STM studies for surface-mounted molecular rotors: a mini review

A molecular rotor is a molecule/molecular system that performs rotary motions under an external stimulus. Molecular rotors are promising for applications in medicine, optical usage, information science, etc. A molecular rotor is also a crucial component in constructing more sophisticated functional molecular machines. Anchoring molecular rotors on surfaces is regarded as a feasible way of building functional molecular rotor systems. Scanning tunneling microscope (STM) is a powerful tool for studying surface dynamics in real space on atomic precision. It provides an ideal platform for both qualitatively and quantitively investigating single and self-assembled molecular rotors mounted on surfaces. Herein, we review a series of studies utilizing STM to unveil the methodologies that are increasingly used in the area of surface-mounted molecule rotors. A combined usage of these methodologies is more and more necessary for researchers to advance the molecular rotor study in future.