Copper-free click chemistry is a chemical reaction method that can achieve rapid intermolecular connection under mild conditions without the use of toxic copper catalysts. Copper-free click reaction reagents mainly include DBCO (dibenzocyclooctyne) and BCN (benzocyclooctyne) compounds. These reagents can react with azides under copper-free conditions to form stable triazole bonds. They are often used in biomedicine, materials science, and drug development.