The Self-Assembly of a Switchable [2]Rotaxane

摘要

Catenanes and rotaxanes are molecular compounds that hold considerable promise for use in molecular devices as a consequence of the relative movements of their ring and dumbbell-shaped components. Initially researchers learned how to make simple rotaxanes, followed by degenerate rotaxanes with molecular shuttling characteristics, and eventually non-degenerate rotaxanes whose dynamic properties could be addressed selectively with external stimuli of a chemical, electrochemical, or photochemical natureto induce them to behave as molecular switches. However, to our knowledge, no constitutionally asymmetric, two-site [2]rotaxane that exhibits 100% selectivity for one of the binding sites between ring and dumbbell-shaped components has yet been reported. Here, we describe the self-assembly of a [2]rotaxane that possesses two very dissimilar cationic binding sites within its dumbbell-shaped component—specifically, a secondary dialkylammonium center and a bipyridinium unit—each of which shows differentaffinities toward dibenzo[24]crown-8 (DB24C8), the ring component of the [2]rotaxane. We also report the pH-controlled shuttling of the DB24C8 ring between the two very different recognition sites, or "stations", in this simple molecular shuttle.