Single-Molecule Studies on Artificial Small-Molecule Machines

Molecular machines transduce energy from one form to another through controlled motion in response to stimuli. Despite the ubiquitous use of molecular machines in biology, understanding the detailed mechanisms of such complex structures remains challenging. Recent progress in studying the modes of operation of synthetic small-molecule machines at the single-molecule level has shed new light on the mechanisms of nano-machinery. In this mini-review, we focus on the study of artificial small-molecule machines using single-molecule techniques, including single-molecule force spectroscopy, single-molecule electrical spectroscopy, and single-molecule optical spectroscopy. We survey the techniques used to monitor single-molecule behavior to date and describe the latest studies on small-molecule machines, highlighting their common features and challenges that need to be overcome to realize the potential of these techniques in unraveling the behavior of small molecule systems.