Modulating the Dimensions of Rectangular Hydrazone-Based Bispyridinium Macrocyclic Receptors

The development of new macrocyclic molecular receptors has driven major advances in supramolecular chemistry. However, realizing the full potential of host-guest systems requires addressing persistent challenges such as improved synthesis, aqueous performance, and implementation of stimuli-responsiveness. Herein, we present a new family of self-assembled polycationic molecular rectangles, derived from our previously reported redbox host. These novel cyclophanes share a common structural core with the parent compound─two pyridinium units linked by a hydrazone bond─but are designed with varying dimensions on the short sides, separating the bispyridinium walls. Synthesized via acid-catalyzed imine condensation reactions in water, these compounds were obtained in acceptable yields in gram scale through a modular and highly efficient approach. The aqueous molecular recognition properties of these new hosts were investigated using NMR spectroscopy with a 1,5-dihydroxynaphthalene derivative as a model aromatic electron donor. These studies demonstrate the formation of highly stable binary or ternary inclusion complexes in aqueous media, highlighting the tunability of the binding properties and applicative potential of this family of pH-responsive macrocyclic receptors.