Controlling molecular machines: A spectroscopic point of view

Molecules with mechanically interlocked components are promising structures for molecular machine-type applications because they permit the controlled, large amplitude, movement and positioning of one mechanically interlocked component with respect to another. Here we will be concerned with one particular class of mechanically interlocked molecules, hydrogen-bond assembled [2]rotaxanes, which consist of a macrocycle locked onto a thread by hydrogen bonds and trapped by two bulky stoppers. The unique advantage these architectures offer is that the submolecular motions of macrocycle with respect to thread can be relatively easily controlled by manipulation of the hydrogen bond interactions. We will show how various forms of IR-UV double resonance high-resolution spectroscopies can be employed to characterize their intrinsic structural properties and intercomponent interactions, as well as how these techniques enable us to bridge the gap from the isolated molecule to solvated systems. We will furthermore show how we can use the same techniques to induce and observe molecular machines to become active under gas phase conditions. Finally, we will discuss timeresolved UV-pump IR-probe spectroscopic experiments that have been used to observe directly the light-induced intramolecular motion in a series of [2]rotaxanes in solution.