Synthesis,characterization and optical properties of novel well-defined di(1-ethynylpyrene)s

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.     

Influence of stereoregularity on the photoinitiated electrical conductivity of poly (3-alkylthiophenes)

Several kinds of synthesis methods leading to regie and stereo chemical control of polymer architecture and also to polymers derived from oligomers possessing internal symmetry or containing suitably spaced alkyl chains have been performed. The different structures have been studied in relation to their electrical conductivity behaviour. Doping of polymers has been photoinitiated with optically dissociative materials (triarylsulfonium salts) which were incorporated with the basic poly(3-alkylthiophene) polymer into the spinning solution. Conditions of light exposure (wavelength range, exposure dose) and concentration of photodopant used have been optimized in order to enhance the electrical conductivity and its thermal stability. High-resolution conducting patterns have been realized by microlithography techniques. Their possible use in microelectronics is investigated.     

前处理工艺对Li[Ni1/3Mn1/3Co1/3]O2正极材料结构、形貌和电化学性能的影响（英文）

以[Ni1/3Co1/3Mn1/3]3O4和氢氧化锂为原料,分别采用球磨法和液相法前处理工艺制备层状正极材料Li[Ni1/3Mn1/3Co1/3]O2。采用X？射线衍射（XRD）、场发射扫描电镜（FESEM）、恒流充放电等手段对材料的物理和电化学性能进行表征。结果表明：采用不同前处理工艺制备出的Li[Ni1/3Mn1/3Co1/3]O2材料在结构、形貌和电化学性能上有较大差异;与球磨处理法制备的材料相比,采用液相法前处理工艺制备的Li[Ni1/3Mn1/3Co1/3]O2不但保持了前驱体较好的球形形貌,同时还具有较好的循环稳定性和倍率性能;该样品在20mA/g电流密度下,首次放电容量为178mA·h/g,50次循环后,容量保持率达98.7%;在1000mA/g电流密度下,样品容量为135mA·h/g。     

Electrochemical properties and conductivity of poly(3-methylpyrrole/ClO4)

Electrosynthesis of conducting poly(3-methylpyrrole) has been carried out at fixed potentials of 0.5 and 0.6 V in a NaClO₄ acetonitrile solution. The electrochemical behaviour of doped-polymer films has been analysed considering the influence of the negative and positive potential limits as well as the scan rate on the voltammograms recorded in acetonitrile. From these studies a mechanism for the redox processes is proposed. Polymer morphology has been examined by scanning electron microscopy, which reveals a cauliflower and compact texture depending on the potential of synthesis and deposition time. Kinetic of conductivity decay with aging time has been determined to be dependent of exp(−t^1/2) with a characteristic time of the degradation process around 20 days.     

Synthesis,optical and electrochemical properties of novel hole-blocking poly(biphenylene-1,3,4-oxadiazole) containing electron-withdrawing trifluoromethyl groups

New poly(biphenylene-1,3,4-oxadiazole) P1 and poly(biphenylene hydrazide) P2 containing electron-withdrawing trifluoromethyl group at the 2 and 2′ positions of biphenyl moiety were synthesized. The biphenyl is forced to adapt a non-coplanar conformation due to the bulky trifluoromethyl group. High quality polymer P1 thin film can be easily obtained by thermal cyclodehydration from its soluble polyhydrazide precursor P2. The polymer P1 exhibited good thermal stability with glass transition temperature of 234 °C and 5% decomposition temperature of 469 °C. The optical and electrochemical properties were investigated by UV–vis spectroscopy, photoluminescence spectroscopy and cyclic voltammetry. For polymer P1 film, two absorption peaks at 370 and 414 nm were observed. It also exhibited a photoluminescent peak at 555 nm when excited by 414 nm light. The cyclic voltammetric studies revealed that polymer P1 had extremely low HOMO (?6.85 eV) and LUMO (?3.71 eV) energy levels due to the presence of strong electron-withdrawing trifluoromethyl group. It also exhibited a large energy gap (3.14 eV) which is an indication of short conjugation length resulted from non-coplanar biphenyl structure. Its HOMO energy was even lower than that of widely used hole-blocking material, 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole PBD (?6.30 eV). The low LUMO energy of polymer P1 could allow the easier electron injection from air-stable cathode such as aluminum. The good electron transfer ability was also shown by measuring the current density of electron-only devices with the structures of Al/P1 (150 nm)/Alq₃ (50 nm)/Al and Al/Alq₃ (200 nm)/Al. Combined with high thermal stability and amorphous morphology, polymer P1 would be a promising candidate as the hole-blocking material for organic light-emitting diodes.     

