Cy5B-trisulfo, NHS, a far-red fluorescent dye, is delivered as an NHS ester to bind with primary amine groups. It is applicable in FRET, smFRET, FLIM, and SRM methods, including dSTORM for both live and fixed cells. Its excitation and emission peaks (λ) are at 669 nm and 685 nm, respectively, with an extinction coefficient of 241,000 M^-1cm^-1 and a quantum yield (QY) of 0.4.