1,721,459 research outputs found
Cationic cyclometallated iridium (iii) complexes
No full textOver the past two decades dramatic advances have been achieved in the field of organic electroluminescent devices, for display and lighting applications. A recent development in this field involves the use of ionic transition metal complexes (iTMCs) that have shown the possibility to fabricate single layer electroluminescent devices, named Organic Light-emitting Electrochemical Cells (OLECs) [1]. This type of device represents an interesting possible alternative to the more investigated organic light- emitting diodes (OLEDs). In OLECs, the charged complexes support all three processes of charge injection, charge transport and emissive recombination. Therefore, no additional layers are needed in the device and the emissive layer can be solution processed, which makes industrial manufacturing easier. At the moment, the most common cationic complexes are based on iridium, ruthenium, osmium, platinum, and copper [2]. Here we present a study on the use of three different cationic iridium(III) complexes [3,4] (Figure 1) in luminescent single layer devices in the presence and in the absence of an ionic liquid (IL).
The complex [Ir(ppy)2(5-CH3-1,10-phen)][PF6] (ppy = 2-phenylpyridine, phen = phenanthroline) reaches the most efficient results compared to the other ones. It has a very competitive brightness of 3040 cd/m2, obtained at 8V. The presence of IL lowers the turn-on time, and therefore, the operation voltage of the device at 3V. However, from the other side, the enhancement of the ions concentration into the film reduces the device lifetime t1/2, which is one of the main concern in light emitting devices.
1. J. Slinker, S. Bernhard, G. G. Malliaras et al., J. Mater. Chem., 17 (2007) 2976-2988.
2. L. De Cola, C. Bizzarri, M. Mydlak et al., Adv. Funct. Mater., 20 (2010) 1812–1820.
3. C. Dragonetti, D. Roberto, A. Valore et al., Inorg. Chem, 46 (2007) 8533-8547.
4. C. Dragonetti, D. Roberto, A. Valore et al., J.Phys. Chem. C, 113 (2009) 12517–12522
Organometallic and coordination compounds with photoemissive and electro-optical properties
No full textOrganometallic complexes with luminescent1 and second-order nonlinear optical (NLO) properties2 are of interest as molecular building blocks of composite materials for light emitting systems such as OLED or for electro-optical devices and optical communications. In particular, they can offer additional flexibility, when compared to organic NLO-phores, by introducing electronic charge-transfer
transitions between the metal and the ligand, usually at relatively low energy and of relatively high intensity, tunable by virtue of the nature, oxidation state and coordiantion sphere of the metal centre.3
In the last few years, many neutral transition metal complexes have emerged as promising emitters for organic light emitting diodes (OLED).1 Neutral iridium (III) cyclometalated complexes were found of particular interest because they show high phosphorescence quantum yields and long lifetime.
Moreover, the wavelength of emitted light can be tuned over a large spectral range by an appropriate choice and combination of ligands. They have been used as active components dispersed in an organic matrix in OLED. In particular the acetylacetonate complexes with various cyclometalated ligands have been deeply studied. Only recently ionic transition metal complexes (iTMC)4 have been used as active layers in electroluminescent devices. Unlike conventional, charge-neutral OLED materials, iTMCs contain mobile counterions that facilitate charge transport through the material and eliminate the
need for electron- and hole-injection layers and operate at a low voltage.2 The first reports involving metal complexes were based on Ru(II)5, Os(II)6 and Re(I)7. Only three years ago, cationic Ir(III) cyclometalated complexes have received considerable attention due to the wide range emission color upon ligand selection.8
My PhD thesis is divided in three main sections:
1) Luminescent properties of cationic cyclometallated Ir(III) complexes
2) Second order NLO properties of cyclometallated Ir(III) and Pt(II) organometallic complexes and Zn(II) and lanthanide coordination compounds.
