Synthetic Metals (v.161, #9-10)
Synthesis, structure and luminescent properties of neodymium(III) coordination polymers with 2,3-pyrazinedicarboxylic acid
by Li-Rong Yang; Shuang Song; Wu Zhang; Huai-Min Zhang; Zhan-Wei Bu; Tie-Gang Ren (pp. 647-654).
► New coordination polymers [Nd2(pzdc)3(H2O)] n· nH2O and [Nd4(pzdc)6(H2O)2] n·3nH2O have been synthesized. ► The two isomorphous complexes may be prepared at different temperatures. ► Luminescent emission of complex I displays selectivity for heavy metal ions such as Pb2+, Hg2+ and so on.The coordination polymer [Nd2(pzdc)3(H2O)] n·nH2O (complexI) with three-dimensional framework has been prepared by hydrothermal synthesis of 2,3-pyrazinedicarboxylic acid (pzdc) and neodymium nitrate and characterized by elemental analyses, IR spectroscopy, thermal analyses and single crystal X-ray diffraction. The complex crystallizes in monoclinic system, space group P2(1)/ c. Every Nd(III) atom in the coordination polymer is nine-coordinated with different coordination environments. The pzdc ligands coordinate to the central Nd(III) atoms in bridging tetradentate, hexadentate, or heptadentate modes. The thermal decomposition of the complex has been predicted with the help of thermal analyses (TG, DTG and DTA). ComplexI exhibits luminescent emissions bands in the solid state at room temperature. The isomorphous complex [Nd4(pzdc)6(H2O)2] n·3 nH2O (complexII) has also been prepared by hydrothermal reaction under different conditions. Luminescent emission of complexI display selectivity for some heavy metal ions.
Keywords: Synthesis; Structure; Luminescent properties; Coordination polymers; 2,3-Pyrazinedicarboxylic acid
Study of synthesis and luminescent properties of a novel terbium rare earth complex Tb(PCAD)3Phen
by Ying Wang; Zhaohua Jiang; Yuguang Lv; Yunjie Zhang; Dongyun Ma; Fujun Zhang; Bo Tan (pp. 655-658).
Rare earth complex Tb(PCAD)3Phen was synthesized by introducing 3-pyridylacetic acid (PCAD) and phenanthroline (1,10-Phen) as the ligands and characterized by UV, fluorescent, IR spectra and X-ray diffraction (XRD) as well as elemental analysis. The complex exhibited ligand-sensitized green emission, and it has higher sensitized luminescent efficiency and longer lifetime. In device ITO/PVK/Tb(PCAD)3Phen/Al, Tb3+ may be excited by intramolecular energy transfer from ligand as observed by electroluminescence. The main emitting peak at 545nm can be attributed to the transition of5D4→7F5 of Tb3+ ion and this process results in the enhancement of green emission from electroluminescence device. The effect and mechanism of the ligands (PCAD and 1,10-Phen) on the luminescence properties of terbium complex were discussed. The present study may be important and helpful for the development of green color rare earth display applications.
Keywords: Tb(PCAD); 3; Phen; Synthesis; Electroluminescence; Energy transfer
Polyaniline modified electrodes for detection of dyes
by Debajyoti Mahanta; N. Munichandraiah; S. Radhakrishnan; Giridhar Madras; Satish Patil (pp. 659-664).
► PANI films on Pt electrode were used for quantitative detection of textile dyes. ► Dye adsorption on PANI films followed a pseudo second order kinetic model. ► PANI coated stainless steel electrodes were also capable of textile dye detection. ► The dye can be detected at concentration as low as 1ppm.Polyaniline (PANI) is one of the most extensively used conjugated polymers in the design of electrochemical sensors. In this study, we report electrochemical dye detection based on PANI for the adsorption of both anionic and cationic dyes from solution. The inherent property of PANI to adsorb dyes has been explored for the development of electrochemical detection of dye in solution. The PANI film was grown on electrode via electrochemical polymerization. The as grown PANI film could easily adsorb the dye in the electrolyte solution and form an insulating layer on the PANI coated electrode. As a result, the current intensity of the PANI film was significantly altered. Furthermore, PANI coated stainless steel (SS) electrodes show a change in the current intensity of Fe2+/Fe3+ redox peaks due to the addition of dye in electrolyte solution. PANI films coated on both Pt electrodes and non-expensive SS electrodes showed the concentration of dye adsorbed is directly proportional to the current intensity or potential shift and thus can be used for the quantitative detection of textile dyes at very low concentrations.
Keywords: Polyaniline; Emeraldine base; Emeraldine salt; Electrochemical sensor
New type of anhydrous organic electrolyte based on carboxylic acid functional triazole as model system
by Melike Türk; Sedat Coşgun; Sevim Ünügür Çelik; Hamit Erdemi; Christine Gérardin-Charbonnier; Ayhan Bozkurt (pp. 665-669).
The model system of dicarboxylic acid functionalized 1H-1,2,3-triazole-terminated alkyl oligomers is presented as a new approach for obtaining high proton conductivity in proton solvating heterocycles covalently bound via spacers. The model materials have been characterized by FT-IR and NMR spectroscopy. Thermal stabilities were examined with thermogravimetric analysis (TGA). Differential scanning calorimetry (DSC) was used to measure melting and crystallization temperatures. The influence of spacer length on proton conductivity was investigated by AC impedance spectroscopy. Analysis of conductivity and permittivity measurements revealed the contribution of local dynamics and proton mobility on conduction mechanism which gives rise to proton conductivities of up to 10−5S/cm at 120°C in completely water-free pristine materials.
Keywords: Organic electrolyte; Triazole; Proton solvent; Proton conductivity; Permittivity
Photophysical and optical limiting properties of multifunctional hemi-ortho ester derivatives of fullerenol: Effects of TBAH doping, fullerenol concentration and solvent polarity
by Rachana Singh; Thakohari Goswami (pp. 670-679).
Interesting effect of strong ground and excited state electronic interaction on photophysical property of multifunctional hemi-ortho ester derivatives of fullerenol are explained in light of doping effect of TBAH and solvent polarity. Flexibly linked multiple isolated terminal double bonds behave like π-conjugated polymeric system due to geometrical orientation and steric repulsion.Interesting doping effect of polar impurity (tetra-butyl ammonium hydroxide, TBAH), solvent polarity and amount of fullerenol on photoluminescence and electron-transfer properties of multifunctional double bond terminated hemi-ortho ester derivatives of fullerenol is correlated on the basis of emission spectral features. Inter- and intra-molecular π–π interaction of terminal vinylic double bonds leads to cluster formation (quantitative image analysis of SEM micrographs using MATLAB tool box) and bigger cage size (on higher concentration of fullerenol) allows easy insertion of TBAH due to ionic nature and fit-in size. Antagonistic effect in fluorescence intensity in heterogeneous phase product (IB) is explained on the basis of possible TBAH intrusion inside the cage. TBAH intrusion disallows inter- and intra-molecular π–π interaction of terminal vinylic double bonds leading to high intensity (weak quenching) at higher amount of fullerenol loading (easy entry of TBAH) and strong quenching in absence of TBAH (entry difficult at low concentration of fullerenol loading). Stronger π-cation interaction is also responsible for blue shift (depopulate S1-state electron) in heterogeneous phase product (IB). Polar solvent has similar effect but lesser in magnitude due to weaker ionic character compared to TBAH. Quenching of fluorescence intensity in the presence of TBAH/polar solvent intuitively proves intra- and inter-molecular π–π electron transfer among terminal vinylic double bonds and also between π-chromophores and foreign ionic species. Preliminary results on Optical Limiting (OL) property of hemi ortho-esters are compared with fullerene and fullerenol.
