Introduction
UV (Ultraviolet)-absorbing dyes, which have the property of absorbing UV radiation in a specific wavelength range, have received a high level of interest. Notably, UV radiation is a form of electromagnetic radiation with high-energy. Side effects of prolonged exposure to UV radiation include premature skin ageing, skin cancer, etc. Compared to visible light, ultraviolet light has a shorter wavelength, ranging from 100 nm to 400 nm. The UV radiation can be divided into UVA, UVB and UVC according to the different wavelength range.
- UVA rays have the least energy among three types of UV rays, ranging from 315 nm-400 nm and accounting for 95% of all the UV rays that reach the earth's surface. These rays cause skin cells to age and cause some indirect damage to cells' DNA.
- UVB rays span a range of wavelengths between about 280 and 315 nm and they are slightly more energetic than UVA rays. UVB rays directly damage DNA in skin cells and are the major cause of sunburn, as well as play a role in causing skin cancer such as malignant melanoma.
- UVC rays have higher energy than the other types of UV rays, with wavelengths in the range of 100 nm-280nm. They have the shortest wavelength of the three forms of UV as well as the most harmful radiation. Fortunately, UVC radiation is blocked by the ozone layer in the atmosphere, so it does not reach the ground and it is not normally a risk factor for skin cancer.
Fig.1 Ultraviolet (UV) spectrum and the damage to the skin[1]
Ultraviolet-absorbing dyes are able to absorb ultraviolet ray with anti-UV finishing property as well as improve the light stability of organic dyes. Therefore, they have aroused great interests of chemists as it offers a powerful tool for the study of functional dyes.
Classification
An essential component of UV-absorbing dye is the UV absorber which selectively and strongly absorbs UV light and converts it into low-energy radiation. UV absorbers are introduced into dyes to obtain the corresponding UV-absorbing dyes. Depending on the functional groups of UV absorbers, UV dyes can be divided into the following categories.
Benzophenone UV absorbers are the most widely used UV absorbers with wavelengths of 290-400 nm. The benzophenone functional groups can be used as diazo or coupling components in azo dyes, and can also be incorporated into the dye structure through a bridging group.
Fig. 2 Benzophenone based disperse dyes[1]
Phenyltriazine has an absorption wavelength of 270-380 nm with high absorption intensity and good safety. By introducing this functional group into dye structures, dyes with anti-UV function can be obtained, which are mainly divided into disperse and reactive dyes[2].
Fig. 3 Synthesis of monoazo disperse dyes containing a triazine photostabilizer[2]
Benzotriazole UV absorbers can absorb UV radiation in the wavelength range of 300 nm-400 nm and are employed for the synthesis of UV absorbing dyes due to their advantages such as resistance to discoloration, low volatility and low toxicity. They are used to synthesize disperse dyes and polymerizable benzotriazole dyes[3].
- Oxalanilide UV-absorbing dyes
Oxalanilide UV absorbing dyes have a strong absorption with wavelength from 280 nm to 320 nm. These UV-absorbing dyes have the property of anti-UV finishing function, improving light fastness and sublimation fastness of the original dyes.
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References
- Shinde, S. et al. Benzophenone based disperse dyes for UV protective clothing: synthesis, comparative study of UPF, light fastness and dyeing properties and computational study. J Text I. 2021, 112:71-84
- Sun, Y.; Zhao, D.; Freeman, H. S. Synthesis and properties of disperse dyes containing a built-in triazine stabilizer. Dyes Pigm. 2007, 74: 608-614
- Konstantinova, T. N.; Lazarova, R. A. Synthesis of some polymerizable triazinylaminobenzotriazole stabilizers and benzanthrone dyes containing a stabilizer fragment. Dyes Pigm. 2007, 74: 208-214
