Vat dyes can be divided into two categories: indigo dyes and anthraquinone dyes. Indigo in the indigo group dyes is a kind of dye with the longest history of application. There are also halogen derivatives and isomers of indigo and thioindigo derivatives of indene framework belonging to the indigo group dyes; The Chromogenic System of indigo dyes is composed of a pair of electron donors and electron acceptors connected by the same vinyl group. This cross conjugated chromogenic system is called H-type chromophore. There are many varieties of anthraquinone vat dyes, among which the simplest is amidoanthaquinone derivative. Anthraquinone itself is light yellow. After the introduction of amino groups, it forms an electron donor electron acceptor chromophore and produces dark effects, such as reduced red 5gk. The structure of polycyclic ketone dyes in anthraquinone vat dyes is relatively complex, and there are roughly two types - fused ring dyes based on anthraquinone (two or more anthraquinone rings are fused by nitrogen heterocycles, such as reduced blue RSN, which has the largest yield) and fused anthrone (such as reduced gold Orange G with pyrene anthrone structure, reduced yellow G with anthraquinone structure, reduced brilliant green FFB with purple anthrone skeleton, reduced brilliant purple 3B with isoviolet anthrone skeleton, etc.). Reduced polycyclic ketone dyes belong to cyclopolyene chromophores. The carbonyl group is reduced to form leucophores. For many dyes, it does not affect the conjugated bond length of their chromophores. On the contrary, some dyes produce dark effects due to the power supply effect of hydroxyl groups. For example, the leucophore solution of reduced yellow G is blue, the leucophore solution of reduced gold Orange G is blue red, the reduced blue RSN dye is blue red, and the leucophore alkaline solution is blue.
