Jean-Claude Bunzli - Tridentate Benzimidazole-Pyridine-Tetrazolates as Sensitizers of Europium Luminescence

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      Shavaleev,Nail M., Eliseeva,Svetlana V., Scopelliti,Rosario,   B nzli,Jean-Claude G. Inorganic Chemistry  2014 53 (10) 5171-5178

      Abstract: We report on new anionic tridentate   benzimidazole-pyridine-tetrazolate ligands that form neutral 3:1   complexes with trivalent lanthanides. The ligands are   UV-absorbing chromophores that sensitize the red luminescence of   europium with energy-transfer efficiency of 74-100%. The lifetime   and quantum yield of the sensitized europium luminescence   increase from 0.5 ms and 12-13% for the as-prepared solids to 2.8   ms and 41% for dichloromethane solution. From analysis of the   data, the as-prepared solids can be described as aqua-complexes   [Ln( 3-ligand)2( 1-ligand)(H2O)x] where the coordinated water   molecules are responsible for the strong quenching of the   europium luminescence. In solution, the coordinated water   molecules are replaced by the nitrogen atoms of the  1-ligand to   give anhydrous complexes [Ln( 3-ligand)3] that exhibit efficient   europium luminescence. X-ray structures of the anhydrous   complexes confirm that the lanthanide ion (LaIII, EuIII) is   9-coordinate in a distorted tricapped trigonal prismatic   environment and that coordination of the lanthanide ion by   tetrazolate is weaker than by carboxylate.

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