Cyclodextrin-Modulated Electrochemical Grafting of Graphite Surfaces with Aryldiazonium Salts

We report the role of cyclodextrins (CDs) in the electrochemical grafting of the basal plane of graphite with aryldiazonium salts through host-guest complexation. Three aryldiazonium ions bearing different substituents in the para position, p-adamantylbenzene diazonium ion 1b, p-bromobenzene diazonium ion 2b, and p-nitrobenzene diazonium ion 3b, were used to elucidate how complex formation with CDs influences their electrochemical behavior and surface functionalization. NMR investigations confirmed the formation of inclusion complexes for 1b/β-CD and 2b/α-CD, whereas 3b showed only weak interaction with α-CD. The electrochemical behavior of the aryldiazonium salts was altered in the presence of CD. The grafting efficiency of 1b and 2b was improved upon complexation with CDs, as supported by Raman spectroscopy, scanning tunneling microscopy (STM), and atomic force microscopy (AFM). In contrast, the effect of CD was limited for 3b, consistent with its weak host-guest interaction. We propose that CD complexation suppresses the formation of a self-assembled layer of the aryldiazonium ion at the water-graphite interface for 1b. In the case of 2b, the effect of CD complexation may find its origin in a reduction of side reactions in the electrolyte solution. These factors facilitate efficient covalent attachment. This study provides fundamental insights into the supramolecular control of electrochemical surface functionalization and offers a versatile strategy for tuning grafting density and layer structure on carbon-based materials.