clearly improved at a certain content of LGS in LGS-PANI. These trends are accompanied by significant structural changes as evidenced by X-ray diffraction studies. The material characterization was also carried out by Fourier transform IR spectroscopy, thermogravimetric analysis and scanning electron microscopy.
Keywords: Polyaniline; Lignosulfonate; Template; Conductivity; Stability
Photophysical and charge-transport properties of hole-blocking material-TAZ: A theoretical study
by Hongze Gao; Houyu Zhang; Rigen Mo; Shiling Sun; Zhong-Min Su; Yue Wang (pp. 1767-1771).
The hole/exciton blocking material (3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole) (TAZ) plays a crucial role in the light emitting diode devices by increasing the possibility of charge recombination. Its photophysical and charge transport properties have been investigated by means of quantum chemical approach. The ground state and ionic structures ofTAZ were optimized by density functional theory (DFT) calculation, while the excited-state structure was obtained with configuration interaction singlet (CIS) method. The molecular composition analysis of frontier molecular orbitals, reorganization energy and density of states (DOS) indicate thatTAZ is in favor of electron transport in its neutral and negative charged states rather than positive charged state.
Keywords: TAZ; Density of state (DOS); Reorganization energy; Hole-blocking material
A phenalenyl-based neutral stable π-conjugated polyradical
by Weibo Yan; Xiangjian Wan; Yanfei Xu; Xin Lv; Yongsheng Chen (pp. 1772-1777).
The first neutral π-conjugated polyradical based on phenalenyl with the spin unit inside the main chain was prepared. Cyclic voltammetry studies showed that this polyradical had excellent redox reversibility and enhanced π-delocalization between the neighboring spin units, in consistent with the UV–vis results. Initial magnetic studies showed that a strong antiferromagnetic interaction existed at solid state. The conductivity of the polyradical was measured with a value σRT≈10−8S/cm.
Keywords: Phenalenyl; Polyradical; Conducting polymers; Electrochemistry; Disorder
Color stable and interlayer free hybrid white organic light-emitting diodes using an area divided pixel structure
by Kyoung Soo Yook; Soon Ok Jeon; Chul Woong Joo; Jun Yeob Lee (pp. 1778-1781).
Color stable and interlayer free hybrid white organic light-emitting diodes were fabricated by using an area divided pixel structure. The area divided pixel structure was realized by stacking red and blue emitting layers using a fine metal mask. A phosphorescent red emitting layer was patterned by a metal mask and a blue fluorescent emitting layer was commonly deposited on the patterned red emitting layer. The blue fluorescent emitting layer could play a role of a hole-blocking layer and a white emission could be obtained due to separate emission of red and blue emitting layers. The interlayer free hybrid WOLEDs showed color stability from 100cd/m2 to 10,000cd/m2.
Keywords: Interlayer free white organic light-emitting diodes; Color stability; Area divided pixel structure
Low driving voltage and efficient orange-red phosphorescent organic light-emitting devices based on a benzotriazole iridium complex
by Zhen-Yuan Xia; Xiao Xiao; Jian-Hua Su; Chi-Sheng Chang; Chin H. Chen; Dan-Lin Li; He Tian (pp. 1782-1785).
Efficient orange-red phosphorescent organic light-emitting devices (PHOLED) with various doping concentrations of benzotriazole–iridium complex [(TBT)2Ir(acac)] (bis[4-(2H-benzotriazol-2-yl)-N,N-diphenyl-aniline-N1,C3] iridium acetylacetonate) in 4,4′-N,N′-di(carbazolyl) biphenyl (CBP) host were fabricated. The sterically hindered iridium ligands alleviate self-quenching of the phosphorescence at high doping levels. Under the optimal doping concentration of 20wt.%, the maximum external quantum efficiency (EQE), luminance and power yield reach 9.06%, 15.81cd/A and 13.8lm/W, respectively. Increasing the doping concentration from 5% to 30wt.% significantly decreases the driving voltage. The driving voltage of 30% (TBT)2Ir(acac) doped device is only 3.16V at 1mA/cm2 with power yield of 13.32lm/W.
