Recent development of photochromic polymer capsules for smart materials

The development of smart photochromic materials, as the materials of the future, is of paramount importance with a wide range of applicability. Active research into photochromic materials began at the end of the last century and has not lost its relevance. The surrounding plays an important role in the manifestation of photochromism. The perspective strategy in this field is the encapsulation of the photochromic dyes in the system based on polymer shells. Encapsulation allows to optimize the kinetic properties of the photochromic molecule, to eliminate the problem of dye migration in the material matrix with loss of activity, to protect the photochromic compound from the harmful environmental factors and therefore to improve the fatigue resistance. Encapsulation could also provide a homogenous distribution of the encapsulated photoactive molecule within the smart material. Photochromes can be incorporated as part of the core of the capsule and can also as part of the polymeric shell that provides the photoswitching capability. The present review is devoted to a brief and conclusive analysis of the latest results on the encapsulation of the photochromic organic compounds from the classes of spiropyrans, spirooxazines and azobenzene derivatives in the polymer capsules. The appropriate application of each system is discussed along with characterization and property analysis. The trends in the development of the photochromic capsules are concluded.