Synthetic Metals (v.151, #3)

Microcapsules as an electronic ink to fabricate color electrophoretic displays by Chul Am Kim; Meyoung Ju Joung; Seong Deok Ahn; Gi Heon Kim; Seung-Youl Kang; In-Kyu You; Jiyoung Oh; Hey Jin Myoung; Kyu Ha Baek; Kyung Soo Suh (181-185).
An encapsulated color electronic ink prepared by an in situ polymerization utilizing urea/melamine and formaldehyde resin as a wall material is presented. We have investigated the microencapsulation of magenta, yellow, and cyan polymer ball suspensions with white pigment for multi-color electrophoretic display implementation. The charged color pigments have been prepared to have a superior affinity for dielectric fluid by the physical coating of magenta, yellow, and cyan particles with functionalized polymers. TiO2 nanoparticles were modified with poly(methyl methacrylate) copolymer for a microencapsulated electrophoretic display system, in order to reduce the density mismatch between nanoparticles and dielectric medium. The modified pigments were characterized by FTIR spectrometry, scanning electron microscope, and thermogravimetry analysis, respectively.
Keywords: Electronic ink; Pigment particles; Microcapsules; Electrophoretic display;

Synthesis of tetra-silylated tetrathiafulvalene derivatives TTF(SiR2H)4 (R = Me, Ph): Novel assembling ligands for the construction of bimetallic transition metal complexes by Fabrice Guyon; Mathuresh N. Jayaswal; Harmel N. Peindy; Aurélien Hameau; Michael Knorr; Narcis Avarvari (186-190).
The HR2Si-functionalized tetrathiafulvalene (TTF) ligand TTF(SiR2H)4 (R = Me 2a; R = Ph 2b) have been synthesized and the molecular structure of 2a determined. The reactivity of the four Si–H bonds for oxidative addition reactions has been exploited. Thus, the bimetallic platinum–silicon complex [(PPh3)2Pt{(Me2Si)2TTF(SiMe2)2}Pt(PPh3)2] 3 incorporating TTF(SiMe2H)4 as bridging unit has been assembled by oxidative addition across [Pt(PPh3)2(CH2 =CH2)]. Electrochemical investigations by means of cyclic voltammetry reveals, for the complex 3, a strong cathodic shift of the two redox processes of the TTF core compared with those of 2a.
Keywords: Tetrathiafulvalene; Silicon; Platinum; Molecular structure; Electrochemistry;

Spectral investigations of the new isostructural organic metals of the formula β″-(BEDT-TTF)4A[M(C2O4)3]·DMF, where A = NH4 +, K+ and M = CrIII, FeIII, were performed. The polarized reflectance spectra of single crystals of these salts were recorded in the range 600–6500 cm−1. Additionally, the optical absorption spectra of the powdered salts dispersed in KBr pellets, in the range 200–40,000 cm−1 were measured. The spectra are characteristic for organic metals and show small anisotropy as typical for quasi-two-dimensional (2D) materials. A Kramers–Krönig analysis of the reflectance data was performed to obtain the optical conductivity spectra. The frequency dependences of the reflectivity were fitted with the Drude or Drude–Lorentz models and the transport parameters were evaluated.
Keywords: Organic conductors based on BEDT-TTF; Infrared spectroscopy; UV–vis–NIR absorption; Reflection spectroscopy;

New method of driving an OLED with an OTFT by Sang Chul Lim; Seong Hyun Kim; Hye Yong Chu; Jung Hun Lee; Jeong-Ik Lee; Ji Young Oh; Dojin Kim; Taehyoung Zyung (197-201).
We present a new method of driving an organic light-emitting diode (OLED) with an organic thin-film transistor (OTFT). The OTFT and the OLED were fabricated on separate substrates, namely on Si for the OTFT and on glass for the OLED and both devices were laminated with silver paste. After driving a 2 mm × 2 mm OLED with an OTFT devices, we obtained 105 cd/m2 from the green OLED with a drain current of 60 μA, a drain voltage of −50 V and a gate voltage of −40 V. For the white OLED (WOLED), we obtained 260 cd/m2 with a drain current of 108 μA, a drain voltage of −60 V and a gate voltage of −60 V.
Keywords: Organic light-emitting diode; Organic thin-film transistor; Semiconductor; Pentacene;

