5(6)-Carboxynaphthofluorescein
5(6)-Carboxynaphthofluorescein is a pH-dependent fluorophore. 5(6)-Carboxynaphthofluorescein shows good sensitivity in an alkaline pH range and it can be exploited in the construction of fiber-optic pH sensors. 5(6)-Carboxynaphthofluorescein can be used as a fluorescent pH indicator (Ex/Em=593/668 nm).