Cy3-PEG2-exo-BCN is a derivative of the Cyanine 3 (Cy3) dye featuring two polyethylene glycol (PEG) units. It incorporates the hydrophilic bidentate ligand exo-cyclooctyne (BCN), which can be further used to synthesize macrocyclic complexes. In click chemistry, exo-BCN reacts with azide-bearing molecules to form stable triazoles in the absence of a catalyst.