Keywords: Multi-functional fullerene; Fullerene core star-like macromolecules; Photophysical properties; Charge-transfer exciplex; Optical limiting property
Modulating spectroelectrochemical properties of [Ni( salen)] polymeric films at molecular level
by João Tedim; Sónia Patrício; Joana Fonseca; Alexandre L. Magalhães; Cosme Moura; A. Robert Hillman; Cristina Freire (pp. 680-691).
Display Omitted► Polymers based on [Ni( salen)] complexes were characterized by UV–visible spectroelectrochemistry ► Complex π delocalisation was manipulated by introduction of different conjugated imine bridges. ► Electronic spectra were interpreted in terms of polaronic states and metal-oxidized ligand CT bands. ► DFT calculations were correlated with observed properties of monomeric and polymeric materials.Electroactive polymer films based on [Ni( salen)]-type complexes were fabricated and their electronic properties characterized using in situ UV–visible spectroelectrochemistry. The extent of π electronic delocalisation and electronic asymmetry were manipulated by introduction of different conjugated imine bridges. Measured electronic spectra were interpreted in terms of polaronic states in the band gap and metal-oxidized ligand charge transfer bands. Density functional theory (DFT) calculations for the monomers showed that the HOMO orbital (which governs oxidation potential) is ligand-dominated, and that substituents with greater electronic delocalisation in the diimine bridge decrease the HOMO–LUMO energy gap. Replacement of methyl by methoxyl substituents in the aldehyde moiety increases the calculated dipole moment. Substitution-driven variations in EHOMO– ELUMO for the monomers were reflected in the corresponding polymer band gaps, demonstrating that monomer electronic properties can be used predictively in the manipulation of polymer electronic properties. An important strategic aspect is the correlation of DFT predictions with the observed electronic properties of monomeric and polymeric materials; the extent to which such modelling can be used to optimise synthetic effort is discussed.
Keywords: Nickel; salen; complexes; Electropolymerisation; Conductive materials; Spectroelectrochemistry; Density functional calculations
Electrical and optical properties of p-type silicon based on polypyrrole-derivative polymer
by Ahmet Faruk Özdemir; Sinem Gürkan Aydin; Durmuş Ali Aldemir; Songül Şen Gürsoy (pp. 692-697).
The junction characteristics of the conducting polymer NpClPh PPy [N-(p-chloro phenyl) polypyrrole] on a p-type Si substrate have been studied at room temperature. A direct optical band gap energy value of conducting polymer (NpClPh PPy) was obtained as 2.94eV. The ideality factor and barrier height of Al/NpClPh PPy/p-Si/Al structure were determined from the forward current–voltage characteristics in the dark and were found to be 1.41 and 0.78eV, respectively. The ideality factor and barrier height values for the Al/NpClPh PPy/p-Si/Al structure are larger than that of conventional Al/p-Si Schottky diode. The contact parameters were calculated from Cheung's functions and modified Norde's function. The results found out from different methods were compared with each other. The barrier height value of 0.89eV was obtained from capacitance–voltage characteristic. The different values of barrier height indicate the existence of barrier inhomogeneities. The conducting polymer (NpClPh PPy) modifies the effective barrier height of conventional Al/p-Si Schottky diode as the organic film forms a physical barrier between Al metal and p-Si.
Keywords: Schottky diode; Barrier height; Ideality factor; Series resistance; Conducting polymer (NpClPh PPy)
Relaxation currents from macroscopic depolarization in poly-4-vinylphenol dielectrics
by A.M. Hamza; J.K. Han; S.D. Bu; J.M. Seo; J.-K. Lee (pp. 698-703).
Polarization and depolarization currents were obtained from a capacitor structure with poly-4-vinylphenol (PVP) dielectrics by on-off switching. A single Debye relaxation was revealed for thin films; while some dispersion appeared for thick samples. The relaxation time constant ( τ) of the currents was ∼1s, and the polarization density depended on the type of top electrodes. The slow relaxation at on-off switching corresponded to a much higher susceptibility ( χ≈103), compared to that ( χ≈100) of the PVP molecular dipoles, suggesting the existence of macroscopic dipoles. Meanwhile, fast ( τ<∼0.1ms) polarization and depolarization of the molecular dipoles in PVP layers were detected by measuring a P– E hysteresis loop at a high frequency. In both cases, the electric susceptibility decreased for thin (∼100–1000nm) PVP layers, showing the dominant effects of the interfacial states.
Keywords: OTFT; PVP; Dipole; Interface states
Non-Ohmic current–voltage characteristics in the positively charged tetrathiafulvalene (TTF) molecular crystals
by Takashi Kato (pp. 704-712).
The mechanism of an extraordinary increase in conductivity at larger applied voltage than the critical voltage generally observed in the one-dimensional electronic systems such as tetrathiafulvalenium–tetracyanoquinodimethanide (TTF–TCNQ) is quantitatively investigated. The tunneling effects of the nondissipative diamagnetic currents between the two neighboring localized TTF unit cells and the current–voltage characteristics at low temperature process (0K< T<14K) are investigated. The transition probability ( PTC) of electrons between two neighboring unit cells is estimated to be in the order of 10−3–10−4. The estimated density of states near the Fermi level in the Peierls distorted structures ( NPD( ɛF)) on the basis of the experimental results of the current–voltage characteristics is always larger than that ( NNM( ɛF)) in the normal metallic states in TTF–TCNQ molecular crystals. This result can be rationalized from the fact that the density of states near the Fermi level in the Peierls distorted states is enhanced as a result of the congestion of the energy levels. That is, the NPD( ɛF) values estimated on the basis of the tunneling effect theory suggested in this paper are well rationalized. The tunneling effects theory of the nondissipative diamagnetic currents is compared with the incommensurate charge-density-wave (ICDW) sliding theory. According to our quantitative calculated results, the phenomena described above can be understood if we consider that such an extraordinary increase in conductivity originates from the tunneling effects of the nondissipative localized diamagnetic currents between the two neighboring unit cells.
Keywords: Non-Ohmic current–voltage characteristics; One-dimensional electronic systems; Peierls distortion; Density of states at the Fermi level; Tunneling effects
3-Carbaldehyde-substituted 2,3′-biimidazo[1,2- a]pyridin-2′-one radicals: Interesting π-stacking structures and magnetic properties
by Yingzhou Li; Guoping Yong; Yiman Zhang; Chongfu Li; Wenlong She (pp. 713-717).
