5(6)-CR6G, SE is the amine-reactive form of 5(6)-CR6G. In general, rhodamine 6G conjugates have higher fluorescence quantum yields than tetramethylrhodamine conjugates, as well as good photostability. The excitation and emission peaks of rhodamine 6G conjugates falling between those of fluorescein and tetramethylrhodamine provide another color choice for the multicolor imaging applications. Additionally the absorption maxima of CR6G conjugates match well with the 514 nm spectral line of the argon-ion laser.