Grand Canonical Quantum Mechanical Study of the Effect of the Electrode Potential on N-Heterocyclic Carbene Adsorption on Au Surfaces

Abstract

Increasing interest has been focused on using N-heterocyclic carbenes (NHCs) as surface ligands to replace thiols in the preparation of self-assembled monolayers (SAMs) on gold due to their larger adsorption energies. However, one of the drawbacks of these NHC-based SAMs is that they are unstable under electrochemically reducing conditions. In this study, grand canonic quantum mechanics (GC-QM) were used to study the effect of the electrode potential (U) on the adsorption of NHC on Au(111). The NHC adsorption energies were significantly weaker (∼0.92 eV) under constant U conditions compared to those under constant charge conditions, demonstrating the importance of using GC-QM for studying electrochemical systems. Consistent with experiments, the results from our calculations indicated that the adsorption energy decreased as U became more negative but increased as U became more positive. These results were rationalized using the frontier orbital theory. Importantly, based on the same analysis, when NHCs or...