Ultra‐Tight Host‐Guest Binding with Exceptionally Strong Positive Cooperativity

Cooperativity plays a critical role in self‐assembly and molecular recognition. A rigid aromatic oligoamide macrocycle with a cyclodirectional backbone binds with DABCO‐based cationic guests in a 2 : 1 ratio in high affinities (Ktotal ≈1013 M−2) in the highly polar DMF. The host–guest binding also exhibits exceptionally strong positive cooperativity quantified by interaction factors α that are among the largest for synthetic host–guest systems. The unusually strong positive cooperativity, revealed by isothermal titration calorimetry (ITC) and fully corroborated by mass spectrometry, NMR and computational studies, is driven by guest‐induced stacking of the macrocycles and stabilization from the alkyl end chains of the guests, interactions that appear upon binding the second macrocycle. With its tight binding driven by extraordinary positive cooperativity, this host–guest system provides a tunable platform for studying molecular interactions and for constructing stable supramolecular assemblies. The complexation of DABCO‐based cationic guests with a rigid aromatic oligoamide macrocycle exhibits remarkably high binding affinities with positive cooperativity that is among the strongest for synthetic host–guest systems. The ultra‐tight binding and extraordinary positive cooperativity are driven by size/shape host–guest matching, guest‐activated stacking of macrocycles, and multiple charge‐dipole and C−H⋅⋅⋅O interactions.