Crown‐Ether‐Based Cryptands with Rarely Strong Affinities for Binding Neutral Organic Molecules

Herein, we present the syntheses of two new crown‐ether‐based cryptands and their complexation behaviors with neutral organic molecules. The interactions between 4/5 and G1/G2 were fast exchange systems forming pseudorotaxane‐like complexes with a 1 : 1 stoichiometric ratio. The association constant (Ka) of “long‐armed” cryptand 5 with G2 was even up to 2.5×105 M−1, which is 10 to 103 times higher than the previously reported host‐neutral guest system to the best of our knowledge. Such a large Ka is even comparable to that of reported cryptands with secondary ammonium salts and paraquat derivatives. Thorough studies demonstrated that excellent spatial fitting and multi non‐covalent interactions (H‐bonding and π–π stacking) are essential for such a large Ka.