Photochromic materials: more than meets the eye.

Photochromic materials are a family of compounds which can undergo reversible photo-switches between two different states or isomers with remarkably different properties. Inspired by their smart photo-switchable characteristics, a variety of light-driven functional materials have been exploited, such as ultrahigh-density optical data storage, molecular switches, logic gates, molecular wires, optic/electronic devices, sensors, bio-imaging and so on. This review commences with a brief description of exciting progress in this field, from systems in solution to modified functional surfaces. Further development of these photo-switchable systems into practical applications as well as existing challenges are also discussed and put in prospect.