Synthetic Metals (v.157, #18-20)

The organic compound Rhodamine-101 (Rh101) film on an n-type GaAs substrate with carrier concentration of 7.3 × 1015  cm−3 has been formed by means of the evaporation process, and thus Al/Rh101/n-GaAs and Cu/Rh101/n-GaAs contacts have been fabricated. Our aim is to realize a modification of Schottky barrier height (SBH) of the devices using a thin non-polymeric organic compound layer. The Al/Rh101/n-GaAs and Cu/Rh101/n-GaAs contacts have behaved like rectifying contact with the SBH values of 0.68 eV and 0.72 eV, and with ideality factor values of 2.61 and 2.60 obtained from their forward bias current–voltage (I–V) characteristics at the room temperature, respectively. It has seen that the SBH values obtained for these devices are significantly different from those obtained for the conventional Al/n-GaAs or Cu/n-GaAs Schottky diodes. Furthermore, it has been demonstrated that the trapped-charge-limited current is the dominant transport mechanism at large forward bias voltage.
Keywords: Organic semiconductor/inorganic semiconductor contacts; Hetero-junction; Schottky contacts; Schottky barrier height; Rectification;

Laccase-catalyzed synthesis of optically active polyaniline by I.S. Vasil’eva; O.V. Morozova; G.P. Shumakovich; S.V. Shleev; I.Yu. Sakharov; A.I. Yaropolov (684-689).
One step, simple and environmentally friendly enzymatic synthesis of optically active polyaniline in the bulk solution and on the surface of glass slides (in situ deposition) was developed. Fungal laccase from Trametes hirsuta was used as the catalyst of the oxidative polymerisation of aniline. The reaction was carried out under aerobic condition in the weak acidic aqueous solution in the presence of the chiral dopant, such as (S)- or (R)-camphorsulfonic acid. The doping/de-doping procedure of optically active polyaniline was reversible. It was shown that a chiral conformation of the polyaniline was quite variable, and the optical activity of the polymer could be changed by the replacement of camphorsulfonic acid enantiomer in the polyaniline structure.
Keywords: Optically active polyaniline; Enzymatic oxidative polymerisation; Laccase; Aniline;

Synthesis, optical and electroluminescent properties of an alternating copolymer of triphenylamine and fumaronitrile by Lijun Huo; Zhan’ao Tan; Xiang Wang; Minfang Han; Yongfang Li (690-695).
A new conjugated alternating copolymer of triphenylamine and fumaronitrile, TPA–FN, was synthesized via Heck coupling reaction and characterized by GPC, UV–vis, 1H NMR and elemental analysis. The polymer film showed two absorption peaks at ca. 370 nm and 500 nm, respectively, and a narrow bandgap of 1.72 eV. The photoluminescence spectrum of TPA–FN film displayed a main peak at ca. 724 nm and a shoulder peak at ca. 808 nm, indicating that the polymer could be a near-infrared luminescent polymer. Cyclic voltammetry measurements revealed a lower LUMO energy level of TPA–FN at −3.85 eV. The lower LUMO level could be ascribed to the introduction of the electron-withdrawing fumaronitrile with two cyano groups attached to trans-vinylene, and it favors the electron injection for the application in the polymer light-emitting diodes (PLEDs). A single-layer PLED based on TPA–FN was fabricated and the device showed the turn-on voltage of 6 V and the maximum luminance of 136 cd/m2 at 11.5 V.
Keywords: Conjugated polymers; Near infra-red electroluminescence; Narrow bandgap polymer; Triphenylamine; Fumaronitrile;

