Synthetic Metals (v.159, #1-2)
Editorial Board (iii).
1/f noise in polyaniline/polyurethane (PANI/PU) blends by C. Liang; G. Leroy; J. Gest; L.K.J. Vandamme; J.-L. Wojkiewicz (1-6).
We have investigated the electrical conductivity and the low-frequency noise of spin coated polyaniline/polyurethane (PANI/PU) films on different substrates (free, on ceramic, PVC and Teflon) and different compositions. The layer thickness is between 12 and 220 μm. The range in conductivity at room temperature is from 102 to 104 S/m and the sheet resistance is between 4 and 50 Ω. The fluctuations in the conductivity have a 1/f spectrum. The 1/f noise normalized for bias, frequency and unit area, C us is proportional with the sheet resistance, R sh .Our proposed model explains the proportionality C us ∝ R sh and the high value of the proportionality factor between C us and R sh . The typical elongated shape of the PANI component with a relative low number of noisy contacts between touching conducting elongated chains explains the strong noise in such materials.
Keywords: 1/f noise; Conducting polymer; Conductivity; Sheet resistance; Contact;
Electrochemical performance of RuO x /activated carbon black composite for supercapacitors by X.J. He; Y.J. Geng; S. Oke; K. Higashi; M. Yamamoto; H. Takikawa (7-12).
Hydrous ruthenium oxide/activated carbon black (RuO x /ACB) composite was synthesized for the first time for supercapacitors by a chemical impregnation method. The RuO x /ACB composite is characterized by thermogravimetric analysis (TGA), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The results of TGA and TEM characterization showed that the reaction temperature of composite moved to lower temperature due to the catalytic effect of RuO x . XRD characterization of RuO x /AC illustrated that amorphous hydrous RuO x structure maintained in the composite heated at 150 °C. The equivalent series resistance (ESR) of the composite almost increased with the increase of RuO x content in the composite. The specific capacitance (C sp) of the composite increased with increasing RuO x content in the composite while the C sp of RuO x decreased from 1255.8 to 533.7 F g−1. The above results showed that the utilization of RuO x decreased with higher loading RuO x on ACB.
Keywords: Activated carbon black; Ruthenium oxide; Composite; Specific capacitance; Supercapacitor;
Synthesis, characterization, mesomorphic and electrical properties of tetrakis(alkylthio)-substituted lutetium(III) bisphthalocyanines by Devrim Atilla; Necmettin Kilinç; Fatma Yuksel; Ayşe Gül Gürek; Zafer Ziya Öztürk; Vefa Ahsen (13-21).
The synthesis of new lutetium(III) bisphthalocyanines substituted with alkylthio groups (1–5) is described. These compounds (Pc2Lu) are soluble in most common organic solvents and have been fully characterized (elemental analysis, FT-IR, UV–Vis spectroscopy, mass spectrometry). The thermal stabilities of the Pc compounds were determined by thermogravimetric analysis (TGA). The mesogenic properties of these new materials forming columnar-hexagonal (Colh) mesophases were studied by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The compounds 2–5 exhibit a double clearing point. DC electrical properties of these compounds in different phases were determined by measuring I–V characteristics and dark current of their thin films on interdigital electrodes. The measurements were carried out in ambient air, in vacuum and in high purity nitrogen (N2) flow in the temperature range between 300 and 420 K. Dark current measurements obtained in the crystal, liquid crystal (LC) and isotropic liquid phases were in agreement with the phase transitions of these compounds obtained by DSC and optical microscopy results. The relation between the phase transition and conductivity of the Pc2Lu derivatives were investigated. Also, the influence of the nature of the substituted group (alkylthia and alkoxy) upon the DC electrical properties of the Pc2Lu derivatives was investigated. The DC conductivities and the thermal activation energies depending on alkyl chain lengths of these compounds were found to be in the range of 10−8 to 10−5 S/cm and 0.12–0.38 eV in solid phase.
Keywords: Lutetium phthalocyanine; Lanthanide; Thin films; Dark current conductivity; Liquid crystal;
Partial metal coated light emitting polymers: Direct observation of enhanced photoluminescence by Dong Hyuk Park; Yong Baek Lee; Hyun Seung Kim; Dae-Chul Kim; Jeongyong Kim; Jinsoo Joo (22-25).
