1,720,979 research outputs found
Influence of the pull ligand on the second order NLO properties in M(II) mixed-ligan dichalcogenolenes: the case of [M(II)(Bz2pipdt)(dsit)
No full textRedox active dithione-thiolato complexes of the nickel triad showing second order nonlinear optical properties
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Square-planar d8 metal mixed-ligand dithiolene complexes as second order nonlinear optical chromophores: Structure/property relationship
No full textThe structure/property relationship of square-planar d8 metal push/pull mixed-ligand dithiolene complexes
is discussed to provide suitable tools to chemists for tailoring compounds with predictable optical
properties. These complexes exhibit a typical HOMO–LUMO electronic transition which falls at low energies
(vis–NIR region). Substituents at the dithiolene core affect the energy of the frontier orbitals and
mixed-ligand complexes based on two different ligands give rise to an asymmetric-symmetric distribution
of the charge according to the differences in the push/pull character of the two ligands. Where the
push/pull character of the two ligands is significantly different, a localized electron distribution occurs.
The pull ligand (dithiolate) contributes mostly to the HOMO, the push ligand (dithione) mostly to the
LUMO, and the HOMO–LUMO transition has ligand-to-ligand charge-transfer (CT) character with some
contribution of the metal. These chromophores exhibit negative solvatochromism and molecular first
hyperpolarizability.
Where the difference in the push/pull character of the two ligands is small, a delocalized electron
distribution occurs and the chromophores exhibit optical features typical of symmetrical complexes (NIR
dyes, no second order NLO activity).
Structural data, spectroscopic and electrochemical features reflect the-delocalized/localized electron
distribution.
The progress of these studies has allowed to prepare several new redox-active complexes with remarkably high second order nonlinear activity, tunable with the metal and the ligands
Recent advances in the structure and properties of metal–dithiolene complexes
No full textThis chapter describes novel or revisited aspects discussed in Chapter 16 of The Chemistry of Metal Enolates published in 2009. In particular, the properties of square-planar homo- and heteroleptic metal–dithiolene complexes, such as the uncertainty of the valence state of the central metal and the ligands, and a variety of their applications as photocatalysts and electrocatalysts for hydrogen production from water, redox-active second-order nonlinear chromophores, single-component molecular conductors (SCMCs) and suitable materials for field-effect transistors (FET), solar cells, and photodetectors, are discussed and more recent literature data reviewed. The chapter summarizes how new or optimized applications of this class of complexes, spanning from bio-medicinal to material chemistry, are relatable to the versatility of the organic synthesis in tailoring the ligand which can bear a variety of functionalities to favor film formation, luminescent properties, donor/acceptor interactions, proton transfer reaction, chirality, to combine with the suitable metal for obtaining the complex exhibiting the desired properties
Progress and perspectives on strategies to control photochemical properties in Metallo-Dithiolene Donor-Acceptor systems
No full textIn this mini-review recent progress in studies on heteroleptic d8-metal dithiolene complexes with a D-M-A donor–π–acceptor electronic structure showing non-linear and linear optical properties, are presented. The ligands, formally dithiolenes, consist in a variety of donors (dithiolato) and acceptors (dithioxamide and dithioxamidate), differing for electronic properties and/or structural features, varying from rigid and planar systems to conformationally-flexible ones. It is shown how the components of these D-M-A systems modulate both the energy and topology of the frontier molecular orbitals involved in the charge transport mechanism to reach a fine tuning of the optical properties and achieve high values of the quadratic hyperpolarizability. Further tailoring of the ligands by integrating specific functional groups in their periphery, such as NH and/or a quinoxaline ring, is presented as a versatile tool to achieve a reversible response to external stimuli. Accordingly, selected cases where exchange color proton and silver ions tunable properties, switching of the nonlinear optical response (with a 2.5–6.5 contrast for HCl exchange) and also uncommon emission color reversibly tunable by different stimuli, such as proton and silver ions, are presented. In the bulk, crystals gave a poor or null second harmonic generation (SHG) response, while a stable and large response has been obtained in a limited number of cases of complexes dispersed in polymethylmethacrylate films. Reported results are addressed to stimulate further work to exploit the potential of this class of complexes as molecular sensors and switches and to optimize the processing procedures to achieve good SHG responses in the bulk
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
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