text: This compound is used for bioconjugation. The target, which contains a terminal alkyne functional group, is treated with the organic azide in the presence of a  Cu(I) catalyst. The resulting 1,2,3-triazole is fluorescent. The coumarin backbone is chosen to be used as the profluorophore due to its small size, biocompatibility, and its ability to be easily manipulated synthetically. Illustrative of this is the labeling of biological compounds such as the protein calmodulin. Neither the azidocoumarin nor the alkyne substrate fluoresce. Azidocoumarin is also inert in biological systems and insensitive to pH and solvent. A variety of azidocoumarin compounds have been evaluated.