What Is Photochromism?

Under the action of an external excitation source, the phenomenon that a substance or a system undergoes a significant change in color is called discoloration. Photochromism means that when a compound A is irradiated with light of a certain wavelength, a photochemical reaction can occur to obtain the product B. The colors of A and B (that is, absorption of light) are significantly different. B can be restored to its original form A under the irradiation of another beam of light or by heating. Photochromism is a reversible chemical reaction, which is an important criterion. Irreversible reactions that occur under the influence of light can also cause changes in color, which belong to the general photochemical category and not to the photochromic category.

Photochromic

Under the influence of an external excitation source, a

Most of the researches on photochromism have focused on diarylethene, tartaric anhydride, spiropyran, spirazine, azos, and related heterocyclic compounds. At the same time, new photochromic systems are being explored and discovered. The countries with the most research on photochromic materials are the United States, Japan, France, etc. Japan developed earlier in the civilian industry. The photochromic pigment is added to the transparent resin to make a photochromic material, which can be used in sunglasses lenses, and it has begun to be used in color-changing glasses in China. By connecting the photochromic pigment and the polymer together, it can be made into a material with photochromic properties, which has great application prospects in photovoltaic technology and light control devices. Coatings made with photochromic materials can be made into a variety of daily necessities, clothing, toys, decorations, strollers or various signs and patterns coated on internal and external walls, highway signs and buildings, etc., which will show colors under light Rich and colorful patterns or patterns to beautify people's life and environment; can be made of transparent plastic film, pasted or embedded in automobile glass or window glass, and the color of sunlight will change immediately, so that sunlight will not glare, protect eyesight, ensure safety, It can adjust the temperature in the room and in the car. It can also be dissolved in or mixed with plastic film and used as an agricultural greenhouse film to increase the output of agricultural products, vegetables, and fruits. Another important use is for military concealed materials, such as military personnel's clothing and cover of combat weapons. ^[1]

The use of photochromic materials in the fields of optical information storage, light regulation, optical switches, optical device materials, optical information gene materials, modified gene chip materials and other fields has attracted widespread attention worldwide. Chinese researchers have made new progress in the research of erasable high-density optical information storage using new thermally stable spironazines. They designed and synthesized a new type of spironazine molecule SOFC with good thermal stability of the ring-opening body. This type of new photochromic material shows good stability for information storage, and can repeatedly write and erase information, and can be applied to multilayer three-dimensional high-density optical information storage based on two-photon technology, showing Very strong application prospects. ^[1]