Atto Oxa12 maleimide ester is a red-emitting dye and a lipophilic variety of Atto 655. Characteristic features of the label are strong absorption, good fluorescence quantum yield, very little triplet formation, excellent thermal and photo-stability, and outstanding ozone resistance. Atto Oxa12 maleimide is a cationic dye (charge +1). Absorption and fluorescence are pH independent in the range pH 2 to 11, used in typical applications. Atto Oxa12 maleimide shows excellent solubility in organic solvents like DMF, DMSO or acetonitrile.