Aniline-based bis(enamines) as new amorphous molecular charge transport materials by E. Puodziukynaite; E. Burbulis; J.V. Grazulevicius; V. Jankauskas; A. Undzenas; V. Linonis (696-701).
A series of new aniline-based bis(enamines) has been synthesized. The full characterization of their structure is presented. The thermal, optical and photoelectrical properties of the newly synthesized enamines are discussed. The reported compounds constitute materials with high thermal stability with 5% weight loss temperatures exceeding 390 °C as characterised by thermogravimetric analysis. They form glasses with the glass transition temperatures ranging from 135 to 154 °C as established by differential scanning calorimetry. Photoelectric properties of the materials were examined by electron photoemission and time of flight technique. The electron photoemission spectra of the layers revealed the ionization potentials of 5.12–5.70 eV. Room temperature hole drift mobility of one newly synthesized derivative molecularly doped in bisphenol Z polycarbonate reached 10−5  cm2  V−1  s−1 at high electric fields.
Keywords: Enamine; Molecular glass; Ionization potential; Charge transport;

Conductive potassium feldspar/polyaniline composites prepared by in situ chemical polymerization by Sevil Çetinkaya; Meral Karakışla; Ali Özer; Mehmet Saçak (702-707).
Conductive potassium feldspar/polyaniline (K-feldspar/PAn) composites were prepared by the chemical polymerization of aniline in the presence of K-feldspar particles using potassium dichromate in an acidic aqueous medium. The effects of K-feldspar particle size, aniline concentration and temperature upon the PAn amount in the composite and the electrical surface resistance of the composites were examined. Electrical conductivity was higher in the composites prepared by the smaller K-feldspar particles in which the PAn yield is low. The microhardness values of K-feldspar/PAn composites increased to a certain PAn content and then decreased. The microhardness of the composites containing PAn in the range of 1–6%, which were prepared by K-feldspar having particle size smaller than 0.125–0.250 nm, was higher that of pure K-feldspar and PAn (0.843 kPa). Scanning electron microscopy (SEM) showed that PAn covered the surface of K-feldspar particles with an unsmooth PAn layer. The characterization of composites was also made by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA).
Keywords: Polyaniline; K-feldspar; Composite; Conducting polymer;

Synthesis and study of nonlinear optical properties of oxazolone containing polymers by Vitaliy Smokal; Robert Czaplicki; Beata Derkowska; Oksana Krupka; Aleksey Kolendo; Bouchta Sahraoui (708-712).
The oxazolone derivatives were synthesized and their structures determined by UV- and H NMR-spectroscopies. The polymerization was carried out in DMF with AIBN as initiator. The products of polymerization were characterized by H NMR. The third-order nonlinear optical properties of oxazolone containing compounds have been investigated in solutions using degenerate four wave mixing (DFWM) method at 532 nm.
Keywords: NLO properties; Oxazolones; Methacrylic monomers; Degenerate four wave mixing method;

A novel binuclear aluminum(III) complex with acylpyrazolone derivative as ligands, bis(salicylidene-o-aminophenol)-bis(4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one)-bis-aluminum(III) [Al2(saph)2(PMBP)2] was designed and synthesized. A detailed study was carried out on its thermal stability, photophysical, electrochemical and electroluminescent properties. It was found that the introduction of 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (PMBP) ligands improved the thermal stability remarkably. Organic light-emitting diodes (OLEDs) based on this Al complex as the sole emitter and the host for red dopant were fabricated. Bright green-yellow emission was observed from the device using Al2(saph)2(PMBP)2 as the emitter and the electron transporting layer. Pure red emission peaked at 632 nm was obtained from the Al2(saph)2(PMBP)2 doped with DCJTB [4-(dicyanomethylene)-2-tertbutyl-6(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran] device with a luminance efficiency of 1.51 cd/A at 200 A/m2. No light from Al2(saph)2(PMBP)2 was found, indicating that the matched energy levels provide an efficient red emission system in Al2(saph)2(PMBP)2 device. Those results demonstrated that Al2(saph)2(PMBP)2 might be a promising material for OLEDs.
Keywords: Acylpyrazolone derivative; Aluminum complex; Green-yellow emitter; Red emission; OLEDs;

