Controlled dethreading/rethreading of a scorpion-like pseudorotaxane and a related macrobicyclic self-complexing system

A scorpion-like pseudorotaxane (1 · H²⁺), composed of a macrocyclic polyether containing a 1,5-dioxynaphthalene (1,5-DON) and a 1,3-dioxybenzene (1,3-DOB) electron-donor unit, the latter bearing a 4,4′-bipyridinium electron-acceptor tail, underwent threading/dethreading motions under control of (i) solvent polarity and (ii) solution acidity. Furthermore, the complexation of 1 · H²⁺ with the trans-1,2-bis(1-benzyl-4-pyridinio)ethylene electron acceptor can be acid/base controlled. The spectroscopic properties of a related macrobicyclic compound 2⁴⁺ (comprised of an electron-donor and an electron-acceptor macrocycle that share a benzene ring) have also been investigated. The results obtained for 2⁴⁺ are consistent with the presence of intramolecular self-complexed species where the electron-donor macrocycle is threaded through the electron-acceptor one. Electrochemical experiments confirm the self-complexing structures of 1 · H²⁺ and 2⁴⁺. It seems likely that both compounds undergo decomplexation upon electrochemical stimulation.