1,720,982 research outputs found
Regioregular electrochromic polymers based on thienyl derivatives of fluorescent pyrene monomers: Optical properties, spectroelectrochemistry and quantum chemical study
No full textA detailed spectroelectrochemical and theoretical study of thienyl derivatives based on pyrene, namely 1-(2-thienyl)-pyrene (1), 1,6-bis(2-thienyl)-pyrene (2), 1,4-bis(2-thienyl)-pyrene (3), 1,3,6-tris(2-thienyl)-pyrene (4) and 1,3,6,8-tetra(2-thienyl)-pyrene (5), and their oxidation products with focus on the formation of their corresponding cationic states are presented. Regioregular polymeric systems were prepared by means of electrochemical polymerization from monomers 2-4. The redox behavior of the corresponding polymers was studied by cyclic voltammetry and in situ EPR/UV-vis-NIR spectroelectrochemistry with the aim of obtaining details on the type of charge carriers within the polymer film. Quantum chemical calculations of the optimal geometries and optical transitions for the neutral and charged forms were performed in order to reveal the influence of electrochemical oxidation on the molecular structure of the monomers and corresponding dimers and/or polymers. (C) 2013 Elsevier Ltd. All rights reserved
Alternative Methoden zur Stabilisierung der Morphologie von Anoden für Hochtemperaturbrennstoffzellen (MCFC)
No full textSynthesis and Optical Properties of Various Thienyl Derivatives of Pyrene
No full textA series of various thienyl derivatives of pyrene were synthesized by Stille cross-coupling procedure. Their structures were characterized by H-1 NMR, C-13 NMR and elemental analysis. The spectroscopic characteristics were investigated by UV-vis absorption and fluorescence spectra. Based on quantum chemical calculations, the energy levels of investigated molecules with respect to the pyrene molecule were also discussed
Metal nitride cluster as a template to tune the electronic and magnetic properties of rare-earth metal containing endohedral fullerenes
Full text linkIn this thesis, Ce-, Pr-, Ho-based and Sc-, Lu- and Y-involved mixed metal nitride clusterfullerenes were synthesized by “reactive gas atmosphere” or “selective organic solid” route. Metal nitride cluster template provides a convenient platform for the construction of rare-earth containing endohedral fullerenes in the form of mixed metal nitride cluster fullerenes (LnxM3-xN@C2n; Ln=lanthanide metal). Different metals and carbon cages can be regarded as the infinite building blocks for the endohedral fullerenes family. Sc, Lu and Y are employed as the second metal (M) to tune: (a) the size and the geometry of entrapped mixed metal nitride cluster; (b) the inherent strain between encaged species and carbon cage; (c) the paramagnetic contribution from Ln3+ (LnxM3-xN@C80) to 13C and 45Sc NMR chemical shifts; (d) the electrochemical oxidation potential of CexY3-xN@C2n. The isolation of (a) C80-based MMNCFs which including HoxM3-xN@C80 (I, II; M=Sc, Lu, Y; x= 1, 2), CeY2N@C80 (I), CeSc2N@C80 (II) and PrSc2N@C80 (I, II) was accomplished by multi-step HPLC. Moreover, Ce-based MMNCFs with cage size larger than C80 were isolated which include CeY2N@C84, CeY2N@C86, Ce2YN@C86, Ce2YN@C88 and CeY2N@C88. The purity of above-mentioned MMNCFs was confirmed by LDI-TOF mass spectroscopy. FTIR spectra own advantages for the analyzing the antisymmetric metal-nitrogen stretching vibrational modes (νM-N) of LnxM3-xN@C80 (I, II; x= 0-3). Raman spectra provide critical information on the interaction between the entrapped metal nitride cluster and the C80 cage. The 4f electron(s) located on the encaged lanthanide metals (e.g. 4f1-Ce3+, 4f2-Pr3+ and 4f10-Ho3+) results in remarkable 13C NMR paramagnetic chemical shifts. The convincing proofs of the strain-driven endohedral redox couple CeIV/CeIII in mixed metal nitride clusterfullerenes CeM2N@C80 (M= Sc, Lu, Y) were presented by the characterization of cyclic voltammtry and 13C NMR spectroscopy
Elektropolymerisation, Spektroelektrochemie und Potentiometrie von funktionalisierten leitfähigen Polymeren
Full text linkDie vorliegende Arbeit behandelt die elektrochemische Synthese (elektrochemische Polymerisation und Copolymerisation) und die Charakterisierung der Redox- und sensorischen Eigenschaften neuer funktionalisierter Polymere für die Ionensensorik. Die Funktionalisierung wird sowohl in der Polymer-Hauptkette (Polysalene) als auch in der Polymer-Seitenkette (ein Thiophen-Copolymer: 3-Methylthiophen/6-Hydroxy-2-(2-(3-thienyl)-ethoxy)-acetophenon) dargestellt. Die Redox-Prozesse der funktionalisierten Polymere wurden mit spektroelektrochemischen Methoden: ESR-, UV-Vis-NIR- und FTIR-Spektroelektrochemie charakterisiert. Durch diese Methoden konnten während der elektrochemischen Oxidation von funktionalisierten leitfähigen Polymeren verschiedene Polymer- bzw. Copolymer-Ladungsträger nachgewiesen werden: Polaronen, Bipolaronen beim Thiophen-Copolymer, zwei Polaronen auf einer Polymerkette im Singulettezustand beim Poly(3-methylthiophen) und eine diamagnetische Spin-Spin-Wechselwirkung zwischen ungepaarten Elektronen der Cu(II)-Ionen und der ungepaarten Elektronen von bisphenolischen Ligand-Kationradikalen beim Poly[Cu(II)-salen]. Sensorische Eigenschaften gegenüber Ni(II)-Ionen wurden durch Potentiometrie an einem Poly[Ni(II)-salen]-Derivat getestet. Es zeigt eine gute potentiometrische Ni(II)-Ionenselektivität (der Logarithmus des potentiometrischen Selektivitätskoeffizienten liegt im Bereich von -0.5 bis -1.5) in Anwesenheit von Cd(II), Mn(II), Zn(II) und Na(I)
