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Synthetic Metals (v.149, #1)

Novel fluorene–pyridine-based alternating copolymers: syntheis, characterization and optical properties by Shou-Ping Liu; Siu-Choon Ng; Hardy S.O. Chan (pp. 1-11).
A novel series of well-defined soluble poly[2,7-(9,9-dialkyfluorenyl)-alt-pyridinyl] (except for PDHFP-25, a polymer with same composition but different weight-average molecular mass ( Mw) was reported in reference [B. Liu, W.L. Yu, Y.H. Lai, W. Huang, Chem. Mater. 13 (2001), 1984–1991] were synthesized using palladium-catalyzed Suzuki cross-coupling reactions in good to high yields. In the series of alternating copolymers, 2,7-(9,9-dialkylfluorenyl) was used as the light emitting unit and the electron deficient pyridinyl unit was employed to provide improved electron transportation. All these polymers were characterized by1H NMR,13C NMR, GPC, thermal analyses, UV–vis and fluorescence spectroscopy. The shorter pendant 9,9-dihexyl at fluorenyl unit is better to polymer for higher thermal stability and higher Tg than 9,9-dioctyl at fluorenyl unit. The meta-linkage (3,5- or 2,6-linkage) of pyridinyl units in the polymer backbone is more favourable to polymer for pure blue emission and prevention of aggregation of polymer chain than the para-linkage (2,5-linkage) of the pyridinyl units.

Keywords: Fluorene; Pyridine; Blue light-emitting polymers; Suzuki cross-link coupling reaction

Influence of the cooling rate on low-temperature Raman and infrared-reflection spectra of partially deuterated κ-(BEDT-TTF)2Cu(N(CN)2)Br by M. Maksimuk; K. Yakushi; H. Taniguchi; K. Kanoda; A. Kawamoto (pp. 13-18).
Raman and infrared-reflection spectra of κ-(BEDT-TTF)2Cu(N(CN)2)Br and its deuterated and partially deuterated analogues were measured at temperatures between 5 and 300K and cooling rates from 1 to 20K/min. It was found that, in partially deuterated samples, the interdimer electron–molecular vibration splitting of ν3 mode in Raman spectra, and linewidths of some phonon peaks both in Raman and infrared spectra depend on the cooling rate. These observations were explained by disorder-related effects.

Keywords: PACS; 78.30.Jw; 71.20.Rv; 71.27.+a; 71.30.+hBEDT-TTF; Raman spectra; IR spectra

Thermo-induced changes in EPR spectra of metal-free oligo- and polyphthalocyanines by Yu.A. Koksharov; A.I. Sherle; A.N. Tikhonov (pp. 19-29).
Conjugated polymers (CP) are promising materials for various electronic, optical and magnetic applications, but clear understanding of their electron structure is not still achieved. Electron paramagnetic resonance (EPR) studies can give valuable information about electron states in polymers. We present a study of metal-free oligomeric (OPc) and polymeric (PPc) phthalocyanines by the EPR technique in the temperature interval from 300 to 500K. Both of air-exposed and vacuum-processed samples have been investigated. The g-value, the intensity, the width and the shape of EPR signals observed in OPC and PPc at room temperature are typical of conjugated polymers. However, we found specificities of the EPR thermal behavior that was dependent on the oligomer molecular weight and sample's treatment. There was a certain temperature T1 above which the EPR signal becomes time-dependent that reflects in a growing of the EPR signal intensity. We detected also another characteristic temperature T2 ( T2> T1) above which the irreversible increasing of the EPR linewidth was observed. After vacuumization of OPc and PPc samples, the temperatures T1 and T2 shift to the higher values. The low-molecular OPc were characterized by the lesser value of T2 in comparison with OPc of higher molecular masses and polymer samples. The computer analysis showed that the specific shape of the EPR line and its thermo-induced evolution can be explained by the coexistence of both localized and delocalized EPR-active centers.

Keywords: Electron paramagnetic resonance; Phthalocyanines; Oligomers; Conjugated polymers

Copolymer of alkylated oligothiophene with polyethylene oxide: synthesis and properties by G. Čík; Z. Végh; F. Šeršeň; J. Krištín; B. Lakatoš; P. Fejdi (pp. 31-38).
A new type of copolymer of alkylated oligomeric thiophene and polyethylene oxide (PEO) was synthesized. Synthesis was performed by the condensation reaction of alkylated dimethylester of oligothiophene dicarboxylic acid with PEO. The synthesized six-membered oligothiophene was prepared by directed synthesis of cyclization of the thiophene ring with strictly defined position of alkyls, settled on the outer thiophenic rings. The copolymer is soluble in common organic solvents and in the solid state, which creates structurally-organized clusters composed of conducting (oligothiophenic) and non-conducting (PEO) segments. Separated thiophenic phase was confirmed by TEM, and localized fluorescence of thiophenic clusters.

