High-Nuclearity Lanthanide-Titanium Oxo Clusters as Luminescent Molecular Thermometers with High Quantum Yields.

Three heterometallic lanthanide-titanium oxo clusters (LnTOCs) formulated as Eu2 Ti4 (μ3 -O)4 (tbba)12 (acac)2 (Eu2 Ti4 , 1, Hacac = acetylacetone), Eu5 Ti4 (μ3 -O)6 (tbba)20 (Htbba)(THF)2 (Eu5 Ti4 , 2), and Eu8 Ti10 (μ3 -O)14 (Ac)2 (tbba)34 (H2 O)4 (THF)2 (Htbba)2 (Eu8 Ti10 , 3) were prepared through the reactions of 4-tert-butylbenzoate (Htbba), rare-earth salts, and Ti(Oi Pr)4 . The solution luminescence investigation discovered a size-dependent quantum yield phenomenon in solution. A solid-state luminescence study showed that these three LnTOCs display temperature-dependent photoluminescent properties. Interestingly, the Eu5 Ti4 cluster exhibited the highest quantum yield of 94.9% in the solid state among the reported 3d-4f clusters.