Electrochemical polymerization, optical and electrical characterizations of polycarbazole on single wall carbon nanotubes by Y. Diamant; J. Chen; H. Han; B. Kamenev; L. Tsybeskov; H. Grebel (202-207).
Electrochemical polymerization of polycarbazole (PCz) on CVD grown, single wall carbon nanotubes (SWCNT), by using two-electrode cell is reported. This process was compared to cyclic voltammetry and three-electrode cell polymerization of PCz on bare conducting glass. The SWCNT were characterized by using Raman spectroscopy. Visible range transmission spectra of the PCz/SWCNT electrode exhibited spectroscopic characteristics similar to those of PCz on conducting glass electrode. On the other hand, differences were detected at the near IR spectral range. IV measurements of the coated SWCNT films exhibited a general ohmic behavior and a substantial increase in the sample conductivity.
Keywords: Polycarbazole; Single wall carbon nanotube; Cyclic voltammetry; Electrochemical polymerization;

Volumetric measurement of hydrogen storage in HCl-treated polyaniline and polypyrrole by Barbara Panella; Lina Kossykh; Ursula Dettlaff-Weglikowska; Michael Hirscher; Giuseppe Zerbi; Siegmar Roth (208-210).
Inspired by very promising results of 6–8 wt.% hydrogen storage in conducting polymers claimed in recent years, we reproduced very carefully these experiments comprising chemical treatment of these materials and hydrogen uptake measurements. However, our results show clearly that no hydrogen storage is measured for HCl-treated polyaniline and polypirrole, neither at room temperature nor at 77 K.
Keywords: Conducting polymers; Polyaniline; Polypyrrole; Hydrogen storage; Volumetric measurement;

Polypyrrole composites for shielding applications by Özlem Yavuz; Manoj K. Ram; Matt Aldissi; Pankaj Poddar; Hariharan Srikanth (211-217).
This article highlights the physical properties of polypyrrole (PPy) coated over MnZn ferrite (MZF), nickel coated over PPy, and PPy coated over Ni-MZF magnetic core particles. The commercial ferrite and Ni-ferrite particles are primarily used, and the PPy-ferrite particles with composite structure are synthesized both via an oxidative polymerization of pyrrole in an aqueous solution, which contains well-dispersed ferrite particles, and electrochemical polymerization technique in acetonitrile (ACN). The materials have been processed in the form of coatings, films, and sheets by blending of conventional polymer such as polyurethane (PU) wherein the composites retain the mechanical properties of the conventional polymers and the electrical conductivity of the conducting polymers. The influence of ferrite content with respect to the electrical and ferromagnetic properties of PPy composites were investigated by electrochemical impedance spectroscopy (EIS) and dc field-cooled, zero-field cooled susceptibilities and MH loop measurements. Their structural characterization is also discussed based on Fourier transform infrared (FTIR) and the X-ray diffraction (XRD) measurements. The shielding effectiveness (SE) properties will be reported in our future studies.
Keywords: Polypyrrole; MnZn ferrite; Composite; Magnetization; Shielding applications;

Light-emitting diodes based on alternating copolymers containing fluorene and oligo(p-phenylenevinylene) by Nam-Ho You; Ji Yeun Lee; Heung Cho Ko; Joo Hyun Kim; Hoosung Lee (218-224).
We synthesized poly[(9,9-di-n-hexylfluorene-2,7-diyl)-alt-co-(2,5-bis(4′-cyanostyryl)benzene-1,4-diyl)] [P(FOPV-CN)] and poly[(9,9-di-n-hexylfluorene-2,7-diyl)-alt-co-(2,5-bis(4′-diphenylaminostyryl)benzene-1,4-diyl)] [P(FOPV-Am)]. These polymers have two axes of longitudinal π-conjugation: one in the direction of the polymer backbone and the other in the direction of the oligo(p-phenylenevinylene) chain. From the spectroscopic study, the emissive color of poly[(9,9-di-n-hexylfluorene-2,7-diyl)-alt-co-(benzene-1,4-diyl)] changed from blue to green by substituting cyanostyryl or diphenylaminostyryl group at the 2,5-positions of the benzene ring. The electronic structures were significantly influenced by the substituents at the ends of oligo(p-phenylenevinylene) moiety. The diphenylamino substituent which has more extended π-conjugation resulted in red-shifted electronic absorption and emission spectra compared to the cyano substituent groups. In the light-emitting diodes (LEDs) based on these two polymers, the turn-on voltage (ca. 9 V) of the device based on P(FOPV-Am) was lower than that of P(FOPV-CN) (ca. 12 V) due to the electron-donating effect of the amino groups. The maximum brightness of the P(FOPV-Am)-based LED was 3100 cd m−2 at 22 V which is much higher than that of the P(FOPV-CN)-based LED (27 cd m−2 at 26 V).
Keywords: Light-emitting polymers; Fluorene; Oligo(p-phenylenevinylene); Green-emitting polymers;