Thiophene Based Semiconductors: Synthesis and Characterizations
Full text linkDiverse conformational transitions and aggregations of regioregular head-to-tail polyhexylthiophene in different environments have been studied by means of AFM and UV-vis spectroscopy. A helical conformation of the main chain with 12 thiophenes rings per each helical turn has been proposed. Length of the particles varies from several nanometers to several hundreds nanometers and can be adjusted by the solvents composition or concentration of PATs. Such well-defined organic semiconductor 1D particles can be used as building blocks for future nanoscale and molecular level electronic devices. Oligothiophenes represent one of the most promising class of semiconductive materials for FET fabrication because of their good mobility and environmental stability. However, most of unsubstituted oligothiophenes are insoluble that suppresses their potential industrial utility. On the first stage of the work, conformation, crystalline structure, molecular packing and charge carrier mobility of the highly soluble regiochemically pure [Beta]-substituted sexithiophene were systematically studied. It was found that [Beta, Beta´]-DH6T possesses moderate PR-TRMC charge carrier mobility, but rather low field-effect mobility. The investigation showed that such a poor macroscopic electrical properties of [Beta, Beta´]-DH6T originate neither from the twist of the conjugated system nor from the crystalline disorder, but rather from low-dense crystalline packing and "wrong" molecular orientation. To overcome these obstacles two thiophene-based azomethines were designed to optimize a solubility, self-assembly, and a charge carrier mobility. The idea was to utilize the ability of the amide group to form strong hydrogen bonds in non-polar solvents and in solid state, but to be easily broken in presence of polar solvents. Thus, at the stage of a dissolution and a deposition, when the solubility is important, the hydrogen bonding can be "switched off" simply by addition of polar solvents and then, after the removal of polar additives, the self-assembly can be "switched on". It was found that incorporation of azomethine and amide moieties in the [Alpha, Omega]-position, and hexyl chains in [Beta]-position of quaterthiophene, indeed considerably improves the self-assembly properties without suppression of the solubility. Self-assembly of azomethine oligomers with (QT-amide) and without amide moieties (QT-aniline) were monitored by UV-vis, XRD, and AFM. It was found that QT-amide, processed from solution, forms highly ordered layered (terrace) structures. This aggregation mode is similar to the self-assembly of unsubstituted conjugated oligomers (such as pentacene) occurred upon their evaporation in vacuum. The sum of charge carrier mobilities (PR-TRMC data) for QT-aniline was shown to be below the detectable limit, but the mobility of QT-amide was determined to be 1.10-2 cm2 V-1 s-1. The later is comparable with the mobilities of the best organic semiconductors. All these significant differences in properties of related compounds can be attributed to the hydrogen bonding between QT-amide molecules responsible for the observed self-assembly
Nanostrukturierte Fullerenschichten für organische Bauelemente
Full text linkDie vorliegende Arbeit behandelt die Herstellung geordneter C60-Schichten, ihre elektrochemische Nanostrukturierung in wässrigen Lösungen und ionischen Flüssigkeiten und den Einsatz geordneter und nanostrukturierter Fullerenschichten in organischen Dünnschichttransistoren.
Geordnete C60-Schichten wurden durch thermische Verdampfung im Hochvakuum hergestellt. Als Substratmaterial wurden HOPG (Graphit), Glimmer und einkristallines Silizium verwendet. Die größten einkristallinen Bereiche werden auf HOPG-Substraten erhalten. Die laterale Ausdehnung der C60-Kristallite parallel zu den Graphitstufen kann bis zu 50 µm erreichen, orthogonal zu den Stufen ist das Wachstum durch die Graphitstufen begrenzt.
Die elektrochemische Reduktion von C60 -Schichten in wässriger Lösung ist elektrochemisch irreversibel. Die geflossene Ladung beträgt ein Vielfaches der theoretisch möglichen Menge. Durch die Reduktion tritt eine Nanostrukturierung der Schichtoberfläche ein, die Größe der gebildeten Cluster beträgt 20 nm bis 50 nm. Fullerenpolymere und hydriertes C60 sind die chemischen Hauptprodukte der elektrochemischen Nanostrukturierung in wässriger Lösung.
Die Reduktion von Fullerenschichten in ionischen Flüssigkeiten ist aufgrund der geschlossenen Schichtoberfläche und des starken Potentialabfalls in der Fullerenschicht zunächst kinetisch gehemmt und setzt erst bei negativeren Potentialen im Bereich der Reduktion zum C60-Dianion ein. Die Reduktion der Fullerenschichten ist elektrochemisch irreversibel, zum Teil aber chemisch reversibel.
Es konnte erstmals der Einsatz nanostrukturierter C60 -Schichten als aktives Halbleitermaterial in Feldeffekt-Transistoren gezeigt werden. Für die Verwendung nanostrukturierter Fullerenschichten in Feldeffekt-Transistoren wurde 11-(3-Thienyl-)undecyl-trichlorosilan als Haftvermittler eingesetzt.
Die gezeigten Ergebnisse von C60 -Transistoren mit hoher Ladungsträgerbeweglichkeit und der erfolgreichen Verwendung nanostrukturierter Fullerenschichten in Transistorstrukturen zeigen die Möglichkeiten des C60 als aktives Halbleitermaterial auf
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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