The Radiative Lifetime in Near‐IR‐Luminescent Ytterbium Cryptates: The Key to Extremely High Quantum Yields

A powerful strategy for the improvement of near‐IR lanthanoid luminescence has been successfully employed for the first time, which involves the rational and deliberate shortening of the radiative luminescence lifetimes τ_rad in molecular ytterbium complexes. In this context, the bidentate chelating unit 2,2′‐bipyridine‐N,N′‐dioxide has been identified as being responsible for decreasing τ_rad substantially in macrobicyclic Yb cryptates. This strategy, when combined with conventional approaches, yields unprecedented absolute near‐IR quantum yields of up to 12 %. This extraordinary efficiency represents the highest value measured for any molecular lanthanoid near‐IR emitter. The proof‐of‐concept for the implementation of the new strategy opens up entirely new prospects for the field of lanthanoid luminescence.