Vacuum ultraviolet spectroscopy of the optical properties and electronic structure of seven poly(di-alkylsilanes)

We report the ultraviolet (UV) and vacuum ultraviolet (VUV) optical properties and electronic structure, up to 44 eV, of thin-film samples of seven poly(di-alkylsilanes) [alkyl = n-butyl, n-pentyl, i-hexyl, n-hexyl, n-octyl, and n-tetradecyl] with three types of Si---Si backbone conformations: helical, planar zigzag, and trans-gauche-trans-gauche' (TGTG′). The backbone conformation determines the UV transitions, with helical materials exhibiting one near-UV absorption, while two UV transitions are seen for the two-phase materials containing both the helical and planar zigzag backbone conformations. The TGTG′ backbone exhibits a single UV absorption at 3.6 eV. At higher energies all materials show a prominent shoulder at 7.2 eV, with a doublet peak structure seen at ≈ 9 and ≈ 12 eV. The 7.2 eV transition is unaffected by the backbone conformation or alkyl substitution, while comparison with the electronic transitions in polyethylene shows that the high-energy double-peak structure corresponds to transitions in the hydrocarbon sidechains. The ≈ 12 eV transitions appear to shift to higher energy with increasing sidechain length and in tetradecyl these sidechain transitions are noticeably narrowed, suggesting unusual sidechain crystallization in poly(di-n-tetradecylsilane). A hierarchy of electronic transitions can be developed whereby the UV transitions arise in the Si backbone, at intermediate energies backbone to sidechain transitions are observed, while the high-energy transitions are of the alkyl sidechains. This hierarchy in the electronic transitions demonstrates the ability of VUV spectroscopy of the electronic structure to serve as a microscopic probe of the bonding and structure of polysilanes, for example providing detailed insight into the properties of the sidechains in these polymers.     

Influence of thermal and plasma treatments on the electrical properties of poly(para-phenylene vinylene)-based diodes

We have studied the influence of plasma and thermal treatments on the electrical properties of poly(para-phenylene vinylene) (PPV) thin films in metal-polymer-metal structures. Thermal heating of the samples modifies the diode characteristic by reducing the voltage threshold and by favouring the formation of the rectifying contact at the bottom side. Plasma treatments with oxygen or nitrogen drastically change the conductivity of the polymer with disappearance of the rectifying behaviour and increase the current by many orders of magnitude. Attempts to explain the modifications of the electrical property of the treated samples are given, using previous results from X-ray photoelectron spectroscopy (XPS) which highlight the role of the interfacial layer formed by chemical reaction between the polymer and metallic electrode.     

Effects of substituents on the third-order nonlinear optical properties of poly(3-alkoxythiophene) derivatives

Poly(3-alkoxythiophenes) (P3AOTs) have been synthesized with octoxyl, dodecaoxyl and 4-nitro-benzyloxyl as sidechains, respectively. The novel poly(3-octoxycthiophen)-co-poly(3-(4-nitro-benzyloxy)-thiophene) (P3OOT-co-P3NBOT) has also been prepared. The absorption spectra of samples indicate that the side groups affect the bandgap of P3AOTs. The nonlinear optical (NLO) properties of P3AOTs were investigated using Z-scan method. The third-order NLO susceptibility (χ⁽³⁾) of the polymers shows a strong dependence on the length of the alkoxyl sidechains and polarity of polymers, which affect the intra- and intermolecular charge transfer. These polymers have potential application in optical limiting device.     

Influence of hydrogen on the structure and mechanical properties of the VT3-1 titanium alloy

NIID. MATI (Stupinskii Branch). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 32–33, January, 1992.     

Electrochemical impedance studies on the electrochemical properties of poly(3-methylthiophene) in aqueous solutions

Electrochemical impedance spectroscopy (EIS) measurements in a wide frequency range were used to study the electrochemical properties of poly(3-methylthiophene) (PMT) films. PMT was synthesized in acetonitril (AC) using BF₄⁻, ClO₄⁻ and CF₃SO₃⁻ as doping anion and Li⁺ as cation. The electrochemical characterization of these films was performed in aqueous solution using the same electrolyte for synthesis. Different parameters as electrolyte resistance, double layer capacitance, pore resistance, fractal dimensions, internal capacitance and charge resistance. SEM observation of PMT films provide strong evidence of the close relationship between type of electrolyte and their morphology, also is in good agreement with ac impedance results interpretation. The results are interpreted on the basis of models developed for intercalation electrodes in relation to the geometry and morphology of the polymer electrode. The results are discussed on the basis of the structural and chemical parameters of the anions and their interaction with the polymer. The discussion shows that the nature of the anion plays a major role on the electrochemical behavior of the polymer.     

Si4+和F-掺杂对LiNi1/3Co1/3Mn1/3O2结构和电化学性能的影响

以Li2CO3、NiO、Co2O3、MnO2、LiF和SiO2为原料,采用机械力活化固相法制备了Si4+和F-掺杂的锂离子电池正极材料LiNi1/3Co 1/3Mn1/3O2.通过X射线衍射(XRD)、扫描电镜(SEM)和电化学性能测试等技术研究了LiNi1/3Co1/3Mn1/3O2的结构特征、形貌及电化学性能等.结...     