The enhanced photoluminescence (PL) for the partially nickel (Ni) metal coated light emitting poly(3-methylthiophene) (P3MT) or polythiophene (PTh) hybrid nanotubes was observed and analyzed. From the laser confocal microscope PL experiments of an isolated single strand of the hybrid nanotubes, we directly observed a ∼40 times and ∼16 times enhancement of the PL peak intensity for the parts of the P3MT or PTh nanotubes that were coated with the Ni metal, compared with the PL peak intensity for the parts of the P3MT or PTh nanotubes without the Ni metal coating. These were confirmed from the laser confocal microscope PL spectra of the hybrid nanotubes. The surface plasmon resonance coupling between the light emitting P3MT or PTh nanotubes and the Ni metal nanotubes contributed to the enhancement of the PL efficiency of the hybrid nanotubes.
Keywords: Hybrid nanotube; Polymer; Laser confocal microscope; Photoluminescence; Surface plasmon;
Effective dehydrogenative oxidation of amines and alcohols via radical mechanism by nano-porous polyaniline catalysis by Ki-Whan Chi; Ho Yun Hwang; Joo Yeon Park; Chan Woo Lee (26-28).
It has been known that doped polyaniline emeraldine salt (PANI-ES) synthesized by self-stabilized dispersion polymerization (SSDP) method has a nano-porous structure. This nano-porous conjugate polymer with a high surface area is effectively used for the dehydrogenative oxidation reaction of benzylamine and benzylalcohol with or without oxygen. The catalytic activity can be controlled by the various oxidation states of PANI. After oxidation, the resulting structure of PANI-ES is transformed into a pernigraniline base (PB). This result suggests the involvement of radical mechanism by the reversible redox properties of conjugated polyaniline.
Keywords: SET; Solid-supported polyaniline; Dehydrogenative oxidation;
A new π-conjugated star-shaped polymer comprising of full fluorene units: An efficient blue emitter without reduction of color purity undergoing an annealing by Shijie Ren; Jiangong Cheng; Danli Zeng; Wenqing Zhu; Jing Sun; Junping Du; Erjian Xu; Hongliang Zhong; Yingchun Liu; Qiang Fang (29-35).
A new star-shaped polymer comprising of full fluorene units was synthesized by Suzuki polycondensation between an A3 type monomer and an AB type monomer. For comparison, a fluorene-based linear polymer was also prepared. The star-shaped polymer was soluble in common organic solvents and gave the number-average molecular weight, Mn, of more than 12,000 and the weight-average molecular weight, Mw, of exceeded 22,000. The polymer showed similar optical behavior both in solution and in the solid state. After an annealing process, the linear fluorene-based polymer showed an additional bathochromic emission at about 550 nm, whereas such red-shifted emission was fully eliminated for the fluorene-based star-shaped polymer. Cyclic voltammetry (CV) measurement of the polymer indicated that the polymer was reversible under p-doping.
Keywords: Fluorene derivatives; π-Conjugated polymers; Star-shaped polymer; Electrochemical properties; Optical properties;
White polymer light emitting diodes with multi-layer device structure by Jian Li; Takeshi Sano; Yasuko Hirayama; Kenichi Shibata (36-40).
White polymer light emitting diodes (WPLEDs) were fabricated with multi-layer device structure using crosslinked poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEHPPV) as a red emitting layer (EML) and crosslinked poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4″,4‴-tertbutyl-tetraphenyl diamine-4,4′-diyl) (PF8-tTPD) as a blue emitting layer. The multi-layer device structure was realized by crosslinking the emitting layers through ultra-violet (UV) irradiation. The results showed that the crosslinking of the emitting layer affected the carrier mobility of the polymer layer and the recombination site of the electrons and holes, therefore affected the emission of the devices. The devices with crosslinked MEHPPV as red emitting layer and crosslinked PF8-tTPD as blue emitting layer showed good white emission with C.I.E. coordinates (X: 0.364; Y: 0.290) at about 500 cd/m2 and showed good color stability with increasing applied voltages. UV irradiation method was found to be an effective way to crosslink the emitting layer and fabricate multi-layer polymer light emitting diodes (PLEDs).
Keywords: White polymer light emitting diodes; Multi-layer device; White emission; Crosslinked emitting layer;
Polythiophene–polyoxyethylene copolymer in polyfluorene-based polymer blends for light-emitting devices by P. Camurlu; U. Giovanella; A. Bolognesi; C. Botta; G. Cik; Z. Végh (41-44).
Polyfluorene (PFO) films doped with different amount of a polythiophene-co-polyoxyethylene (P1) polymer were studied with the aim to obtain white emission. The Förster resonant energy transfer (FRET) is the basic mechanism that takes place in the photoluminescence of these blends. The non-conducting poly(oxyethylene) behaves as a inert spacer leading to a larger donor–acceptor chromophores separation and then a better control of FRET efficiency. As result, the light-emitting device with the architecture Al/Ca/P1:PFO/PEDOT:PSS/ITO was found to be more efficient than either the devices using pure PFO or P1. Near white CIE coordinates of (0.26, 0.33) with a maximum luminance of 2500 cd/m2 were found for 2 wt.% device.A maximum external quantum efficiency of 1% was obtained, hence, suggesting that the enhancement of the electronic and optoelectronic properties could be achieved by incorporating P1 into the PFO.