Keywords: Conducting polymers; Polyalkylthiophenes; Polyethylene oxide; Fluorescence

Electrosynthesis of a copolymer containing C60 in the main chain by C. Kvarnstrm; H. Kulovaara; P. Damlin; T. Vuorinen; H. Lemmetyinen; A. Ivaska (pp. 39-45).
The electrochemical synthesis of a copolymer consisting of phenylene vinylene units and C60 was studied. The starting materials were α,α,α′,α′-tetrabromo- p-xylene and C60. The fullerene is introduced into the polymer synthesis as a film on the working electrode. The C60 film is dissolved upon reduction and the reduced fullerene species interacts with the simultaneously reduced precursor at the electrode surface resulting in a film on the substrate. The coupling reaction between the reduced species leads to a material where the fullerene units are incorporated into the main polymer chain. The film formed is characterized by cyclic voltammetry and by FTIR, Raman and UV–vis spectroscopy. The charging discharging reaction of the copolymer film was studied by in situ ATR-FTIR. The spectroscopic results indicate short chains of copolymeric structure. Fluorescence spectra were recorded from films of the copolymer and from PPV. The fluorescence of PPV was quenched to one tenth of its origin in the copolymer film.

Keywords: Polypara (phenylene vinylene), fullerene film; Electrosynthesis; Copolymer; Fluorescence

Complexes of oligopyrrole dications with inorganic anions: a comparative theoretical HF/post-HF study by Tarmo Tamm; Jri Tamm; Mati Karelson (pp. 47-52).
The complexes of pyrrole oligomer dications with various inorganic anions were studied using a variety of computational methods ranging from semi-empirical to density functional theory (DFT) and MP2. The geometry of the complexes and the differences in complexation energies are discussed. The differences in the stability of the complexes compare favorably to experimentally known trends of anion mobilities in polypyrrole films.

Keywords: Quantum chemical calculations; Polypyrrole; Pyrrole oligomer dications; Counter-ions

New electro-active paper actuator using conducting polypyrrole: actuation behaviour in LiClO4 acetonitrile solution by S.D. Deshpande; Jaehwan Kim; Sung-Ryul Yun (pp. 53-58).
The construction of electromechanical actuator has been achieved by using the conducting polypyrrole films deposition onto a gold-coated cellophane paper. This is probably the first report of this type of paper actuator. The conducting polypyrrole was electro-generated using either galvanostatic or potentiostatic conditions at 0.5mA/cm2 current density or 0.7V applied potential, respectively. The two types of actuators were constructed, namely: (1) Ppy/cellophane bi-layer; (2) Ppy/cellophane paper/Ppy tri-layer. These actuators showed a reversible and reproducible displacement in acetonitrile solution containing LiClO4 (1M). The maximum displacement of 9.1mm was recorded for tri-layer device and 3.5mm for bi-layer device in 1M LiClO4 acetonitrile solutions. The results obtained in acetonitrile solution containing 1M LiClO4 shows that the actuator requires very low excitation voltage of 0.2MVm−1. The mechanism for this paper actuation phenomenon is addressed in this paper.

Keywords: Electro-active paper actuator (EAPap); Ppy/cellophane paper bi-layer; Ppy/cellophane paper/Ppy tri-layer; CP-EAPap actuators; Lightweight actuators; Large displacement actuators

A study on the dual emissions of organic light emitting devices by Tahsin J. Chow; Shang-Heng Tsai; Ching-Wen Chiu; Tzu-San Yeh (pp. 59-62).
The color of light-emitting diodes is tunable by adjusting the dual emissions of two type of devices containing 2,3-bis(2′, N-dimethyl-3′-indolyl)- N-methylmaleimide. The first device, utilizing Alq3 (tris(8-hydoxyquinolinato)aluminum) as the electron transporting layer (ETL), displays yellow color which is invariant to applied bias. The second device, utilizing TPBI (2,2′,2″-(l,3,5-benzenetriyl)tris(l-phenyl-lH-benzimidazole) as ETL, displays a continuous change of color from orange to blue depending on the doping level as well as the applied bias. The different emitting characteristics can be rationalized by the variation of potential energy barriers at the interface between different layers, which control the movements of electrons as well as holes

