1,721,123 research outputs found
A topologically new ruthenium porphyrin-fullerene donor acceptor ensemble
No full textA novel ruthenium porphyrin complex bearing an axially coordinated fullerene ligand (RuP-C60), that is, a fulleropyrrolidine that bears a pyridine moiety, was developed as an artificial reaction center mimic. Generally, the new donor acceptor dyad gives rise to rapid intramolecular deactivation of the ruthenium porphyrin triplet excited state, which evolves from instantaneous intersystem crossing. The product of the ruthenium porphyrin excited-state deactivation depends on the solvent polarity. While in non-polar solvents a transduction of triplet excited energy predominates, in medium and strongly polar media, charge-separation leads to the formation of RuP*+ C60*-
Facile and quick preparation of carbon nanohorn-based counter electrodes for efficient dye-sensitized solar cells
No full textFor the first time, Pt-free counter electrodes based on carbon nanohorns for highly efficient dye-sensitized solar cells were assembled by a facile and fast drop cast technique. These novel electrodes feature an effective catalytic behavior towards the reduction of I3− and, as such, afford even higher short-circuit current densities compared to Pt-based references. In a final device, solar cells with 7.7% efficiency were achieved
Synthesis and characterization of a new porphyrin-fullerene dyad containing a β-pyrrolic linkage
Full text linkTwo new ß-substituted arylethynyl meso-tetraphenylporphyrins, 2[(4'-formyl)phenyl]ethynyl-5,10,15,20-tetraphenylporphyrin (System A) and 2-[(4'-methyl)phenyl]ethynyl-5,10,15,20tetraphenylporphyrin (System B) and their zinc derivatives were synthesized. Comparative UV/Visible and cyclic voltammetry studies of such macrocycles reveal the presence of an extensive conjugation between the tetrapyrrolic ring and the linker, through π-π orbitais interaction. This interaction was observed in form of a "push-pull" effect that moves the electronic charge between the porphyrin and the aldehyde group of the System A. System B, bearing a methyl instead of the formyl group, was synthesized in order to evaluate the effect of the substitution on the charge derealization, which is necessary to corroborate the push-pull mechanism hypothesis. The new porphyrin, System A, was also used as starting material for the synthesis of new porphyrinfullerene dyads in which the [60]fullerene is directly linked to the tetrapyrrolic rings by ethynylenphenylen subunits. Fluorescence and transient absorption measurements of the new dyads reveal that ultrafast energy and electron transfer occur respectively in non polar and polar solvents, with high values of the rate constant. Copyright The Electrochemical Society
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
Porphyrin-beta-Oligo-Ethynylenephenylene-[60]Fullerene Triads: Synthesis and Electrochemical and Photophysical Characterization of the New Porphyrin-Oligo-PPE-[60]Fullerene Systems
Full text linkThe synthesis and electrochemical and photophysical studies of new electron donor-acceptor arrays, bearing porphyrins covalently linked to fullerene, are described. In the reported investigation, phenyleneethynylene subunits were chosen as a linking bridge to guarantee a high conjugation degree between the donor (i.e., porphyrin), the molecular bridge (i.e., oligo-phenyleneethynylenes), and the acceptor (i.e., fullerene). To enhance the electronic interactions through the extended pi-system, the molecular bridge has been directly linked to the beta-pyrrole position of the porphyrin ring, generating a new example of donor-bridge-acceptor systems where, for the first time, the meso-phenyl ring of the macrocycle is not used to hold the "bridge" between porphyrin and fullerene moieties. This modification allows altering the chemical and physical properties of the tetrapyrrole ring. Steady-state and time-resolved fluorescence studies together with transient absorption measurements reveal that in nonpolar media (i.e., toluene) transduction of singlet excited-state energy governs the excited-state deactivation, whereas in polar media (i.e., tetrahydrofuran) charge transfer prevails generating a long-lived radical ion pair state. The lifetimes hereof range from 300 to 700 ns. The study also sheds light onto the wirelike behavior of the oligo-phenyleneethynylene bridges, for which a damping factor (beta) of 0.11 +/- 0.05 angstrom(-1) has been determined in the current study
Synthesis and photophysical investigation of new porphyrin derivatives with beta-pyrrole ethynyl linkage and corresponding dyad with [60] fullerene
Full text linkTwo new beta-substituted arylethynyl meso-tetraphenylporphyrins, 2-[(4'-formyl) phenyl] ethynyl-5,10,15,20-tetraphenylporphyrin ( system A) and 2-[(4'-methyl) phenyl] ethynyl-5,10,15,20-tetraphenylporphyrin ( system B) and their zinc derivatives were synthesized by palladium catalysis, using a synthetic approach that affords high yields of the target systems. Comparative ultraviolet-visible (UV-vis), NMR, and cyclic voltammetry studies of such macrocycles reveal the presence of an extensive conjugation between the tetrapyrrolic ring and the linker, through pi-pi orbital interaction. This interaction was observed in the form of a "push-pull" effect that moves the electronic charge between the porphyrin and the aldehyde group of system A. System B, bearing a methyl group instead of the formyl group, was synthesized in order to evaluate the effect of the substitution on the charge delocalization, which is necessary to corroborate the push-pull mechanism hypothesis. The new porphyrin, system A, was also used as a starting material for the synthesis of new porphyrin-fullerene dyads in which the [60] fullerene is directly linked to the tetrapyrrolic rings by ethynylenephenylene subunits. Fluorescence and transient absorption measurements of the new dyads reveal that ultrafast energy and electron transfer occur, respectively, in nonpolar and polar solvents, with high values of the rate constant. The UV-vis, NMR, and cyclic voltammetry results show that it is possible for both energy and electron transfer between porphyrin and fullerene to take place through the pi-bond interaction. Such results evidence that the coupling between the donor and acceptor moieties is strong enough for possible photovoltaic applications
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
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
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