General Dye structures

General Dye structures:

Unlike most organic compounds, dyes possess colourbecause they

1) Absorb light in the visible spectrum (400–700 nm),

    2) have at least one chromophore (colour-bearing group),

    3) have a conjugated system, i.e. a structure with alternating double and single bonds, and

     4) exhibit resonance of electrons, which is a stabilizing force in organic compounds.

When any one of these features is lacking from the molecular structure the colour is lost. It is important to note that the chromophore must be part of a conjugated system & at least 5-6 conjugated system is required for producing color. In addition to chromophores, most dyes also contain groups known as auxochromes(colour helpers). It contributes to achieve target color, increase solubility, making bond with fibre etc. Total dye structure including chremophore & auxochrome is known as chromozen.