Keywords: Orange-red phosphorescent OLED; Benzotriazole derivative; Iridium complex
Confinement-induced enhancement of hole mobility in MEH-PPV
by Joseph P. Cannon; Steven D. Bearden; Fauzia M. Khatkhatay; Joseph Cook; Sandra Zivanovic Selmic; Scott A. Gold (pp. 1786-1791).
Template wetting nanofabrication was used to create high-aspect-ratio, nanotubular structures from the semiconducting polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene). Carrier transport in these nanostructures was determined to be space-charge-limited and thermally activated, with low-field mobilities shown to up to three be orders of magnitude higher than those typically reported for thin-films of the same material. Ultraviolet–visible spectroscopy showed a 0.3–0.6eV reduction in the leading-edge absorption energy of polymer nanotubular structures compared to thin-films or solutions. Photovoltaic devices constructed from the nanotubes demonstrated photovoltaic fill factors superior to those measured in similarly constructed thin-film devices. These results are indicative of a confinement-induced ordering present in the nanotubular material.
Keywords: MEH-PPV; Phenylenevinylene; Template nanofabrication; Template wetting; Hole mobility; Space-charge-limited current; Ultraviolet–visible spectroscopy; UV–vis; Nanotube; Photovoltaic
Post-functionalization of poly(3-hexylthiophene) via anodic chlorination
by Shotaro Hayashi; Shinsuke Inagi; Kenta Hosaka; Toshio Fuchigami (pp. 1792-1795).
Selective anodic chlorination of a poly(3-hexylthiophene) was successfully carried out by electrochemical polymer reaction. NMR and EDX analyses revealed the selective and sufficient substitution of chlorine atom at the 4-position of the repeating thiophene ring. GPC measurement of the polymer before and after electrolysis indicated that neither decomposition nor propagation of the polymer occurred even after passage of the excess charge. The optical and electrochemical properties of the obtained chlorinated polymer were investigated in detail.
Keywords: Polythiophene; Electrochemical polymer reaction; Anodic chlorination; Solid-phase synthesis
Synthesis and characterization of new photorefractive polymers with high glass-transition temperatures
by Yang Pan; Xiaozhen Tang (pp. 1796-1799).
This paper reports detailed synthesis and characterization of some new high- Tg photorefractive polymers, polyphosphazene P3–P8. They were obtained via a post-azo coupling reaction. The resulting materials have been characterized by means of1H NMR,31P NMR, FT-IR, UV–vis, GPC and DSC. Chromophore contents up to 14mol% have been realized. The polymers had high glass-transition temperatures and good optical transparency. Measurements reveal that they possess relatively large magnitude of photoinduced birefringence.
Keywords: Azo polymers; Imidazole; NLO; Polyphosphazene
Impact of side-chain length on alternating current mobility of charge carriers in regioregular poly(3-alkylthiophene) films
by Akinori Saeki; Shin-ichi Ohsaki; Yoshiko Koizumi; Shu Seki; Seiichi Tagawa (pp. 1800-1803).
The charge carrier mobility in films of regioregular polythiophenes substituted by n-alkyl side-chains, of butyl, hexyl, octyl, decyl, and dodecyl, was investigated by flash-photolysis time-resolved microwave conductivity (FP-TRMC), and transient photoabsorption spectroscopy excited at 355nm. The charge carrier concentration was estimated from inspecting radical anions of perylenecarboxydiimide (PDI), which also acts as an efficient electron acceptor to improve the yield of photocarrier generation. We discuss the dependence of side-chain length in terms of decay dynamics, quantum yield of charge carrier generation, and alternating current (ca. 9GHz) mobility, which exceeded 0.12cm2/(Vs).
Keywords: Microwave conductivity; Poly(alkylthiophene); Perylenecarboxydiimide; Charge carrier mobility
Synthesis of an acrylic copolymer bearing fluorescent dye pendants and characterization as a luminescence conversion material in fabrication of a luminescence conversion light-emitting diode
by Ji-Young Jin; Young-Mo Kim; Sang-Hee Lee; Youn-Sik Lee (pp. 1804-1808).
