Self-Limited Grafting of Sub-Monolayers via Diels-Alder Reaction on Glassy Carbon Electrodes: An Electrochemical Insight

The grafting of molecular monolayers is critical for the functionalization of surfaces. In molecular electrochemistry, the surface modification of electrodes and the way molecules are attached to the electrode surface are highly critical to electron transfers and electrochemical reactions. In this paper, sub-monolayers were covalently grafted onto glassy carbon (GC) electrodes via Diels-Alder cycloaddition with two soluble dienophiles, that is, propargyl bromide and ethynyl ferrocene. Such an approach is clean (no by-product, no catalyst/additive) and occurs under mild conditions by heating at 50 degrees C in toluene for few hours. The as-modified electrodes were thoroughly characterized by FTIR, XPS, and cyclic voltammetry using both millimetric GC electrodes and ultra-microelectrodes. Cyclic voltammetry gave access to surface coverage and clearly evidenced the covalent grafting of sub-monolayers. The grafting of functional sub-monolayers via Diels- Alder cycloaddition could be easily extended to various functionalities and carbons to prepare electrochemical sensors or electrocatalytic surfaces.