Controlling Competitive Radical Pathways: Insights From Aryl Diazonium Electrografting.

Understanding and controlling the reactivity of radical species remains a major challenge in many chemical reactions, with the goal of steering and precisely tuning key processes. Recognized as a simple and efficient method for the preparation of 2D nanomaterials, diazonium electrografting is a prime example of a functionalization technique that still requires deeper mastery to meet the demands of future bottom-up approaches. In this work, supported by multiphysics simulations, we achieve an unprecedented understanding of the grafting mechanism involved in nitrobenzene diazonium electrografting and its impact on the resulting nanofilm composition. It is demonstrated that film growth arises from a competition between aryl and diazenyl radicals, leading to the incorporation of variable amounts of azo-bridged nitrophenyl units. By implementing control strategies using radical scavengers and redox inhibitors, corroborated by simulations, we show that diazenyl radicals are preferentially grafted at the substrate/film interface rather than within the film structure itself. Finally, we demonstrate that selective trapping of aryl radicals over diazenyl radicals enables the formation of azo-enriched films, thus opening the way for precise tuning of film composition and selective radical reactivity.