Photoswitchable Molecular Spur Gears: An Entry Point to Motorized Gearing

Molecular gears represent fundamental archetypes of molecular machines as they provide crucial capacity in redirecting, translating, and rate-shifting of nanoscale motions. Most prevalent are thermally driven molecular bevel gears, while other architectures such as spur gears are much rarer owing to their specific requirement of parallel spatial alignment. More recently, implementation of additional control over gearing via a secondary stimulus has emerged as a new frontier, allowing one to build more sophisticated molecular machinery. In this work, we present a light-switchable molecular spur-gear setup, which allows one to engage and disengage a parallel-oriented gear system on command. Using hemithioindigo (HTI) as a photoswitchable central unit, the correlated motion of two parallel engaged triptycene gear wheels can be engaged and disengaged via light-induced double-bond isomerization. This molecular setup further paves the way toward realizing a light-driven and directional photogear motor as the engaging/disengaging motion can straightforwardly be coupled to the gearing motion.