Keywords: Organic light-emitting devices; Dual emissions; Tunable color; Bis-indolylmethylmaleimide

Chlorine precursor route to poly(2-phenoxy p-phenylene vinylene): synthesis and characterization by James N. Wilking; Bing Hsieh; Georgia A. Arbuckle-Keil (pp. 63-72).
A new PPV derivative, poly(2-phenoxy p-phenylene vinylene)(PO-PPV), has been synthesized via the chlorine precursor route (CPR). PO-PPV and its chlorine precursor polymer were fully characterized by thermal (TGA and DSC), mechanical and spectroscopic (UV–vis, PL and IR) methods. The results indicate that the precursor polmer and the yellow-green light-emitting PO-PPV have excellent stability and mechanical properties. The easily processible precursor is stable at room temperature and therefore has a better shelf-life than PPV synthesized via the sulfonium precursor route. Thermal conversion provides high quality films, relatively free of oxidative defects.

Keywords: PO-PPV; Poly(2-phenoxy; p; -phenylene vinylene); PPV derivative; Chlorine precursor route; Photoluminescence; Thermal analysis; FT-IR

The application of soluble and regioregular poly(3-hexylthiophene) for organic thin-film transistors by Meyoung Ju Joung; Chul Am Kim; Seung Youl Kang; Kyu-Ha Baek; Gi Heon Kim; Seong Deok Ahn; In Kyu You; Jin Hee Ahn; Kyung Soo Suh (pp. 73-77).
We have investigated the effect of solvent medium, thermal annealing and dedoping reducing agent such as hydrazine on the performance of poly(3-hexylthiophene) (P3HT) device. The performance of P3HT device varied significantly from different solvents, among them, p-xylene proved to be the best solvent medium, and also hydrazine as dedoping agent made progress in the mobilities by one or two orders of magnitude. Especially, in our experiments, solution preparing, deposition and device measurements were all performed in the air for the application of P3HT without further purification to the ink-jet printing, spin coating or solution casting process for large area and flexible organic thin-film transistors (OTFTs).

Keywords: Soluble organic semiconductor; Organic thin-film transistor; Poly(3-hexylthiophene)

Spectroscopic investigations of the BEDT-TTF charge transfer salts with NO3 anions (β″- and δ-phase) by R. Świetlik; A. ?apiński; M. Połomska; N.D. Kushch; A.N. Chekhlov (pp. 79-88).
We report the polarized reflectance spectra (650–6500cm−1) as well FT-NIR Raman spectra of β″-(BEDT-TTF)3(NO3)2 and δ-(BEDT-TTF)2(NO3)0.9(NO2)0.1 salts as a function of temperature. Additionally, the crystal structure of δ-phase salt was determined at room temperature and the temperature dependence of electrical conductivity was measured. The reflectance spectra of metallic β″-phase salt were fitted with the Drude model; the metal–insulator transition at T=20–27K has practically no influence on IR spectra. The δ-phase salt shows semiconducting behavior; inside conducting organic layers the BEDT-TTF molecules are arranged in dimers. The specific vibrational features of the δ-salt are discussed in terms of hydrogen bonding between BEDT-TTF and anions.

Keywords: BEDT-TTF charge transfer salts; Crystal structure; IR and Raman spectra; Phase transition

Structural origin of inhomogeneous properties in (fluoranthene)2PF6 crystals by C. Buschhaus; J. Gmeiner; H. Henke; M. Ulrich; E. Dormann (pp. 89-94).
Twinned and untwinned (FA)2PF6 crystals are analysed by X-ray scattering at varied temperature. A rotation by 180 around the a axis (stacking axis) is identified as the typical twinning rule. The influence of twinning on the crystal quality in general is derived, as well as its irrelevance for the Peierls transition at TP=180K and for the high-temperature structural transition at TS=200K, accompanied by the loss of the FA-stack's mirror plane (space group A2/ m to P21/ c). These observations are discussed with respect to recent electron spin resonance imaging results. Differing concentration of localized defects in the different growth sectors of macroscopic single crystals is identified as an obvious explanation of inhomogeneous ESR properties.

Keywords: PACS; 61.66.Hq; 61.72.Mm; 64.70.Kb; 71.30.+hX-ray analysis; One-dimensional organic conductor; Structural phase transition; Peierls transition; Twinning; Growth sectors

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