Observation of Strong Electron Coupling among Trivalent Lanthanide Ions in Molecular Cluster-Aggregates

Lanthanide-based nanomaterials have been extensively studied, owing to their unique optical properties. Strong electron coupling intensely affects the optical properties, as a kind of interaction between the metal luminescence centers, which usually depend on the otherness in valence states and/or spin states of metal ions. Herein, we presented that the strong electron coupling between trivalent lanthanide ions (Ln(III)) existed in molecular cluster-aggregates (MCAs) beyond the general consideration in valence and/or spin states. We synthesized a series of lanthanide-based MCAs with the generalized formula [Ln(20)(chp)(30)(CO3)(12)(NO3)(6)(H2O)(6)] ({Ln(20)}). By comparing and analyzing the characteristics of homometallic and heterometallic {Ln(20)} MCAs, we found a regular and controlled phenomenon of metal-to-metal charge transfer (MMCT) which is a typical expression of strong electron coupling. This observation can be attributed to the shorter spacing between metals inside the polynuclear nanosized core of MCAs, indicating that MCAs are an excellent matrix material to study the effects of intermetallic interactions of Ln(III), thus tailoring even customization in their luminescence performance.