Controlling ring translation of rotaxanes.

Novel rotaxanes containing two 9-aryl-9-methoxy-10-methyl-9,10-dihydroacridine moieties (acridanes) at both ends of the molecular axle as recognition stations for the tetracationic ring CBQT(4+) were synthesized together with their acridinium counterparts. A new concept of controlling the ring movement within rotaxanes has been realized with these rotaxanes. Owing to Brownian molecular movement, the ring shuttles from one end of the axle to the other one in acridane rotaxanes. The shuttle process is stopped by converting two or one of the acridane stations into the corresponding acridinium unit. If both acridanes are transformed by addition of an acid, the ring resides on evasive stations present in the center of the axle. Photons convert only the unoccupied acridane station, thus the ring remains on the unchanged acridane station. The shuttle process can be switched on by addition of a base and by the thermal reaction of the methoxide with the formed acridinium ion, respectively.