Polyene films prepared by poly(ethylene glycol)s-catalyzed dehydrochlorination of poly(vinyl chloride): chemical and electrochemical properties

Poly(vinyl chloride) (PVC) film containing certain amounts of poly(ethylene glycol)s (PEG) catalyst can be extensively dehydrochlorinated by aqueous potassium hydroxide. The molar mass of the PEG used as phase transfer catalyst is ranged from 200 to 800 g mol⁻¹. According to the results of elemental analysis and UV–visible, Fourier transform-infrared (FT-IR) and FT-Raman spectra, the polyene films obtained from these systems are polyacetylene-like and contain relatively long conjugated sequences. The highest conversion of the reaction at room temperature is measured to be about 90% (f_H). The conductivity of iodine-doped polyene films can reach to the order of 10⁻² S cm⁻¹. The electrochemical doping process of dehydrochlorinated PVC film is controlled by diffusion mechanism like polyacetylene, and some irreversible degradation at the polyene surface occurs when the potential is rising above 1.6 V.     

Modification of poly(3-methylthiophene) (PMeT) structure during electrochemical doping-undoping,studied by in situ atomic force microscopy (ECAFM)

Doping and undoping of poly(3-methylthiophene) (PMeT) layers were performed in an electrochemical atomic force microscopy (ECAFM) microcell, and images accounting for modification of the polymer surface were continuously recorded. The main result is that the variation of polymer morphology is very slow in relation to the modification of doping charge. The discrepancy between the two time constants, related respectively with ion and solvent molecule transfer and by electronic charge transfer, was emphasized by in situ ellipsometry. In this case the variation of optical properties against doping charge is very fast.     

Synthesis,electrochemical, and spectroelectrochemical properties of conductive poly-[2,5-di-(2-thienyl)-1H-pyrrole-1-(p-benzoic acid)]

Poly(ter-heteroaromatic(thiophene-pyrrole-thiophene)), PDPB, was electrochemically prepared from the 2,5-di(2-thienyl)-1H-pyrrole-1-(p-benzoic acid) (DPB) monomer using the Paal-Knorr pyrrole condensation reaction. The structure of the monomer was confirmed using ¹H-, ¹³C NMR, FT-IR and mass spectroscopy. The maximum UV–visible absorption and PL emission bands of DPB were observed at 330 nm and 500 nm, respectively. The cyclic voltammograms (CVs) recorded for the electrochemically polymerized DPB revealed a set of redox peaks at 0.65/0.53 V. The conductivity monotonically increased with respect to the applied potential from 0.0 V to 1.0 V, exhibiting a maximum conductivity of 0.18 S/cm at +0.80 V. The in situ UV–visible spectroelectrochemical analysis of PDPB revealed electronic transitions at 420 nm, 654 nm, and 870 nm corresponding to the π–π* transition, polaron, and bipolaron states, respectively. The optical band-gap (E_g) of PDPB was 2.16 eV. The color of the PDPB film transitioned yellow (at 0.0 V) to blue (at 1.0 V) when the potential was switched between the reduced and oxidized states with a good electrochromic response time (0.95 s).     

Synthesis and optical properties of poly(fluorene)-based alternating copolymers

The novel poly(9,9-bis(2-ethylhexyl)fluorene-alt-2′,5′-thiophene), and the similar poly(9,9-bis(2-ethylhexyl)fluorene-alt-2′,5′-thiophene-1,1-dioxide) and poly(9,9-bis(2-ethylhexyl)fluorene-alt-1′,4′-phenylene) luminescent copolymers were synthesised by the Suzuki coupling reaction. Within this series, we show that an adequate choice of the unit combined with the fluorene monomer, effectively controls the energetic position of the frontier levels of the copolymer. This effect is evidenced by the different optical energy band gaps and different emission colours. Furthermore, the results of cyclic voltammetry (CV) studies show that the S,S-dioxide substitution on the thiophene ring increases both the ionisation potential (IP) and the electron affinity (EA) in relation to the similar thiophene-based copolymer.     

Double-walled carbon nanotube (DWCNT)–poly(3-octylthiophene) (P3OT) composites: Electrical,optical and structural investigations

In the present study, we report experiments based on in situ polymerization of 3-octylthiophene with DWCNT and many hitherto unstudied properties for the first time. The specialty of DWCNT being the inner tube retaining its intrinsic electronic and optical properties, while the outer tube could be involved in the composite formation. From the IR aromatic and out-of-plane C–H stretching frequencies, the interaction between the polymer and the nanotubes is probed. Further to this absorption spectroscopy, photoluminescence and Raman measurements were carried out to characterize the composites. The conductivity contributions of the nanotubes and Hall voltage measurements are used to understand the utility of the composites for solar cell applications.