A polymerizable arcyl group was incorporated into modified 4- N, N-diphenyl-9-(4- tert-butylphenyl)-1,8-naphthalimide (DBN), and the resulting compound (P-DBN) was copolymerized with methyl methacrylate (MMA) to obtain the corresponding copolymer (PMMA- co-DBN). A DBN/PMMA blend film underwent phase separation upon heating, while PMMA- co-DBN did not exhibit the phase separation problem under the same conditions. However, the fluorescence quantum yield ( Фrel) of P-DBN was much lower (65%) than that of free DBN, and the Фrel of PMMA- co-DBN (36%) was lower still. The luminescent output power of a luminescence conversion light-emitting diode (LUCO LED), fabricated using PMMA- co-DBN, was not detectably changed during 288h of operation at 20mA, due to adequate stability of the copolymer under the experimental conditions.
Keywords: Luminescence conversion material; Fluorescent polymer; Phase separation; 4-; N; ,; N; -Diphenyl-9-(4-; tert; -butylphenyl)-1,8-naphthalimide; Stability
Origin of bistability in polyfluorene-based organic bistable devices
by Chul Woong Joo; Soon Ok Jeon; Kyoung Soo Yook; Jun Yeob Lee (pp. 1809-1811).
This study examined the origin of bistability in polyfluorene (PFO)-based organic bistable memory devices (OBDs) by changing the bulk properties of PFO and metal electrodes. Two different PFOs with and without internal trap sites and two Al and Au electrodes were used. Bistability was induced in all devices when Al was deposited on PFO. On the other hand, bistable switching was observed only in the PFO device with internal trap sites when Au was deposited on PFO. Therefore, both the formation of internal trap sites and an organic–metal interface are essential for bistability in PFO-based OBDs.
Keywords: Bistability; Organic memory device; Interface
Synthesis and nonlinear optical properties of polyurethanes containing nitro-substituted 1,3,4-oxadiazole chromophores
by R.G. Tasaganva; M.Y. Kariduraganavar; S.R. Inamdar (pp. 1812-1819).
NLO active nitro-substituted oxadiazole chromophores were prepared and condensed with tolylene-2,4-diisocyanate (TDI) and 4,4′-methylenedi(phenyl isocyanate) (MDI) to yield a series of polyurethanes. The resulting polyurethanes exhibited an excellent solubility in many common organic solvents, suggesting that these polyurethanes offer good processability. Molecular structural characterization of these polyurethanes was achieved by FT-IR, UV–vis,1H NMR and analytical technique. The weight-average molecular weights of polyurethanes determined by gel permeation chromatography (GPC) were in range of 21,000–23,000 ( Mw/ Mn=1.87–2.00). Thermal behavior of polyurethanes was investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperatures of the polyurethanes were in the range of 155–170°C. The second harmonic generation (SHG) coefficients ( d33) of the poled polyurethanes were in the range of 38.93–48.64pm/V at 532nm. High thermal endurance of poled dipoles was observed for all the polyurethanes. Further, it was found that all the developed polyurethanes were stable up to 140°C, signifying the acceptability for nonlinear optical devices.
Keywords: NLO chromophores; Polyurethanes; Corona poling; Thermal stability; SHG coefficient
Acylation and oxidation of primary amines and alcohols catalyzed by nanoporous polyaniline emeraldine salt
by Chan Woo Lee; Ho Yun Hwang; Han Mo Jeong; Ung Chan Yoon; Ki-Whan Chi (pp. 1820-1823).
We described the convenient and efficient catalytic acylation and oxidation of primary amines and alcohols compounds into amide/ester or aldehyde compounds using nanoporous polyaniline emeraldine salts catalysts. The reaction mechanism of acylation by polyaniline emeraldine salt catalyst is explained by acid catalyzed addition–elimination reaction, whereas oxidation process is proposed to occur through a radical pathway.
