1,720,978 research outputs found
Photoinduced Electron and Energy Transfer in Metal-mediated Multi-porphyrin arrays
No full textInteresting supramolecular architectures can be obtained exploiting the exocyclic coordination ability of pyridylporphyrins. Thus, coordination to metal centers can be used to build metal-bridged porphyrin assemblies (e.g., 1). On the other hand, axial coordination to metalloporphyrins can be used to produce a variety of side-to-face porphyrin assemblies (e.g., 2). The two structural motifs can be combined in higher order assemblies (e.g., 3). Other interesting supramolecular systems can be designed along the same lines using pyridyl-functionalized perylene bisimides (e.g., 4).
Within this framework, several discrete assemblies of various nuclearities have been recently constructed in our laboratories.1,2
The photophysics of these multichromophoric assemblies is characterized by the occurrence of fast intercomponent energy and electron transfer processes. Experimental studies leading to the identification and kinetic characterization of the photoinduced processes have been performed by fast (nanoseconds) and ultrafast (femtoseconds) time resolved techniques. Recent examples will be discussed.
1 E. Iengo, F. Scandola, E. Alessio Struct. Bond., 2006, 121, 105.
2 F. Scandola, C. Chiorboli, A. Prodi, E. Iengo, E. Alessio, Coord. Chem. Rev. 2006, 250, 1471
Metal-mediated multi-porphyrin discrete assemblies and their photoinduced properties
No full textThe metal-driven construction of multi-porphyrin assemblies, which exploits the formation of coordination bonds between exocyclic donor site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supramolecular architectures whose complexity and function begin to approach the properties of naturally occurring systems. Within this framework, meso-pyridyl/phenyl porphyrins (PyPs), or strictly related chromophores, can provide geometrically well-defined connections to as many as four metal centers by coordination of the pyridyl peripheral groups. Several discrete assemblies of various nuclearities, in which the pyridylporphyrins are connected through external coordination compounds, have been constructed in recent years. In this review, we summarize recent work in this field from our and other laboratories. The photophysical properties of some ruthenium-mediated assemblies of porphyrins prepared by our group are also described
Photophysics of Metal-mediated Assemblies of Porphyrins and Perylene Bisimides
No full textInteresting supramolecular architectures can be obtained exploiting the exocyclic coordination ability of pyridylporphyrins. Thus, coordination to metal centers can be used to build metal-bridged porphyrin assemblies (e.g., 1). On the other hand, axial coordination to metalloporphyrins can be used to produce a variety of side-to-face porphyrin assemblies (e.g., 2). The two structural motifs can be combined in higher order assemblies (e.g., 3). Other interesting supramolecular systems can be designed along the same lines using pyridyl-functionalized perylene bisimides (e.g., 4). The photophysics of these multichromophoric assemblies is characterized by the occurrence of fast intercomponent energy and electron transfer processes. Recent examples will be discusse
Electronic Energy Transfer in a Multiporphyrin-based Molecular Box
No full textThe molecular box 1 comprises of two zinc-porphyrin metallacycles connected bytwo free-base 4’-trans-dipyridylporphyrins, axiallycoordinated to the zinc centers. The photophysics of 1 were studied in chloroform byemission and ultrafast absorption spectroscopy. In the molecular box, fast singlet energy transfer (main component, t=32 ps) is observed to occur from the zinc-porphyrin metallacycles to the free-base chromophores. From wavelength- dependent spectrofluorimetric data, the efficiencyof the energy-transfer (ET) process is estimated as 0.5. The lower-thanunityvalue is tentativelyattributed to the possibilityof a competing electron-transfer quenching pathway. Molecular box 1 can be considered to be a simple, self-assembling, six-chromophore antenna system. It has an inner cavity, 11.4 < wide, that could be used, in principle, to host a varietyof guest molecules and obtain higher-order assemblies
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
Photophysical Properties of Metal-Mediated Assemblies of Porphyrins
No full textThe metal-driven construction of multi-porphyrin assemblies, which exploits the formation of coordination bonds between peripheral basic site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supramolecular architectures whose complexity and function begin to approach the properties of naturally occurring systems. Within this framework, meso-pyridyl/phenyl porphyrins (PyPs), or strictly related chromophores, can provide geometrically well-defined connections to as many as four metal centers by coordination of the pyridyl peripheral groups. Several discrete assemblies of various nuclearities, in which the pyridylporphyrins are linkers binding metalloporphyrins and/or coordination compounds, have been constructed in recent years. In this review, we summarize recent work from our laboratories on metal-mediate
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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