Keywords: Polymer blends; Förster resonant energy transfer; Electroluminescence; Polythiophene; Polyfluorene;
Synthesis and structure of charge transfer salts of tetrathiafulvalene (TTF) and tetramethyl-TTF with 2,4,7-trinitro and 2,4,5,7-tetranitro-9-fluorenone by Eric W. Reinheimer; J.R. Galán-Mascarós; Kim R. Dunbar (45-51).
Charge transfer salts of tetrathiafulvalene (TTF) and tetramethyltetrathiafulvalene (TMTTF) with the organic acceptors 2,4,7-trinitro-9-fluorenone and 2,4,5,7-tetranitro-9-fluorenone have been prepared and characterized. The compounds (TTF)[TENF] (1), (TTF)3[TRNF]2 (2) and (TMTTF)[TRNF] (3) contain mixed stacks of alternating TTF and nitrofluorenone units. Surprisingly, the degree of charge transfer that occurs in these salts is not controlled solely by the redox potentials of the building blocks, but apparently also by the most effective intermolecular interactions in the solid, as determined from the crystal structures obtained. These three compounds exhibit poor electron delocalization and therefore they behave as diamagnetic insulators.
Keywords: Charge transfer salts; Tetrathiafulvalene (TTF); Tetramethyltetrathiafulvalene (TMTTF);
Photocurrent mechanism and photovoltaic properties of photo-electrochemical device based on PPAT and PPAT:TY blend by P. Suresh; Shailendra Kumar Sharma; M.S. Roy; G.D. Sharma (52-61).
The solid state photo-electrochemical cell (PEC) solar energy conversion devices based on pure PPAT and PPAT:TY blend has been fabricated having structure ITO/nc-ZnO/PPAT or PPAT:TY/electrolyte/PEDOT:PSS-ITO and characterized. The redox properties of PPAT and TY were characterized using cyclic voltammetery (CV). The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have been estimated from their CV and UV–vis absorption spectra. The PPAT and PPAT:TY were used as sensitizer for ZnO nano-particle (nc-ZnO) in the film of PEC devices. Device that consist of PPAT:TY/nc-ZnO photoactive electrode showed improved photovoltaic performance over that consist of PPAT/nc-ZnO. This improvement attributed to the formation bulk heterojunction between PPAT and TY resulting efficient exciton dissociation into free charge carrier and photoinduced charge transfer. The photovoltaic performance of the device is further enhanced when the annealed PPAT:TY blend is used as sensitizer, which attributed to the increase in absorption and red shift in the absorption peak upon thermal annealing. This effect is due to the increased crystallinity of PPAT in the blend. PEC assembling with nc-ZnO adsorbed PPAT:TY blend using polar solvent treated PEDOT:PSS coating on ITO as a counter electrode, was studied. It was observed that when DMSO treated PEDOT:PSS counter electrode is used, the photovoltaic performance of the device is highest, which is attributed to enhanced conductivity of PEDOT:PSS and increased surface roughness. The PEC using carbon black (0.2 wt.%) modified DMSO treated PEDOT:PSS counter electrode reached a device efficiency of 5.54% under illumination 10 mW/cm2. This efficiency is higher than a PEC using untreated PEDOT:PSS as counter electrode. The thermal annealing of nc-ZnO photoelectrode improves the power conversion efficiency of the device, attributed to the increase crystallinity of the ZnO.
Keywords: Photo-electrochemical device; Photoinduced charge transfer; PEDOT:PSS counter electrode; PPAT:TY sensitizer;
Preparation of silica-layered multi-walled carbon nanotubes activated by grafting of poly(4-vinylpyridine) by Myunghun Kim; Jinho Hong; Chang Kook Hong; Sang Eun Shim (62-68).
Herein, uniformly silica coated carbon nanotubes (CNTs) were fabricated by step reactions with minimized damage of CNTs during oxidation process. First, hydroxyl groups were generated on the surface of CNTs using KMnO4 in conjunction with tetrapropyl ammonium bromide (TPABr) as a phase transfer catalyst, followed by the grafting of a vinyl group carrying silane coupling agent, methacryloxypropyl trimethoxy silane (MPTMS). Utilizing terminal vinyl groups in in-situ solution polymerization, poly(4-vinylpyrridine) (P4VP) brush was grown from the CNTs which promotes the acid–base interaction between CNTs and tetraethylorthosilicate (TEOS). By means of well-known ammonia catalyzed sol–gel reaction of TEOS in the presence of P4VP-functionalized CNTs, uniformly silica-coated CNTs were obtained. The thickness of the silica layer could be readily controlled by the amounts of reactants. After calcination of silica-coated CNTs, only outer silica remained which resulted in silica nanotubes.
