Chiral Self-Assembly and Chiral Separation of Ext-TEB Molecules on Bi(111).

The two-dimensional chiral self-assembly and chiral separation of achiral Ext-TEB molecules on a Bi(111) surface were investigated using low-temperature scanning tunneling microscopy (LT-STM). At low coverage, the molecules self-assembled into chiral clusters. As the coverage increased, a monolayer film with a non-edge-sharing honeycomb structure was formed. This supramolecular structure exhibited organizational chirality, accompanied by chiral separation. Upon annealing, part of the non-edge-sharing honeycomb structure transformed into a close-packed structure, while retaining the organizational chirality, supramolecular chirality, and pronounced chiral separation. Furthermore, applying a higher bias was found to induce a transition in the electronic state of the non-edge-sharing honeycomb structure, converting it into an edge-sharing honeycomb configuration. This study reveals that the chirality of 1,3,5-tris(4-ethynylphenyl) benzene (Ext-TEB) arises from the rotation of the side-chain phenyl rings, which is induced by the rotation of the molecular axis relative to the substrate lattice. This work presents a strategy for the preparation of chiral nanostructures from achiral molecules due to the spontaneous chiral symmetry generation.