Fluorescent dye that is water-soluble and forms stable Schiff Base with carbonyl group. The fluorescence emission maximum of Fluorescent Dye 790-I around 810nm is well separated from commonly used far-red fluorophores, including Fluorescent Dye 647-I, Fluorescent Dye 680-I or allophycocyanin (APC), facilitating the rapid growing NIR biological analysis. Fluorescent Dye 790-I is one of the bightest NIR fluorescent labeling dyes with fluorescence quantum yield close to 0.1. Its conjugates have been successfully used for NIR fluorescent probe-based in vivo imaging analysis.