242: Electrochemistry as both a synthetic and analytical tool to understand the growth and behavior of electrografted molecular films

Abstract: Electrografting is a powerful surface modification method where a molecular precursor is reduced or oxidized under an applied potential to produce a radical intermediate that rapidly forms a covalent bond with the electrode surface. While the high reactivity of the radical intermediate is responsible for the speed, reliability, and applicability of this method to a wide variety of metal and semiconductor electrode materials, it often leads to disordered and heterogeneous multilayer films. Here, we studied the role that various electrografting parameters play in the resulting thickness, structure and electrochemical behavior of electrografting films. First, we compared redox-active molecular films formed through reductive aryl diazonium and oxidative aryl amine electrografting processes and found that the oxidative pathway yields thinner films with less disordered redox behavior when charactized via cyclic voltammetry. Next, we systematically varied the precursor concentration and applied grafting potential for aryl diazonium grafted films. Using electrochemical impedance spectroscopy to study the film thickness over time, we found regimes where growth is potential-limited and others where growth is concentration-limited. Finally, we studied the effect of substituent position (meta vs. para) in aryl diazoniums on the film growth and electrochemical properties. The results from these studies will be used to inform the design and synthesis of films with tunable thickness and functionality.