Observation of cascade f → d → f energy transfer in sensitizing near-infrared (NIR) lanthanide complexes containing the Ru(<scp>ii</scp>) polypyridine metalloligand

Distinguishable d → f or f → d energy transfer processes depending on lanthanide ions are observed in isomorphous d–f heterometallic complexes containing the Ru(II) metalloligand (LRu), which lead to sensitized NIR emission (for Nd3+ and Yb3+) or enhanced red emission of LRu (for Eu3+ and Tb3+), and represent the first eye-detectable evidence of f → d energy transfer processes in Ln–Ru bimetallic complexes. Based on the systematic luminescence and decay lifetime study, cascade f → d → f energy transfer has been proposed in Ln1–Ru–Ln2 trimetallic systems for improved NIR sensitization.