Artificial molecular rotors and motors on surfaces: STM reveals and triggers

Inspired by the biomolecular motors that can be found everywhere in nature and are essential to numerous processes of life, nanoscientists have been developing artificial molecular rotors and motors with the ultimate aim to include them into bottom-up constructed working devices. Once mounted onto a surface, scanning tunnelling microscopy (STM) is a powerful technique to characterise these rotor and motor molecules, since it allows their direct visualisation at submolecular resolution. It can furthermore track translational motion in real-time, and rotational motion even at the millisecond level by performing tunnelling current-time spectroscopy. Finally, the STM can be a useful tool to power molecular rotors and motors, by injecting tunnelling electrons of sufficient energy into the molecules via the STM tip. This review addresses recent advances in revealing the structure, motion, and manipulation of molecular rotors and motors on a surface by STM.