Keywords: Carbon nanotubes; Silica; Surface modification; Poly(4-vinylpyridine); Sol–gel reaction;
Low driving voltage in organic light-emitting diodes using MoO3 as an interlayer in hole transport layer by Kyoung Soo Yook; Jun Yeob Lee (69-71).
Driving voltage of organic light-emitting diodes (OLEDs) was lowered by applying MoO3 as an interlayer between hole injection layer (HIL) and hole transport layer (HTL). MoO3 was effective as an interlayer between HIL and HTL due to its valence band of around 5.3 eV which is suitable for hole injection. Hole injection from HIL to HTL was enhanced by MoO3 interlayer and driving voltage of green fluorescent device could be lowered by 1.3 V at 1000 cd/m2 by using thin MoO3 interlayer.
Keywords: Low driving voltage; MoO3 interlayer; Interfacial energy barrier;
Synthesis, photoluminescent and electroluminescent properties of a novel europium(III) complex involving both hole- and electron-transporting functional groups by Huaijun Tang; Hao Tang; Zhiguo Zhang; Jibing Yuan; Changjie Cong; Keli Zhang (72-77).
A novel europium(III) complex involving a carbazole fragment as hole-transporting group and an oxadiazole fragment as electron-transporting group was synthesized and used as red light-emitting material in organic light-emitting diodes (OLEDs). The complex is amorphous, and exhibits high glass transition temperature (T g = 157 °C) and high thermal stability with a 5% weight loss temperature of 367 °C. Two devices, device 1: ITO/NPB (40 nm)/Eu(III) complex (30 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (100 nm) and device 2: ITO/NPB (40 nm)/3% Eu(III) complex: CBP (30 nm)/BCP (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (100 nm), were fabricated, where NPB is N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine, Alq3 is tris(8-hydroxyquinoline) Al(III), CBP is 4,4′-bis(carbazole-9-yl)-biphenyl, and BCP is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, respectively. In contrast with device 1, owing to less self-quenching and better charge confinement, device 2 shows improved performances: the maximum luminance of device 2 was dramatically increased from 199 to 1845 cd/m2, the maximum current efficiency was increased from 0.69 to 2.62 cd/A, the turn-on voltage was decreased from 9.5 to 5.5 V, and higher color purity was attained.
Keywords: Europium(III) complex; Red light-emitting materials; Carbazole; Oxadiazole; Electroluminescence;
Synthesis, photophysics and electroluminescence of dendronized styryl-substituted fluorene with triphenylamine units by John A. Mikroyannidis; Lin-Ren Tsai; Yun Chen (78-84).
Compound 2, a dendronized styryl-substituted fluorene with bulky hole-transporting triphenylamine units, was synthesized by a simple two-step procedure. At the first step of synthesis two triphenylamine units were attached to the C-9 of fluorene while at the second step styryl segments were introduced both on fluorene and triphenylamine by Heck coupling. Compound 2 dissolved in common organic solvents like THF, chloroform, dichloromethane and toluene. This compound was stable up to ∼320 °C and showed high glass transition temperature (T g) of 175 °C. Compound 2 absorbed around 370 nm with optical band gap of 2.89 eV. It behaved as blue-green light emitter with photoluminescence (PL) emission maximum at 444–465 nm and PL quantum yield of 0.36 in THF solution. The HOMO and LUMO levels of compound 2, estimated from cyclic voltammograms, were −5.20 and −2.40 eV, respectively. The electroluminescence (EL) emission maxima (530–570 nm) were very different from PL maximum (465 nm), which could be explained by the direct cross recombination transition between electrons and holes trapped on triphenylamine subunits. The maximal brightness (current efficiency) of the EL devices (ITO/PEDOT:PSS/2/Ca/Al) was 1348 cd/m2 (0.12 cd/A) and the color showed obvious blue-shift with an increase in operating voltage.
Keywords: Photophysics; Fluorene; Triphenylamine; Light-emitting diode (LED); Synthesis; Photoluminescence; Electroluminescence;
Synthesis and characterization of polytriphenylamine containing ether bond in the main chain by Jae Ho Sim; Soo Jong Kim; Kohei Yamada; Seiji Yokokura; Itaru Natori; Shizue Natori; Hisaya Sato (85-90).