Some physical investigations on Ag2S thin films prepared by sequential thermal evaporation by T. Ben Nasrallah; H. Dlala; M. Amlouk; S. Belgacem; J.C. Bernède (225-230).
Ag2S thin films have been prepared on glass substrates by the sequential thermal evaporation technique. X-ray diffraction analysis shows that the films annealed at Ta = 250 °C in argon atmosphere are well crystallised in the β-Ag2S phase with crystallinity preferentially oriented towards ( 1 ¯ 0 3 ) direction. Microprobe analysis shows that a nearly stoichiometric composition is obtained under such annealing temperature. The optical properties of the films are investigated using spectrophotometric measurements of transmittance T(λ) and reflectance R(λ) in the wavelength range 500–2000 nm. The refractive and absorption indexes, n and k, of Ag2S thin films are calculated from the values of the measured transmittance and reflectance. The study of the absorption coefficient of these films versus incident energy revealed that the value of the band gap energy is of the order of 1.1 eV. For the first time, a photovoltaic effect is reported using Ag2S as absorber.
Keywords: Ag2S thin films; Thermal evaporation; Optical properties; Photovoltaic device;

Crystal structure and magnetic properties of an ionic multi-component complex of fullerene (OMTTF·I3)·C60 by Dmitri V. Konarev; Salavat S. Khasanov; Akihiro Otsuka; Gunzi Saito; Rimma N. Lyubovskaya (231-238).
A new ionic multi-component complex (OMTTF·I3)·C60 comprising neutral C60 molecules and OMTTF• + and I3 ions has been obtained by the diffusion method. The complex has a layered structure with the alternation of closely packed hexagonal C60 layers and the layers composed of OMTTF• + and I3 ions arranged in a chequer-like manner. The polycrystalline complex shows a strongly asymmetric EPR signal consisting of four components in the 4–293 K range attributable to OMTTF• +. Temperature dependent magnetic susceptibility indicates an antiferromagnetic interaction of spins localized on OMTTF• + with an antiferromagnetic hump near 4.5 K. According to the one-dimensional Heisenberg antiferromagnet model the exchange interaction was estimated to be J/k B  = −3.3 K. Two possible pathways contribute to this interaction: through the diamagnetic I3 anions and the direct interaction between adjacent OMTTF• +. The crystal structures of three phases of the OMTTF·I3 salt are also presented.

A theoretical study of the effects produced by N-hydroxyalkyl substitution in pyrrole oligomers by Jordi Casanovas; Liu Yao Cho; Cintia Ocampo; Carlos Alemán (239-245).
This work reports a quantum mechanical investigation of the effects produced by the N-hydroxyalkyl substitution on the molecular and electronic structure of pyrrole-containing oligomers. First, the molecular geometry, torsional potential, ionization potential and π–π* transition energy predicted for N,N′-dihydroxymethyl-2,2′-bipyrrole and N,N′-dihydroxypropyl-2,2′-bipyrrole have been compared with those obtained for 2,2′-bipyrrole and N,N′-dimethyl-2,2′-bipyrrole. After this, the properties of pyrrole and N-hydroxymethylpyrrole-containing oligomers formed by n repeating units, where n ranges from 1 to 5, have been examined. Results are explained as a combined actuation of electron donation effects induced by the hydroxyl groups, repulsive steric interactions generated by the N-substitution and attractive specific interactions associated to the hydroxyl groups.
Keywords: Polypyrrole; Hydroxyalkyl substitution; N-substitution; Bipyrrole; Quantum mechanical calculations;