3) Experimental section
The first section is dedicated to the preparation and study of the luminescence properties of new cationic Ir(III) cyclometalated complexes with variously substituted 1,10-phenanthrolines such as [Ir(ppy)2(5-X- 1,10- phen)][PF6] (ppy= 2-phenylpyridine, phen= phenanthroline, X= Me, NMe2, NO2, H) and [Ir(ppy)2(4- R’, 7-R’- 1,10- phen)][PF6] (R’= Me and Ph), in order to evidence how the nature,
number and position of the phenanthroline substituents tune the luminescence (color of the emission, quantum yield and lifetime) properties. The effect on the emission properties of the substitution of cyclometallated 2-phenylpyridine with more π- delocalized cyclometallated 2-phenylquinoline (pq), 3’-(2-pyridil)- 2,2’:5’,2”-terthiophene (ttpy), 4-5-diphenyl-2-methyl-thiazole (dpmt) and 5- trifluoromethyl-2-(2,4-difluorophenyl)pyridine (dF(CF3)ppy) is also investigated. Preliminary results on the preparation of an OLEC device are given in the case of [Ir(4-5-diphenyl-2-methyl-thiazole)2(5-Methyl-1,10-phenanthroline)][PF6], [Ir(2- phenypyridine)2(5-Methyl-1,10-phenanthroline)][PF6] and [Ir(2- phenyquinoline)2(5-Methyl-1,10-phenanthroline)][PF6].
In the second section the second order NLO properties of the cationic cyclometalated Iridium (III) complexes, described in the first section, are investigated. Then the study is extended to related neutral cyclometallated Ir(III) and Pt(II) complexes. Besides, the role of f electrons on the dipolar and octupolar contributions to the quadratic hyperpolarizability of fluorinated β-diketonates diglyme lanthanide complexes is investigated. Finally, the second order NLO properties of a highly π-delocalized bidentate ligand, dibutyl-(4,5-diazafluorenyl- 9-ilidene-penta-1,3-dienyl)-amine, and related Zn(II) complexes are studied. In the last section, details are given on the synthesis and characterization of all the complexes. This PhD thesis leds to the discovery of new organometallic complexes and coordination compounds appealing as building blocks for molecular materials with both non linear and luminescence properties
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
Simple novel cyclometallated iridium complexes for potential application in dye-sensitized solar cells
No full textDye-sensitized solar cells (DSSCs) are considered a real solution for harnessing the energy of the sun and converting it into electrical energy, exceeding the value of 11% efficiencies with the most performing Ru(II) sensitizers. The photosensitizer dye plays a key role in DSSCs, and iridium complexes are potentially good candidates for application in those kind of cells. Here we report the synthesis and characterization of three new simple cyclometallated Ir(III) complexes of the type: [Ir(C^N)2(4,4′- dicarboxybipyridine)][PF6] (C^N = variously substituted phenylpyridine cyclometallating ligand) and we try to understand if there is an influence of the nature of the cyclometallating ligand on the photovoltaic performance of the related dye-sensitized solar cells. The use of more conjugated π-delocalized cyclometallating ligands, that slightly shifts the UV bands to higher wavelengths, affords little better photovoltaic parameters. In addition we report the emission spectra and the emission quantum yields of all the phosphorescent Ir(III) complexes
Cyclometallated Iridium(III) complexes with substituted 1,10- phenanthrolines for organic light emitting diodes.
No full textComplesso del rame e suo utilizzo in celle solari sensibilizzate da colorante
No full textComplesso del rame avente formula generale (I):
[CuL1L2]+Y- (I)
in cui L1 e L2, diversi tra loro, sono leganti eteroaromatici azotati bidentati.
Detto complesso del rame è particolarmente utile quale colorante in un elemento di trasformazione fotoelettrica sensibilizzato da colorante che, a sua volta, può essere utilizzato in una cella solare sensibilizzata da colorante (“Dye Sensitized Solar Cell” - DSSC)
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
Second order non linear optical properties of neutral Ir(III) and Pt(II) complexes with substituted b-diketonate ligands.
No full textAppropriate 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
- …
