Counterion-Induced Translational Isomerism in a Bistable [2]Rotaxane

Translational isomerization can be induced by changing the anions associated with a bistable rotaxane in which the tetracationic cyclophane (blue box), cyclobis(paraquat-<i>p</i>-phenylene), encircles a dumbbell component containing bispyrrolotetrathiafulvalene (green) and a dioxynaphthalene (red) recognition sites. The rotaxane was isolated as both its hexafluorophosphate and tris(tetrachlorobenzenediolato)phosphate(v) (TRISPHAT<sup>-</sup>) salts. Photophysical measurements and NMR spectroscopy carried out in acetone (CD<sub>3</sub>COCD<sub>3</sub>) and acetonitrile (CD<sub>3</sub>CN) solutions reveal that the much larger TRISPHAT<sup>-</sup> anion favors predominantly the encirclement of the green site by the blue box.