Photochromism is a chemical and physical phenomenon, including light-induced chemical and physical reactions of organic, inorganic, biological and polymer.
In 1867, Fritsche observed the fading phenomenon of yellow tetracene under the action of air and light, and the generated substance was regenerated into tetracene when heated. In 1876, Meer reported that the color of the potassium salt of dinitromethane changed under light. In 1881, Phipson observed that the color of a zinc pigment darkened when exposed to sunlight, and returned to its original white color at night. In 1899, Markwald studied the reversible color change behavior of 1,4- dihydro -2,3,4,4- tetrachloronaphthalene -1- one under the action of light, and thought it was a new phenomenon and called it photochromism. Today, however, phototropism is understood as a phenomenon of light-induced changes in biological systems, and phototropism refers to the phototropism of plants.
In the 1920s and 1930s, photochromic has not attracted people’s special attention. During this period, only the research on malachite green l6,7 and semi-kappa gland [8~10] is worth mentioning.
Since 1940, people have done a lot of work to find out the mechanism of photochromic process, the structure of products, the formation of intermediates and the causes of fatigue. During this period, most of the work focused on the cis-trans isomerization of stilbene and azo compounds.
In 1950s, Hirshberg-11~18] proposed to call the above phenomenon “photochromism”, that is, photochromism.
Phenomenon. They found that the living ring of spiropyran compounds, especially ants, formed a chemical memory model, which led to the study of photochromic. Hirshberg 1 shot U made it possible for photochromic materials to be used for optical information storage. Porter’s time-resolved spectrum makes it clear that OIY’s four external absorption measurement modes are extended to fluorescence of A new field of research. This technology itself is constantly developing and improving, expanding from the ultraviolet absorption measurement mode.
And with the help of these technologies, it is possible to study the transition, excitement and anger with the help of the dynamic process between the molecules of the Taihe sub-pheromone. This technology has also accelerated the research process of biological photochromic substances. As Heller-21] pointed out, one of the most important factors for photochromic materials with practical application prospects is the appearance of.
The color body must have sufficient thermal stability, and the other is the fatigue resistance of photochromic compounds.
At present, the research on photochromism is mostly focused on fulgide, diarylethene, spiropyran, spirooxazine and related heterocyclic compounds, and new photochromic systems are also being explored and discovered. The combination of photochromic molecules and polymers to form photochromic polymers may be a research topic with more practical application value.
A large number of research papers and patents have been published on the study of organic photochromic materials. So far, three authoritative monographs have been published. First, the book “Photochromism” edited by Brown in the early 1970s [22l] introduced the development history and research survey of organic photochromic compounds in detail; Another book, Photochromism: Molecules and Systems, edited by Dtirr and Pouas-Laurent [23], mainly introduces the progress of photochromic in 1970s and 1980s. The latest theoretical and applied research is fully discussed in the book Organic Pho-to Chromic and Thermochromic Compounds edited by Crano and Guglielmitti [2]. In 1990s, the concept of photochromics was gradually developed.