Dinuclear Heteroleptic Erbium Complexes for Improving Molecular-Based Light Upconversion in Solution?
Year: 2025
Type: article
Abstract: In an attempt to boost molecular-based excited-state absorption (ESA) via cross-relaxation (CR), the back-to-back ditridentate polyaromatic 2,2′,6,6′-tetrakis(1-methyl-1 H -benzo[ d ]imidazole-2-yl)-4,4′-bipyridine ligand ( L4 ) was reacted with neutral [Ln(hfac) 3 ] lanthanide cargoes (Ln = Y, Eu, and Er and H-hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) to give dinuclear erbium [(hfac) 3 Ln L4 Ln(hfac) 3 ] ≡ [ L4 Ln 2 (hfac) 6 ] adducts. Their crystal structures confirm the formation of dimeric molecular scaffolds made of two nine-coordinated trivalent [LnN 3 O 6 ] chromophores separated by a 4,4′-bipyridine bridge with Ln···Ln distances within the nanometric range (Eu···Eu = 11.69 Å, Y···Y = 11.65 Å, and Er···Er = 12.12 Å). Thermodynamic studies in dichloromethane provide critical insights into the formation and stability of these adducts. Under near-infrared (NIR) excitation at 801 nm in solution, [ L4 Er 2 (hfac) 6 ] exhibits ESA light upconversion with blueish-green emissions at 525 and 542 nm corresponding to Er( 2 H 11/2, 4 S 3/2 → 4 I 15/2 ) transitions. Thanks to the pertinent speciation in dichloromethane, we could extract a reliable upconversion quantum yield and brightness for the targeted dinuclear [ L4 Er 2 (hfac) 6 ] adduct in solution. They largely overpass by 2 orders of magnitude those of the unsaturated mononuclear [ L4 Er(hfac) 3 ] intermediate but remain comparable to data reported for related saturated monomeric adducts in the same conditions. No global beneficial cross-relaxation effect could thus be unambiguously identified.
Source: Inorganic Chemistry
Institution: University of Geneva
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4407809163