Tuning Selectivity and Stability in Heteroleptic Lanthanide Adducts by Ligand Design.

Terdentate ligands - and their heteroleptic [Ln(hfac)] complexes (Ln = La, Eu, Gd, Er, or Y; H-hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) exhibit multifactorial correlations between the ligand's structural frameworks, including their level of preorganization and steric congestion and their affinities and selectivities for catching the trivalent lanthanide containers [Ln(hfac)]. The polyaromatic ligand scaffolds could be stepwise modulated via lanthanide-template synthetic strategies, using intermolecular rhodium-catalyzed insertion reactions. The increasing level of preorganization along the → → series leads to a duality in which larger thermodynamic formation constants with lanthanides in CDCl are accompanied by an unexpected decrease in the Ln-N affinities in the solid state, which could be assigned to a limited match between the lanthanide size and the enlarged preorganized cavities.

Symmetry and Rigidity for Boosting Erbium-Based Molecular Light-Upconversion in Solution.

Previously limited to highly symmetrical homoleptic triple-helical complexes [Er(Lk) ] , where Lk are polyaromatic tridentate ligands, single-center molecular-based upconversion using linear optics and exploiting the excited-state absorption mechanism (ESA) greatly benefits from the design of stable and low-symmetrical [LkEr(hfa) ] heteroleptic adducts (hfa =hexafluoroacetylacetonate anion). Depending on (i) the extended π-electron delocalization, (ii) the flexibility and (iii) the heavy atom effect brought by the bound ligand Lk, the near-infrared (801 nm) to visible green (542 nm) upconversion quantum yield measured for [LkEr(hfa) ] in solution at room temperature can be boosted by up to three orders of magnitude.