Theoretical Investigation on the Initial Reaction Mechanism of Hexaethynylbenzene on Au(111) Surface

Graphyne has attracted considerable interest and attention since its successful synthesis, due to its enormous potential for applications in the fields of electronics, energy, catalysis, information technology, etc. Although various methods for synthesizing graphyne have been explored, single-layer graphynes have not been successfully developed. Hexaethynylbenzene (HEB) is considered an ideal precursor molecule because it can undergo Glaser coupling reactions between molecules to synthesize single layer graphdiyne on single crystal metal surfaces via on-surface reactions. Unfortunately, this method fails to achieve the expected results, and the underlying mechanism is not clear. In this work, we employed a combination of ab initio molecular dynamics (AIMD) and quantum mechanics (QM) methods to investigate the initial reaction mechanism of HEB molecules on a Au(111) surface. We revealed that HEB molecules undergo both intermolecular coupling and intramolecular cyclization on the Au(111) surface. The favorable pathways of these two types of reactions were then distinguished, confirming that the distance between the terminal carbon atoms of the ethynyl groups plays an important role in C-C coupling. The insights revealed from this work could facilitate the rational design of precursor molecules and deepen the understanding of the reaction processes.