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. 2021 Jun 22;26(13):3813. doi: 10.3390/molecules26133813

Table 1.

Classification and characteristics of dyes depending on the structure of the chromophore.

Dye Chemical Classes Chromophore Structure Examples of Dyes Characteristics Reference
Azo graphic file with name molecules-26-03813-i001.jpg Methyl Orange Azo dyes are frequently used (60%). These dyes have a functional group (-N=N-) linking two alkyl or aryl radicals, symmetrical and or asymmetrical, identical or non-azoic. [87]
Congo Red
Orange G
Amaranth
Anthraquinone graphic file with name molecules-26-03813-i002.jpg Remazol Brilliant Blue R Anthraquinone dyes are the second most widely used dyes due to their low price, accessibility and performance in the dyeing process. They have anthraquinone chromophore groups comprising two carbonyl groups on either side of a benzene ring. [88]
Reactive Bright Blue X-BR
Reactive Blue 4
Alizarin Red S
Triphenylmethane graphic file with name molecules-26-03813-i003.jpg Malachite Green These molecules have a central sp3 hybridised carbon atom, bonded to three aryl groups and belong to the most commonly used synthetic dyes in the textile industry. [89]
Crystal Violet
Bromophenol Blue
Light Green SF
Nitro and Nitroso graphic file with name molecules-26-03813-i004.jpg Naphthol Yellow S In nitro dyes, a nitro group conjugates to an electron donor group via an aromatic system. Nitro dyes always contain a hydroxyl group as a donor. [90]
Disperse Yellow 26
Disperse Yellow 14
Indigoid graphic file with name molecules-26-03813-i005.jpg Indigo Carmine Synthetic indigo is the most widely used dye in the textile industry worldwide. It is highly resistant to light and high temperatures. [91]
Ciba Blue 2B
Xanthene graphic file with name molecules-26-03813-i006.jpg Rhodamine 6G Xanthenes are dyes used in the food, cosmetics, paper and ink manufacturing industries because of their superior dyeing and colouring properties, but are poorly biodegradable, and some of them are very toxic. [92]
Rhodamine 123
Fluorescein
Acridine graphic file with name molecules-26-03813-i007.jpg Acridine orange Acridine dyes are heat-resistant, although they have low lightfastness. They are currently not very important commercially. [93]
Basic Yellow 9
Phthalein graphic file with name molecules-26-03813-i008.jpg o-cresolphthalein Phthalein dyes are employed to titrate weak acids. Phthalein dyes are insoluble in water but soluble in alcohol. There are frequently in the construction, coatings, electronics and electrical industries. [94]
Thymolphthalein
Dixylenolphthalein
Phenolphthalein

The chemical structures were elaborated in the software ACD/ChemSketch, version 2020.1.2, (ACD/ChemSketch, version 2020.1.2, Advanced Chemistry Development, Inc., Toronto, ON, Canada, www.acdlabs.com, 2020 (accessed on 27 May 2021)).