A conformationally dynamic chain compound that rapidly and reversibly samples both self-entangled and disentangled conformations, yet favors disentangled conformations. and an exclusively self-entangled [1]rotaxane were separately prepared and characterized. The conformationally dynamic state and the conformationally locked state were shown to reversibly and controllably interconvert under appropriate conditions, with an accompanying observable change in size that was calculated to approximate a 35% contraction in length upon capture of the self-entangled state.