Dyes, Paints and Pigments

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A dye is an organic compound used to impart color to textiles, food, silk, wool, and other materials. It must be able to fix itself to the fabric and be resistant to water, soap, light, acids, and alk…

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Chromophores are groups in a molecule that impart color due to the presence of multiple bonds. Examples: -NO₂ (nitro), -N=O (nitroso), -N=N- (azo), and quinonoid structures.

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Auxochromes are groups that do not produce color themselves but deepen the color when attached to a chromophore. Examples: -OH, -NH₂, -NHR, -COOH.

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Dyes absorb light in the visible region (400–730 nm). The color we see is the complementary color of the absorbed light. For example, if a dye absorbs green light, it appears violet.

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Dyes are classified by constitution into: 1) Nitro dyes (-NO₂), 2) Azo dyes (-N=N-), 3) Phthalein dyes, 4) Triphenyl methane, 5) Anthraquinone, 6) Indigoid.

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Methyl orange is an azo dye. Its characteristic structural unit is -N=N- (azo group).

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Phenolphthalein belongs to the phthalein dye class and contains a phthalic anhydride-derived structure with a central carbon bonded to two aromatic rings and a lactone ring.

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Malachite green is a triphenyl methane dye. It is used as a biological stain and in the dyeing of silk and leather.