Wavelength-steered unidirectional rotation in an autonomous light-driven molecular motor

Artificial molecular motors are at the forefront of research in nanotechnology due to their ability to perform tasks by harnessing directionally controlled motion at the molecular scale. In particular, the development of light-driven nanomotors is a challenging task that nonetheless holds great potential for the development of sunlight-powered systems and active materials. Herein, we describe a novel azoimidazolium photochemical molecular rotary motor which operates along a triangular reaction cycle by taking advantage of the formation of diastereomeric species as a consequence of photoisomerisation. The different thermal stability and photochemical reactivity of these diastereomers allow for net directional motion by combining a thermal rotation about a C–N single bond and two light-induced configurational rearrangements that proceed predominantly by a rotational mechanism, as corroborated by computational studies. The composition of the dissipative state obtained upon continuous supply of light can be modified by changing the irradiation wavelength, and as a result the preferred rotation direction of the motor is inverted.