History and fundamentals of molecular photochromism

Photochromic molecules reversibly change their colour upon exposure to light. The increasing need for smart materials in the real world, coupled with progress in synthetic chemistry, fast spectroscopic techniques, and theoretical power in research laboratories, have seen research in organic photochromism accelerate over the past few decades. In this Primer Review, the topic of organic photochromism is introduced. The fundamental concepts and histories are given to contextualise this field. Moreover, key photochromic molecules and selected applications are showcased to provide the interested reader with an entry to this fascinating field of science and emerging technology.