Wavelength-steered directional 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. The development of light-driven nanomotors is a particularly challenging task that holds great potential for the development of sunlight-powered systems and active materials. Here we describe an azoimidazolium photochemical molecular rotary motor which operates along a triangular reaction cycle exploiting the formation of diastereomeric species upon photoisomerisation. The different thermal stability and photochemical reactivity of these diastereomers permit net directional motion combining a thermal rotation about a C-N single bond and two light-induced configurational rearrangements that proceed predominantly through 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.