Dyes derived by condensation of phthalic anhydride with resorcinol (and derivatives)
or
m-aminophenol (and derivatives), of which fluorescein is the prototype (all such dyes
have the xanthene
nucleus).
Source:
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on
structure (IUPAC Recommendations 1995))
on page 1374