A new 3-formyl-2,3′-biimidazo[1,2- a]pyridin-2′-one radical was synthesized via Vilsmeier reaction under mild conditions, which exists as 1D double-stranded chain formed by lateral close contacts between π-dimers. Its perchlorate salt exists as 1D slipped π-stacking chain. The different stacking structures obviously affect their magnetic and photoluminescence properties in solid state. Neutral radical shows a dominant antiferromagnetic interaction between radicals and the magnetic phase transition at ∼72K, while radical salt exhibits a strong irreversibility between FC and ZFC states, attributed to the anisotropic contraction and nonuniform slippage of π-stacking chain.
Keywords: Radicals; 2,3′-Biimidazo[1,2-; a; ]pyridin-2′-one; Crystal structures; Magnetic property; Photoluminescent property
Synthesis and characterization of efficient luminescent materials based on 2,1,3-benzothiadiazole with carbazole moieties
by Yun-Mei Tao; Hong-Yan Li; Qiu-Lei Xu; Yu-Cheng Zhu; Ling-Chen Kang; You-Xuan Zheng; Jing-Lin Zuo; Xiao-Zeng You (pp. 718-723).
Two new luminescent materials named 4-bromo-7-carbazyl-[2,1,3]-benzothiadiazole (3) and 4,7-dicarbazyl-[2,1,3]-benzothiadiazole (4) were obtained by a modified Ullmann reaction in one step from 4,7-dibromo-[2,1,3]-benzothiadiazole (2) (based on 2,1,3-benzothiadiazole (1, BTD)) and carbazole. The structure and purity of them were characterized by crystal structures,1H NMR and elemental analysis. Compared with compounds 1 and 2, the compounds 3 and 4 have better optical properties and thermostability due to the introduction of the carbazole moieties, and the compound 4 shows better performances than that of compound 3. For compound 4, a strong absorption peak at 236nm with a high extinction coefficient up to 1.205×105L·mol·cm−1 and bright green to orange photoluminescence with quantum yields of 9.0%, 48.4%, 51.0% and 75.6% in different solvents of acetonitrile, dichloromethane, ethyl acetate, and diethyl ether, respectively, were measured.
Keywords: 2,1,3-Benzothiadiazole; Carbazole; Photoluminescence; Thermostability
Electrical field directed electropolymerization of free-standing film of polypyrrole and poly(1-(2-carboxyethyl)pyrrole at the air/liquid interface
by Linli Zhang; Ze Zhang (pp. 724-730).
Thin flexible films of conductive polymers are useful in biosensors and flexible batteries. These films are typically prepared through electropolymerization on the surface of electrode and are subsequently peeled off. The present work reports a novel approach of synthesizing free-standing conductive polymer films of polypyrrole and poly(pyrrole-co-(1-(2-carboxyethyl)pyrrole)) at the air/liquid interface under the control of electrical field. The films grew along the direction of the electrical field and showed unique morphology at the air-facing side of the film. SEM, XPS, ATR-FTIR, WAXD and cyclic voltammetry were used to characterize the films. A mechanism of film growth was proposed with the important experimental parameters discussed. This approach may be used for other types of conducting polymers and also for the monomers sensible to electrical field.
Keywords: Interfacial polymerization; Electrical field; Conducting polymer; Electropolymerization
Synthesis and photovoltaic property of a novel low band gap conjugated donor–acceptor copolymer consisting of 2,7-carbazole and (bithiophenevinyl)-(2-pyran-4-ylidenemalononitrile) (TVM)
by Qiang Li; Leijing Liu; Zhaoyang Liu; Zaifang Li; Weidong Cheng; Shanpeng Wen; Pengfei Li; Zijian Li; Wenjing Tian (pp. 731-736).
► A novel soluble conjugated donor-acceptor copolymer, CZPM, was synthesized. ► CZPM has a relatively low band gap of 1.81eV. ► CZPM has a deep highest occupied molecular orbital level of −5.55eV. ► The solar cell based on CZPM as donor exhibited a Voc of 0.74V and a PCE of 0.1%. ► The low PCE is due to the ineffective exciton dissociation and the imperfect film.A novel soluble conjugated donor–acceptor (D–A) copolymer, poly(2-(2-((E)-2(3,4-dihexyl-5-(7-methyl-9-octyl-9H-carbazole-2-yl)thiophene-2-yl)vinyl)-6((E)-2-(3,4-dihexyl-5-methylthiophen-2yl)vinyl-4H-pyran-4-ylidene)malononitrile) (CZPM), consisting of alternating 2,7-carbazole and (bithiophenevinyl)-(2-pyran-4-ylidenemalononitrile) (TVM) was synthesized by Suzuki coupling polymerization. The photophysical and photovoltaic properties of the copolymer were investigated. The UV–vis absorption spectrum and cyclic voltammetry measurements of CZPM film showed that the copolymer has a relatively low band gap (1.81eV) and a deep highest occupied molecular orbital (HOMO) level (−5.55eV). Bulk heterojunction photovoltaic devices were fabricated using CZPM as donor and (6,6)-phenyl C61-butyric acid methyl ester (PCBM) as acceptor with the weight blend ratio ranging from 1:1 to 1:4. The device with the blend ratio of 1:2 between CZPM and PCBM exhibited an open-circuit voltage ( Voc) of 0.74V and a power conversion efficiency (PCE) of 0.1% under simulated AM1.5 solar irradiation (100mW/cm2). The relatively low conversion efficiency of the device is attributed to the ineffective exciton dissociation at the CZPM/PCBM interface and the imperfect film-forming property of the polymer resulting from the low molecular weight.
Keywords: Conjugated copolymer; Donor–acceptor; Low band gap; Photovoltaic device
Oxygen sensing nanofibers doped with red-emitting Eu(III) complex: Synthesis, characterization, mechanism, and sensing performance
by Shigang Li; Xiaoyun Zhao (pp. 737-742).
In this paper, we synthesize a novel diamine ligand of PIP and its corresponding Eu(III) complex of Eu(DBM)3PIP, where PIP=2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline, and DBM=1,3-diphenyl-propane-1,3-dione. The UV–Vis absorption spectra, low temperature phosphorescence spectra, energy transfer mechanism, excited state lifetime of Eu(DBM)3PIP, as well as its photoluminescence spectra, are investigated in detail. Data suggest that the emission of Eu(DBM)3PIP is quenchable by molecular oxygen due to the back-energy transfer process. By doping Eu(DBM)3PIP into a polymer matrix of poly(vinylpyrrolidone) (PVP), the oxygen sensing performance of the resulted nanofibrous membrane is investigated. Finally, the 0.6wt% doped sample exhibits a linear response towards molecular oxygen, with a sensitivity of 3.5 and response/recovery time of 15s/24s.
Keywords: Eu(III) complex; Photoluminescence; Phosphorescence; Oxygen sensing
Controlling the turn-on-voltage in low-voltage Al2O3 organic transistors with mixed self-assembled monolayers
by Niklas Björklund; Fredrik S. Pettersson; Daniel Tobjörk; Ronald Österbacka (pp. 743-747).
Display Omitted► Turn-on-voltage ( V0) sensitive to insulator/semiconductor interface properties. ► Self-assembled monolayers (SAMs) shift V0 in poly(tri-arylamine)/Al2O3 OFETs. ► The V0-shift can be controlled with SAMs of heterogeneous molecular blends.In this paper we present a method of using blends of two silanes with different functional groups to precisely tune the turn-on-voltage to 0V. In addition, we show how the transistor behaviour of an amorphous polymer low-voltage transistor is affected by modification of the Al2O3 dielectric with self-assembled monolayers of molecules with different functional groups. Controlling the turn-on voltage is essential for any practical applications, especially for low-voltage transistors. This method opens new doors to designing stable, low-voltage organic circuitry in a reproducible manner.
Keywords: Organic field-effect transistor; Self-assembled monolayer; Threshold voltage; Turn-on voltage; Amorphous organic semiconductor; Poly(tri-arylamine)
An efficient luminescent bonding-type Eu-containing copolymer as a red-emitting phosphor for fabrication of LED
by Haigang Yan; Huihui Wang; Pei He; Jianxin Shi; Menglian Gong (pp. 748-752).
A luminescent europium-containing copolymer, poly(MMA-MA-co-Eu(TTA)2phen), was synthesized though a reaction of EuCl3, 1,10-phenanthroline (phen), α-thenoyltrifluoroacetone (TTA) with copolymer of maleic acid (MA) and methyl methacrylate (MMA). The copolymer was characterized by FT-IR, UV–vis, gel permeation chromatograph (GPC), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. The Eu-copolymer phosphor exhibited high thermal stability and excellent photoluminescence properties, appropriate CIE chromaticity coordinates for red and a quantum yield of 24% under near-UV light excitation. It emitted intense red light at 613nm under UV excitation at room temperature, which is attributed to the5D0→7F2 transition of Eu(III) ions. An intense red-emitting light-emitting diode (LED) was fabricated by combining poly(MA-MMA-co-Eu(TTA)2phen) with a 395nm-emitting InGaN chip. The results indicate that the Eu-copolymer phosphor may act as a red component for fabrication of white LEDs.
Keywords: Eu-containing copolymer; Phosphor; Luminescence; LED
Influence of self-doped poly(aniline-co-4-amino-3-hydroxy-naphthalene-1-sulfonic acid) on corrosion inhibition behaviour of iron in acidic medium
by Hema Bhandari; Veena Choudhary; S.K. Dhawan (pp. 753-762).
This paper presents the corrosion inhibition performance of soluble self-doped copolymers of aniline and 4-amino-3-hydroxy-naphthalene-1-sulfonic acid synthesized by chemical oxidative polymerization method. The corrosion inhibition behaviour of the copolymers in 1.0M HCl has been evaluated using Tafel Extrapolation method and electrochemical impedance spectroscopy (EIS) which was also used to propose the mechanism besides surface morphology. The results showed that the copolymer film exhibited the significant shifting in the corrosion potential and greater charge transfer resistance. The corrosion inhibition efficiency was found to increase from 50% to 90% by increasing the concentration of copolymer from 10 to 70mg/l in HCl medium. Moreover, the copolymer showed the larger degree of surface coverage onto the iron surface, reflecting the higher inhibition for corrosion of the iron in highly acidic medium.
Keywords: Conducting copolymer; Corrosion inhibitors; Cyclic voltammetry; EIS; AFM
Vinylene-linked pyridine-pyrrole donor–acceptor conjugated polymers
by Alessandro Abbotto; Erika Herrera Calderon; Norberto Manfredi; Claudio Maria Mari; Chiara Marinzi; Riccardo Ruffo (pp. 763-769).
Vinylene-linked donor–acceptor–donor semiconducting polymers have been prepared by electropolymerization of the new monomers 2,6-bis[( E)-2-(1-methylpyrrol-2-yl)vinyl]pyridine and 2,5-bis[( E)-2-(1-methylpyrrol-2-yl)vinyl]pyridine. The monomers, consisting of two pyrrole donor units and a central pyridine acceptor ring spaced by vinylene links, differ by the substitution pattern around the central pyridine core (2,6 vs. 2,5-substitution). The electropolymerization process is more efficient on the 2,5-derivative. The new polymers show reversible electrochemistry dominated by a strong charge trapping effect. Poly(2,5-bis[( E)-2-(1-methylpyrrol-2-yl)vinyl]pyridine) energy levels closely match those of design rules for optimized polymers in combination with fullerene derivatives in bulk heterojunction solar cells.
Keywords: Conducting polymers; Pyrrole derivates; Electropolymerization; Spectroelectrochemistry; Energy levels
Preparation and characterization of Langmuir–Blodgett films of endohedral metallofullerene Gd@C82
by Bin Yang; Rufang Peng; Bo Jin; Shijin Chu (pp. 770-774).
Monolayer Langmuir–Blodgett (LB) films of metallofullerene Gd@C82 mixed with stearic acid (Gd@C82/SA) were deposited onto mica substrates from the air/water interface. The structural characteristics of these films were studied by atomic force microscopy (AFM) and contact angle (CA). The results showed that the metallofullerene Langmuir–Blodgett (LB) films with SA (Gd@C82/SA) were easily fabricated by vertical dipping method compared to the pure metallofullerene film. When the molar ratio of SA:Gd@C82 was up to 4:1, the corresponding LB films exhibited a uniform and ordered layer structure.
Keywords: Metallofullerene; Langmuir–Blodgett films; Structural properties; Atomic force microscopy
Synthesis, characterization and optical properties of novel well-defined di(1-ethynylpyrene)s
by Javier Illescas; Carolina Caicedo; Gerardo Zaragoza-Galán; Yessica S. Ramírez-Fuentes; Adriana Gelover-Santiago; Ernesto Rivera (pp. 775-782).
Three di(ethynylpyrenes) were synthesized and characterized: (Z)-1,1′-(buta-1,3-diene-1,3-diyl)dipyrene (DEPS), (E)-1,1′-(buta-1,3-diene-1,3-diyl)dipyrene (DEPA) and 1,1′-(but-3-ene-1,3-diyl)dipyrene (DEPH). The optical properties of these oligomers were studied by absorption and fluorescence spectroscopies and the results were compared to those previously obtained for the related polymer trans-poly(1-ethynylpyrene) ( trans-PEP). Intramolecular interactions occur between adjacent pendant pyrene units (associated pyrenes) in DEPS and DEPH, giving rise to static excimer emissions resulting from the stacking of aromatic rings. Excitation spectra jointly with life time fluorescence decays proved that such interactions take place in the ground state.
Keywords: Pyrene; Dimer; Optical properties; Fluorescence
Photophysical and two-photon absorption properties of protonation-induced tribranched chromophore having 1,3,5-triazine core and pyrrole end-groups
by Li Liu; Zhiqiang Zhou; Jieping Shi; Zeyu Liu; Changgui Lu; Weijiang He; Jing Ma; Yiping Cui; Guo-Yuan Lu (pp. 783-788).