Keywords: Polyaniline catalyst; Emeraldine salt; Acylation; Oxidation; Amine; Alcohol
Exploration of the formation mechanisms of polyaniline nanotubes and nanofibers through a template-free method
by Y.F. Huang; C.W. Lin (pp. 1824-1830).
This study reports the polymerization of aniline monomers in different HCl concentrations to investigate the formation mechanisms of one-dimensional polyaniline (PANI) nanostructures. Fourier transform infrared (FT-IR) spectra indicate that the products obtained in different acidic solutions have different molecular structures. In low-acidity conditions (HCl concentration ≤0.1M), aniline monomers form phenazine-like aniline units in the initial reaction stage. As the reaction continues, a structure consisting of a head of phenazine-like aniline units and a tail of para-linked aniline units develops. By contrast, the reaction only produces para-linked aniline units as the concentration of HCl increases to 0.2M. PANI products with different molecular structures exhibit different shapes, including nanotubes and nanofibers. For nanotubes, electron microscopy images reveal the flake-like intermediates formed in the initial reaction stage and then curl into nanotubes as the reaction proceeds. The phenazine-like aniline units serve as the axis for PANI nanotube curling. On the other hand, the para-linked aniline units act as a template for the formation of PANI nanofibers. This study demonstrates the formation mechanisms of PANI nanotubes and nanofibers. The acid concentration in the polymerization solution is the critical factor determining whether the aniline monomers form nanotubes or nanofibers.
Keywords: Conducting polymer; Polyaniline; Nanotubes; Self-curling; Nanofibers
Electrical d.c. conduction mechanism in some newly synthesized mono- and dipyridine quaternary salts in thin films
by L. Leontie; I. Druta; B. Furdui; V. Nica; G.I. Rusu (pp. 1831-1836).
The study of temperature dependence of the electrical conductivity and thermoelectric power, for some recently synthesized quaternary salts of bipyridine and indolisine pyridine, is reported. Thin film samples ( d=0.10–0.60μm) deposited from dimethylformamide solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range 290–500K.The studied organic salts behave as typical p-type semiconductors. The activation energy of electrical conduction laid in the range 1.40–1.75eV, while the ratio of charge carrier mobilities ranged between 0.77 and 0.93.The correlations between determined semiconducting parameters and specific molecular structure of the compounds have been discussed.In the higher temperature range (360–500K), the electronic transport in examined compounds can be interpreted in terms of band gap representation model, while for lower temperatures, Mott's variable-range hopping conduction model may be conveniently used.
Keywords: Organic semiconductors; Thin films; AFM; Electrical conductivity; Seebeck coefficient
Effect of synthesis conditions on the properties of wet spun polypyrrole fibres
by Javad Foroughi; Geoffrey M. Spinks; Gordon G. Wallace (pp. 1837-1843).
High molecular weight doped polypyrrole (PPy) has been synthesized by the incorporation of the di(2-ethylhexyl) sulfosuccinate dopant anion which renders the polymer soluble in various organic solvents. The intrinsic viscosity of PPy solutions show that the molecular weight of PPy is very sensitive to the polymerization temperature. A significant increase in molecular weight was achieved by reducing the polymerization temperature from 0 to −15°C. The resultant solutions were amenable to a wet-spinning process that produced continuous, doped polypyrrole fibres. The ultimate tensile strength, elastic modulus and elongation at break of the higher molecular weight fibres were 136MPa, 4.2GPa and 5%, respectively. These values were 500%, 250% and 280% higher than obtained from the lower molecular weight fibers. X-ray diffraction showed that the low temperature PPy powder exhibited a similar degree of ordering to the standard PPy powder. UV and FT-IR spectroscopy showed that the conjugation length of PPy could be increased significantly depending on the polymerization conditions. Cyclic voltammetry demonstrated the electroactivity of the polypyrrole fibres. These fibres are likely to be important for bionic, electronic textile, artificial muscles, battery and sensor applications.
