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-p-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^-) salts. Photophysical measurements and NMR spectroscopy carried out in acetone (CD₃COCD₃) and acetonitrile (CD₃CN) solutions reveal that the much larger TRISPHAT^- anion favors predominantly the encirclement of the green site by the blue box.