The present invention relates to improved conjugates of biological molecules with an improved class of water-soluble, green to near infra-red (NIR) cyanine labelling dyes. The dyes are asymmetric fluoro-substituted polymethines, and exhibit a high degree of photostability and reduced dye-dye quenching, as well as a high fluorescence quantum yield. The conjugates are useful for in vivo optical imaging, as well as fluorescence detection methods. Also disclosed are pharmaceutical compositions containing the conjugates, kits for the preparation of such compositions, and methods of in vivo imaging using the conjugates.
