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 Yb2ErQ9 and on the corresponding Yb3Q9 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.