CR110-C5-maleimide (full name: 5(6)-Carboxyrhodamine 110-C5-maleimide) is a maleimide derivative of the green fluorescent dye carboxyrhodamine 110. The dye has spectral properties (&lamba; Ex/&lamba; Em (MeOH) = 502/524 nm) similar to those of fluorescein (fluorescein-5-maleimide, for example), but the photostability of the dye is among the best of all green fluorescent dyes. Thus, the dye is a superior green fluorescent dye for labeling thiols.