ATTO 680 belongs together with ATTO 655 and ATTO 700 to a new generation of fluorescent labels. Characteristic features of the label are strong absorption, high fluorescence quantum yield, good water solubility, and high thermal and photo-stability. ATTO 680 is a zwitterionic dye. After coupling to a substrate the dye moiety is electrically neutral. ATTO 680 is a strong electron acceptor. Its fluorescence is efficiently quenched by electron donors like guanine, tryptophan, etc. The fluorescence is excited most efficiently in the range 645 - 695 nm. A suitable excitation source for the dye is the Krypton-Ion laser using the 676 nm line or a diode-laser emitting at 670 nm.