Innovative Multipodal Ligands Derived from Tröger's Bases for the Sensitization of Lanthanide(III) Luminescence
Résumé
We describe the synthesis and characterization of the first family of multipodal ligands with a Tröger's base framework designed for the preparation of luminescent lanthanide(III) complexes. Eight ligands were designed and synthesized using different strategies, including alkylation reactions, amide couplings and Ugi multicomponent reactions. All ligands bear carboxylate groups for the coordination of the lanthanide(III) ion, with lanthanide(III) sensitizing units consisting of the Tröger's base framework itself or attached benzamides. Upon irradiation of the chromophoric ligands, the green terbium(III) emission was efficiently generated, whereas the europium(III) emission signal was negligible. The geometry and the substitution pattern of the ligands allow the control of the stoichiometry of the species formed and the Tb(III) luminescence sensitization efficiency, showing that para-substitution patterns are more efficient than meta-substitution ones for the formation of coordination compounds with lower Tb(III)/ligand ratio. We propose that the formed species are self-assembled 2:2 or 2:4 metallosupramolecular structures.
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