1,720,990 research outputs found
Aryl, bi-functionalised imidazo[4,5-f]-1,10-phenanthroline ligands and their luminescent rhenium(I) complexes
Full text linkFive new imidazo[4,5-f]-1,10-phenanthroline based ligands (1–5) have been synthesised and characterised. The facile synthesis of 1–5 allows two regiochemical points of structural variety allowing highly conjugated and bulky aryl groups of varying functionalities, including azobenzene, trityl and terpyridine constituents, to be attached to the ligand core. 1–5 are fluorescent (λem = 410–415 nm), and react readily with [ReBr(CO)5] in toluene to give neutral coordination complexes of the form fac-[ReBr(CO)3(1–5)]. The series of complexes was characterised using a variety of spectroscopic and analytical techniques. Two examples of this series were characterised in the solid state using single crystal X-ray diffraction which confirmed the octahedral geometry and formulation. Photophysical studies showed that fac-[ReBr(CO)3(1–5)] are phosphorescent in solution under ambient conditions, revealing visible emission (558–585 nm) in aerated solution with corresponding lifetimes in the range 149–267 ns. These attributes are consistent with a triplet metal to ligand charge transfer (3MLCT) emitting state
Fluoride anion binding by cyclic boronic esters: influence of backbone chelate on receptor integrity
No full textA systematic investigation of fluoride anion binding properties as a function of chelate backbone has been carried out for ferrocene functionalised boronic esters of the types FcB(OR)(2) and fc[B(OR)(2)](2) [Fc = ferrocenyl = (eta(5)-C5H5) Fe(eta(5)-C5H4); fc = ferrocendiyl = Fe(eta(5)-C5H4)(2)]. Cyclic boronic esters containing a saturated five- or six-membered chelate ring are readily synthesized from ferrocene, and selectively bind fluoride via Lewis acid/base chemistry in chloroform solution. The resulting complexes are characterized by relatively weak fluoride binding ( e. g. K = 35.8 +/- 9.8 M-1 for FcBO(2)C(2)H(2)Ph(2)- S, S), and by cathodic shifts in the ferrocene oxidation potential that form the basis for electrochemical or colorimetric fluoride detection. The fluoride selectivity of these systems is attributed to relatively weak Lewis acidity, resulting in weak F- binding, and essentially no binding of potentially competitive anions. By contrast, more elaborate Lewis acid frameworks based on calix[4] arene (calixH(4)), such as (FcB)(2)calix or fcB(2)calix, do not survive intact exposure to standard fluoride sources (e.g. [(Bu4N)-Bu-n] F center dot xH(2)O solutions in chloroform or acetonitrile). Instead B - O bond cleavage occurs yielding the parent calixarene; the differences between alkoxo- and aryloxo-functionalised derivatives can be rationalised, at least in part, by consideration of the differences in electron donating capabilities of RO( R = alkyl, aryl)
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
Alkyl chain functionalised Ir(iii) complexes: synthesis, properties and behaviour as emissive dopants in microemulsions
Full text linkSix iridium(iii) complexes of the general form [Ir(C^N)2(N^N)]X (where C^N = cyclometalating ligand; N^N = disubstituted 2,2′-bipyridine), and incorporating alkyl chains of differing lengths (C8, C10, C12), have been synthesised and characterised. The complexes have been characterised using a variety of methods including spectroscopies (NMR, IR, UV-Vis, luminescence) and analytical techniques (high resolution mass spectrometry, cyclic voltammetry, X-ray diffraction). Two dodecyl-functionalised complexes were studied for their behaviour in aqueous solutions. Although the complexes did not possess sufficient solubility to determine their critical micelle concentrations (CMC) in water, they were amenable for use as emissive dopants in a N-methyl C12 substituted imidazolium salt microemulsion carrier system with a CMC = 36.5 mM. The investigation showed that the metal doped microemulsions had increased CMCs of 40.4 and 51.3 mM and luminescent properties characterised by the dopant.</p
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
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
Synthesis and characterisation of phosphorescent rhenium(I) complexes of hydroxy- and methoxy-substituted imidazo[4,5- f ]-1,10-phenanthroline ligands
Full text linkEight new fluorescent ligands (L1-L8) derived from the fused imidazo[4,5-f]-1,10-phenanthroline core, have been synthesised utilising a one-pot methodology. The ligands include two points of structural variety, allowing multiply-substituted aryl groups (including hydroxy and methoxy moieties) to be attached to the ligand core. The ligands L1-L8 are fluorescent (λem = 399–426 nm) and react with pentacarbonylbromorhenium to give coordination complexes of the form fac-[ReBr(CO)3(NˆN)] (where NˆN = L1-L8). The complexes were characterised using a variety of spectroscopic and analytical techniques, including single crystal X-ray diffraction studies on two examples. The rhenium complexes were all found to be luminescent, revealing classical 3MLCT emission at 579–587 nm in aerated solution with corresponding lifetimes in the range 149–166 ns
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