First-Principles Study of the Adsorption Behavior of Triptycene Molecular Tripods on Au(111): Site Selectivity and Unambiguous Molecular Orientation

Through a first-principles theoretical study, thiol tripods with a rigid C3-symmetric triptycene are proposed as excellent building blocks to achieve well-defined molecule–metal contact. We designed two types of tripods, where three thiol groups are connected to the triptycene skeleton either directly (1) or via a methylene bridge (2), whose geometries fit the lattice structure of Au(111). Structural relaxation of systematically generated initial adsorption configurations of the tripods on Au(111) showed that all three sulfur atoms of 1 and 2 selectively adsorb on fcc hollow and bridge sites, respectively, in such a way that the aromatic blades of triptycene are arranged almost perfectly perpendicular to the metal surface. The absorption energy differences between the most stable and second most stable configurations on Au(111) for 1 (0.126 eV) and 2 (0.298 eV) are larger than the thermal energy at room temperature, indicating excellent site selectivity, particularly for 2