• Optimizing Millisecond Time Scale Near-Infrared Emission in Polynuclear Chrome(III)-Lanthanide(III) Complexes
    L. Aboshyan-Sorgho, H. Nozary, A. Aebischer, J.-C.G. BŁnzli, , K.R. Kittilstved, A. Hauser, S.V. Eliseeva, S. Petoud and C. Piguet
    Journal of the American Chemical Society, 134 (30) (2012), p12675-12684
    DOI:10.1021/ja304009b | unige:22645 | Abstract | Article HTML | Article PDF
 
This work illustrates a simple approach for optimizing long-lived near-infrared lanthanide-centered luminescence using trivalent chromium chromophores as sensitizers. Reactions of the segmental ligand L2 with stoichiometric amounts of M(CF3SO3)2 (M = Cr, Zn) and Ln(CF3SO3)3 (Ln = Nd, Er, Yb) under aerobic conditions quantitatively yield the D3-symmetrical trinuclear [MLnM(L2)3](CF3SO3)n complexes (M = Zn, n = 7; M = Cr, n = 9), in which the central lanthanide activator is sandwiched between the two transition metal cations. Visible or NIR irradiation of the peripheral Cr(III) chromophores in [CrLnCr(L2)3]9+ induces rate-limiting intramolecular intermetallic Cr→Ln energy transfer processes (Ln = Nd, Er, Yb), which eventually produces lanthanide-centered near-infrared (NIR) or IR emission with apparent lifetimes within the millisecond range. As compared to the parent dinuclear complexes [CrLn(L1)3]6+, the connection of a second strong-field [CrN6] sensitizer in [CrLnCr(L2)3]9+ significantly enhances the emission intensity without perturbing the kinetic regime. This work opens novel exciting photophysical perspectives via the buildup of non-negligible population densities for the long-lived doubly excited state [Cr*LnCr*(L2)3]9+ under reasonable pumping powers.
  
  • Near-Infrared to Visible Light Upconversion in a Trinuclear d-f-d ComplexVery Important Paper
    L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K.R. Kittilstved, A. Aebischer, J.-C.G. BŁnzli, A. Hauser and C. Piguet
    Angewandte Chemie International Edition, 50 (2011), p4108-4112
    DOI:10.1002/anie.201100095 | unige:15714 | Abstract | Article PDF
The connection of two CrIII sensitizers around a central ErIII acceptor in a self-assembled cation provides high local metal concentrations that favor efficient nonlinear energy transfer upconversion luminescence (see picture). Upon selective low-energy near-infrared irradiation of CrIII-centered transitions, 1 displays an unprecedented molecular two-photon upconverted green ErIII-centered emission.
  • Tuning the Decay Time of Lanthanide-Based Near Infrared Luminescence from Micro- to Milliseconds through d->f Energy Transfer in Discrete Heterobimetallic Complexes
    S. Torelli, D. Imbert, M. Cantuel, G. Bernardinelli, S. Delahaye, A. Hauser, J.-C.G. BŁnzli and C. Piguet
    Chemistry - A European Journal, 11 (11) (2005), p3228-3242
    DOI:10.1002/chem.200401158 | unige:3273 | Abstract | Article HTML | Article PDF
Inert and optically active pseudo-octahedral CrIIIN6 and RuIIN6 chromophores have been incorporated by self-assembly into heterobimetallic triple-stranded helicates HHH-[CrLnL3]6+ and HHH-[RuLnL3]5+. The crystal structures of [CrLnL3](CF3SO3)6 (Ln=Nd, Eu, Yb, Lu) and [RuLnL3](CF3SO3)5 (Ln=Eu, Lu) demonstrate that the helical structure can accommodate metal ions of different sizes, without sizeable change in the intermetallic M…Ln distances. These systems are ideally suited for unravelling the molecular factors affecting the intermetallic nd→4f communication. Visible irradiation of the CrIIIN6 and RuIIN6 chromophores in HHH-[MLnL3]5/6+ (Ln=Nd, Yb, Er; M=Cr, Ru) eventually produces lanthanide-based near infrared (NIR) emission, after directional energy migration within the complexes. Depending on the kinetic regime associated with each specific d-f pair, the NIR luminescence decay times can be tuned from micro- to milliseconds. The origin of this effect, together with its rational control for programming optical functions in discrete heterobimetallic entities, are discussed.

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