Four triarylamine monomers that have an ether linkage, bis(N-phenyl-N-4-t-butylphenyl-4-aminophenoxy)ethane (TPAE), bis(N-phenyl-N-4-t-butylphenyl-4-aminophenoxy)butane (TPAB), bis(N-phenyl-N-4-t-butylphenyl-4-aminophenyl)ether (TPAO), and bis(N-4-tolyl-N-1-naphtyl-4-aminophenoxy)ether (NPAO) were prepared and polymerized using iron (III) chloride as an oxidant. Polymers, which are soluble in common organic solvents, were obtained at the yields of higher than 70%, and with glass transition temperatures of higher than 170 °C. The hole mobility decreased in the order of PNPAO > PTPAO > PTPAE = PTPAB > PBTPA, which indicates that the ether oxygen increases mobility.
Keywords: Charge transport; Conjugated polymers; Oxidative polymerization; TPA(Triphenylamine);
New electro-active oxetanyl-functionalized oligomers containing carbazol-3,6-diyl and different aromatic amino groups in the main chain by S. Lengvinaite; J.V. Grazulevicius; S. Grigalevicius (91-95).
A series of new cross-linkable oligomers based on 9-(3-methyloxetan-3-ylmethyl)carbazol-3,6-diyl and different aromatic amino groups were synthesized through modified Ullmann coupling reactions. The resulting derivatives were characterized by gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. These materials possess high thermal stability with onset decomposition temperatures of 351–384 °C. Their glass transition temperatures range from 154 to 250 °C. Layers of the oligomers exhibit low ionization potentials ranging from 5.05 to 5.15 eV as established by electron photoemission technique.
Keywords: Oxetanyl; Oligomer; Aromatic amine; Amorphous; Ionization potential;
Electropolymerization of N-methylanthranilic acid and spectroelectrochemical characterization of the formed film by Maija Blomquist; Tom Lindfors; Rose-Marie Latonen; Johan Bobacka (96-102).
The electropolymerization of N-methylanthranilic acid (NMAA) is reported in this paper. The monomer is substituted both at ortho- and N-position and, to the best of our knowledge, it has not been previously electropolymerized. Electropolymerization of NMAA was done on glassy carbon and optically transparent (indium) tin oxide electrodes. The obtained films, which are probably of an oligomeric nature (oligoNMMA), were characterized with cyclic voltammetry (CV), in situ UV–vis and Raman spectroscopy, ex situ FTIR spectroscopy and scanning electron microscopy (SEM).Our results show that NMAA can be electropolymerized as thin films in 1.0 M HClO4, but the oxidation and reduction peak currents in the CVs indicate that the formed oligoNMAA films are thinner than poly(N-methylaniline) or poly(N-butylaniline) films prepared under similar conditions. The CV and UV–vis measurements confirm that oligoNMAA have three oxidation states like suggested in the redox scheme of substituted polyanilines. The Raman spectra of oligoNMAA also verify that more quinoid units are formed at higher potentials in accordance with the redox scheme. The ex situ FTIR measurement proves that covalently attached carboxylic acid groups are present in the film structure and attached to the oligoNMAA backbone.
Keywords: Poly(N-methylanthranilic acid); Electropolymerization; Cyclic voltammetry; UV–vis; Raman and FTIR spectroscopy;
Synthesis and characterization of oxazinone and oxazoline substituted pyrroles: Towards electrically conducting bi-functional copolymers by Jan Hegewald; Lothar Jakisch; Jürgen Pionteck (103-112).
The synthesis of N-(3-aminopropyl)pyrrole and N-(2-carboxyethyl)pyrrole was reviewed and repeated. Both compounds were utilized as pre-cursors for the synthesis of oxazinone and oxazoline modified pyrroles by different synthetic pathways. The N-substituted pyrroles were characterized by 1H NMR, ATR-FTIR, and MALDI-TOF MS. The chemical oxidative copolymerization of pyrrole and its derivatives was carried out in various solvent systems using FeCl3 and (NH4)2S2O8 as oxidants. Furthermore, sodium poly(styrene sulfonate) was used as dopant leading to core-shell-like structures, and, after the copolymerization of pyrrole with oxazinone or oxazoline functionalized monomers, to exceptionally increased conductivities. The produced (co-)polymers were characterized in terms of their chemical composition, morphology, and electrical conductivity. Oxazinone and oxazoline moieties in the copolymers were confirmed by ATR-FTIR. Furthermore, the retained reactivity of oxazinone and oxazoline functions after chemical oxidative copolymerization was evidenced by model reactions with 1-pyrenemethylamine and 1-pyreneacetic acid, respectively, and subsequent fluorescence microscopy and spectroscopy.
