The first bench-stable triple-diazonium reagent (TDA-1) was rationally designed and synthesized for coupling and crosslinking. The three reactive sites of TDA-1 can react with phenol-containing molecules as well as plant viruses in aqueous buffers efficiently. In addition, a new-type azo-linked cage was constructed by the direct reaction of TDA-1 with a triple-phenol molecule and was characterized by X-ray crystallography.