Otto N. Witt discovered the theory of Chromophore and Auxochrome in 1876. He explains-
All organic compounds that contain certain unsaturated groups which are responsible for color are called chromophore.
Examples- —N=O (Nitroso), —NO2 (Nitro), —N=N— (Azo), >C=C< (Ethylenic), >C=O (Keto)
01. Independent chromophore – When a single chromophore is sufficient and does not need auxochrome to impart color to the compound, then it is called independent chromophore.
Examples- —N=O (Nitroso), —NO2 (Nitro), —N=N— (Azo) etc.
02. Dependent chromophore – When more than one chromophore is required to impart color in the chromogen, then it is called dependent chromophore.
Examples- >C=C< (Ethylenic), >C=O (Keto) etc.
They are color helping or color intensifying groups. The auxochrome by itself does not produce color but it-
(i) Generally deepen the color of a chromogen.
(ii) Helps the chromogen to adhere to the textile fiber.