Molecular Crystals on the Move: From Single‐Crystal‐to‐Single‐Crystal Photoreactions to Molecular Machinery

Molecular musclemen: Local stress from organic solid-state photoreactions may be released in a catastrophic manner, causing single crystals to fragment (see picture, bottom). Alternatively, crystals in topotactic reactions (see picture, top) release the stress by changing size and shape. These mechanical processes may be used to design photoactuators capable of performing work at the nano- to micrometer scales.