Improved Energy Transfer in the Sensitization of Americium Enables Observation of Circularly Polarized Luminescence

The first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and a chiral diphosphine oxide ligand yielded a complex with strong sensitized metal-centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has often been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of ²⁴¹Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the ⁵D₁→⁷F₁ transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5 f elements.