Synthetic Metals (v.150, #1)

A new biocatalyst route for the synthesis of a conducting polyaniline (PANI)/sulfonated polystyrene (SPS) complex is presented. Hemoglobin (Hb) is used to polymerize aniline in the presence of a polyanionic template SPS. The synthesis is simple, and the conditions are mild in that the polymerization may be carried out in lower pH (1.0–4.0) buffered aqueous solution, with a stoichiometric amount of hydrogen peroxide and a catalytic amount of Hb. UV–Vis absorption, FT-IR, elemental analysis, and conductivity measurements, cyclic voltammetry (CV), thermogravimetric analysis (TGA), fluorescence spectra and XRD studies all confirm that the electroactive form of PANI, similar to that which is traditionally chemically synthesized, is formed and complexed to the SPS. Cyclic voltammetry studies show three sets of redox peaks over the potential range of −0.2 to 1.0 V, and the formation of peak does not change at a series of scanning 20 times, which suggests that the PANI/SPS complex is more stable. The PANI complexes produced at different pH show the different conductivity. This biomimetic approach offers unsurpassed ease of synthesis, processability, stability, and environmental compatibility.
Keywords: Hemoglobin; Biocatalysts; Polyaniline; Conductivity; Polyanionic template; Sulfonated polystyrene;

Time-resolved photoluminescence (PL) of a red emitting dye, tetraphenylchlorin (TPC), doped in poly(methylmethacrylate) (PMMA) at various concentrations was studied to clarify the mechanism of concentration quenching often observed in organic electroluminescence devices. At doping concentrations lower than 10−2  mol/L, PL lifetimes of TPC were relatively constant (∼10 ns) and equal to that of TPC in dilute solution. At doping concentrations higher than 10−2  mol/L, PL lifetime decreased rapidly with increasing concentration, down to 2 ns at 8 × 10−2  mol/L. This decrease in PL lifetime was related to the concentration quenching of TPC monomer emission by the increasing number of TPC dimer sites formed at such higher concentrations. Our experimental results of concentration-dependence trapping agree fairly well with the theoretical model of trapping by dimers reported in literature.
Keywords: Tetraphenylchlorin; Lifetime of photoluminescence; Concentration quenching; Trapping constant; Dimer; Electroluminescence materials;

Sn/polypyrrole (PPy)/n-Si structure has been fabricated and the IV characteristics of the structure have been measured in the temperature range 90–300 K. It is shown that the PPy is a good rectifying contact on the n-Si semiconductor. The analysis of IV characteristics based on the thermionic emission (TE) mechanism has revealed an abnormal decrease of zero-bias barrier height and increase of the ideality factor at lower temperatures. This behavior has been interpreted by the assumption of a Gaussian distribution of barrier heights due to barrier height imhomogeneities that prevail at the interface. Φ b0 versus 1/T plot has been used for the evidence of Gaussian distribution of the barrier height. The values of Φ ¯ b 0  =0.862 eV and σ 0  = 0.0924 V for the mean barrier height and zero-bias standard deviation have been obtained from the plot. Thus, a modified ln(I 0/T 2) −  q 2 σ 0 2 /2k 2 T 2 versus 1/T plot has given Φ ¯ b 0 and A * values as 0.824 eV and 19.17 A/cm2  K2, respectively. It can be concluded that Sn/PPy/n-Si structure has a good rectifying contact and the temperature dependence of IV characteristics of the Schottky barrier on n-Si successfully have been explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.
Keywords: Sn/PPy/n-Si; Semiconductor; Gaussian distribution;

Electrosynthesis and characterisation of polypyrrole doped with [Bi(dmit)2] by Robson Pacheco Pereira; James L. Wardell; Ana Maria Rocco (21-26).
The electrosynthesis and characterisation of polypyrrole doped with [Bi(dmit)2](Ppy/[Bi(dmit)2]) are reported. It was shown by means of IR spectroscopy that the anion [Bi(dmit)2] is incorporated into the polymeric matrix. Thermogravimetric analysis showed that Ppy/[Bi(dmit)2] decomposes at 180 °C, a higher temperature than [NBu4][Bi(dmit)2] or Ppy/DS. Cyclic voltammetry of Ppy/[Bi(dmit)2] exhibited one irreversible process with peak potentials independent of the scan rate. The superficial conductivity is about 10−4  S cm−1 and the material presented a double-layer capacitance of 70.5 μF cm−2, approximately twice that of Ppy/DS.
Keywords: Polypyrrole; Electrosynthesis; Complexes; Dmit;

