Xanthene dyes are derived from xanthene. This class of dyes is divided into three subgroups: Fluorenes, fluorones and rhodols. Fluorenes and fluorones contain dyes of importance in histotechnology, the rhodols do not. The fluorenes are further subdivided into five groups. Of these the pyronins and rhodamines include dyes we use. The others do not.
The rhodamine subgroup of fluorenes have the general formula shown to the right. Rhodamine B is an example.
Fluorones have the general formula shown to the right. The fluorones are sometimes referred to as the eosins, and include many dyes used as counterstains to alum hematoxylin. Their general formula shown above is actually that of fluorescien, from which they are derived.