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

Three heterometallic lanthanide-titanium oxo clusters (LnTOCs) formulated as Eu2Ti4(μ3-O)4(tbba)12(acac)2 (Eu2Ti4, 1, Hacac = acetylacetone), Eu5Ti4(μ3-O)6(tbba)20(Htbba)(THF)2 (Eu5Ti4, 2), and Eu8Ti10(μ3-O)14(Ac)2(tbba)34(H2O)4(THF)2(Htbba)2 (Eu8Ti10, 3) were prepared through the reactions of 4-tert-butylbenzoate (Htbba), rare-earth salts, and Ti(OiPr)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 Eu5Ti4 cluster exhibited the highest quantum yield of 94.9% in the solid state among the reported 3d-4f clusters.