Synthesis and characterization of new blue light emitting material with tetraphenylsilyl by Jong-Uk Kim; Hyo-Ban Lee; Ji-Soo Shin; Yun-Hi Kim; Yong-Kuk Joe; Hyung-Yun Oh; Chun-Gun Park; Soon-Ki Kwon (27-32).
The new amorphous blue light emitting material, which is composed of biphenylenevinylene with α-phenyl as main unit and bulky triphenylsilyl as side units, is designed, synthesized and characterized. The tetraphenylsilane groups of tetrahedral molecular skelecton makes the material have high glass transition temperature of 130 °C and good film quality. Blue organic light emitting device (OLED) employing this compound as the emitter exhibit the maximum luminescence of 4100 cd/m2, the maximum external quantum efficiency of 0.7% and current efficiency of 1.67 cd/A at 12.8 V.
Keywords: Biphenylenevinylene; Tetraphenylsilane; Blue organic light emitting diode;

Luminescent properties of a novel naphthalimide-fluorene molecule by S. Wang; P.J. Zeng; Y.Q. Liu; G. Yu; X.B. Sun; H.B. Niu; D.B. Zhu (33-38).
A novel naphthalimide-fluorene molecule, 4-(N,N-dimethylamino)-N-(2′-fluorenyl)-1,8-naphthalimide (DFN), has been synthesized and characterized, and its luminescent properties have been studied. DFN has an absorption maximum at 420 nm and possesses solvent polarity dependent changes. The environmental sensitivity exhibited the characteristics of an excited state charge transfer complex. DFN also showed strong luminescence, good electron-affinity, and temperature independence of fluorescence. The application of DFN in organic light-emitting diodes (OLEDs) as an electron-transporting electroluminescent material was investigated. The OLED with a structure of ITO/N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine/DFN/Al shows a yellow-green emission (chromaticity coordinates: x  = 0.424, y  = 0.543) with a brightness of 3563 cd/m2. The external quantum efficiency and the highest luminous efficiency of the device reach 0.2% and 0.55 lm/W, respectively.
Keywords: Organic light-emitting diode; Naphthalimide-fluorene; Electron-transport;

Synthesis of a regular polymer containing pseudo-polyether cages by Atilla Cihaner; Ahmet M. Önal (39-45).
A new compound consisting of 2-thienyl units linked by polyether bridge has been synthesized and its electrochemical polymerization was performed via constant potential electrolysis (CPE) in an electrolytic solution containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) dissolved in CH3CN. Chemical polymerization was carried out using FeCl3 as oxidizing agent. It is found that both methods gave the same polymer product without any cleavage of the polyether bridge between thiophene (Th) rings. Although as synthesized polymers exhibited no conductivity, they gain conductivity via chemical doping using I2 vapor exposure. The polymers were characterized using FT-IR spectroscopic technique and I2 doping was monitored using in-situ electron spin resonance (ESR) spectroscopy. Thermal behavior of electrochemically prepared polymer was investigated using differential scanning calorimetry, DSC and thermogravimetric analysis, TGA.
Keywords: Electrochemical polymerization; Chemical polymerization; ESR; Polymer containing polyether cages;

SEM study of the morphology of high molecular weight polyaniline by Danming Chao; Jingyu Chen; Xiaofeng Lu; Liang Chen; Wanjin Zhang; Yen Wei (47-51).
High molecular weight polyaniline (PANI) was synthesized by adding neutral salt technique with MacDiarmid's method and the morphology of the obtained PANI was examined by the scanning electron microscope (SEM). A remarkable and special phenomenon has been found that the SEM images of resulting PANI show a mass of clews, the average diameter of which is about one micrometer. Furthermore, these honeycombed clews are tenuous, interconnected fibrillar network with characteristic cross-sectional fibril dimensions of a few tens of nanometers. In addition, various preparation parameters which will probably influence the morphology of the high molecular weight PANI in our investigation are: (a) the concentration of lithium chloride ([LiCl]); (b) reaction temperature (t); (c) molar ratio of aniline:oxidant ([An]/[APS]); (d) the concentration of aniline ([An]); (e) the concentration of hydrochloric acid ([HCl]). Some correlations between the sample preparation process and its morphology properties have been obtained.
Keywords: Polyaniline; SEM; Lithium chloride; Morphology; Clews; Network;