Keywords: Oxazoline; Oxazinone; Functionalized polypyrrole; Electrical conductivity; Fluorescence; Core-shell-like particles;
Optical and electronic properties of phosphorescent iridium(III) complexes with phenylpyrazole and ancillary ligands by Teng Fei; Xin Gu; Ming Zhang; Chunlei Wang; Muddasir Hanif; Houyu Zhang; Yuguang Ma (113-118).
Phosphorescent Ir(III) complexes Ir(ppz)3, Ir(ppz)2(acac), Ir(ppz)2(pic) and Ir(ppz)2(dbm) (here ppz = phenylpyrazole, acac = acetylacetonate, dbm = dibenzoylmethane, and pic = picolinate) have been synthesized and investigated by optical spectroscopy, electrochemistry as well as density functional theory (DFT) calculations. These complexes show either no emission or medium intensity emission in solution or solid state at room temperature, but exhibit very strong emission from blue (422 nm) to orange-red (587 nm) at low temperature (77 K). Combined experimental and theoretical study, we reveal that replacing one of ppz ligand by ancillary ligand acac, dbm, and pic is a feasible way to alter the electronic structures of complexes resulting in changing emission colors. Both the cyclic voltammetry and DFT study testify that ancillary ligands have little influence on the highest occupied molecular orbital (HOMO) but great effect on lowest unoccupied molecular orbital (LUMO) by lowering the LUMO levels dramatically. The decreased LUMO level induced by the ancillary ligand makes the excited state of the complex far from the non-radiative states, which might enhance the quantum efficiency.
Keywords: DFT; Phosphorescent; Iridium; Ancillary ligand; Cyclometalating ligand;
Preparation, FTIR spectroscopic characterization and isothermal stability of differently doped fibrous conducting polymers based on polyaniline and nylon-6,6 by Mohd. Khalid; Faiz Mohammad (119-122).
The fibrous conducting polymers based on polyaniline and nylon-6,6 are obtained by stirring with magnetic bar. The increase in the ratio of conducting polymer volume in case of such fibers make them attractive materials for potential applications. As it is difficult directly to form fibers of conducting polymers, stirring process is attempted to form fibers of conducting polyaniline and nylon-6,6. In the present paper, the fibrous polyaniline:nylon-6,6 (PANI:Ny-6,6) with different weight percentages (5–20%, w/w) are prepared by stirring process. The fibers obtained are characterized using Fourier-transform infrared spectra (FTIR) and scanning electron microscopy (SEM), the variation of electrical conductivity with different type doping agents 0.1 M (HCl, H2SO4 and HClO4) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.
Keywords: Conducting polymer; Electrical conductivity; Thermal stability;
One-step reverse micelle polymerization of organic dispersible polyaniline nanoparticles by Youn-Gyu Han; Takafumi Kusunose; Tohru Sekino (123-131).
Organic solvent dispersible dodecylbenzenesulfonic acid (DBSA)-doped polyaniline (PANI) was prepared from DBSA micelles with ammonium persulfate (APS) as an oxidant in hexane by one-step polymerization. Morphology observation showed PANI–DBSA powder polymerized with 0.0375 mol DBSA consisting of spherical particles having diameters of 40–60 nm that formed irregular aggregates with about 1 μm diameter. Polymerization was carried out in the hydrophilic aqueous microdomains of micelle dissolved reactants. The experimental conditions were optimized for direct synthesis of DBSA-doped PANI with high electrical conductivity by adjusting various reaction conditions. This research showed the importance of adjusting reaction conditions such as DBSA, aniline, ammonium persulfate, and acidity for polymerization. It was also found that a portion of an electrically neutral anilinium–DBSA complex could be assembled into reverse micelles together with DBSA molecules, where DBSA and anilinium–DBSA acted as both surfactants and doping agents to achieve nano-scaled DBSA-doped PANI with high conductivity. The doping level of DBSA in PANI particles was studied by UV–vis spectroscopy and X-ray diffraction (XRD). From TG/DTA/mass spectrometry, it was found that the PANI–DBSA was doped with both free and bound DBSA.
Keywords: Conducting polymer; Nanoparticles; Micelle; Polyaniline; Reverse microemulsion;
Semiconducting polymers based on electron-donating bithiophene and electron-accepting 5,5′-bithiazole units for organic thin-film transistors by Bang-Lin Lee; Kuk-Min Han; Eun-Kyung Lee; In-Nam Kang; Do Hwan Kim; Sangyun Lee (132-136).
