Macrocyclic Pyridone Pentamers for Highly Selective High‐Capacity Removal of Caesium Ions from Radioactive High‐Salinity Waste

We report here that macrocyclic H‐bonded pyridone pentamers, containing five properly and convergently spaced electron‐rich O‐atoms that decorate a rigid cavity of 2.85 Å across, exhibit an extraordinarily high yet pH‐independent capacity and selectivity in Cs + removal. In particular, with [host]=240 μM and [Cs + ]=15 μM, a single extraction efficiently removes more than 91% of Cs + ions from artificial sea water, containing various competitive metal ions at a total concentration of 0.68 M ([total M n+ ]/[Cs + ]=4.5×10 4 ]). To our best knowledge, these pyridone pentamers represent the best small organic molecule‐based extractants that target Cs + ions.