The defining characteristic of photochromic colorants is that they change color reversibly in response to variations in the intensity of particular wavelengths of light to which they are exposed. Light-responsive dyes worth millions of dollars are manufactured each year as a result of their successful exploitation over the last quarter century . The bulk is consumed in the production of ophthalmic lenses that darken reversibly when exposed to strong sunshine. Photochromism continues to attract the interest of both industrial and academic researchers, who are looking to harness photochromic colorants in fields like optoelectronics and nanotechnology.
The widely accepted definition of photochromism is that of a reversible color change induced in a compound driven in one or both directions by the action of electromagnetic radiation [2, 3]. Photochromic systems are classified as either “P-type” or “T-type”. The former kind can be switched in each direction with...
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