CF™620R succinimidyl ester (SE) is a far-red rhodamine-based fluorescent dye with an amine-reactive group. The SE group of the dye permits the dye to be attached to an aliphatic primary or secondary amine group via a very stable amide bond under mild condition. CF™620R is highly fluorescent and extremely photostable. With its absorption and emission maxima centered at 617 and 639 nm, respectively, the dye may be used as an excellent energy acceptor in fluorescence resonance energy transfer (FRET), or used in multi-color detection applications where the excitation and emission windows can be matched with the spectral profiles of the dye for maximal fluorescence collection. The exceptional water solubility of the dye facilitates bioconjugation in aqueous media and better retains the biological specificity of the conjugates.