Conductive polymer particles, poly(sulfonated N-hydroxyethyl aniline, SHEA)–polyaniline–poly(SHEA)–polystyrene (PSHEA–PANI–PSHEA–PSt) multi-core shell composite particles, were synthesized by chemical oxidation polymerization and an effect of poly(SHEA) on the colloidal and thermal stability enhancement was investigated. The PSHEA–PANI–PSHEA–PSt particles showed spherical shape and nearly monodisperse particle size distribution. Elemental analysis, UV–vis spectra, and Raman spectra revealed that polyaniline (PANI) was successfully coated onto the poly(SHEA) modified polystyrene particles. Conductivity of the PSHEA–PANI–PSHEA–PSt particle was higher than that of PANI–PSt particle after annealing at elevated temperature due to the non-volatile properties of poly(SHEA) as a co-dopant compared with inorganic dopants such as HCl. XPS analysis unveiled that the PANI in the PSHEA–PANI–PSHEA–PSt particle was co-doped by sulfonic acid in poly(SHEA), which increased conductive thermal stability of the particles.
Keywords: Emulsion polymerization; Oxidation polymerization; Conductive polymer; Multi-core shell particles; Colloidal stability; Thermal stability;

EPR studies of blends of polyaniline with poly(methyl methacrylate-co-glycidyl methacrylate iminodiacetic acid) by H.K. Liu; C.C. Shih; G.P. Wang; T.R. Wu; K.H. Wu; T.C. Chang (256-260).
A novel conductive blends of polyaniline (PANI) with poly(methyl methacrylate-co-glycidyl methacrylate iminodiacetic acid) (PANI–PMGI) was prepared by in situ dispersion polymerization. The PANI–PMGI blends were characterized by UV–vis, FTIR and electron paramagnetic resonance (EPR) spectra. The structure of the PANI–PMGI blends was similar to emeraldine salt proved by UV–vis and FTIR. The value of ΔH pp, lineshape, g factor, N s and A/B ratio of blends were investigated by EPR. The results of EPR indicated that the intermolecular interaction between PANI and PMGI was dependent on the content of PANI and temperature.
Keywords: PMGI; Polyaniline; Blends; EPR;

New amorphous electron-transporting materials based on Tris-benzimidazoles for all wet-process OLED devices by Masayoshi Nomura; Yuji Shibasaki; Mitsuru Ueda; Kouhei Tugita; Musubu Ichikawa; Yoshio Taniguchi (261-268).
New amorphous electron-transporting materials 1,3,5-tris[1-(phenoxy phenyl)-1H-benzimidazol-2-yl]benzene (6a and 6b) were synthesized by dehydration reaction of corresponding triamides and fully characterized. Compounds 6a and 6b showed high thermal stability (T g  = 108 to 110 °C) and good solubility in common organic solvents, such as acetone, 2-methoxyetanol, tetrahydrofuran, chloroform, and 2-butanone. Pinhole-free transparent films were obtained by spin-casting the 2-butanone solution. 6a and 6b were fabricated as electron-transporting layer by spin-casting on a hole-transporting layer that was deposited by spin-cast beforehand and was insoluble in 2-butanone. Both devices showed no emission, but carrier transporting property was observed (400 mA/cm2). The device showed a blue emission (35 cd/m2) from 9,10-diphenylanthracene (DPA) when 10 wt.% DPA was mixed into the 6b layer.
Keywords: Organic light-emitting diodes; Amorphous electron-transporting materials; Luminescence; Spin-coating; 9,10-Diphenylanthracene; Glasses;

Optical properties of nanosize aggregation of phenylene vinylene oligomers by T.P. Nguyen; S.H. Yang; J. Gomes; M.S. Wong (269-274).
In this paper, we report the experimental results on the optical properties of oligo-phenylene vinylenes (OPVs) formed in nanosize pores of porous silicon substrates. Strong modifications of the photoluminescence properties of nanosize aggregation of OPVs were observed at room temperature, such as a blue shift of the PL spectra, whereas the structure of the oligomers is preserved as proved by Raman scattering experiments. However, the penetration of the oligomers into the nanopores was found to depend on the conformation of the chains, which is, in turn, conditioned by the solvents, used to dissolve the oligomer powder.
Keywords: PPV oligomers; Photoluminescence; Raman scattering; Nanosize;

