1,720,961 research outputs found
An investigation of Solid‐State Emission of Halogenated Diphenyl Phosphanyl Anthracenes
No full textIn today's world, the development and research of optoelectronic materials and devices based on solid-state luminescence is essential. Due to their versatile application possibilities, e.g. as light-emitting diodes or lasers, they are already indispensable. This work presents three halogenated anthracene derivatives [9-PPh2-10-X-(C14H8)] and their respective photoluminescent behavior in solution and in the solid state. The formation of halogen–π interactions in the solid state leads to unanticipated luminescence properties for the chlorinated species, resulting in a strong bathochromic shift, green fluorescence and a longer lifetime. In contrast, the other two derivatives, which in turn form only weak π–π interactions due to a small overlap of the anthracene rings, barely change their luminescence behavior in the solid state. By employing additional charge density studies, the structure–property correlation is also investigated. In particular, focus is given to halogen bonding and halogen–π interactions and their influence on photophysical properties of the studied compounds. Through the new knowledge gained, this study will help in the future development and selective application of the photophysical properties of solid-state luminescent materials.PL‐GRID infrastructur
Structure Elucidation of Lithium Compounds Using 7Li Residual Quadrupolar Couplings
No full textA new NMR method for the structure elucidation of lithium compounds under solution-like conditions is presented. It is based on the measurement of 7Li residual quadrupolar couplings (RQCs) in a stretched polystyrene (PS) gel, and comparison to RQCs predicted from crystal or DFT-derived model structures in combination with alignment tensors derived from one-bond 1H,13C residual dipolar couplings (RDCs). The method was applied to five lithium model complexes containing monoanionic, bidentate bis(benzoxazole-2-yl)methanide, bis(benzothiazole-2-yl)methanide and bis(pyridyl)methanide ligands, of which two are first introduced in this work. In agreement with the crystalline state, four complexes are monomeric with Li coordinated fourfold by two additional THF molecules, whereas in one complex bulky tBu groups only provide space for one additional THF molecule.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165
Synthesis and Characterization of a Carbene‐Stabilized Silylene–Phosphinidene
No full textThe isolation of silylene–phosphinidene is challenging due to its rapid dimerization or oligomerization during the reaction. Recently, the synthesis of a novel silylene ( 1 ) is reported, which leads to the formation of an unsymmetrical bis‐silylene ( 2 ), and it's their intriguing reactivity toward silylene(II) is further studied. Expanding on this reactivity, the reaction of 2 with Me cAACPCl is explored, which affords silylene–phosphinidene [R(MecAAC)SiPCAAc Me ( 3 )] oxidatively in low yield. Alternatively, when RSiCl(CAAc Me ) ( 1 ) is treated with Me cAACPCl under reducing conditions, compound 3 is obtained in an isolated yield of 78%. In addition, quantum chemical calculations are carried out to elucidate the electronic structures of compounds 3 and 4 , providing deeper insight into the nature of their chemical bonding
Tuning Solid‐State Fluorescence in BODIPY Dyes through Substitution‐Controlled Packing Motifs
No full textAbstract Understanding how molecular packing governs solid‐state fluorescence is key to unlocking new emissive materials. A comprehensive study of BODIPY derivatives with diverse substitution patterns is presented, showing how these modifications govern intermolecular interactions, packing motifs, and ultimately photophysical behavior in the solid state. Substituent effects dictate whether π–π stacking, hydrogen bonding, or halogen interactions dominate, resulting in distinct emission shifts and variations in fluorescence quantum yield. While increased chromophore overlap often leads to bathochromic emission, it also correlates with reduced quantum efficiency because of enhanced non‐radiative relaxation processes. Notably, compounds with similar degrees of overlap can exhibit different emission profiles, underscoring the pivotal role of substituent‐controlled packing. These insights provide a foundation for rational design of solid‐state luminescent materials based on BODIPY scaffolds.Infrastruktura PL-Grid https://doi.org/10.13039/501100011089Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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