Under the action of light, polymers that can reversibly change color are called photochromic polymers, which belong to polymer materials. According to Krongauz’s definition of a photochromic polymer, a photochromic polymer means that the photochromic pigment molecules are chemically bonded to large molecules. In the strict sense, photochromic polymers usually have two structural forms: photochromic pigment molecules are connected to main chain macromolecules directly or through spacers as side chain groups, or photochromic pigment molecules are formed as main chain structural units or copolymerization units to form polymers through copolymerization or grafting reactions in the form of covalent bonds, which is a true photochromic functional polymer. When a photochromic compound is added to the polymer, the polymer blended with the photochromic material has a photochromic function, but it is not in the definition.
In the process of photochromism, the phenomenon of discoloration is mostly related to the structural changes of the polymer after absorption of light, such as tautomerism, cis-trans isomerism, ring opening reaction, ion formation, dissociation into free radicals or REDOX reaction.
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