1,721,039 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
Bipolar properties of polythiophene derivatives with 1,3,5-triazine units
No full textBipolar properties of model polythiophene derivatives with 1,3,5-triazine units are investigated. The conjugation length is controlled by the meta substitution. In situ spectroelectrochemical UV-Vis-NIR and ESR measurement recorded during electrochemical reduction and oxidation are presented. Spectroelectrochemistry recorded during reduction of polymers in the solid state is especially interesting. Most literature data of spectroelectrochemistry of solid state polymers has been obtained during oxidation which is due to poor stability of radical anions in reduced polymers. Cathodic reduction leads to the formation of stable radical anions in a certain potential range. Exceeding this range leads to overreduction. A similar effect is observed during electrooxidation. Obtained results indicate that not only oligomers with 1,3,5-triazine units but also respective polymers are worth considering during studies on new bipolar polymer materials to broad range of optoelectronic and photovoltaic applications. (C) 2013 Elsevier Ltd. All rights reserved
Doping behaviour of electrochemically generated model bithiophene meta-substituted star shaped oligomer
No full textThe redox processes accompanying electrochemical oxidation of 1,3,5-tris(bithiophene)benzene (6TPh) and its products have been investigated using a suite of spectroelectrochemical tools. Investigated trifunctional molecule, featuring reactive bithiophene units can be considered a model of numerous star shaped compounds the building blocks of dense pi-conjugated polymer networks. Accounting for conjugation disruption between the meta-arranged bithiophene groups, it is found that electrochromic films generated upon 6TPh electrooxidation comprise primarily dimers (6TPh)2, whose alpha,omega-diphenylquaterthiophene units are the principal redox doping active species. Upon reaching a certain, electrochemically inconspicuous oxidation threshold, profound changes take place in the oligomer film, incurring irreversible changes to its electroactive properties, previously observed for these systems. An attempt is made to examine the nature of these changes and the impact they have on the doping behaviour of this intriguing pi-conjugated system. (C) 2014 Elsevier B.V. All rights reserved
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
Synthesis 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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Synthesis and electrochemical properties of tetrathienyl-linked branched polymers with various aromatic cores
No full textA series of various tris(2,2'-bithiophen-5-yl)-aromatic derivatives were synthesized by Stille cross-coupling procedure. Their structures were characterized by H-1 NMR, C-13 NMR, and elemental analysis. DFT calculations for monomers were also performed. The optical properties of the synthesized materials as well as their energy levels were investigated by UV-vis absorption supported by fluorescence spectra and CV analysis. Oligomers obtained in the process of electropolymerization, possess a tetrathienyl bond with various aromatic and heteroaromatic cores. Electrochemical results confirm that the gained materials can apply successfully for a diversity of organic-electronic devices like organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic solar cells. (C) 2012 Elsevier Ltd. All rights reserved
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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