title: Optimizing sensitization processes in dinuclear luminescent lanthanide oligomers: selection of rigid aromatic spacers.
abstract: This work illustrates a simple approach for optimizing the lanthanide luminescence in molecular dinuclear lanthanide complexes and identifies a particular multidentate europium complex as the best candidate for further incorporation into polymeric materials. The central phenyl ring in the bis-tridentate model ligands L3–L5, which are substituted with neutral (X = H, L3), electron-withdrawing (X = F, L4), or electron-donating (X = OCH3, L5) groups, separates the 2,6-bis(benzimidazol-2-yl)pyridine binding units of linear oligomeric multi-tridentate ligand strands that are designed for the complexation of luminescent trivalent lanthanides, Ln(III). Reactions of L3–L5 with [Ln(hfac)3(diglyme)] (hfac– is the hexafluoroacetylacetonate anion) produce saturated single-stranded dumbbell-shaped complexes [Ln2(Lk)(hfac)6] (k = 3–5), in which the lanthanide ions of the two nine-coordinate neutral [N3Ln(hfac)3] units are separated by 12–14 Å. The thermodynamic affinities of [Ln(hfac)3] for the tridentate binding sites in L3–L5 are average (6.6 ≤ log(β(2,1)(Y,Lk)) ≤ 8.4) but still result in 15–30% dissociation at millimolar concentrations in acetonitrile. In addition to the empirical solubility trend found in organic solvents (L4 > L3 >> L5), which suggests that the 1,4-difluorophenyl spacer in L4 is preferable, we have developed a novel tool for deciphering the photophysical sensitization processes operating in [Eu2(Lk)(hfac)6]. A simple interpretation of the complete set of rate constants characterizing the energy migration mechanisms provides straightforward objective criteria for the selection of [Eu2(L4)(hfac)6] as the most promising building block.
authors: Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland.
authors: Jean-François
authors: JF
authors: Lemonnier
authors: Laure
authors: L
authors: Guénée
authors: César
authors: C
authors: Beuchat
authors: Tomasz A
authors: TA
authors: Wesolowski
authors: Prasun
authors: P
authors: Mukherjee
authors: David H
authors: DH
authors: Waldeck
authors: Kristy A
authors: KA
authors: Gogick
authors: Stéphane
authors: S
authors: Petoud
authors: Claude
authors: C
authors: Piguet
mesh_terms: D001562:Benzimidazoles / Q000737:chemistry; D005063:Europium / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D049408:Luminescent Agents / Q000737:chemistry*; D008958:Models, Molecular; D011108:Polymers / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry
chemical_list: C500137:2,6-bis(benzimidazol-2-yl)pyridine; D001562:Benzimidazoles; D028581:Lanthanoid Series Elements; D049408:Luminescent Agents; D011108:Polymers; D011725:Pyridines; D005063:Europium