title: Improving visible light sensitization of luminescent europium complexes.
abstract: The synthesis and characterization of the new ligands L(1), L(2) and L(4) are described with the series of four europium complexes of formula [EuL(n)(TTA)(3)] in which TTA refers to 2-thenoyltrifluoroacetonate and L(n) to tridentate ligands with nitrogen containing heterocyclic structure, such as a 2,6-bis(3-methyl-pyrazolyl)-4-(p-toluyl-ethynyl)-triazine for L(1), or terpyridines functionalized at the 4' position by a phenyl-vinylene for L(2), a p-dimethylamino-phenylene for L(3), or a p-aminophenyl-ethynylene for L(4). The spectroscopic properties of the ligands and of the complexes are studied by means of UV-Vis absorption spectroscopy, as well as steady-state and time-resolved luminescence spectroscopy. All complexes display europium centred luminescence upon ligand excitation. Careful examination of the excitation spectra revealed differences in the ligand based sensitization efficiencies. For complexes of L(1) and L(2), excitation of europium is mainly achieved through the TTA moieties and the photo-physical studies on [EuL(1)(TTA)(3)] evidenced a weaker coordination of the bispyrazolyltriazine tridentate ligand, resulting from a partial decomplexation upon dilution. Complexes of L(3) and L(4) display intense excitation through the tridentate units, which extend down to 460 nm in the visible region. In the case of L(3), selective excitation reveals the presence of a ligand-centred emission band at 520 nm which is likely ascribed to a L(3) centred charge transfer state.
authors.affiliation: Laboratoire de Chimie Moléculaire, CNRS UMR 7509, ECPM-ULP, 25 rue Becquerel, 67087 Strasbourg Cedex, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Kadjane
authors.forename: Loïc
authors.initials: L
authors.lastname: Charbonnière
authors.forename: Franck
authors.initials: F
authors.lastname: Camerel
authors.forename: Philippe P
authors.initials: PP
authors.lastname: Lainé
authors.forename: Raymond
authors.initials: R
authors.lastname: Ziessel
mesh_terms: D005063:Europium / Q000737:chemistry*; D008024:Ligands; D008027:Light; D049408:Luminescent Agents / Q000737:chemistry*; D015394:Molecular Structure; D010777:Photochemistry; D013056:Spectrophotometry, Ultraviolet
chemical_list: D008024:Ligands; D049408:Luminescent Agents; D005063:Europium