Photochromic phenomena associated with reversible changes in the chemical structure of two species have received much interest. This is due to the light-induced drastic changes of various physical and chemical properties. Among photochromic materials, spiropyrans have a variety of potential applications as light modulation materials, optical recording materials, optical switches, and photochromic ink. Some of these spiropyrans are being put to practical use. It is well known that the closed form of spiropyran (SP) can be transformed into the corresponding open form (merocyanine form, MC) by UV light irradiation.
The incorporated spiropyran with N-isopropylacrylamide (NIPAM) as a base material for producing photoresponsive gels receives increasingly intensive attention due to the autonomous manner in which they respond to changes in their local environment. Consequently, they are often referred to as “smart materials” because they can perform functions without the need for any human input. Examples include materials that respond to temperature, pH, light, and magnetic and electric fields