Formation of a 2D Chiral Honeycomb Self-Assembled Molecular Network on Ag(111)

Organic molecules with 3-fold symmetry have attracted widespread attention for the formation of robust 2D molecular structures through a bottom-up approach. Here, we utilized a molecule with a π-conjugated planar core and a nonplanar achiral functional group (cyanomethyl) to form a long-range-ordered 2D molecular honeycomb network comprising a chiral arrangement of molecules, stabilized by directional intermolecular hydrogen bonding. Our data illustrate that the cyanomethyl functional group provides the required conformational and organizational prochirality and plays a key role in creating a 2D chiral molecular network on Ag(111). Our scanning tunneling microscopy images reveal 2D networks with mirror symmetry, where the chiral honeycomb network and hexagonal-like pores are resolved as arrangements of six molecules in clockwise and counterclockwise order, composed of “left” and “right” prochiral configurations, respectively. The honeycomb network stability was explored through postannealing as well as by interaction with an aldehyde-substituted molecule, also with 3-fold symmetry, before desorption from the surface. Our density functional theory calculations provide simulated models of molecular arrangements and compare their stabilization energies on the surface. This study presents the role of conformational and organizational prochirality, molecular symmetry, and directional intermolecular interactions in the formation of 2D chiral porous honeycomb self-assembled molecular networks.