Nano tungsten trioxide has photochromic properties so that it may be applied for producing thermal insulating glass, which plays a role of heat insulation. And therefore, it saves cooling fee, prevents furniture from fading, and protects people from sunburn. When it comes to photochromism, what you may have known is the early appearance of photochromic materials.
The appearance of those photochromic materials: In 1867, it was first discovered that yellow tetracene compounds faded under the influence of air and light, and the resulting materials were heated to regenerate yellow tetracene compounds. In 1876, the potassium salt of dinitromethane was found to undergo a color change with light. In 1881, a zinc pigment was found to be dark in the sun, and it new_ed to its original white color at night. In 1899, the reversible color change behavior of 1,4-dihydro-2,3,4,4-tetrachloronaphthalene-l-ketone was found under the action of light. And this new phenomenon was called photochromism.
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