The octupolar chromophoreTA with a 1,3,5-triazine core and pyrrole electron-donating end-groups was prepared via Knoevenagel coupling. Its photophysical and two-photon absorption (TPA) properties upon the protonation with CF3COOH were investigated by absorption, fluorescence, NMR spectroscopy and TPA cross-section determination. The UV–vis spectroscopic study shows that the absorption band is shifted from 401nm to 471nm with the color change from pale-yellow to red upon CF3COOH addition. The fluorescence spectra shows that the emission band is red-shifted from 490nm to 553nm accompanied by the distinct emission quench effect caused by the protonation. NMR spectropic study demonstrates the protonation of triazine upon CF3COOH addition, and the protonated molecule retain the C3h symmetry. In addition, the theoretical calculations of the absorption spectra of neutral and protonatedTA demonstrate an obvious red-shift of λmax in the absorption after protonation. TPA cross-section ofTA measured by nonlinear transmission (NLT) exhibits the obvious TPA cross-section enhancement effect upon protonation, provides a simple way to enhance the TPA cross-section of molecules and makes it attractive for application involving the proton-controlled optical sensor.
Keywords: Octupolar; Photophysical properties; TPA cross-section; Triazine; Protonation
Effects of hole and electron trapping on organic field-effect transistor transfer characteristic
by Jean-Christophe Bolsée; Jean Manca (pp. 789-793).
Routine organic field-effect transistor measurements are performed at negative and positive gate voltages leading to the occurrence of both hole and electron trapping. Despite this fact, the big majority of studies have focused either on hole trapping or on electron trapping but not on both at the same time. This paper presents the influences of trapped electron concentration n trap and trapped hole concentration p trap on the transfer characteristic (TC) features: onset voltage, hysteresis and transconductance, i.e. apparent mobility. Some effects are common to both charge types: (1) hysteresis is due to a combination of lower detrapping rate than sweep rate for n trap and p trap, (2) the transconductance is decreased by the super-linear V G dependence of p trap and by n trap detrapping. One effect is opposite to both charge types: p trap ( n trap) shifts the onset voltage towards negative (positive) value. We consider that the knowledge of trap-induced effects from both charge types is useful for correctly interpreting and understanding TCs.
Keywords: Hole trapping; Electron trapping; Organic transistor; Transfer characteristic
Temperature and electric field dependent hole mobility in a polyfluorene copolymer
by Francesca Tinti; Siraye E. Debebe; Wendimagegn Mammo; Teketel Yohannes; Nadia Camaioni (pp. 794-798).
Transport of holes in thin films of a low-bandgap alternating polyfluorene copolymer, APFO-Green5, was investigated by means of admittance spectroscopy as a function of field and temperature. The values of hole mobility were evaluated from the position of the maxima in the plots of the negative differential susceptance as a function of frequency. Hole mobility was found to be strongly field- and temperature-dependent. The charge transport parameters were extracted by analyzing the mobility data by the uncorrelated and the correlated Gaussian Disorder Models.
Keywords: Hole mobility; Transport properties; Conjugated polymers; Polyfluorene; Admittance spectroscopy
ET based conductors with different behavior of resistivity along and across conducting layers
by E.I. Zhilyaeva; O.A. Bogdanova; A.M. Flakina; G.V. Shilov; E.I. Yudanova; R.B. Lyubovskii; S.I. Pesotskii; R.N. Lyubovskaya (pp. 799-805).
Display Omitted► (ET)4MBr4(solvent), M=Hg, Cd, layered organic conductors with tetrahedral dianions. ► Metallic resistivity behavior in conducting layers and nonmetallic one across them. ► (ET)4MBr4·C6H4Cl2 are the first ET-based conductors with such behavior at 300–4.3K. ► Crystal structure is specified by different stacking directions in neighboring layers.A series of novel bis(ethylenedithio)tetrathiafulvalene (ET) based radical cation salts with tetrahedral [HgBr4]2− and [CdBr4]2− dianions of (ET)4MBr4(solvent) stoichiometry (M=Hg, Cd; solvent=C6H5X or 1,2-C6H4X2, X=Cl, Br) has been prepared. Crystal structures of θ-(ET)4HgBr4(1,2-C6H4X2) (X=Cl, Br) were found to involve conducting ET radical cation layers of the θ-type packing and insulating layers consisting of [HgBr4]2− anions and solvent molecules. The donor stacking directions of the neighboring conducting layers are perpendicular to each other.Depending on salt composition, intralayer electrical resistivity of θ-(ET)4MBr4(solvent) showed metal-like behavior down to temperatures varying within 4.3–100K range. Electrical resistivity perpendicular to the layers revealed nonmetallic behavior. The study of magnetoresistance of θ-(ET)4HgBr4(1,2-C6H4Cl2) revealed Shubnikov-de Haas oscillations in fields up to 15T with the only frequency F=900T. The θ-(ET)4MBr4(C6H4Cl2) M=Hg, Cd compounds are the first ET-based conductors which show metallic behavior of conductivity in layers and semiconducting behavior across layers down to 4.3K.
Keywords: Organic conductors based on radical cation salts; Electrical conductivity; X-ray diffraction
Synthesis and characterization of water-soluble polyaniline films
by Liang Shao; Jianhui Qiu; Mingzhu Liu; Huixia Feng; Lin Lei; Guohong Zhang; Yang Zhao; Chunmei Gao; Lijun Qin (pp. 806-811).
Water-soluble polyaniline (PANI) films were synthesized by using poly(2-acrylamido-2-methyl propanesulphonic acid) (PAMPS) as a water-soluble dopant. The aqueous solution conductivities of PANI/PAMPS films were in the range of 10−1 to 100mS/cm which were increased compared with PAMPS films aqueous solution. The structure and microstructure characteristics of PANI/PAMPS films which varied greatly with different molar ratios of aniline/AMPS were investigated by SEM, UV–vis absorption spectroscopy and XRD analysis. Moreover, the photoluminescence properties of PANI/PAMPS films were studied, and water-soluble PANI having appropriate size fitted to the increase of fluorescence emission intensity. PANI/PAMPS films were also investigated by FTIR spectroscopy and TG analysis.
Keywords: Water-soluble polyaniline; Double-strand; Stack; Photoluminescence
Microwave assisted click chemistry on a conductive polymer film
by Anders E. Daugaard; Thomas S. Hansen; Niels B. Larsen; Søren Hvilsted (pp. 812-816).
Microwave (MW) irradiation has been used to accelerate the functionalization of an azide functional poly(3,4-ethylenedioxythiophene) film by click chemistry. The absorption of MW energy by the conductive polymer has been exploited for localized activation of the reaction on the polymer surface. By use of an alkyne modified fluorescein derivative the reaction conditions have been optimized in a conventional MW oven, enabling the use of different sizes of substrates. The optimization resulted in a reduction of reaction times of approximately 20h to only 2min for bulk film functionalization. The method has been applied for anchoring of the chelating agent nitrilotriacetic acid (NTA) on the conductive polymer. The chelating linkage ability of NTA on the surface was investigated through a sandwich ELISA study confirming the selective bonding of a histidine tagged protein.
