Phthalocyanines

Phthalocyanines are essentially made up of four molecules of isoindole:

These molecules are connected to each other in a phthalocyanine by nitrogen atoms.  The structure of phthalocyanine is:

These molecules are connected to each other in a phthalocyanine by nitrogen atoms.  The structure of phthalocyanine is:

Phthalocyanines coordinate with metal atoms.  The most important, contributing about 2% of all colorants, are the copper phthalocyanines, used for their brilliant blue and green colours. An example is C.I. Direct Blue 86:

The sulfonic acid groups assist the solubility of the dye in water.

The formula indicates that the sulfonic acid groups can be at different positions on the aromatic rings.