Fluorescent dyes are compounds with special structures, and their structural features mainly include the following three points:
(1) The molecule contains a fluorescent-emitting group, such as a carbonyl group, a nitrogen-nitrogen double bond, a carbon-nitrogen double bond, etc.
(2) The molecule contains auxochrome groups. The auxochrome group makes the spectrum red shift and increases the fluorescence efficiency, such as primary amino group, secondary amino group, hydroxyl group, ether bond, amide group and so on.
(3) The molecule contains conjugated π bonds with a rigid planar structure. The larger the intramolecular conjugated system, the stronger the planarity, the higher the fluorescence intensity. Some factors that can improve the degree of conjugation can increase the fluorescence efficiency and shift the fluorescence wavelength to the long-wave direction.