Keywords: Conductive polymers; Microwave reaction; Click chemistry; Poly(3,4-ethylenedioxythiophene) (PEDOT); Nitrilotriacetic acid (NTA)
Impedance spectroscopy properties of polypyrrole doped with boric acid
by F. Yakuphanoglu; I.S. Yahia; B.F. Senkal; G.B. Sakr; W.A. Farooq (pp. 817-822).
The electrical conductivity and dielectric properties of polypyrrole doped with boric acid have been investigated. The direct current conductivity (dc) of the polymer increases with increasing temperature. The alternating current (ac) conductivity of the polymer obeys the power law, i.e., σ ac( ω)= Aω s. The alternating conductivity of polypyrrole doped with boric acid is controlled by the correlated barrier hopping model. The activation energy for alternating current mechanism decreases with increasing frequency which confirms the hopping conduction to the dominant mechanism as compared with the dc activation energy. The density of localized states N( E F) for polypyrrole doped with boric acid was in the range of 2.5–9.2×1022cm−3 for various temperatures. The dielectric relaxation mechanism was explained on the basis of complex dielectric modulus. The imaginary modulus plot at different temperatures shows a dielectric mechanism with non-Debye relaxation. Boric acid can be a good candidate for controlling the electrical conductivity of the conducting polymer.
Keywords: Conducting polymer; Polypyrrole doped with boric acid; dc and ac electrical conductivities; Activation energy; Conduction mechanism; Impedance spectroscopy; Dielectric properties and relaxation time
The characteristics of organic light emitting diodes with Al doped zinc oxide grown by atomic layer deposition as a transparent conductive anode
by Su Cheol Gong; Ji Geun Jang; Ho Jung Chang; Jin-Seong Park (pp. 823-827).
Al doped zinc oxide (AZO) films, deposited by atomic layer deposition (ALD) were investigated for applying a transparent conductive oxide (TCO) layer as an anode for organic light emitting diode (OLED) devices. AZO films with a thickness of 100nm were deposited at various Al atomic ratios ranging from 0 to 5% at a deposition temperature (250°C). The optimum electrical properties: the carrier mobility, the resistivity, and the sheet resistance for the 2% AZO film were found to be 16.2cm2V−1s−1, 1.5×10−3cm−3, and 217Ω/sq, respectively. The red OLED devices were fabricated using AZO anodes utilizing the various Al atomic ratios; the electrical and optical characteristics were then investigated. The best luminance, quantum efficiency, and current efficiency were found in the OLED device using the 2% AZO TCO; the results were 16599cd/m2, 8.2%, and 7.5cd/A, respectively.
Keywords: Al doped ZnO (AZO); Transparent conductive oxide (TCO); Organic light emitting diodes (OLEDs); Atomic layer deposition (ALD)
Charge transport studies in thermally evaporated 2,2′,7,7′-tetrakis-( N, N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-MeOTAD) thin film
by Omwati Rana; Ritu Srivastava; Rakhi Grover; M. Zulfequar; M. Husain; M.N. Kamalasanan (pp. 828-832).
Charge transport mechanism in 2,2′,7,7′-tetrakis-( N, N-di-4-methoxyphenyl amino)-9,9′-spirobifluorene (spiro-MeOTAD) has been investigated as a function of temperature and organic layer thicknesses. Hole only devices of different thicknesses were fabricated in configuration ITO/spiro-MeOTAD/Au by vacuum evaporation technique. The hole current is space charge limited which provides a direct measurement of the hole mobility μ as a function of electric field and temperature. Gaussian disorder model has been used to explain the temperature and field dependent behavior of mobility. The values of energetic disorder ( σ=0.088eV), positional disorder ( Σ=3.35) and mobility prefactor ( μ0=0.0147cm2/Vs) have been evaluated using this model.
Keywords: Charge transport; SCLC; Hole mobility; Gaussian disorder model
5′-(Anthracene-9,10-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene) derivatives bearing 5-ethynyl-5′-hexyl-2,2′-bithiophene and 2-ethynyl-5-hexylthieno[3,2-b]thiophene: Thin film transistors and photovoltaic applications
by Soyoung Jo; Jicheol Shin; Suk Young Bae; Kyung Hwan Kim; Tae Wan Lee; Sunkyung Son; Kyungkon Kim; Dong Hoon Choi (pp. 833-843).
► Soluble p-type semiconducting materials based on anthracene unit. ► Those molecules showed very good film forming properties. ► Two-dimensional conjugated structures. ► High field effect mobility in TFT devices. ► The molecules were applied to solar cells (power conversion efficiency=0.5–0.6%).Novel 5,5′-(anthracene-9,10-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene)-based conjugated molecules have been synthesized via the Sonogashira coupling reaction. Newly synthesized anthracene-based molecules exhibit good solubility in common organic solvents and good self-film-forming properties. The semiconducting properties of the two molecules were evaluated in organic thin film transistors (OTFTs). The two π-conjugated molecules4 and7 exhibit fairly high charge carrier mobilities—as high as 0.010–0.022cm2V−1s−1 ( Ion/ Ioff>103)— without any annealing process. The high charge carrier mobilities of the as-spun films are attributed to the fact that the molecules demonstrated pronounced J-aggregation behavior, resulting in easy crystallization and dense coverage of the surface of a dielectric layer. In addition, two molecules were employed to fabricate organic photovoltaic (OPV) cells with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) without thermal annealing. As a result, the photovoltaic cell containing7 had the best preliminary results with an open-circuit voltage of 0.92V, a short-circuit current density of 1.82mA/cm2, and a fill factor of 0.32, offering an overall power conversion efficiency (PCE) of 0.54%.
Keywords: Conjugated molecules; Anthracene; Semiconductor; Mobility; Organic thin film transistor; Bulk heterojunction; Photovoltaic cell
Soluble functionalised fullerenes for photovoltaics
by M. Sharma; R. Bhatia; V. Gupta; S. Chand; P. Raghunathan; S.V. Eswaran (pp. 844-849).
Two mono-adducts of fullerene C60 have been synthesised using new aryl azides in good yields. These were characterized with spectroscopic techniques and then used to fabricate bulk heterojunction solar cells with regioregular poly (3-hexylthiophene) (RR-P3HT). A photocurrent density of 3.89mA/cm2, open-circuit voltage of 0.53V and power conversion efficiency of 0.89% for adduct I and photocurrent density of 2.93mA/cm2, open-circuit voltage of 0.53V and power conversion efficiency of 0.71% for adduct II have been achieved.
Keywords: Aryl azides; Thermolysis; 1; H/; 13; C NMR; Solar cells; Cyclic voltametry
Effects of anchoring groups in multi-anchoring organic dyes with thiophene bridge for dye-sensitized solar cells
by Yu Seok Yang; Hyung Do Kim; Jang-Hyun Ryu; Kyung Kon Kim; Sung Soo Park; Kwang-Soon Ahn; Jae Hong Kim (pp. 850-855).
