Dye theory according to Witt
The dye theory of Otto Nikolaus Witt dates back to 1876 . With this theory it was possible for the first time to predict the color of fabrics based on aromatic systems. A first great triumph of this theory was the targeted synthesis of the azo dye chrysoidin , which was based on Witt's theoretical considerations.
However, this theory is only suitable for application to aromatic or generally organic , conjugated dyes. For inorganic color pigments in particular , other theories, such as the ligand field theory, have to be used for predictions.
Statements of the theory
According to Witt, the color of a dye is based on the presence of a chromophore , the natural color of which can be influenced by auxochromes . In addition, Witt's auxochromes ensure that the dye molecule binds to the carrier material during dyeing.
See also: Bathochrome , Hypsochrome
Extensions
The color theory according to Witt was extended by Robert Witzinger, among others . He distinguished two types of auxochromes. According to this, a dye consists of three components:
- From a chromophore (delocalized π-electron system )
- from an auxochrome part ( electron donor with a + M effect )
- and from an antiauxochromic part ( electron acceptor with an −M effect).
See also: antiauxochrome
Example: nitrophenol
The yellow p - nitrophenol is composed of the following components:
- An auxochrome group: OH group
- An antiauxochromic group: NO 2 group
- A delocalized π-electron system : benzene ring as chromophore