Fully Efficient Direct Yb-to-Er Energy Transfer at Molecular Level in a Near-Infrared Emitting Heterometallic Trinuclear Quinolinolato Complex

Combined chemical/photophysical studies on the mixed Yb–Er trinuclear lanthanide quinolinolato compound Yb<sub>2</sub>ErQ<sub>9</sub> and on the corresponding Yb<sub>3</sub>Q<sub>9</sub> analogue have been performed. In the mixed-metal molecular species, the ligands, acting as a bridge, allow the two metals to lie at optimal distance for direct Yb-to-Er resonance energy transfer, which reaches nearly unitary efficiency. The obtained results show that polynuclear lanthanide complexes provide a suitable strategy for achieving effective erbium sensitization in solution-processable molecular materials.