Ligand-Dependent Luminescence Properties of Lanthanide-Titanium Oxo Clusters.

A series of lanthanide-titanium oxo clusters (LnTOCs), LnTi-Ac, LnTi--Toluic, and LnTi-Anthra (Ln = Eu and Tb), were prepared based on acetic acid (HAc), -toluic acid (Hp-Toluic), and anthracene-9-carboxylic acid (HAnthra). Crystal structural analysis showed that these clusters possess the same metal topology framework, in which eight Ti ions form a cube and two Ln ions are located on the opposite faces of the cube. The luminescence investigation discovered that the EuTi-Ac displays the highest quantum yields with 15.6%, and the conjugation effect of ligand substituents can lower the triplet state energy of ligands, thus regulating the luminescence quantum yield of the LnTi clusters. These results suggest that the triplet excited-state energy of the ligands should match well with the energy levels of Ln to enhance the luminescence.