A new polythiophene derivative with highly sensitive and selective affinitychromism properties by Massimiliano Lanzi; Paolo Costa Bizzarri; Luisa Paganin; Gaia Cesari (719-725).
A new poly(3-alkyl)thiophene bearing a piperidinic moiety in the side chain was synthesized in different ways with satisfactory yields in soluble fractions at high molecular weights. The chromic behaviors of the different polymeric samples were studied by UV–vis spectroscopy in different solvent/non-solvent mixtures and in the presence of some analytes; a strong affinitychromism toward bicarboxylic acids was observed. The good chromic response and its independence from the structural parameters of the polymer indicate the development of a very useful and easily obtainable colorimetric tool for the quick, sensitive and selective detection of diacid molecules in organic solvents.
Keywords: Conjugated polymers; Cooperative effects; Functionalization of polymers; Molecular recognition; Polythiophenes;

Swelling of poly(3-alkylthiophene) films exposed to solvent vapors and humidity: Evaluation of solubility parameters by J. Jaczewska; I. Raptis; A. Budkowski; D. Goustouridis; J. Raczkowska; M. Sanopoulou; E. Pamuła; A. Bernasik; J. Rysz (726-732).
White light interferometry was used to determine the swelling of poly(3-alkylthiophene)s (P3ATs), with different head-to-tail regioregularity, exposed to different volatile compounds (VCs): humidity, cyclohexanone, tetrahydrofuran and chloroform. Film expansion increases always from regioregular R-P3DDT, R-P3HT to regiorandom P3BT, P3DDT. Regular solution approach was used to determine Flory–Huggins interaction parameter between P3ATs and VCs. Solubility parameters δ P  ∼ 16.9 ± 0.8, 15.3 ± 0.4, 13.1 ± 0.3, and 12.5 ± 0.2 MPa1/2 evaluated for P3DDT, P3BT, R-P3HT, and R-P3DDT, respectively, were confirmed by the values extrapolated from surface tension data. Evaluated δ P values should allow an easier strategy for P3AT solution processing aimed at optimized film structure of P3AT polymers and their blends.
Keywords: Interferometry; Swelling; Poly(3-alkylthiophene)s; Regioregularity; Solubility parameter; Solution processing;

The electrochemical properties of conducting polymers are highly dependent on the microstructure. We report a method to produce specific microstructures of polypyrrole through electro-polymerization in the presence of the amphiphile N-{11-(2-hydroxyethyldimethylammonium)undecanoyl}-N,N′-dioctyl-l-glutamate, bromide, which forms supramolecular hydrogels with pyrrole in aqueous solution. These hydrogels were used as templates during polypyrrole electro-polymerization to give microstructures composed of the bundles of bilayer membranes. The highly porous nature of these films resulted in electrochemical properties superior to polypyrrole deposited under the same condition without use of an amphiphilic template. Analysis of the scan rate dependence on cyclic voltammogram reveals that the porous templated films facilitate fast diffusion of dopant ions. The actuation properties were also investigated in aqueous solutions containing sodium p-toluene sulfonate electrolyte. The strains displayed by the template polypyrrole films were twice those synthesized without the use of a template.
Keywords: Polypyrrole; Self-assembly; Electro-polymerization; Actuation properties;

Study on energy transfer in organic multilayer well structure by Jinzhao Huang; Zheng Xu; Suling Zhao; Haina Zhu; Dandan Song (739-742).
Photoexcited energy transfer in organic multilayer well structure devices in which Alq3 is the well layer material is discussed in terms of the different barrier layer materials, the well number, the wavelength of excitation light and the thickness of well layer. The photoluminescence intensity from the Alq3 layer is enhanced and that from the barrier layer is weakened in the devices with the multilayer well structure compared with the conventional double-layer structure as a result of effective Förster energy transfer from the barrier to the well. The photoluminescence characteristics of organic multilayer well structure devices are investigated in detail.
Keywords: Organic multilayer well structure; Energy transfer; Photoluminescence;

