Stiff, and sticky in the right places: binding interactions in isolated mechanically interlocked molecules probed by mid-infrared spectroscopy.

We report the results of high-resolution spectroscopic studies on isolated, jet-cooled [2]rotaxanes. Employing IR absorption spectroscopy, we show how these noncovalently bound, multicomponent molecular systems that so far have been out of reach from high-resolution techniques, can now be characterized at an unprecedented level. IR absorption spectra of prototypical hydrogen-bond assembled rotaxanes as well as their associated threads and macrocycles are shown to provide a direct view on the effects of interlocking the macrocycle and thread, and to offer a straightforward approach for the study of their structural and dynamical properties.