Organic Pigments:

Organic pigments are intensely colored, particulate organic solids that are essentially insoluble in, and physically and chemically unaffected by, the vehicle or substrate into which they are incorporated.

Characteristics of Organic Pigments
Bright, pure, rich colors
More expensive than inorganic pigments
Less resistant to sunlight, humidity, and chemicals
Key raw materials are petroleum based
Color is produced in compounds by selective absorption and reflectance of specific wavelengths of the visible spectrum.  Selective effect arises from the presence of vibrating (resonating) electrons in the strucure of a molecule or molecular group.  If a molecule absorbs in the visible range, it possesses a color complementary to that which is absorbed.  Thus, a compound absorbing in the violet is seen as yellow.  Chemical groups which cause absorption and give rise to color are called chromophores.  Groups which intensify or modify color are known as auxochromes.

Some examples of chromophore chemical groups:

Some examples of auxochrome chemical groups:

Organic pigments are divided into six categories:

  1. Monoazo pigments
  2. Diazo pigments
  3. Acid and base dye pigments
  4. Phthalocyanine pigments
  5. Quinacridone pigments
  6. Other polycyclic pigments
Below are some azo pigments:
 
          Pigment Red 3                                                                         Monoazo yellow
Pyrazolone

Benzimidazolone Pigment:


               Hansa yellow
 

Phthalocyanine Pigments:

Phthalocyanine pigments are the single most successful class of organic pigments.


Phthalocyanine Blue
 


Phthalocyanine Green
(X = H, Cl or Br,  empirical formula  C32HxN8ClyBrzCu   x + y + z = 16)

Major reasons for use:

          Excellent stability to solvents, heat, light, and weathering
          High tinctorial strength
          Cost effectiveness
          Consistency and uniqueness of shades
          Completely non-toxic

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