A 'Texas-sized' molecular box that forms an anion-induced supramolecular necklace

The 'blue box' (cyclobis(paraquat-p-phenylene) or CBPQT(4+)), developed by Stoddart and colleagues, forms effective charge transfer complexes with a variety of electron-rich species and has been used to support the formation of a wide range of interlocked structures. However, little effort seems to have been devoted to generalizing the blue box concept. We describe a new flexible tetracationic macrocycle-a 'Texas-sized' molecular box. This positively charged receptor is capable of binding the mono-terephthalate anion, forming pseudorotaxanes. These pseudorotaxanes self-assemble into short supramolecular pseudo-oligorotaxanes in solution and more extended pseudo-polyrotaxanes in the solid state. The supramolecular oligomers formed in solution are environmentally responsive; they undergo deaggregation as the overall concentration of the cationic and anionic constituents is reduced, the temperature is increased, or the protonation state of the threading mono-terephthalate anion is changed.