Wiktionary
photoswitch
n. 1 A switch that is activated by light 2 (context biochemistry English) A compound whose structure is changed, and whose function is activated by light
Wikipedia
Photoswitch
A photoswitch, or photo-electric switch, is a sensor that detects the presence in or change of light. A popular example is that of azobenzene. Photoswitches are one type of molecular machines, a class of molecules that can be switched between at least two distinct thermodinamically stable forms by the application of an external stimulus. Development of such devices is crucial in the framework of the field of nanotechnology: nowadays photoswitches are used in a variety of places from scientific applications to residential light timers.