Azo-dye chromophore molecules

In this way, many green azo dyes have been made by combining separate conjugated systems in the same molecule, eg, one yellow and the other blue. The blocking or the insulating group prevents the electronic interaction of one chromophore system with the second. Chloramine Fast Scarlet 4BS... 

Cationic azo dyes carry a positive charge ia the chromophore portion of the molecule. The salt-forming counterion is usually a chloride or acetate. Cl basic dyes are ammonium, sulfonium, or oxonium salts. Commercial basic azo dyes for which chemical stmctures are revealed by U.S. producers are listed ia Table 15. 

All azo dyes contain one or more azo groups (-N=N-) as chromophore in the molecule on the basis of the number of azo groups in each molecule, they are named monoazo-, disazo-, trisazo-, etc. The azo groups are in general bound to a benzene or naphthalene ring, but they can also be attached to heterocyclic aromatic molecules or to enolizable aliphatic groups. On the basis of the characteristics of the processes in which they are applied, the molecule of the dye is modified to reach the best performances so they can be acid dyes, direct dyes, reactive dyes, disperse dyes, or others. 

Dyes and colorants are complex organic molecules with conjugated or delocalized iT-electron systems (chromophores). Based on the different relevant chemical functionalities that act as chromophores in specific dyes, the latter can be grouped into azo dyes, carbonyl dyes, methine dyes, and phthalocyanines. The dye indigo shown in Table 5.3.19 belongs to the group of carbonyl dyes. 

---