Diazonium Grafting Control through a Redox Cross‐Reaction: Elucidation of the Mechanism Involved when using 2,2‐Diphenylpicrylhydrazyl as an Inhibitor

Abstract Investigation into the mechanism involved in the control of layer growth through the reduction of diazonium salts by using 2,2‐diphenylpicrylhydrazyl (DPPH). This approach, previously assumed to be based on the radical capture of highly reactive aryl intermediates via the scavenging activity of DPPH, actually rests on redox cross reactions involving its electro‐reduced form. A numerical approach was developed to model the proposed processes, involving a redox reaction between diazonium cations and the reduced species of DPPH as a central step. Extension of this approach was validated by using substituted benzoquinones instead of DPPH, leading to good control of the radical polymerization to give sub‐monolayer surface coverage. Modulation of the surface coverage can be obtained by adjusting the concentration of the redox mediator and a near‐monolayer can be prepared in this way. The difference in formal redox potential between the diazonium salt and the electro‐reducible mediator was identified as a key parameter, and could be exploited to generalize the grafting control.