Substrate-Selective Intermolecular Interaction and the Molecular Self-Assemblies: 1,3,5-Tris(4-bromophenyl)benzene Molecules on the Ag(111) and Si(111) (√3 × √3)-Ag Surfaces.

We report the formation processes of the self-assembled layer of 1,3,5-tris(4-bromophenyl)benzene (TBB) molecules on the Ag(111) and Si(111) (√3 × √3)-Ag surfaces by STM measurements and density functional theory (DFT) calculations. The self-assembled layers on the surfaces show characteristic structures controlled by the interplay between the intermolecular interaction and the molecule-substrate interaction. Through the cooperative interplay between the molecule-substrate interaction and the intermolecular halogen bond (XB), the periodic arrangement of TBB molecules appears on the Ag(111) surface. On the other hand, the two types of TBB arrangement appear on the Si(111) (√3 × √3)-Ag surface (phases 1 and 2). Phase 1 is the periodic arrangement of the TBB molecules and is derived from the cooperative interplay between the molecule-substrate interaction and the intermolecular van der Waals (vdW) interaction and the hydrogen bond (HB), and phase 2 is a random arrangement and is derived from the competitive interplay between the molecule-substrate interaction and the intermolecular XB and HB. Our present study specifies the role of the substrate in the molecular self-assembly of the substrate. Although the structure of the molecular self-assembly is controlled by the choice of the substrate, the cooperative interplay between the molecule-substrate interaction and the intermolecular interaction is necessary to realize the ideal periodic arrangement.