Changqing Ye

The adsorption and self-assembly of racemic [5]thiaheterohelicene (rac-[5]TH) adsorbed on Ag(111) were investigated using molecular dynamics (MD) simulations and density functional theory (DFT) calculations and compared with scanning tunneling microscopy (STM) results. While the molecule is physisorbed on Ag(111), the results of DFT calculations also exhibit pronounced site and orientation dependence with respect to the substrate lattice. Displacements from preferred adsorption sites and orientations on Ag(111) result in an energy cost nearly an order of magnitude larger than that associated with deviations from the optimal intermolecular distances favoured by simple intermolecular interactions. This indicates that self-assembly is governed primarily by substrate registry, while intermolecular interactions act as secondary constraints. Consequently, the ordered structures observed experimentally can be understood as a balance in which molecules anchor at their preferred adsorption sites and orientations on the substrate, while locally adopting dimer motifs favoured by intermolecular interactions. These findings provide insight into how helical length controls the balance between intermolecular and molecule–substrate interactions in chiral self-assembly on the Ag(111) surfaces.

We investigated the adsorption and aggregation properties of 2,13-bis(hydroxymethyl)-[7]thiaheterohelicene ([7]TH-diol) on the Ag(111) surface by scanning tunneling microscopy (STM) and molecular dynamics (MD) simulation. STM observation revealed that both racemic and enantiopure [7]TH-diol formed apparently similar “zigzag” chain structures. To elucidate the molecular arrangements in these structures, MD simulation successfully differentiates the formation mechanisms of these structures, demonstrating that hetero-chiral chains are stabilized primarily by van der Waals forces, whereas homo-chiral chains are stabilized through hydrogen bonding. The formation of homo-chiral chains is driven by the alignment of hydroxymethyl groups between the neighboring molecules, whereas the steric hindrance of helical skeletons affects chain growth. These findings highlight the critical role of inter-molecular interactions—particularly hydrogen bonding—in the self-assembly of helicene molecules.

The chiral recognition of a self-assembled structure of enantiopure ( M )-type 2,13-diphenyl[7]thiaheterohelicene (( M )-Ph-[7]TH) was investigated on a Ag(111) substrate by scanning tunnelling microscopy (STM) and tip-enhanced Raman spectroscopy (TERS).