New type of π-conjugated polymers composed of electron-donating bithiophene and electron-accepting 5,5′-bithiazole were prepared by organometallic polycondensation using a zerovalent nickel complex, which have charge-transfer (CT) structures in the polymer backbone. The number average molecular weights (M n ) of the obtained polymers, PT2Z2-C8 and PT2Z2-H, were 45000 and 20000, respectively, estimated from GPC measurements. Head-to-head (HH) arrangements of 5,5′-bithiazole units leads to good solubility of the polymers in common organic solvents. Ionization potentials (IPs) of PT2Z2-C8 and PT2Z2-H were measured to be 5.15 and 5.20 eV, respectively. UV–vis peaks of the polymer films corresponding to the π–π* transition were shifted to longer wavelengths over 70 nm relative to those obtained for the corresponding chloroform solutions. PT2Z2-C8 is considered to have a coplanar π-conjugated backbone conformation, as judged from UV–vis data and XRD data. OTFTs fabricated using the polymer PT2Z2-C8 as a channel material show a typical p-type behavior and provide a mobility of 0.001 cm2/Vs with a low off-state current (of about 1 pA).
Keywords: Conjugated polymers; 5,5′-Bithiazole units; Organic thin-film transistors;
Electron transport and electroluminescent efficiency of conjugated polymers by S.R. Tseng; Y.S. Chen; H.F. Meng; H.C. Lai; C.H. Yeh; S.F. Horng; H.H. Liao; C.S. Hsu (137-141).
The relation between charge balance and electroluminescent efficiency for polymers is studied systematically in this work. Light-emitting diodes of several kinds of polymers with very different efficiency are compared. The electron and hole currents are measured in the uni-polar devices and fitted by the theoretical model to get carrier mobilities. The universal features of the high efficiency polymers are that the electron and hole mobilities are comparable and the electron current is larger than the hole current due to the higher hole barriers. The electron current is more crucial than hole current to determine the efficiency in the bipolar light-emitting diode. The purity of polymers and low electron injection barriers both play significant roles in producing stronger electron currents. These results give the physical rules for designing new polymers and the device structures to achieve highly electroluminescent devices.
Keywords: Polymer light-emitting diodes; Mobility; Efficiency;
Alternating phenylenevinylene and thienylenevinylene copolymers with cyano groups: Synthesis, photophysics and photovoltaics by John A. Mikroyannidis; Minas M. Stylianakis; Kai Yin Cheung; Man Kin Fung; Aleksandra B. Djurišić (142-147).
Two alternating conjugated copolymers TTP and TTT were synthesized by Heck coupling of 2,3-bis-(5-bromothiophene-2-yl)acrylonitrile with 1,4-dihexyloxy-2,5-divinylbenzene and 3-hexyl-2,5-divinylthiophene, respectively. The absorption spectra of the copolymers in THF solution showed three maxima around 270, 370 and 460 nm with optical band gaps of 2.30–2.34 eV. The electrochemically estimated band gaps of copolymers were 2.04–2.10 eV. The thin film absorption spectra were broad and extended about from 250 to 600 nm with a long wavelength maximum near 470 nm. The copolymers emitted yellow-orange light with maximum at 528–551 nm in THF solution and 567–610 nm in thin film. TTP showed the most red shifted emission maximum between the copolymers. The performance of the photovoltaic cells which were fabricated using blends of the copolymers with 6,6-phenyl C61-butyric acid methyl ester (PCBM) (1:1 and 1:4, w/w) as well as pure copolymers was investigated.
Keywords: Conjugated polymers; Synthesis; Copolymerization; Phenylenevinylene; Thienylenevinylene; Photophysics; Polymer solar cells;
Synthesis and characterization of organo-soluble conducting polyaniline doped with oleic acid by Peng Liu (148-152).
An emulsion polymerization process has been developed for the direct synthesis of the organo-soluble polyaniline (PANI) with oleic acid (OA) as the surfactant and dopant. The polyaniline doped with oleic acid (PANI/OA) powders, prepared by the proposed method, are highly soluble in many organic solvents such as dimethyl sulfoxide (DMSO), dimethyformamide (DMF) and N-methyl,2-pyrrolidinone (NMP). The PANI/OA powders were characterized by elemental analysis (EA), FTIR, UV–vis, TGA and SEM. The conductivities of the PANI/OA powders decreased with the increasing of the amounts of water in the emulsion polymerization.
Keywords: Organo-soluble; Conducting polyaniline; Oleic acid; Emulsion polymerization;
Synthesis, photophysical and electroluminescent properties of donor–acceptor–donor molecules based on α-cinnamoyl cyclic ketene dithioacetals by Ping Peng; Yinhua Zhou; Kunpeng Li; Houyu Zhang; Haijian Xia; Yixin Zhao; Wenjing Tian (153-157).