Keywords: Polypyrrole; Fibre; Wet spinning; Conducting polymer; Electronic textile
Nanostructured poly(aniline- co-2,4-diaminophenol) synthesized via chemical copolymerization and the properties of the resulting copolymer
by Ya Zhang; Shaolin Mu; Jianping Zhai (pp. 1844-1851).
A conducting copolymer poly(aniline- co-2,4-diaminophenol) (PADAP) with two kinds of functional groups was first synthesized via the chemical copolymerization of aniline and 2,4-diaminophenol (DAP) in the acidic medium. The fast copolymerization rate resulted in the formation of PADAP copolymer nanostructures in the absence of templates. The spectra of FTIR and1H NMR demonstrate that there is DAP unit in the polymer chain. The Δ Hpp of the ESR signal and unpaired spin density of PADAP are very sensitive to the copolymer composition that is a function of monomer concentration ratio in the mixture. The properties of PADAP are affected by several polymerization factors, but the most important one among them is the monomer concentration ratio in the mixture used for the copolymerization. PADAP synthesized under the optimal copolymerization conditions has good redox activity from highly acidic solution to pH 12.0 in a wider potential range and has a conductivity very close to that of polyaniline. However, the pH dependence of the conductivity of PADAP is improved compared to that of polyaniline. The fast copolymerization rate and novel electrical properties of the copolymer are attributed to the synergistic effect of –NH2 and –OH functional groups in the copolymer chain.
Keywords: Chemical copolymerization; Aniline and 2,4-diaminophenol; Nanostructured copolymer; Electric activity; Spectra
Dendronized organic–inorganic nonlinear optical hybrid materials with homogeneous morphology
by Yung-Chung Chen; Yu-Jen Yang; Tzong-Yuan Juang; Li-Hsin Chan; Shenghong A. Dai; Franklin M.C. Chen; Wen-Chiung Su; Ru-Jong Jeng (pp. 1852-1858).
To obtain excellent thermal stability, a series of dendronized organic–inorganic hybrids were synthesized and characterized. Dendronized alkoxysilane dyes were prepared via the ring opening addition reaction of azetidine-2,4-dione of chromophore-containing dendrons, with 3-aminopropyltriethoxysilane. Subsequently, the precursor, dendronized alkoxysilane dyes could be hydrolyzed and copolymerized with phenyltriethoxysilane (PTEOS) with the weight ratios of 1:1, 1:3, 1:5 and 1:7 in the presence of water and formic acid. After curing and poling process, organic–inorganic hybrid thin films with homogeneous morphology were obtained. Electro-optical (EO) coefficients ( r33) of 2.9–13.0pm/V were achieved. Due to the site-isolation effect, the sample with high generation dendrons possessed a higher EO coefficient/dye content ratio. In addition, because of the improved miscibility between organic and inorganic segments due to highly branched hydrogen bonding-rich dendrons, NLO polymers with waveguide properties ranging from 3.2 to 4.2dB/cm at 1310nm were obtained. These dendronized organic–inorganic NLO hybrids also show greatly enhanced temporal stability at 100°C.
Keywords: Dendronized alkoxysilane dyes; Homogeneous; Nonlinear optical (NLO); Organic–inorganic materials; Temporal stability
Fabrication of enzyme electrodes with a polythiophene derivative and application of them to a glucose fuel cell
by Takashi Kuwahara; Toshimasa Homma; Mizuki Kondo; Masato Shimomura (pp. 1859-1864).
Two kinds of enzyme electrodes were fabricated by covalent immobilization of glucose oxidase (GOx) and bilirubin oxidase (BOx) on the films of a thiophene derivative having carboxyl groups as binding sites on their surfaces. The electrode bearing GOx (GOx/Copolymer electrode) and that bearing BOx (BOx/Copolymer electrode) were applied to a glucose fuel cell as an anode and a cathode, respectively. The open circuit voltage of 0.61V was achieved by use of the BOx/Copolymer as the cathode, whereas the voltage became 0.41V when a Pt black (PtB) electrode was used instead. The short circuit currents of 0.54 and 0.84mAcm−2 were obtained by use of the BOx/Copolymer and PtB cathodes, respectively. The biofuel cell equipped with the GOx/Copolymer anode and the BOx/Copolymer cathode gave the maximum power density of 0.15mWcm−2 at the cell voltage of 0.35V, which was twice as large as that generated with the PtB cathode.
