Auxochrome and Chromophore


A chromophore is a chemical molecule that absorbs light of a specific wavelength, giving a substance its distinctive colour. The chromophore charecteristics structure define the colour of compound.

Few example of chromophore is given below:

  • Alternative double bonds, such as those found in carotenoids and chlorophyll.
  • The ring containing benzene, such as those found in anthocyanins and flavonoids, and metal ions.


On the other hand, an auxochrome is a functional group that enhance a compound’s colour by changing the chromophore’s electronic distribution, which causes the absorption of light at a longer wavelength containing lower energy.

How Auxochrome work?

Auxochromes did not contain their own absorption bands; instead, they change the chromophore’s absorption bands’ place or strength.  Few example of Auxochromes is given below

  • hydroxyl (-OH) group.
  • amino (-NH2) group.
  • and carboxyl (-COOH) groups.

Effect of auxochrome and chromophore on compounds structure:

A compound’s colour and spectral characteristics can be considerably effected by the presence of both these significant structures. For instance, by using a hydroxyl group (-OH) as an auxochrome, the absorption spectra of an azo dye can be changed from the ultraviolet to the visible area. Similar to how variations in pH can vary the degree of ionisation of an auxochrome’s carboxyl groups (-COOH), anthocyanins can also change their colour.


 NOTE: it is crucial to learn the function of chromophores and auxochromes. In many field, such as chemistry, biology, and material science, where the design and synthesis of substances with certain optical properties is of significant interest, these structures play an important role.