1,721,103 research outputs found
Tailoring the photoredox properties of organic dyes
No full textThe increasing interest for photoredox-induced processes has recently led to the exploitation of a large variety of inorganic and organic chromophores to trigger chemical reactions through photoinduced electron transfer (PET), generating highly reactive radical species. Until now, efforts in the field have been focused on the type of organic transformations, and rarely centred on the rational design of dyes featuring excited states with tailored photoredox properties for a given reaction. It is with this aim, that in this chapter we report on the general designing principle to engineer organic dyes (both as small molecules and macromolecules) featuring tailored photoredox properties. Understanding the behaviour of chromophores depicting programmed redox potentials in photo-triggered chemical transformations is crucial if one wants to rationally trigger novel organic reactions
Solvent-dependent moulding of porphyrin-based nanostructures: solid state, solution and on surface self-assembly
Full text linkA novel porphyrin derivative 1∙Zn was synthesised in order to mimic the self-assembly properties of natural light-harvesting antennas and its self-assembly behaviour in solution and in solid state were studied by NMR and X-Ray spectroscopies. The self-assembly of this molecule was triggered in apolar solvents and studied in solution by UV-Vis spectroscopy, suggesting it is able to form slipped face-to-face aggregates, or J-aggregates. The nanoscopic and microscopic morphology of the aggregates was elucidated by atomic force microscopy, revealing the formation of extended two-dimensional structures
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
Configurational Selection in Azobenzene-Based Supramolecular Systems Through Dual-Stimuli Processes
Full text linkAzobenzene is one of the most studied light-controlled molecular switches and it has been incorporated in a large variety of supramolecular systems to control their structural and functional properties. Given the peculiar isomeric distribution at the photoexcited state (PSS), azobenzene derivatives have been used as photoactive framework to build metastable supramolecular systems that are out of the thermodynamic equilibrium. This could be achieved exploiting the peculiar E/Z photoisomerization process that can lead to isomeric ratios that are unreachable in thermal equilibrium conditions. The challenge in the field is to find molecular architectures that, under given external circumstances, lead to a given isomeric ratio in a reversible and predictable manner, ensuring an ultimate control of the configurational distribution and system composition. By reviewing early and recent works in the field, this review aims at describing photoswitchable systems that, containing an azobenzene dye, display a controlled configurational equilibrium by means of a molecular recognition event. Specifically, examples include programmed photoactive molecular architectures binding cations, anions and H-bonded neutral guests. In these systems the non-covalent molecular recognition adds onto the thermal and light stimuli, equipping the supramolecular architecture with an additional external trigger to select the desired configuration composition
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
O-Annulation to Polycyclic Aromatic Hydrocarbons: A Tale of Optoelectronic Properties from Five- To Seven-Membered Rings
Full text linkWe take advantage of the Pummerer oxidative annulation reaction to extend PAHs through the formation of an intramolecular C-O bond with a suitable phenol substituent. Depending on the peripheral topology of the PAH precursor (e.g., pyrene, boron-dipyrromethene, or perylene diimide) five-, six-, and seven-membered O-containing rings could be obtained. The effect of the O-annulations on the optoelectronic properties were studied by various methods with the pyrano-annulated pyrene and BODIPY derivatives depicting quantitative emission quantum yields
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
- …