Keywords: Conducting polymer; Polythiophene derivative; Glucose oxidase; Bilirubin oxidase; Biofuel cell
Uniform TiO2–PANI composite capsules and hollow spheres
by Xiaocong Wang; Saide Tang; Chen Zhou; Jing Liu; Wei Feng (pp. 1865-1869).
Here we demonstrated a simple and reliable method to prepare single or multiple core/shell structured capsules and then demonstrate how to produce single or multiple-layer hollow spheres. Those capsules or hollow spheres could be made of organic and/or inorganic functional materials depending on the experimental design. Core–shell composite capsules consisting of TiO2–polyaniline (PANI) shell and polystyrene (PS) core were prepared by using core–shell structured sulfonated-PS spheres as templates. Aniline was polymerized in the shell of sulfonated-PS spheres. Since the PANI was in situ doped by sulfonic acid, the as-synthesized composite capsules had good conductivity. After PS cores were dissolved in solvent, hollow TiO2–PANI spheres formed, which could be further calcined to produce mesoporous hollow TiO2 spheres. The cavity size of the hollow spheres was uniform, at approximately 170nm in diameter and with a shell thickness of 30nm. The cavity size and the shell thickness can be synchronously controlled by adjusting the sulfonation reaction time of PS spheres. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray powder scattering were employed to characterize these as-prepared spheres.
Keywords: Core–shell structure; Nano-composites; Hollow spheres; Polyaniline; Titania
Synthesis and electro-optical properties of carbazole derivatives for organic device applications
by Ki-Soo Kim; Seonju Jeong; Cham Kim; Jae-Yong Ham; Younghwan Kwon; Byoung-Dae Choi; Yoon Soo Han (pp. 1870-1875).
Two materials, DNCz and TCzPB, which contain carbazole moieties and exhibit high band gap energies, were synthesized via CN coupling and Suzuki coupling reactions, respectively. The ionization potential and electron affinity of the synthesized TCzPB were measured at 5.89 and 2.39eV, respectively, implying that it is suitable for a host material. A doped multilayer device, ITO/DNTPD/NPD/TCzPB+Ir(ppy)3/BCP/Alq3/LiF/Al, exhibited a bright green emission with a maximum luminance of 27,200cd/m2 (17.6cd/A at 18.0V) when the synthesized TCzPB was used as the host material for a phosphorescent green dopant. The compound DNCz exhibited similar electronic energy levels to those of NPD, and was applied as a hole-transporting material. Bright green light originated from the Alq3 layer was observed in the double layer device, ITO/DNCz/Alq3/LiF/Al. The high hole-transporting property of DNCz was also demonstrated.
Keywords: Carbazole; Electroluminescence; Host material; Hole-transporting material
White polymer phosphorescent light-emitting devices with a new yellow-emitting iridium complex doped into polyfluorene
by Bo Liang; Yunhua Xu; Zhao Chen; Junbiao Peng; Yong Cao (pp. 1876-1879).
A new yellow-emitting iridium complex Ir(3-piq)2pt with 3-phenylisoquinoline(3-piq) as cyclometalated ligand by introducing 2-(2 H-1,2,4-triazol-3-yl)pyridine (pt) as ancillary ligand was synthesized. Efficient yellow polymer light-emitting devices (PLEDs) with the new iridium complex Ir(3-piq)2pt in device structure ITO/PEDOT/PVK/Ir-complex ( x%):PFO (or +PBD (30%))/Ba/Al (with or without PBD electron transports additive) were fabricated. The device doped with 4% Ir(3-piq)2pt displayed a quantum efficiency of 9.4% (16.2cd/A) at 5.06mA/cm2 with PBD additive. A white emission was also obtained at a doping concentration of 0.5% Ir(3-piq)2pt with no PBD added. CIE coordinate (0.34 and 0.31) close to National Television Standards Committee (NTSC) white standard, external quantum efficiency of 2.25%, and luminance of 2250cd/m2 at applied voltage of 15V were obtained. The results indicated that introducing triazole group based ancillary ligand into iridium complexes could enhance the electron-transporting ability of the iridium complexes.