New host materials with high triplet energy level for blue-emitting electrophosphorescent device by Joo Hyun Kim; Do Yeung Yoon; Ji Whan Kim; Jang-Joo Kim (743-750).
A series of new 9-phenylcarbazole (Cz-Ph)-based host materials with 1,2,4-trizole (TAZ) were synthesized for blue-emitting electrophosphorescent device. The substitution position of Cz-Ph on TAZ ring did not influence photoluminescence maximum (band gap) but the triplet energy level (T 1). The electron mobility of 3,5-bis-(3-(9-carbazoyl)-phenyl)-4-(4-butyl-phenyl)-4H-[1,2,4]triazole (6) is 10 times higher than the hole mobility. This is due to the electron transporting/hole blocking characteristics of TAZ moiety. The triplet energy level of the new host materials ranges from 2.8 to 3.0 eV which are suitable for blue-emitting electrophosphorescent devices. The time-resolved photoluminescence decay curve of 4% of FIrpic (iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate) doped in the film of compound 6 showed a single exponential decay curve with a lifetime of 1.2 μs. The absolute PL quantum efficiency (η PL) of 6 doped with 4% of FIrpic was (82 ± 2%), which is significantly higher than the case of commonly used CBP (4,4′-bis-(9-carbazoyl)-biphenyl) (44 ± 2%). These results also strongly support that triplet excitons formed in FIrpic was not transferred to 6. For a device based on 6 (ITO/PEDOT:PSS (40 nm)/NPB (15 nm)/6:6% FIrpic (30 nm)/BAlq (35 nm)/LiF (1 nm)/Al (100 nm), the maximum photometric efficiency was 14.2 cd/A at a current density of 1.1 mA/cm2, which is higher than that observed with a device based on CBP (ITO/PEDOT:PSS (40 nm)/NPB (30 nm)/CBP:6% FIrpic (40 nm)/BAlq (30 nm)/LiF (1 nm)/Al (100 nm)).
Keywords: Blue-emitting electrophosphorescent device; Host material; Carbazole; 1,2,4-Triazole; Time-of-flight (TOF);

Preparation of polyaniline–Fe2O3 composite and its anticorrosion performance by S. Sathiyanarayanan; S. Syed Azim; G. Venkatachari (751-757).
Polyaniline–Fe2O3 composites were chemically prepared by oxidative polymerization of aniline in phosphoric acid medium with ammonium persulphate as oxidant. Different ratios of aniline–Fe2O3 were taken to prepare polyaniline–Fe2O3 composites, i.e. 1:2, 1:1, 2:1. The composites were characterized by FTIR, XRD and SEM. Using the prepared composites, primer paints with acrylic binder were prepared and coated on the steel samples. The corrosion protection ability of the coating was found out by EIS method in 3% NaCl solution. It has been found that the coating with composite of 1:1 ratio of aniline:Fe2O3 is found to offer higher protection than the coating with other ratios and plain Fe2O3.
Keywords: Polyaniline; Polyaniline–Fe2O3 composite; EIS; FTIR; Corrosion protection; Steel;

First preparation of optical quality films of nano/micro hollow spheres of polymers of aniline by Everaldo C. Venancio; Pen-Cheng Wang; Osiris Y. Toledo; Alan G. MacDiarmid (758-763).
In the present study, an experimental procedure used to prepare high-quality, transparent, uniform thin film of a new nano/micro material, a new type of polymer of aniline, is described. The method was used to prepare, for the first time, a solid-state thin film of nano/micro material for various types of studies, such as ultraviolet and visible spectroscopy (UV–vis), scanning electron microscopy (SEM) and electrochemistry. The UV–vis spectra showed that the as-prepared solid thin film of the nano/micro material was apparently not protonated when it was formed in an acidic solution of pH 3.0 since no change in the UV–vis spectrum was observed when it was treated with a deprotonating solution of 1.0 mol dm−3 of ammonium hydroxide. To our surprise, it was found that the UV–vis spectrum of a nano/micro material deposited on a glass slide was completely different from its solution UV–vis spectrum when the film was dissolved in NMP (N-methyl-2-pyrrolidinone). The SEM studies showed that the thin film consists of rod-like nanostructures as well as nano/micro spheres. The electrochemical studies showed that the thin film of the nano/micro material deposited on ITO surface presented only one redox process in the potential interval of −0.20 and +0.80 V (versus SCE) in the presence of 1.0 mol dm−3 hydrochloric acid.
Keywords: Polyaniline; Aniline; Thin film; Hollow spheres; Azane;

