Elementary Concept of Color and Colorants

Elementary Concept of Color and Colorants (Chromophore, Chromogen, Auxochrome)

In this post, I have tried to cover the topic "Elementary Concept of Color and Colorants (Chromophore, Chromogen, Auxochrome)" according to the BUTEX Syllabus of Wet Process Engineering, Textile Coloration - I.

Question: Discuss the Elementary Concept of Color and Colorants.

Color: According to Wikipedia, Color (American English) or Colour (British English) is the aspect of any object that may be described in terms of hue, lightness, & saturation.

In textiles, color is something that makes the object more appealing and attractive, and gives the pleasure of observation.

Colorants: Colorants are substances that are used for coloring a material. Examples of colorants: Dyes, Pigments.

Elementary Concept of Color and Colorants

To explain the Elementary Concept of Color and Colorants, we have to discuss 3 main parts of color & colorants. The parts are Chromogen, Chromophore, and Auxochrome.

Chromogen: Chromogen retains chromophore and plays a crucial role to determine the final hue and its affinity for fiber, fastness, stability, etc.

So, a compound containing a chromophore is called chromogen. Or, The dye structure which contains both chromophore & autochrome is called chromogen.

Chromophore: Chromophore is an unsaturated group that absorbs light and reflects it at a specific angle to give the hue. So, the color-bearing unsaturated group of a dye molecule is called the chromophore group. Examples of chromophore groups: Azo, Keto, Nitro, nitroso, Thioketo, ethylene, etc.

• The name is derived from the Greek words Chroma & Phore “Chroma” means “color‟ & “Phore” means “to bear”
• Their specific state of unsaturation enables them to absorb & reflect incident electromagnetic radiation within the very narrow band of visible light. It gives the dye molecule its particular color. 
• A molecule without any chromophore would be colorless.

Auxochromes: Auxochromes refers to a group of atoms which is attached to a chromophore and increases the ability of the chromophore to absorb light. Basicly, they are functional groups with one or more lone pairs of electrons. The auxochrome (color helping group) by itself does not produce any color but deepens the color of a chromogen.

• The name is derived from greek word “auxein” meaning “to increase” & “chroma” meaning “color”.
• They intensify & deepen the hue of the dye molecules color. 
• They also make the dye more soluble in water & also improve the color fastness properties.

Examples of Auxochrome: –OH, –COOH, SO₃H, –NH₂, –NH(CH₃) etc.

Illustrate the different parts of a dye molecule with their specific functions

Chrysophenine G, C I Direct Yellow 12, C I 24895, is a direct dye, in which chromophores are –N=N– and –CH=CH–, auxochrome –OC2H5 on both sides and chromogen is the part containing three chromophores but excluding the auxochromes as depicted in Figure.

Various parts of Chrysophenine G