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- (κ3-ligand)3], and an eight-coordinate complex with ytterbium, [Yb(κ3-ligand)2 · (κ1-ligand) · H2O], 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) × 103 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 μs, 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.
Paul Joseph Dyson, Farzaneh Fadaei Tirani, Mouna Hadiji
Kay Severin, Farzaneh Fadaei Tirani, Noga Eren
Kay Severin, Farzaneh Fadaei Tirani, Sylvain Alexandre Marie Sudan