2',7'-Fluorescein

2-Carboxyphenylfluorone

o-Hydroxyhydroquinonephthalein

2-hydroxyhydroquinonephthalein

2',3',6',7'-Tetrahydroxyfluorane

2',3',6',7'-Tetrahydroxyspiro[isobenzofuran-1(3H),9'-[9H]xanthen]-3-one