A synthetic approach to the preparation of rotaxanes (1-5·6PF6) incorporating bispyridinium derivatives and two 1,5-dioxynaphthalene (DNP) units situated in the rod portions of their dumbbell components that are encircled by a single cyclobis(paraquat-p-phenylene) tetracationic (CBPQT4+) ring has been developed. Since the π-electron-deficient bispyridinium units are introduced into the dumbbell components of the rotaxanes 1-5·6PF6, there are Coulombic charge-charge repulsions between these dicationic units and the CBPQT 4+ ring in the rotaxanes. Thus, the CBPQT4+ rings in the degenerate rotaxanes exhibit slow shuttling between two DNP recognition sites on the 1H NMR time-scale on account of the electrostatic barrier posed by the bispyridinium units, as demonstrated by variable-temperature 1H NMR spectroscopy. Electrochemical experiments carried out on the rotaxanes 1·6PF6 and 2·6PF 6 indicate that the one-electron reduced bipyridinium radical cation in the dumbbell components of the rotaxanes serves as an additional recognition site for the two-electron reduced CBPQT2(+) diradical cationic ring. Under appropriate conditions, the ring components in the degenerate rotaxanes 1·6PF6 and 2·6PF6 can shuttle along the recognition sites - two DNP units and one-electron reduced bipyridinium radical cation - under redox control.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry