1,721,406 research outputs found
Iridium(III) Complexes for OLED Application
No full textThis chapter focuses on Iridium(III) complexes for organic light-emitting diode (OLED) applications and gives a general introduction to metal complexes and OLED devices, and then describes selected examples, to illustrate the tunability of the emission energies. The iridium complexes will be organized by emission colors and therefore divided in green, red, and blue emissive materials. Most of the Ir(III) complexes used in OLEDs are based on homoleptic triscyclometalated Ir(III), Ir(C^N)3, or neutral heteroleptic bis-cyclometalated [Ir(C^N)2(L^X)] complexes. Among all the transition metal complexes, iridium(III) complexes are considered the most studied for optoelectronic applications. The host material with the phosphorescent emitter is very critical for achieving high efficiency in phosphorescent OLEDs (PHOLEDs). During the operation of the device, the phosphorescent emitters in the doped emissive layer (EML) are electrically excited to generate the electrophosphorescence by either host-guest energy transfer (ET) or direct charge carrier trapping
Rhenium complex as emitting material in highly efficient phosphorescent organic light-emitting diodes
Full text linkInterest in luminescent materials able to efficiently emit in the solid state is continuously
growing, because in most applications the dyes are used as solid films. This is the case of the
Organic Light Emitting Diodes (OLEDs), where electroluminescent
metal complexes have been widely investigated as dopants, able to
increase their performances [1]. We present here a dinuclear Re(I)
complexes (1, see Scheme 1) whose emission is higher in solid state
and in PMMA matrix than in solution and is used as dopant in
OLEDs.
This complex belong to the family of neutral Re(I) complexes
with general formula [Re2(CO)6(μ-1,2-diazine)(μ-X)2], where X is halogen. Some of them
have recently gained interest for their intense yellow/green emission, occurring from triplet
metal-to-ligand charge transfer (3MLCT) states [2], showing a modulation effect of the
diazine substituents on wavelengths, lifetimes and quantum yields of the emission. Φ up to
0.53 has been measured for the di-chloro complexes containing diazines bearing alkyl groups
in both the β positions [3]. At variance with the chloro derivatives, the bromo analogue 1 is
almost not-emitting in solution (Φem 0.002 in deareated toluene). We have now found that in
the solid state 1 shows intense yellow-orange emission (Φem 0.50 in neat powder), blue
shifted with respect to the solution (560 nm vs. 620 nm). The emission is intense also in
PMMA matrix (Φem 0.19 in PMMA at 10% w/w, 556 nm).
This very high aggregated emission here is discussed in terms of the restriction of the
intramolecular roto-vibrational motions of the “Re2(CO)6(μ-Br)2” scaffold imposed by the
rigid environment, as evidenced by the strong decrease of the knr. Moreover a parallel increase
of kr is noticed, which clearly shows the influence of the halides in determining not only the
energy of the excited state, but also the nature of the lowest (emitting) state.
These properties allowed its successful use as a phosphorescent dopant in OLEDs and
here we report the performances of OLED devices prepared both by solution- and vacuumprocessing.
The values of the external quantum efficiency are 1.7% (4.3 cd/A and 1.7 lm/W)
and 10% (29.1 cd/A and 22.1 lm/W) respectively and are the highest ever reported for
rhenium-based devices, comparable to state-of-the-art devices employing Ir(III)- and Pt(II)-
based metal complexes. The combination of synthetic strategy and encouraging results in
potential OLEDs applications should make these dinuclear Re(I) complexes highly attractive
to a broad spectrum of research fields.
1. “Highly efficient OLEDs with Phosphorescent Materials” H. Yersin Ed. Wiley-VCH, (2008).
2. D. Donghi, G. D’Alfonso, M. Mauro, M. Panigati, P. Mercandelli, A. Sironi, P. Mussini, L. D’Alfonso, Inorg.
Chem. 28 (2008) 4243-4255.
3. M. Mauro, E. Quartapelle Procopio, Y. Sun, C. H. Chien, D. Donghi, M. Panigati, P. Mercandelli, P. Mussini,
G. D’Alfonso, L. De Cola, Adv. Funct. Mater. 19 (2009) 2607-2614
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
Transition metal complexes in ECL: diagnostics and biosensing
No full textThis chapter addresses the main principles, challenges and achievements in ECL using metal complexes. Selected applications in diagnostics and biosensing are described
Tetrazolates: a versatile class of ligands for luminescent metal complexes
No full textWe recently reported tetrazolates, [R-CN4]-, as an excellent class of ligands for the construction of highly photo- and electrochemiluminescent Ru(II)-polypyridyls and of intensely emitting and colour tunable Ir(III)-cyclometalates for OLEDs and LEECs devices, in which the extent of photophysical performances could be modulated by the addition of electrophiles to the coordinated tetrazolate ring. Our research has been nowadays extended to the preparation of new families of tetrazole complexes, such as Ru(II)-Ir(III) and Re(I)-Ir(III) bimetallic dyads and, as the latest development, of novel and intensely emitting Cu(I)-tetrazole cationic complexes. The main synthetic features and the photophysical properties of these new metal-containing molecules, will be described
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
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