Observations of Gradual Chiral Self-Recognition of Adsorbed Aromatic Compound

The self-assembly of two-dimensional chiral 1 H,5 H-benzo(1,2- d:4,5- d')bistriazole (H₂bbta) on a Ag(110) surface was investigated by ultra-high-vacuum scanning tunneling microscopy. The gradual formation of ordered structures by H₂bbta molecules with the same chirality recognizing each other was observed as the annealing temperature was increased from 300 to 333 K. When the sample was annealed at 355 K, the homochiral structures were converted to coexisting structures containing λ-H₂bbta and δ-H₂bbta in a ratio of 6:1. Density functional theory (DFT) calculations revealed that thermally driven and intermolecular interactions induced chiral self-recognition to form enantiomorphous H₂bbta structures in which N-H···N hydrogen bonds and C-H···N hydrogen bonds are the main attractive forces.