Indigoid Dyes

Abstract

Although one of the dyes of antiquity, the deep blue indigo is still used as vat dye. Structural modifications have made accessible a broad assortment of dyestuffs giving orange, red, blue or bluish-black shades on cellulosic fibres, silk and wool [31, 245, 246]. Indigo dyes are, in general, characterized by high melting points and low solubility in organic solvents. They can be reduced to dihydro derivatives (leuco form). Some indigo dyes display photochromic properties [569].