In numerical terms, azo dyes are the largest dye class of synthetic dyes. They can be characterized by the general formula R1-N=N-R2. An azo group is particularly typical for azo dyes. This is -N=N- and has chromophoric nitrogen double bonds.
Amines and in the simplest case aniline are used as starting materials. The variety of the azo dyes is justified by the simple substitution of the hydrogen atoms on benzene rings, which then influence the azo bond auxochrom and allow an exact adjustment of the color nuances.
The representatives of these dyes are often lightfast, color stable and can have particularly strong colors.