title: Tridentate benzimidazole-pyridine-tetrazolates as sensitizers of europium luminescence.
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(κ(3)-ligand)2(κ(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 κ(1)-ligand to give anhydrous complexes [Ln(κ(3)-ligand)3] that exhibit efficient europium luminescence. X-ray structures of the anhydrous complexes confirm that the lanthanide ion (La(III), Eu(III)) is nine-coordinate in a distorted tricapped trigonal prismatic environment and that coordination of the lanthanide ion by tetrazolate is weaker than by carboxylate.
authors.affiliation: École Polytechnique Fédérale de Lausanne, Institut des Sciences et Ingénierie Chimiques , Avenue Forel 2, BCH, CH-1015 Lausanne, Switzerland.
authors.forename: Nail M
authors.initials: NM
authors.lastname: Shavaleev
authors.forename: Svetlana V
authors.initials: SV
authors.lastname: Eliseeva
authors.forename: Rosario
authors.initials: R
authors.lastname: Scopelliti
authors.forename: Jean-Claude G
authors.initials: JC
authors.lastname: Bünzli
mesh_terms: D001562:Benzimidazoles / Q000737:chemistry*; D005063:Europium / Q000737:chemistry*; D008024:Ligands; D049449:Luminescence; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D013777:Tetrazoles / Q000737:chemistry*
chemical_list: D001562:Benzimidazoles; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D013777:Tetrazoles; D005063:Europium; C031000:benzimidazole; C023666:pyridine