(or thioindigoid), any of several vat dyes of the indigoid group that contain sulfur. The parent compound of the thioindigoid dyes is thioindigo (2,2-bis-thionaphtheneindigo), the sulfur analogue of indigo:
Thioindigoid dyes are used to dye cotton, wool, flax, rayon, silk, and fur; they produce orange, red, violet, brown, and black. Various shades may be obtained by using different thioindigoid derivatives, particularly asymmetric derivatives such as 2-thionaphthene–2-indolindigo.
Thioindigoid dyes form fast colors. They are obtained from aromatic amines and certain other aromatic compounds by a complicated multistage process.