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Optimizing Sensitization Processes in Dinuclear Luminescent Lanthanide Oligomers: Selection of Rigid Aromatic Spacers

Authors
Mukherjee, Prasun
Waldeck, David H.
Gogick, Kristy A.
Petoud, Stéphane
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Published in Journal of the American Chemical Society. 2011, vol. 133, no. 40, p. 16219-16234
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(β2,1Y,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.
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Other version: http://pubs.acs.org/doi/abs/10.1021/ja206806t
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LEMONNIER, Jean-François et al. Optimizing Sensitization Processes in Dinuclear Luminescent Lanthanide Oligomers: Selection of Rigid Aromatic Spacers. In: Journal of the American Chemical Society, 2011, vol. 133, n° 40, p. 16219-16234. https://archive-ouverte.unige.ch/unige:17237

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Deposited on : 2011-10-21

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