Weight reduction increased the amount of deposited polypyrrole (PPy) on the polyester (PET) fiber surface, leading to a considerable decrease in electrical resistance and improved heat generation capacity for the PPy coated PET fabrics. Application of dc voltages to an insulated roll of PPy-coated fabric increased the temperature to about 90 °C. This showed the suitability of these fabrics for heating applications. The optimum PPy deposition of about 2.8% was obtained in samples weight reduced by aqueous sodium hydroxide treatment. AFM images revealed a smooth surface morphology of the untreated fiber whereas the treated fiber had a high surface roughness.
Keywords: Weight reduction; PET woven fabric; Polypyrrole coating; Electrical properties; Thermal properties;

Structure, electronic and optical characterization of oligothiophenes terminated with (9H-fluoren-9-ylidene)methyl chromophores by Vladimír Lukeš; Martin Matis; Daniel Végh; Martin Štefko; Pavol Hrdlovič; Viliam Laurinc (770-778).
The synthesis, spectral measurements and theoretical study of oligothiophenes terminated by (9H-fluoren-9-ylidene)methyl chromophores at the one (series A N ) and both (series B N ) ends are presented. The electron absorption and fluorescence spectra of prepared molecules were measured in polymer matrices and chloroform solution. The absorption and fluorescence spectra of the investigated systems are represented by broad band without vibrational structure. Well detectable fluorescence is observed for the compounds of the B N family. The experimentally observed medium large Stokes shifts (less than 5000 cm−1) indicate restricted geometrical changes in molecular chain upon optical excitation. Experimental lifetimes of fluorescence are shorter than 1 ns. Theoretical calculations have been performed at the semiempirical Austin Model 1 (AM1) and density functional theory (DFT) levels of the theory. The planarisation of dihedral angles between the fluorene and thiophene chromophores upon optical excitation theoretically was characterised, as well.
Keywords: Thiophene–fluorene derivatives; Syntheses; Electron absorption spectra; Fluorescence spectra;

Electro-assisted precipitation of electrolytes in poly(3,4-ethylenedioxythiophene) film by Peng Hou; Dongxue Han; Zhijuan Wang; Guifu Yang; Xiaoyu Xu; Li Niu (779-783).
The electrolyte, NaBF4, can be enriched into the matrix of poly(3,4-ethylenedioxythiophene) (PEDOT) film during the p-doping potential cycling between 0.6 and −0.9 V. It has been demonstrated that this enrichment is originated from the mixed ion transfer between doping and dedoping, i.e. BF4 anion migrate into the PEDOT film during the oxidation process, the Na+ cation insert into the film during the reduction process, and then, the electrolyte is accumulated into the film matrix after the multiple CV cycling. The quantitative analysis of energy-dispersive X-ray spectroscopy (EDX) confirmed the enrichment of NaBF4 in the PEDOT film.
Keywords: Mixed ion transfer; Electro-assisted; Conducting polymers;

Polyaniline/nano-Fe3O4 composites were prepared by a novel solids-stabilized emulsion (Pickering emulsion) route for the first time. The products were characterized by SEM, XRD, FTIR spectra and particle size analyzer. Sphere-like morphology and sub-micrometer fibers of polyaniline/nano-Fe3O4 composites were synthesized in a toluene/water emulsion stabilized by Fe3O4 nanoparticles. It was found that the morphology of the resulting PANI/nano-Fe3O4 composites depended not only on the volume ratio of toluene to water (R), but also the amount of Fe3O4 in the reaction system. A possible mechanism for the formation of the different morphologic composites has been proposed. The room-temperature conductivity of PANI/nano-Fe3O4 composites also depended not only on the volume ratio of toluene to water (R), but also the amount of Fe3O4 in the reaction system. In addition, it was found that the magnetization under applied magnetic field for the as prepared the PANI/nano-Fe3O4 composites exhibited a clear hysteretic behavior, and both M S and H C for the PANI/nano-Fe3O4 composites exhibited a decrease with decreasing the nano-Fe3O4 content.
Keywords: Polyaniline; Fe3O4 nanoparticle; Composites; Pickering emulsion;