Mixed Phenanthroline–Bipyridine Europium and Ytterbium Cryptates─Bright Luminophores with Small Radiative Lifetimes

New phenanthroline-based tris(biaryl) europium(III) and ytterbium(III) cryptates with great luminescence efficiencies in solution are reported. 1,10-Phenantroline, in combination with 2,2′-bipyridine-N,N′-dioxide, delivers cryptates with high rigidity, efficient lanthanoid(III) sensitization (ηsens) and small radiative lifetimes τrad for Eu and Yb. The powerful synergy of both bidentate chelating units results in excellent absolute quantum yields of up to 20% for the europium complexes in aqueous solution, which indicates an impressive improvement compared to other well-known tris(bipyridyl)-based Eu(III) cryptates.