New symmetrical π-conjugated donor–acceptor–donor functionalized molecules consisting of different electron-donating moieties but same α-cinnamoyl cyclic ketene dithioacetals (CCKDA) acceptor have been synthesized. The photophysical properties of these compounds indicate that the absorption and emission result from the intramolecular charge-transfer between the donor and the acceptor. Cyclic voltammetry data show that the band gaps of the compounds vary by introducing different donor moieties. Density functional theory calculations provide an insight into the electronic structure of the molecules. The double-layer electroluminescent devices are fabricated by using these molecular materials as light emitting layer. The electroluminescent performance of the device suggests that these donor–acceptor–donor molecules can be good candidates for the application in organic light-emitting diodes.
Keywords: Donor–acceptor–donor molecule; Intramolecular charge-transfer; Solvatochromism;
RuO2/carbon nanotubes composites synthesized by microwave-assisted method for electrochemical supercapacitor by Shancheng Yan; Haitao Wang; Peng Qu; Yong Zhang; Zhongdang Xiao (158-161).
A simple and efficient way has been developed to decorate multiwalled carbon nanotubes (MWCNTs) with RuO2 nanoparticles for use of electrochemical supercapacitor. In this method, RuO2 nanoparticles was directly synthesized and attached onto MWCNTs in the mixture with RuCl3 solution by microwave-assisted irradiation. Energy dispersive X-rays analysis (EDXA) elucidated the presence of ruthenium oxide in the as-prepared composites. Transmission electron microscopy (TEM) results showed that RuO2 nanoparticles had the narrow size distribution and were attached on MWCNTs. Cyclic voltammetry results demonstrated that RuO2/MWCNTs had significantly greater specific capacitance than that of the pristine MWCNTs in the same medium.
Keywords: Supercapacitor; Ruthenium oxide; Carbon nanotubes;
Purity determination of 8-hydroxyquioline aluminum by differential scanning calorimetry by Haifeng Wang; Jia Li; Guohua Sun; Kang Ma; Qinghe Zhang (162-165).
The purity of small-molecule electroluminescents (ELs) was generally determined by chromatography. However, the accuracy of results by chromatography sometimes is unsatisfactory due to systematic errors. In present work, an improved method by using differential scanning calorimetry (DSC) was employed to determine the purity of 8-hydroxyquioline aluminum (Alq3), one of the most important small-molecule ELs. A detailed study on the thermal stability and polymorphism revealed that Alq3 undergoes volatilization and phase transition during melting. The effects of volatilization and polymorphism were greatly reduced via employing volatile pans and annealing close to melting point. Then the purity of Alq3 was determined and compared with that by high performance liquid chromatography. The reproducibility and accuracy of purity determination by DSC suggest that this method could be widely applicable for small-molecule ELs, combining with the chromatography.
Keywords: Differential scanning calorimetry; Chromatography; Purity; 8-Hydroxyquioline aluminum; Polymorphism;
Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells by Kristofer Fredin; Erik M.J. Johansson; Tobias Blom; Maria Hedlund; Stefan Plogmaker; Hans Siegbahn; Klaus Leifer; Håkan Rensmo (166-170).
We describe a method to fill thin films of nanoporous TiO2 with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 μm below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO2/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.
Keywords: TiO2; Dye; Nanoporous; Hole-conductor; Triarylamine;
Perylenetetracarboxylic di-imide-based bottom-contact devices: A study on two kinds of source/drain electrodes, ITO and MoW by Chia-Chun Kao; Pang Lin; Yu-Yuan Shen; Jing-Yi Yan; Jia-Chong Ho; Cheng-Chung Lee; Li-Hsin Chan (171-175).
High-performance bottom-contact devices based on an air-stable n-type organic semiconductor N,N-bis(4-trifluoromethoxybenzyl)-perylene-3,4,9,10-tetracarboxylic di-imide, were fabricated, and the effects of crystal packing on indium tin oxide and molybdenum–tungsten alloy were shown in two different electric characteristics. The estimated work function of indium tin oxide and molybdenum–tungsten alloy were 4.7 and 5.0 eV. The calculated lowest unoccupied molecular orbital energy level of the organic material was 3.7 eV. Transistors with indium tin oxide bottom electrodes exhibited a high mobility of 3.37 × 10−2 cm2 V−1 s−1, an on/off current ratio of 6.5 × 105 and threshold voltage of −4.0 V.
Keywords: Organic thin-film transistors (OTFTs); n-Type; Perylene;