University Federico II
of Naples, Italy
European Chemistry
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Artificial (synthetic) dyes

Colorants and pigments are distinguished by the way they are applied rather than their chemical nature. A general distinction for dyes is between organic dyes (either synthetic or from natural sources) and inorganic dyes (minerals).

Organic dyes
Organic dyes are molecules, generally of aromatic nature, characterised by the presence of special atomic groupings, called chromophores and auxochromes, that give the chemical compound an ability to absorb light (in case of colored substances, visible light). The set including the system of conjugated double bonds, the chromophores (for instance azo group), that are electron-acceptor groups, and auxochromes (for instance amino or hydroxyl group), that are electron-donor groups, is called chromogen.

A few examples:

Structure of an azo dye
Azo dyes

Dyes containing a diazo group (-N=N-), ranging from lemon yellow to maroon. They are much used at present in paint, ink and plastics industries.

A triphenylmethane derived dye

Such dyes, ranging from malachite green to crystal violet are derived from triphenylmethane.

General structure of phthalocyanines

Phthalocyanines are coloring compounds constituted by a metal complex where a copper atom is bonded to four phthalonitrile molecules.
The pigment is blue, with a big coloring power, remarkably bright tone and outstanding stability to light. By chlorinating this pigment, one gets colors horizon blue (Cyan), turquoise and eventually very bright green. Blue and green phthalocyanines are at present the most used pigments in paint, print inks, plastics, and so on, industries.

Formula of quinacridone

Quinacridone is a red powder. It is an organic compound with the molecular formula C20H12N2O2. It is used as a pigment; analogs bearing this motif are known as quinacridones. Major uses for quinacridones include automobile coatings as well as other industrial coatings. Tipically deep red to violet in color, the hue of quinacridone is affected not only by the R-groups on the molecule but also by the crystal form of the solid. Some magenta shades of quinacridone are labeled under the proprietary name "Thio Violet" and "Acra Violet".