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Iridium cyclometalated complexes with axial symmetry. Synthesis and photophysical properties of a trans-biscyclometalated complex containing the terdentate ligand 2,6-diphenylpyridine
No full textThe first example of an iridium biscyclometalated complex with a Cboolean ANDNboolean ANDC 2,6-diphenylpyridine (dppy)-type ligand, [(4'-(4-bromophenyl)-2:2',6':2"-terpyridine)lr(2,6-diphenyl-4-(4-tolyl)pyridine)](NO3) (1), has been synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, H-1 and C-13 NMR, cyclic voltammetry, and both steady-state and time-resolved emission and absorption studies. Preliminary density functional theory calculations have also been conducted. 1 crystallizes in the monoclinic space group P2(1)/n. The crystallographic data are as follows: C(45)H(31)BrN(4)lrO(3).2H(2)O, a = 17.4308(4) Angstrom, b = 9.0312(2) Angstrom, c = 26.7601(7) Angstrom, beta = 104.496(1)degrees, V = 4078.5(2) Angstrom,, Z = 4. The relatively long Ir-C distances (2.122 and 2.094 Angstrom) reflect the strong mutual trans effect of the cyclometalating carbons. The complex exhibits strong visible absorption and long-lived (1.7,mus) emission ( lambda(max), 690 nm) in room temperature solution. The inherent asymmetry of the coordination environment offers a unique directional character to the emitting excited state, which is predominately ligand-to-ligand charge transfer (dppy --> 2,2':6',2"-terpyridine) in nature
Site-specific electronic couplings in dyads with MLCT excited states. Intramolecular energy transfer in isomeric Ru(II)-Ru(II) cyclometalated complexes
No full textThe rod-like binuclear complexes [(ttpy)Ru(tpy-ph2-phbpy)Ru(ttpy)]4+ and
[(ttpy)Ru(tpy-ph2-tpy)Ru(phtbpy)]4+ (for abbreviations, see text) have been synthesized and
characterized. In both complexes, the polypyridine Ru(II) centers have (N∧N∧N)Ru(N∧N∧N) and
(N∧N∧N)Ru(C∧N∧N) coordination environment. The two isomeric species differ in whether the
cyclometalating carbon resides on the bridging or on the terminal ligand. The two complexes have
virtually identical energy levels, but MLCT excited states of different (bridging or terminal) ligand
localization. They are thus ideally suited to investigate possible effects of excited-state localization on
intramolecular energy transfer kinetics. In fact, ultrafast spectroscopic measurements yield different
energy transfer time constants for the two isomers, with the bridge-cyclometalated complex (2.7 ps)
being faster than the terminal-cyclometalated one (8.0 ps). This difference can be explained in terms of
different electronic factors for Dexter energy transfer. The study highlights the peculiar intricacies of
intramolecular energy transfer in inorganic dyads involving MLCT excited states
Primary processes in photoinduced multielectron storage systems. A dinuclear ruthenium(II) species featuring a charge-separated state with a lifetime of 1.3 ms
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PHOTOINDUCED PROCESSES IN AN ALUMINUM-PORPHYRIN / NAPHTHALENEDIIMIDE AXIAL DYAD.
No full textPorphyrins are widely studied cromphorores, well-known as constituents of both natural and artificial supramolecular systems which show interesting photophysical features such as photoinduced electron and/or energy transfer. Recently, attention has been paid to the possibility of exploiting Aluminium(III) porphyrins as supramolecular building blocks1,2, due to the stability of the axial coordination between the Al-porphyrin and ligands carrying oxygen-containing groups. Here we present an example of such a supramolecular system, a dyad based on an Al(III)-tetra-phenyl-porphyrin moiety linked by axial coordination to a naphtalene-diimide unit carrying a carboxylate group. The photophysical properties of the dyad system and of appropriate model systems have been studied by means of both stationary and time-resolved spectroscopic techniques, including single-photon counting, nanosecond laser flash photolysis and ultrafast transient absorption spectroscopy. The experimental data indicate the occurrence of photoinduced electron transfer in the dyad, with clear evidence given by solvent effects on excited-state kinetics. Density functional theory (DFT) calculations have been performed to gain a better insight on the electronic structure and provide a reliable geometry for the system in order to remedy the lack of any pentacoordinated Al-porphyrin x-ray structure in literature
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
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
Primary Photoinduced Processes in Bimetallic Dyads with Extended Aromatic Bridges. Tetraazatetrapyridopentacene Complexes of Ruthenium(II) and Osmium(II)
No full textThe photophysics of the binuclear complexes [(phen)2M(tatpp)M(phen)2]4+, where M ) Ru or Os, phen ) 1,10-
phenanthroline, and tatpp ) 9,11,20,22-tetraazatetrapyrido[3,2-a:2¢3¢-c:3¢¢,2¢¢-l:2¢¢¢,3¢¢¢]pentacene, has been studied
in acetonitrile and dichloromethane by femtosecond and nanosecond time-resolved techniques. The results
demonstrate that complexes of different metals have different types of lowest excited state: a tatpp ligand-centered
(LC) triplet in the case of Ru(II); a metal-to-ligand charge-transfer (MLCT) triplet state in the case of Os(II). The
excited-state kinetics is strongly solvent-dependent. In the Ru(II) system, the formation and decay of the LC state
take place, respectively, in 25 ps and ca. 5 ns in CH3CN and in 0.5 ps and 1.3 ís in CH2Cl2. These solvent effects
can be rationalized on the basis of a thermally activated decay of the LC state through the upper MLCT state. In
the Os(II) system, the formation and decay of the MLCT state take place, respectively, in 3.8 and 60 ps in CH3CN
and in 0.5 and 4 ps in CH2Cl2. These effects are consistent with the solvent sensitivity of the MLCT energy, in
terms of driving force and energy-gap law arguments. The relevance of these results for the use of ladder-type
aromatic bridges as potential molecular wires is discussed
Iridium Cyclometalated Complexes with Axial Symmetry: Time-Dependent Density Functional Theory Investigation of trans-Bis-Cyclometalated Complexes Containing the Tridentate Ligand 2,6-Diphenylpyridine
No full textA new series of iridium cyclometalated complexes with a C^N^C dppy-type ligand and a N^N^N tpy-type ligand have been synthesized and characterized by various techniques such as mass spectrometry, 1H and 13C NMR, cyclic voltammetry, both steady-state and time-resolved emission and absorption studies, and time-dependent DFT (TDDFT) calculations. The complexes exhibit strong visible absorptions and long-lived (1.6-2.0 ís) emissions (ìmax, ca. 680 nm) in room-temperature solution. DFT calculations on the ground-state geometry match that of an X-ray crystal structure. TDDFT calculations give accurate predictions of the electronic absorption energies and intensities, while geometry optimizations on the lowest energy triplet state give accurate energies for the emission. Examination of the relevant molecular orbitals shows that the inherent asymmetry of the coordination environment offers a unique directional character to the emitting excited state, which is predominately LLCT (dppy f tpy) in nature
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