Chiral Recognition Mechanism of 2,13-Bis(hydroxymethyl)-[7]thiaheterohelicene on Ag(111) Investigated by STM and MD Simulation

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.