Coverage Modulated Transformation of the Supramolecular Assembly Structure of Brominated N-Heterocyclic Molecules on Au(111) Surfaces

Using brominated N-heterocyclic molecules with different lengths 4,4 ',7,7 '-tetrabromo-1H,1 ' H-2,2 '-bibenzo[d]-imidazole (TBBI) and 1,4-bis(4,7-dibromo-1H-benzo[d]-imidazol-2-yl) benzene (DBBIB), we successfully constructed and characterized several large-area supramolecular assembly structures on Au(111) surfaces by molecular beam epitaxy and bond-resolved scanning tunneling microscopy. At low coverage (sub-monolayer), both molecules tend to form energetically favorable supramolecular assembly structures. At high coverage (full layer), TBBI can be assembled into grid-like structures with higher space utilization but less non-covalent interactions. However, the transition-like structure of DBBIB assembly with insufficient diffusion can also be kinetically captured at a high deposition rate. In addition, the hindrance between H atoms caused by the spatial configuration of different precursors also affects the self-assembly behavior of molecules. Density functional theory calculations suggest that the formation of various 2D supramolecular assembly structures is due to two types of halogen bonds (Br center dot center dot center dot Br and Br center dot center dot center dot N halogen bonds) and H center dot center dot center dot Br/ H center dot center dot center dot N hydrogen bonds. It is undeniable that this strategy can effectively provide a potential route for constructing more supramolecular nanostructures, which may influence the future design of molecular nanomaterials.

Automated summary

Using brominated N-heterocyclic molecules, supramolecular assembly structures were successfully constructed on Au(111) surfaces. The formation of these structures was influenced by coverage, spatial configuration, and the types of bonds involved. This study provides a potential route for constructing more supramolecular nanostructures, which may impact the future design of molecular nanomaterials.