Used primarily as a fluorescent labeling reagent in bioconjugation and imaging applications. The azide group enables click chemistry reactions, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), allowing efficient attachment to biomolecules such as proteins, nucleic acids, or glycans that have been modified with alkyne groups. Its spirocyclic xanthene core provides strong fluorescence with high quantum yield, making it suitable for sensitive detection in microscopy, flow cytometry, and immunoassays. The carboxamide linker enhances water solubility and stability in physiological buffers, supporting use in live-cell imaging and diagnostic assays.