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

Abstract

Previously limited to highly symmetrical homoleptic triple‐helical complexes [Er(Lk)3]3+, 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)3] 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)3] in solution at room temperature can be boosted by up to three orders of magnitude.