Controlling association kinetics in the formation of donor-acceptor pseudorotaxanes

We report a systematic investigation of size-complementary stoppering groups used to determine the kinetics of threading a cyclophane, namely cyclobis(paraquat-p-phenylene), onto a series of molecular dumbbells. We have identified a set of simple functionalized phenyl and biaryl groups that present activation energy barriers between 16.7 and 26.6 kcal mol(-1) to threading the dumbbells. These barriers will be employed as 'steric speed bumps' to modulate kinetics in artificial molecular pumps that operate based upon a delicate balance of noncovalent bonding interactions.