Electrophilic radical coupling at the edge of graphene

We report the selective functionalization of an edge of graphene via the electrografting of 4-nitrobenzene diazonium tetrafluoroborate. The edge - a single line of carbon atoms - forms during the process of cutting a graphene monolayer with an atomically sharp microtome knife. Embedded in a polymeric matrix, the just cut bare graphene edge efficiently transfers electrons to a ferricyanide probe in solution. By monitoring the electron exchange reactions of the edge upon functionalization, we observe an annihilation of the reduction and oxidation peaks of the ferricyanide probe, characteristic of the formation of a nitroaryl passivation layer on the edge of graphene. For the first time, the chemical state of a single line of carbon atoms is influenced and monitored using an electrochemical cell, therefore bypassing the usual requirements of atomic resolution characterization techniques, which often demand very clean graphene samples and vacuum processing.