| Abstract
| - Derivatives of dipicolinic acid with a polyoxyethylene pendant arm at the pyridine 4-position have been functionalized for potential grafting with biological material. Four ligands with different terminal functions (alcohol, methoxy, phtalimide and amine) have been synthesized, which react with trivalent lanthanide ions LnIII to yield triple helical [Ln(L)3]3− complexes, as shown by NMR and UV−vis titrations. The tris chelates display large thermodynamic stability with log β13 ≈ 19−20 for all EuIII complexes for instance. Photophysical measurements reveal adequate sensitization of the metal-centered luminescence in the europium (ηsens = 33−72%) and terbium complexes, which is modulated by the nature of the terminal function. The lifetimes of the metal-centered excited states are long, up to 1.4 ms for [Eu(L)3]3− and 1.6 ms for [Tb(L)3]3− at room temperature, in line with hydration numbers essentially equal to zero. Quantum yields are as high as 29% for the [Eu(LNH2)3]3− and 18% for the [Tb(LOH)3]3− tris chelates in water at physiological pH. These series of complexes demonstrate the extent of fine-tuning achievable for lanthanide luminescent probes and are simple models for investigating the effect of binding to biological molecules on the metal-centered luminescent properties.
- A remarkable tuning from 12 % (X = OH) to 29 % (X = NH2) of the quantum yield of EuIII tris chelates with polyoxoethylene-substituted dipicolinates is evidenced depending on the nature of the terminal substituent, whereas the quantum yield of the corresponding TbIII chelates is less sensitive.
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