Coupling Between Br-Hexahelicene Molecules Through Br···H Bonds: A Theoretical Study

The control of molecular self-assembly on surfaces via specific noncovalent interactions is a key challenge in nanoscience. Using density functional theory (DFT) at the r ${}^2$ SCAN-3c level, we investigate the intermolecular forces within dimers of Br-Hexahelicene (Br[6]H) adsorbed on Au(111). Through wavefunction analysis using Interaction Region Indicator (IRI), electrostatic potential (ESP), and Quantum Theory of Atoms in Molecules (QTAIM), we characterize the nature of the halogen contacts. Our results show that the stabilization of the homo-chiral dimers is driven by a distinct CBr···HC halogen-hydrogen bond. Conversely, the Br···Br contact is identified as a weak, nondirectional van der Waals interaction with negligible bonding character. This work clarifies the hierarchy of interactions in these surface-confined systems and highlights the CBr···HC bond as a specific design element for guided supramolecular assembly.