Electrospun poly(3-hexylthiophene-2,5-diyl) fiber field effect transistor by Rosana González; Nicholas J. Pinto (275-278).
One of the ways to reduce the size and increase component density in circuits is via the fabrication of devices based on semiconductor nanofibers. We report on the fabrication of an electrospun regio-regular poly(3-hexylthiophene-2,5-diyl) fiber field effect transistor (FET). The hole mobility of the device was calculated to be 4 × 10−4  cm2/V-s and the ON/OFF ratio was ∼7. The results are compared to those obtained on a thin film FET. The large surface to volume ratio of the fiber makes it susceptible to doping, however, proper handling in an inert environment and pretreatment of the substrates should enhance device performance. Electrospinning is proposed as an easy one step process to fabricate one-dimensional polymer FET's.
Keywords: Poly(3-hexylthiophene); Transistor; Fiber; Electrospinning;

Synthesis and characterization of a partial-conjugated hyperbranched poly(p-phenylene vinylene) (HPPV) by Haiqiao Wang; Na Song; Hongyu Li; Yongfang Li; Xiaoyu Li (279-284).
A novel partial-conjugated HPPV has been designed and easily synthesized from A2  + B3 monomers, employing distrylbenzene, an oligomer of poly(p-phenylene vinylene) with high fluorescence quantum yield, as one of starting materials. HPPV was characterized by FT-IR, H-NMR, GPC and elemental analysis. Its properties, such as thermal, electrochemical and photoluminescent, etc., have been investigated systematically. HPPV exhibits good solubility and processability, a high glass transition temperature (T g) and high fluorescence quantum yield in chloroform solution (much higher than fully conjugated hyperbranched and linear PPV).
Keywords: Hyperbranched polymer; Synthesis; Photoluminescence; Electroluminecence;

Bis(2,2-diphenylvinyl)spirobifluorene: An efficient and stable blue emitter for electroluminescence applications by Fang-Iy Wu; Ching-Fong Shu; Tsai-Te Wang; Eric Wei-Guang Diau; Chin-Hsiung Chien; Chang-Hao Chuen; Yu-Tai Tao (285-292).
We have synthesized a spirobifluorene-based DPVBi [4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl] analogue, DPVSBF [2,7-bis(2,2-diphenylvinyl)-9,9′-spirobifluorene], in which the bis(2,2-diphenylvinyl) groups are connected through the 2 and 7 positions of the spirobifluorene framework, and have characterized its thermal properties, electronic properties (viz. absorption and photoluminescence), and electrochemical behavior. The presence of the rigid spirobifluorene linkage imparts significant improvement in the material's glass transition temperature and morphological stability, while preserving most of the photophysical and electronic properties of its non-spiro, biphenyl analogue, DPVBi. Organic electroluminescent devices having the structure ITO/NPB/DPVSBF/AlQ/LiF/Al display bright emissions with a λ max at 474 nm (CIE coordinates: 0.16, 0.24) and exhibit maximum luminescence exceeding 40,000 cd/m2. At a driving current density of 100 mA/cm2 (6.4 V), a luminance of 4110 cd/m2 was obtained with external quantum efficiency of 2.54%, luminance efficiency of 4.1 cd/A, and power efficiency of 2.0 lm/W. Moreover, the DPVSBF-based device exhibits a 16-fold enhancement in the operation lifetime relative to that of a similar device based on DPVBi.
Keywords: Spirobifluorene; Glass transition temperature; Blue emission; Lifetime; OLED;

Core–shell nanocomposites of polyaniline and carbon black (PAni/CB) were electrochemically synthesized in acidic aniline and carbon black suspension. SEM and TEM observations reveal that the PAni synthesized in HClO4 media exhibits one-dimensional (1D) growth and results in a porous PAni deposit constructed by coralloid interlinking branches having about 2 μm average diameter. In contrast, the existence of CB suspension produces rod-like PAni/CB core–shell nanocomposites, and decreases the average diameter to nearly 200 nm. XRD and Raman spectroscopy were employed to characterize the as-obtained CB powders, PAni and PAni/CB nanocomposites. Measurement of electric conductivity shows that incorporation on CB particles during electrochemical synthesis increased the obtained conductance.
Keywords: Electrochemical synthesis; Characterization; Core–shell nanocomposite; Polyaniline; Carbon black;