Redox-ControlledCovalent Nanopatterning of GraphiticSurfaces by Graftable Viologen

We demonstrate the feasibility of covalently functionalizing graphitic surfaces, including graphene, relying on the redox-triggered electrografting of a viologen diazonium salt, abbreviated as g-DBV. This compound is in situ prepared from 1,1′-bis(4-aminobenzyl)-4,4′-bipyridinium dibromide (a-DBV). Dediazotized g-DBV moieties covalently graft onto graphitic surfaces. The efficiency of this grafting approach was revealed by employing a state-of-the-art toolbox of characterization techniques, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). Triggering the redox states of the g-DBV under electrochemical control enables functionalization of graphitic surfaces by either random (g-DBV2+), dimer phase (g-DBV•+), or stripe (g-DBV0) patterns. Importantly, the g-DBV0 striped graphene surface reveals n-doping caused by the charge transfer from the electron-rich uncharged g-DBV0 species to graphene. This finding opens a new way to nanopatterned functionalization and doping of graphene and other two-dimensional (2D) substrates by electrochromic molecules.