Self-Assembly of N-Heterocyclic Carbenes on Au(111)

The production of ordered arrays of organic molecules on metallic surfaces by means of self-assembly is one of the most powerful methods for controlled patterning on the nanometer scale. Although the self-assembly of sulfurbased ligands has been studied for decades, the thermal and oxidative instability of these systems introduces challenges in many potential applications. In recent years, it has been shown that a new ligand class, N-heterocyclic carbenes (NHCs), bind to metal surfaces via a metal–carbon covalent bond, resulting in monolayers with much greater stability. However, fundamental questions surrounding self-assembly in this new ligand class remain unanswered, including the simple questions of what controls NHC orientation on the surface and under what conditions they self-assemble. Herein we describe how NHC structure, surface density, deposition temperature, and annealing temperature control mobility, thermal stability, NHC surface geometry, self-assembly, and the exact chemical nature of the surface structures. These data provide the first general set of guidelines to enable the rational design of highly ordered NHC-based monolayers. Considering that NHCs may supplant thiols as the functionalization agent of choice in a wide range of applications, a detailed understanding of their surface chemistry is crucial for the success of these next-generation monolayers.