Cy5-PEG-N3 (MW 2000) is a Cy5 azide fluorescent dye, designed for use with amines in peptides, proteins, and oligonucleotides. As a click chemistry reagent, this compound features an azide group, enabling copper-catalyzed azide-alkyne cycloaddition reactions (CuAAC) with molecules containing alkyne groups. Additionally, it can undergo strain-promoted azide-alkyne cycloaddition reactions (SPAAC) with molecules that have DBCO or BCN groups.