Organic photo-sensitizers were designed and synthesized based on a phenothiazine framework containing single- and double-electron acceptors that were bridged with thiophene for the dye sensitized solar cells (DSSCs). The optimized geometries were determined with density functional theory (DFT) calculations to estimate the photovoltaic properties of the dyes in the design stage. The organic dye with the double electron acceptors exhibited a better light absorption at long wavelength and an effective electron extraction pathway from the electron donor to the TiO2 surface, leading to an improved short-circuit current (11.6mAcm−2), compared with that of the dye with the single electron acceptor (10.2mAcm−2) and the conventional N3 Ru-dye (10.4mAcm−2). Contrarily, the open-circuit voltage of the organic dye with the double electron acceptors decreased because the additional protonated carboxylic groups caused a positive shift in the Fermi level of TiO2.
Keywords: Dye-sensitized solar cells; Organic dyes; Multi-anchoring groups; Short-circuit current enhancement; Thiophene bridge; Structure optimization
Band-gap tuning of pendant polymers for organic light-emitting devices and photovoltaic applications
by Akhil Gupta; Scott E. Watkins; Andrew D. Scully; Th. Birendra Singh; Gerard J. Wilson; Lynn J. Rozanski; Richard A. Evans (pp. 856-863).
The preparation of a series of novel polymers comprising pendant electro-active “push–pull” chromophores and their performance in solution-processed organic electronic devices is described. The design of the electro-active pendant chromophores was based on the well-known motif of cyano-substituted poly( p-phenylenevinylene). Optical band-gap engineering within this series of polymers was achieved by varying the conjugation length and the electron donor/acceptor functionalities of the pendant chromophores. The introduction of a cyanoimine group into the electro-active pendant module resulted in a marked narrowing of the optical band-gap compared with the other electro-active pendant chromophores investigated in this work. Bulk heterojunction solar cell devices comprising these polymers were prepared by solution processing blends of each polymer with [6,6]-phenyl-C61-butyric acid methyl ester, and their performance was evaluated by measuring power conversion efficiencies. The best-performing solar cell in this series exhibited a power conversion efficiency of 0.29% and a maximum incident photon-to-current conversion efficiency of 22% and was produced using the polymer in which the electro-active chromophore comprised the cyanoimine group.
Keywords: Organic electronic devices; Polymer solar cells; Pendant polymers; Bulk heterojunction; Cyanoimine; Organic light emitting diodes; Electroactive
Synthesis of a side chain conjugated polythiophene copolymer and its photovoltaic property
by Chao Gao; Bo Qu; Zhongliang Jiang; Di Tian; Hongli Liu; Zhijian Chen; Lixin Xiao; Qihuang Gong (pp. 864-868).
A new soluble polythiophene copolymer with phenylene–vinylene conjugated side chain (PEHOPVTh-Th) was synthesized. Polymer photovoltaic solar cells using PEHOPVTh-Th as donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as acceptor was demonstrated. The absorption spectrum of the PEHOPVTh-Th showed strong absorption in the visible region and a 55nm red-shift in comparison with that of its homopolymer (PEHOPVTh). By adjusting the ratio of PEHOPVTh-Th to PC61BM, the polymer solar cells based on PEHOPVTh-Th showed a power conversion efficiency of 0.37% under 100mW/cm2 AM 1.5G simulated sunlight when the weight ratio of the polymer to PC61BM equals to 1:3.
Keywords: Photovoltaic cells; Bulk-heterojunction; Side chain conjugated polymer; Polythiophene
Synthesis and characterization of novel 2,5-diphenyl-1,3,4-oxadiazole derivatives of anthracene and its application as electron transporting blue emitters in OLEDs
by M. Ananth Reddy; G. Mallesham; Anup Thomas; Kola Srinivas; V. Jayathirtha Rao; K. Bhanuprakash; L. Giribabu; Rakhi Grover; Arunandan Kumar; M.N. Kamalasanan; Ritu Srivastava (pp. 869-880).
With a general aim to make anthracene derivatives multifunctional (n-type emitter) and also study their suitability as electron transport layers for organic light emitting diodes (OLED), we report the synthesis and characterization of five novel molecules in which the 9 and 10 positions of anthracene have been directly substituted by 2,5-diphenyl-1,3,4-oxadiazole groups. We have carried out detailed characterization of these molecules which include photophysical, electrochemical, thermal, electroluminescent and computational studies. The electron affinity is very high, around 3.7eV, and the ionization potential is around 6.7–6.8eV, which is relatively higher than the most commonly used electron transport electroluminescent layer Alq3. The studies reveal that the new molecules being reported by us, in addition to the high thermal stability, are quite efficient in a two layer unoptimized nondoped device with the device structure ITO/α-NPD/10a–11b/LiF/Al and have an emission in pure blue. They also show very high efficiency as electron transport layer in device structure ITO(120nm)/α-NPD(30nm)/Ir(ppy)3 doped CBP(35nm)/BCP(6nm)/10a(28nm)/LiF(1nm)/Al(150nm). From these studies we conclude that these anthracene derivatives also have considerable potential as multifunctional layers and as electron transport layers in OLED.
Keywords: OLED; Blue emitters; Electron transport; Anthracene derivatives; Nondoped device
Temperature dependence of electronic parameters of organic Schottky diode based on fluorescein sodium salt
by I.S. Yahia; A.A.M. Farag; F. Yakuphanoglu; W.A. Farooq (pp. 881-887).
The electrical properties of an organic Schottky diode based on fluorescein sodium salt were investigated by current density–voltage and capacitance–voltage measurements. The crystal structure of fluorescein sodium salt, FSS in powder form was analyzed by X-ray diffraction method. X-ray diffraction results showed that the fluorescein sodium salt has a polycrystalline structure with a monoclinic system. The current density–voltage and capacitance–voltage characteristics of Al/FSS Schottky diode were investigated in the temperature range of 300–400K. The diode exhibits a rectifying behavior, indicating the formation of the Schottky type junction at the interface of Al/FSS. The predominant charge transport mechanism of the Al/FSS Schottky diode was discussed and the proposed current injection processes was presented. The temperature dependence of the calculated acceptor concentration, the built-in potential and the width of the depletion region of Al/FSS Schottky barrier was also determined.
Keywords: Organic semiconductor; Al/FSS Schottky diode; Rectification; Current–voltage; Capacitance–voltage
Top gate copper phthalocyanine thin film transistors with laser-printed dielectric
by A.K. Diallo; L. Rapp; S. Nénon; A.P. Alloncle; P. Delaporte; F. Fages; C. Videlot-Ackermann (pp. 888-893).
Dielectric layers involved in top gate organic thin film transistors (TG-OTFTs) have been fabricated by using laser induced forward transfer (LIFT) technique. Poly(methyl methacrylate) (PMMA) as insulating polymer was spin-coated on a quartz substrate and transferred by laser on an acceptor substrate to form a dielectric layer on top of an organic semiconducting layer and source/drain contacts both previously vapour phase deposited. Copper phthalocyanine (CuPc) has been chosen to form p-type organic active layers. The nature of transferred patterns and the efficiency of LIFT confirm the important potential of a laser printing technique in the development of plastic microelectronics. Electrical characterizations in TG configuration demonstrated that transistors are fully operative with hole mobility up to 8.6×10−3cm2/Vs. A comparative study with others dielectric layers in bottom gate transistors (BG-OTFTs), as PMMA spin-coated and silicon dioxide SiO2, points out more precisely the limiting parameters to an efficient charge transport in the conducting channel created at the interface between PMMA and CuPc.
