Azide derivatives of AF fluorescent dyes react with alkynes via copper-catalyzed azide-alkyne cycloaddition (CuAAC). This click chemistry is increasingly used in a variety of biological applications. AF dye azides share the same chemical structure as AF dye azides and can react with terminal alkynes through CuAAC. Besides serving as extremely bright and photostable fluorophores for use with flow cytometry, microscopy, and HCS (High Content Screening), they also function as bioorthogonal or biologically unique haptens in applications requiring signal amplification.