THz time domain spectroscopy of doped poly p-phenylene vinylene (MEH-PPV) by Tae-In Jeon; Keun-Ju Kim; A.K. Mukherjee; Reghu Menon (53-56).
An optoelectronic contactless method by THz time domain spectroscopy (THz-TDS, in the frequency range 0.5–3.0 THz) has been used to measure the absorption, dispersion, and reflectance of FeCl3-doped poly(2-methoxy-5-(2′-ethyl)hexyloxy-p-phenylene vinylene) [MEH-PPV] film. The measured data fit well to Lorentz oscillator (LO) model indicating that free carriers are negligible though the system is fairly conducting (∼0.1 S/cm) at room temperature. The large value of the coupling constant (Ω p1/2π  = 14.7 THz) in LO model indicates that intra-chain localization of carriers is rather strong and the inter-chain transport is quite weak.
Keywords: Time-resolved fast spectroscopy; Conductivity; Terahertz;

Four ion-pair compounds that are based on the [Pd(mnt)2] anion were synthesized and structurally characterized. Crystal structure determinations revealed that, in all four cases, the anions and cations stack as segregated columns, and that adjacent [Pd(mnt)2] anions exhibit a strong tendency of dimerization within an anionic column. Values of χ m(T) in 2–350 K indicated that these compounds are nearly diamagnetic. Results of the spin dimer analyses for the magnetic exchange interactions between the nearest-neighbor spins qualitatively illustrated the magnetic behaviors of these compounds.
Keywords: Bis(maleonitriledithiolato)palladium compound; Crystal structure; Magnetic property; Molecular orbital calculation and analysis;

Synthesis and luminescence properties of novel phenyl-substituted poly(p-phenylene vinylene) derivatives by Rupei Tang; Xinjun Xu; Caixia Cheng; Gui Yu; Yunqi Liu; Fu Xi (63-71).
Three novel phenyl-substituted poly(p-phenylene vinylene) (PPV) derivatives, BDP-PPV, BDMP-PPV, and BDP-co-BDMP-PPV (1:1), have been successfully synthesized according to the Gilch route. The structures and properties of the monomers and the resulting polymers were characterized by using 1H, 13C NMR, elemental analysis, GPC, TGA, UV–vis absorption spectroscopy, photoluminescence (PL) and electroluminescence (EL) spectroscopy. The EL polymers possess excellent solubility in common solvents, good thermal stability with 5% weight loss temperature of more than 370 °C, and higher photostability. The number-average molecular weight (M n) and polydispersity index (PDI) of the polymers were in the range of (1.52–2.53) × 105 and 1.22–1.36, respectively. Double-layer light-emitting diodes (LEDs) with the configuration of ITO/polymer/Alq3/Al devices revealed that the copolymer, BDP-co-BDMP-PPV (1:1), possessed the highest luminescence properties, which exhibited maximum luminance of up to 3850 cd/m2 at 23.5 V, and maximum luminescence efficiency of up to 2.68 cd/A.
Keywords: Poly(p-phenylene vinylene); Electroluminescence; Light-emitting diodes;

A new poly(p-phenyleneethynylene) type polymer consisting of an electron-accepting 2,1,3-benzothiadiazole unit was prepared by polycondensation between 4,7-di(4-bromophenyl)-2,1,3-benzothiadiazole and 1,4-didodecyloxy-2,5-diethynylbenzene using Pd(PPh3)4 and CuI as the catalyst. The polymer was soluble in chloroform and showed photoluminescence in solutions and in the solid state. The quantum yield was considerably enhanced by the introduction of the two p-phenylene units at 2,1,3-benzothiadiazole unit. The polymer was electrochemically active and had good heat resistance.
Keywords: Poly(p-phenyleneethynylene); 2,1,3-Benzothiadiazole; CT-type polymer; Luminescence;

Phenylazomethine dendrimer complexes as novel hole-transporting materials of organic light-emitting diodes by Jun-Sang Cho; Kensaku Takanashi; Masayoshi Higuchi; Kimihisa Yamamoto (79-82).
The EL (electroluminescence) performances of a double-layer organic light-emitting diodes (OLED) that used metal complexable phenylazomethine dendrimers (PAM-Gn, n  = 1–5) as novel hole-transporting materials and tris-(8-hydroxyquinoline) aluminum (Alq3) as an emitter with electron-transport material, have been demonstrated. The device that used PAM-G3 showed the highest EL performance compared to that of the other generations. Moreover, by using the metal ion (SnCl2) complexed PAM dendrimers as a hole-transporting layer, the luminance and the EL efficiency of the devices were drastically increased over those of the dendrimers. These results suggested a lower energy gap of the hole-transporting layer and/or increased the ohmic conductivity of the layers by metal complexation. In particular, we found that the optimum metal ion equivalent for the highest EL performance was dependent on the dendrimer generation.
Keywords: Dendrimers; Metal complexes; Organic light-emitting diodes; Hole-transporting materials;

