Highly Efficient Light Harvesting of Eu(III) Complex in a Host-Guest Film by Triplet Sensitization

Lanthanide complexes are attractive light emitters owing to their ideal high color purity. Sensitization using ligands with high absorption efficiency is a powerful approach to enhancing photoluminescence intensity. However, the development of antenna ligands that can be used for sensitization is limited due to difficulties in controlling the coordination structures of lanthanides. Here, we demonstrate a system comprising triazine-based host molecules and Eu(hfa)3(TPPO)2 (hfa: hexafluoroacetylacetonato, TPPO: triphenylphosphine oxide), which shows drastically improved total photoluminescence intensity compared to conventional luminescent Eu(III) complexes. Time-resolved spectroscopic studies revealed that the energy transfer from the host molecules to Eu(III) occurs via the triplet states over several molecules with nearly unity efficiency. Our discovery paves the way for efficient light harvesting of Eu(III) complexes with simple fabrication using a solution process.