Keywords: Organic transistors; Top gate; Copper phthalocyanine; Laser printing
Performance reproducibility of organic light-emitting devices under exposure to atmospheric water vapor during fabrication: Sensitivity and chaotic-like behaviour of the quantum yield
by P.P. Ferguson; G.G. Allogho; S. Pitre; R. Morrisey; S. Gauvin (pp. 894-898).
Organic electronic devices are generally sensitive to atmospheric conditions, especially to water vapor when combined with oxygen. Organic light-emitting devices are such an example. Usually, atmospheric water vapor has detrimental consequences on the devices performance. However, as shown by our experimental results, in some (still uncontrolled) circumstances, oxidation processes accelerated by water vapor can be beneficial to performance. Thus, high humidity level is not only a detrimental issue to OLEDs. In addition, it appears that the occurrence of antagonist mechanisms and the devices sensitivity to initial structural conditions of organic materials and electrodes leads to an unpredictable, chaotic-like, behaviour of organic light-emitting quantum yield when they are exposed to atmospheric water vapor.
Keywords: PACS; 85.60.Jb; 81.05.FbOrganic electroluminescence; Performance reproducibility; Detrimental and beneficial processes; Fabrication conditions; Metallic electrodes; Humidity and oxygen; TPD/Alq; 3; devices
Electrical behavior of conducting polymer based ‘polymeric–inorganic’ nanocomposite: Polyaniline and polypyrrole zirconium titanium phosphate
by Asif Ali Khan; Leena Paquiza (pp. 899-905).
Display Omitted► The proposed ‘polymeric–inorganic’ nanocomposites are found semi-conducting in nature. ► The DC electrical conductivities of both were found stable upto 110°C. ► The electrical conductivity of the sample increases with increase in temperature.Composites are 21st century material used to meet the demand of improved materials and possess a combination of several desirable properties. Present study focussed on the conducting behavior of ‘polymeric–inorganic’ nanocomposite of conducting polymer polyaniline and polypyrrole. ‘Polymeric–inorganic’ nanocomposite cation-exchangers, i.e., polyaniline zirconium titanium phosphate ( PANI-ZTP) and polypyrrole zirconium titanium phosphate ( PPy-ZTP), were synthesized via sol–gel mixing of electrical conducting polymers into the matrices of inorganic precipitate of zirconium titanium phosphate ( ZTP) having excellent ion exchange properties. The proposed nanocomposite possessed DC electrical conductivity in the semi-conducting range, i.e., 10−5–10−3Scm−1. The stability in terms of DC electrical conductivity retention was also studied in an oxidative environment by two slightly different techniques viz. isothermal and cyclic techniques. The DC electrical conductivity of composite material was found stable upto 110°C under ambient conditions.
Keywords: Polyaniline; Polypyrrole; Zirconium titanium phosphate; Electrical conductivity; Isothermal stability; Composite
Effect of monodisperse Cu2S nanodisks on photovoltaic performance of P3HT/PCBM polymer solar cells
by Yunzhang Lu; Yanbing Hou; Yan Wang; Zhihui Feng; Xiaojun Liu; Yanwu Lü (pp. 906-910).
Hybrid solar cells using monodisperse Cu2S nanodisks compositing with the mixture of poly (3-hexylthiophene):1-(3-methoxycarbonyl) propyl-1-pheny [6,6] C61 (P3HT:PC60BM) as the active layer have been fabricated and characterized. The hybrid solar cells exhibit the highest efficiency of 1.35% when the weight ratio of P3HT:PC60BM:Cu2S is 1:0.8:0.224. The power conversion efficiency (PCE) of nanocomposite device is increased 22.7% comparing with that of the device based on pure P3HT/PC60BM. It is due to that the effect of high-quality Cu2S nanodisks with good dispersity contributes the increased electronic transportation in the active layer and results in the enhancement in photovoltaic performance. We also investigated the morphology of photoactive layer by microscope; it is found that the dispersity of nanomaterial in active layer is very important for device performance and improvement of carrier mobility.
Keywords: Polymer solar cell; Cu; 2; S; P3HT; Nanodisk
Dielectric properties at microwave frequencies of poly(ɛ-caprolactone)/CNF films and electrospun mats
by Francesca Nanni; Costantino Del Gaudio; Ilaria Armentano; Mariaserena Dottori; Alessandra Bianco; J.M. Kenny; G. Gusmano (pp. 911-918).
► Synthesis of hybrid polyɛ-caprolactone/carbon nanofiber films and electrospun mats. ► Electromagnetic properties at microwaves (8–12.4GHz) via wave guide measurements. ► Permittivity of mats is far lower than that of films. ► Effect of microstructure and CNF loading on electromagnetic performance.The electromagnetic (EM) properties of hybrid poly(ɛ-caprolactone)/carbon nanofiber films and electrospun mats at microwave frequencies (8.2–12.4GHz) were assessed by means of wave guide measurements. It was found that, on equal composition, the two systems present very different permittivities, that in the case of electrospun mats is far lower than that of films. These results are explained in view of the different microstructures. In particular, the massive presence of porosity is demonstrated to be the major parameter affecting the EM properties of mats. Shielding effectiveness was evaluated and was found to be poor for both systems, despite the relative large amount of conductive nanofiller. This results was attributed, in the case of films, to the presence of multiple reflections among CNF, while in the case of mats to their porous microstructure that let the waves easily pass through.
Keywords: Microwave properties; CNF films; Electrospun mats; Waveguide measurements
A phosphorescent copper(I) complex: Synthesis, characterization, photophysical property, and sensing performance towards molecular oxygen
by Jijun Xu (pp. 919-924).
In this paper, we report the synthesis, crystal structure, photophysical properties, and electronic nature of a phosphorescent Cu(I) complex of [Cu(PYB)(POP)]BF4, where PYB and POP stand for 2-pyridin-2-yl-1H-benzoimidazole and bis(2-(diphenylphosphanyl)phenyl) ether, respectively. [Cu(PYB)(POP)]BF4 renders yellow phosphorescence peaking at 561nm, with a long excited state lifetime of 13.4μs. Density functional calculation reveals that the emission comes from a triplet metal-to-ligand-charge-transfer excited state. We electrospun composite nanofibers of [Cu(PYB)(POP)]BF4 and polystyrene, hoping to explore the possibility of using the composite nanofibers as an oxygen sensing material. The finally obtained samples with average diameter of ∼900nm exhibit a maximum sensitivity of 4.20 towards molecular oxygen with short response/recovery time (8s/16s) due to the large surface-area-to-volume ratio of nanofibrous membranes. No photobleaching is detected in these samples.
Keywords: Cu(I) complex; Oxygen sensor; Single crystal; Luminescence