Electrografting via Diazonium Chemistry: The Key Role of the Aryl Substituent in the Layer Growth Mechanism

A series of diazonium salts bearing different para substituents was used to functionalize glassy carbon (GC) and pyrolyzed photoresist film (PPF) under electrografting conditions in the absence and presence of the radical scavenger diphenyl-1-picrylhydrazyl (DPPH). Depositions were monitored by electrochemical quartz crystal microbalance (EQCM) and the grafted layers were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). DPPH was used to selectively suppress film growth by radical coupling and thereby to reveal the existence of secondary mechanisms involved in the polymerization. Differences in grafting behaviors between various diazonium ion derivatives can be explained by the influence of the para substituent's electronic properties on the electrophilic aromatic substitutions of diazonium ions on already grafted aromatic groups.