Keywords: Iridium complexes; Phosphorescence; White polymer light-emitting devices
Room-temperature interface state analysis of Au/Poly(4-vinyl phenol)/p-Si structure
by Nese Kavasoglu; Cem Tozlu; Osman Pakma; A. Sertap Kavasoglu; Sadan Ozden; Bengul Metin; Ozcan Birgi; Sener Oktik (pp. 1880-1884).
The Poly(4-vinyl phenol) insulator layer was grown by spin coating technique onto p-Si substrate. Diode ideality factor ( n), insulator layer thickness ( δ), space charge region width ( W D), interface state density ( N ss), series resistance ( R s), acceptor concentration ( N A) of the Au/Poly(4-vinyl phenol)/p-Si structure have been extracted from the current–voltage ( I– V), frequency dependent capacitance–voltage ( C– V) and conductance–voltage ( G– V) measurements. It is pointed out that the interface states lead to deviation of the ideality factor value from 1 and frequency dispersion of the C– V characteristics. N ss profiles as a function of (Ess−Ev) obtained using I– V and low frequency C– V measurements are in good agreement. N ss values varying between 1012 and 1013eV−1cm−2 mean that Poly(4-vinyl phenol) is a candidate for insulator layer forming on Si as powerful as SiN4, SnO2, TiO2.
Keywords: Poly(4-vinyl phenol); Ideality factor; Interface states; DC and AC characterization
Electrochromic, magnetotransport and AC transport properties of vapor phase polymerized PEDOT (VPP PEDOT)
by K.G. Padmalekha; Shimelis Admassie (pp. 1885-1889).
Poly(3,4-ethylenedioxy)thiophene (PEDOT) doped with tosylate ion (PEDOT–tosylate or VPP PEDOT) was synthesized by vapor phase polymerization (VPP) technique on glass as well as on glass/ITO and the electrochromic properties were investigated. Compared with that of PEDOT–PSS spin-coated on glass/ITO, the studies showed that VPP PEDOT has a lower work function and better electrochromic properties. The magneto and AC transport properties studies were done on VPP PEDOT coated on glass substrate. The system shows 2-dimensional variable range hopping and wave function shrinkage of charge carriers.
Keywords: VPPPEDOT; Magnetotransport; AC transport; Electrochromic
Fused thiophene-split oligothiophenes with high ionization potentials for OTFTs
by Yanying Zhang; Musubu Ichikawa; Jinya Hattori; Tatsuya Kato; Ayumi Sazaki; Shusuke Kanazawa; Shimpei Kato; ChunHan Zhang; Yoshio Taniguchi (pp. 1890-1895).
Fused thiophene-split oligothiophenes were synthesized by Suzuki coupling. The relationship between the structure of these fused thiophene-split oligothiophenes and DH-6T (α,ω-dihexylsexithiophene) and their performance in OTFTs was discussed. The realignment of HTTfTTTH (2,5-bis-(5′-hexyl-[2,2′]bithiophenyl-5-yl)-thieno[3,2-b] thiophene) molecule on the substrate after annealing was revealed by X-ray diffraction and atomic force microscopy. A similar but novel compound, TTfTTT (2,5-bis-[2,2′]bithiophenyl-5-yl-thieno[3,2-b]thiophene), was also prepared and evaluated as an organic transistor material. Air stabilities of these three compounds in OTFT devices were affected mainly by chemical properties, but also by the ionization potentials ( Ip) of these materials. Among the three compounds, HTTfTTTH had a higher Ip because the thiophene sequence was split by fused thiophene and the best air stability, due to the end-capping of its active α-positions by hexyl substitution.
