Jean-Claude Bunzli - Modulating the Near-Infrared Luminescence of Neodymium and Ytterbium Complexes with Tridentate Ligands Based on Benzoxazole-Substituted 8-Hydroxyquinolines

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  Shavaleev,N.M., Scopelliti,R., Gumy,F., Bunzli,J.C.G.   Inorganic Chemistry 2009 48  (7) 2908-2918

  Abstract: An improved synthesis of   2-(2'-benzothiazole)- and 2-(2'-benzoxazole)-8-hydroxyquinoline   ligands that combine a tridentate N,N,O-chelating unit for metal   binding and extended chromophore for light harvesting is   developed. The 2-(2'-benzoxazole)-8-hydroxyquinoline ligands form   mononuclear nine-coordinate complexes with neodymium,   (Nd-(kappa(3)-ligand)(3)], and an eight-coordinate complex with   ytterbium, [Yb(kappa(3)-ligand)(2)center   dot(kappa(1)-ligand)center dot H(2)O], as verified by   crystallographic characterization of five complexes with four   different ligands. The chemical stability of the complexes   increases when the ligand contains 5,7-dihalo-8-hydroxyquinoline   versus an 8-hydroxyquinoline group. The complexes feature a   ligand-centered visible absorption band with a maximum at 508-527   nm and an intensity of (7.5-9.6) x 10(3) M(-1) . cm(-1). Upon   excitation with UV and visible light within ligand absorption   transitions, the complexes display characteristic lanthanide   luminescence in the near-infrared at 850-1450 nm with quantum   yields and lifetimes in the solid state at room temperature as   high as 0.33% and 1.88 mu s, respectively. The lanthanide   luminescence in the complexes is enhanced upon halogenation of   the 5,7- positions in the 8-hydroxyquinoline group and upon the   addition of electron-donating substituents to the benzoxazole   ring. Facile modification of chromophore units in   2-(2'-benzoxazole)-8-hydroxyquinoline ligands provides means for   controlling the luminescence properties of their lanthanide   complexes

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