Infrared and Raman studies of the phase transition in the organic conductor (TTM-TTP)I3 by Roman Świetlik; Kyuya Yakushi; Kaoru Yamamoto; Tadashi Kawamoto; Takehiko Mori (83-92).
We report the polarized IR reflectance as well as Raman scattering investigations of the organic charge transfer salt (TTM-TTP)I3 as a function of temperature, below and above the metal–insulator phase transition at T  = 160 K. The IR reflectance was measured in the frequency region from 600 to 10,000 cm−1, for the electrical vector of the polarized light parallel and perpendicular to the TTM-TTP stacking axis. For the polarization parallel to stacks the IR spectra are typical for semiconducting charge transfer salts. The electronic part of IR spectra was analysed in terms of a Lorentz model and temperature dependence of the optical transport parameters was determined. For the polarization perpendicular to the stacks we observed two electronic bands at about 5000 and 8000 cm−1. The phase transition at 160 K has nearly no influence on the IR spectrum. The Raman scattering for different excitations (λ  = 514.5, 632.6 and 785 nm) was mainly studied within the region of C=C stretching vibrations. In this frequency range, three Raman lines at 1426, 1453 and 1486 cm−1 attributed to TTM-TTP molecules are observed. Below 160 K a splitting of the band 1486 cm−1 into two peaks at about 1488 and 1498 cm−1 is found. The intensity and temperature behaviour of the split band at 1498 cm−1 is strongly dependent on sample. The observed spectral modifications are related to an asymmetric deformation of TTM-TTP. Taking into account temperature dependence of bands attributed to the C―H stretching and SCH3 bending vibrations, we suggest that the TTM-TTP deformation can exist also above the phase transition temperature. Above 160 K molecules fluctuate between distorted and symmetrical state forming non-stable domains (pre-transitional effects), but below 160 K the molecular distortion and domains are stable. The existence of electronic band at 5000 cm−1 for the polarization perpendicular to TTM-TTP supports this picture.
Keywords: Organic conductor; TTM-TTP charge transfer salt; IR and Raman spectroscopy; Phase transition;

Polyamidoamine dendrimers functionalized with electrochemiluminescent polypyridyl Ru(II) complexes by Do Nam Lee; Jung Kee Kim; Hee Sang Park; Young Moo Jun; Ra Young Hwang; Won-Yong Lee; Byeong Hyo Kim (93-100).
Polyamidoamine (PAMAM) dendrimers that is surface-modified with electrochemiluminescent (ECL) polypyridyl Ru(II) complexes, Dend-4-[Ru(L)2(L′)] (L = bpy, o-phen; L′ = bpy-CO–, mbpy-(CH2)3CO–), were synthesized through complexation of dendritic polypyridyl ligands to Ru(II) complexes to study the effect of both ligand and dendritic network on the ECL. Their electrochemical redox potentials, photoluminescence (PL) and relative ECL intensities were also studied. The ECL emissions produced by the reaction between electro-oxidized Ru3+ species of PAMAM dendrimers and tripropylamine as a coreactant were measured in a static system with potential cycles between 0.8 and 1.3 V or a flow injection analysis with a potential of +1.3 V and compared with that of [Ru(bpy)3](PF6)2. Dend-4-[Ru(bpy)2(mbpy-(CH2)3CO–)](PF6)8 showed two-fold intense ECL intensity, greater than that shown by [Ru(bpy)3](PF6)2 complex. It is observed that both ligand and length of spacer connected to dendrimer affected the ECL intensity.
Keywords: Electrochemiluminescence; Ruthenium(II) complexes; PAMAM dendrimer;

Oxidative electrochemical polymerization of pyrrole at gold, indium doped tin oxide on glass, and stainless steel type 304 was accomplished from neat monomer solution containing only supporting electrolyte (0.05–0.3 M n-tetrabutyl ammonium perchlorate, n-tetrabutyl ammonium hexafluorophosphate, or n-tetrabutyl ammonium tetrafluoroborate) by multiple scan cyclic voltammetry. The results presented demonstrate that thick (>1–14 μm), stable, highly conductive (up to 0.6 S/cm) polypyrrole films can be readily prepared on a wide range of electrode substrates using this simple electrochemical method.
Keywords: Electrochemistry; Conducting polymer; Polypyrrole; Cyclic voltammetry;