Keywords: OTFT; Fused thiophene; Oligothiophene; Ionization potential; Air stability
One-Step Synthesis of MnO2 Particles Distributed Polyaniline–Poly(styrene-sulfonic acid)
by Feng-Jiin Liu (pp. 1896-1899).
In this paper, polyaniline–poly(styrene-sulfonic acid)–manganese dioxide (PANI–PSS–MnO2) composite was prepared by an interfacial reaction of potassium permanganate (KMnO4) in PSS/ANI in chloroform. This method synthesizes MnO2 particles incorporated in PANI–PSS by reduction of Mn7+ to Mn2+ and oxidation of Mn2+ to Mn4+ (MnO2) with the simultaneous chemical oxidation polymerization of ANI. The immiscible liquid interface offers a unique microenvironment for confining the growth of PANI to form PANI–MnO2 in the presence of PSS. The PANI–PSS–MnO2 composite was verified through characterization by scanning microelectronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and FTIR spectroscopy. Cyclic voltammetric (CV) results showed that PANI–PSS–MnO2 effectively catalyzed the oxidation of hydrogen peroxide (H2O2). The simple and inexpensive route for the preparation of PANI–PSS–MnO2 composites can be used in the production of sensor electrodes in H2O2 and glucose detection.
Keywords: Polyaniline; Poly(styrene-sulfonic acid); Manganese dioxide; Interfacial polymerization; Hydrogen peroxide oxidation
Thienylmanganese halides for the preparation of regioregular poly(3-hexylthiophene)
by Seung-Hoi Kim; Reuben D. Rieke (pp. 1900-1902).
For the first time, thienylmanganese halides have been used for the synthesis of regioregular head-to-tail poly(3-hexylthiophene). A variety of conditions were examined, and the polymerization was successfully completed in the presence of Ni(dppe)Cl2 at ambient temperature affording the title polymer in high yields with excellent regioregularity.
Keywords: Thienylmanganese halides; Poly(3-hexylthiophene)
Dependence of the corrosion performance of polyaniline films applied on stainless steel on the nature of electropolymerisation solution
by Mouna Mrad; Leila Dhouibi; Ezzedine Triki (pp. 1903-1909).
Polyaniline (PANI) films were deposited under cyclic voltammetric conditions on 304L stainless steel by aniline electropolymerisation from acidic and slightly basic solutions containing respectively the followed support-electrolytes: H2C2O4 and KNO3.It was found that the film produced in oxalic acidic medium was more conductive than that obtained in potassium nitrate one.The PANI coatings corrosion performances in 0.5M NaCl were investigated and compared using standard electrochemical methods, electrochemical impedance spectroscopy (EIS) and SEM analysis.The highest corrosion resisting efficiency was obtained for PANInitrate which exhibited a significant physical barrier property against the attack of corrosive products. However, the corrosion protection of conductive PANIoxalic coating was related to its catalytic behavior.
Keywords: Polyaniline; Electropolymerisation; 304L stainless steel; Corrosion
Influence of metal cathode for organic photovoltaic device performance
by Yong Seok Eo; Hee Woo Rhee; Byung Doo Chin; Jae-Woong Yu (pp. 1910-1913).
Influences of metal electrode on the performance of organic photovoltaic device were studied. An appropriate energy level was set between HOMO of donor material and LUMO of acceptor material used to fabricate device and metals with workfunction above, below and within this appropriate range were selectively chosen to form electron collecting electrode. Metals which can form an Ohmic contact showed enhanced power conversion efficiency, while metals forming a Schottky type contact showed poor power conversion efficiency. Series resistances showed characteristic values for each range. Open circuit voltages were in the same order with power conversion efficiency, showing a dependence on injection barrier at negative electrode contact. The power conversion efficiency of low workfunction metal electrode (i.e. calcium electrode device) was higher than that of gold electrode where the electron extraction is spontaneous process.
Keywords: Organic photovoltaic; Metal electrode; Charge extraction; Series resistance; Open circuit voltage