What are the hazards of sun exposure to fabrics?

The basic principles of photochemistry of dye fading

In the process of sun exposure, the effect of light on dyes can be explained in two ways.

First of all, as far as the structure of the dye is concerned, under the action of ultraviolet light, the chemical bond in the dye changes or even breaks, causing the structure of the chromophore and auxochrome group in the dye to be destroyed, thereby losing the color; it may also be affected by ultraviolet light. Under irradiation, the three-dimensional structure of the dye changes, causing the color to change, which is the color change.

On the other hand, it is explained from the changes in the electronic structure and energy of the dye molecule. Under the irradiation of a large amount of higher energy ultraviolet light, some of the bonded electrons obtain higher energy and transition to higher energy level anti-bonding orbitals, or electrons in lower energy level bonding orbitals transition to anti-bonding orbitals . When these electrons return to the original orbit, they release different energy and show a different color from the original, thus showing different light fastness.