title: Modulating the near-infrared luminescence of neodymium and ytterbium complexes with tridentate ligands based on benzoxazole-substituted 8-hydroxyquinolines.
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) x (kappa(1)-ligand) x 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) x 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 micros, 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.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratory of Lanthanide Supramolecular Chemistry, BCH 1405, CH-1015 Lausanne, Switzerland.
authors.forename: Nail M
authors.initials: NM
authors.lastname: Shavaleev
authors.forename: Rosario
authors.initials: R
authors.lastname: Scopelliti
authors.forename: Frédéric
authors.initials: F
authors.lastname: Gumy
authors.forename: Jean-Claude G
authors.initials: JC
authors.lastname: Bünzli
mesh_terms: D001583:Benzoxazoles / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D049449:Luminescence; D008958:Models, Molecular; D015394:Molecular Structure; D009354:Neodymium / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D015125:Oxyquinoline / Q000737:chemistry*; D015018:Ytterbium / Q000737:chemistry*
chemical_list: D001583:Benzoxazoles; D008024:Ligands; D009942:Organometallic Compounds; D009354:Neodymium; D015125:Oxyquinoline; D015018:Ytterbium