Covalent Modification of Highly Ordered Pyrolytic Graphite with a Stable Organic Free Radical by Using Diazonium Chemistry

A novel, persistent, electrochemically active perchlorinated triphenylmethyl (PTM) radical with a diazonium functionality has been covalently attached to highly ordered pyrolytic graphite (HOPG) by electrografting in a single-step process. Electrochemical scanning tunneling microscopy (EC-STM) and Raman spectroscopy measurements revealed that PTM molecules had a higher tendency to covalently react at the HOPG step edges. The cross-section profiles from EC-STM images showed that there was current enhancement at the functionalized areas, which could be explained by redox-mediated electron tunneling through surface-confined redox-active molecules. Cyclic voltammetry clearly demonstrated that the intrinsic properties of the organic radical were preserved upon grafting and DFT calculations also revealed that the magnetic character of the PTM radical was preserved.
We acknowledgeGuillaume Sauthier from the Ca talan Ins tituteof Nanoscience and Nanotechnology (ICN2) for XPS measure-ments.This work was supported by ACMOL (GA no. 618082),the Swiss National Science Foundation (grant no. 200020-144471), ERC StG 2012-306826 e-GAMES,ITN iSwitch (642196)project, the Networking Research Center of Bioengineering,Biomaterials and Nanomedicine(CIBER-BBN), the DGI (Spain)with project BE-WELL CTQ2013-40480-R, and the Generalitatde Catalunya with project 2014-SGR-17. N.C acknowledges theRyC program. We also acknowledge financial suppo rt from theSpanishMinistry of Economyand Competitiveness, throughthe “Severo Ochoa” Programme for Centres of Excellence inR&D (SEV-2015-0496).