Jean-Claude Bunzli - Optimizing Millisecond Time Scale Near-Infrared Emission in Polynuclear Chrome(III)-Lanthanide(III) Complexes

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  Aboshyan-Sorgho,L., Nozary,H., Aebischer,A., Bunzli,J.C.G.,   Morgantini,P.Y., Kittilstved,K.R., Hauser,A., Eliseeva,S.V.,   Petoud,S., Piguet,C. Journal of the American Chemical   Society 2012 134 (30) 12675-12684

  Abstract: 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 D-3-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

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