Diarylethene photoswitches have reversible cyclization and cycloreversion reactions that are photoinduced. They are a class of compounds that have aromatic functional groups bonded to each end of a carbon-carbon double bond. An example of this class of molecule that is used in photopharmacology is stilbene. Under the influence of light, stilbene switches between its two isomers (E and Z). 
Figure 4. Figure showing stilbene isomerizations under light from E to Z
Diarylethenes have been shown to have some advantages over the more researched azobenzenes switches, such as thermal irreversibility, high photoswitching efficiency, favorable cellular stability, and low toxicity. Diarylethenes have been shown to have promise in fields other than photopharmacology as well. These fields include optical data storage, optoelectronic devices, supramolecular self-assembly and anti-counterfeiting.