Naphthofluorescein has emission maxima of approximately 670 nm in aqueous solution at pH 10. The fluorescence from this dye is pH dependent (pK_a~7.6) requiring a relatively alkaline pH for maximal fluorescence. The carboxylic acid of Naphthofluorescein has emission maxima of approximately 670 nm in aqueous solution at pH 10. The fluorescence from this dye is pH dependent (pK_a ~7.6) requiring a relatively alkaline pH for maximal fluorescence. The carboxylic acid of 5-(and-6)-carboxynaphthofluorescein can be activated in an aqueous solution with a water-soluble carbodiimide such as EDAC (E2247) in order to couple this fluorophore to amines, hydrazines or hydroxylamines on biomolecules of interest.can be activated in an aqueous solution with a water-soluble carbodiimide such as EDAC (E2247) in order to couple this fluorophore to amines, hydrazines or hydroxylamines on biomolecules of interest.