Dipole-Programmed Chiral Porous Superlattice from Triangular Molecular Platforms on Ag(111)

Trioxatriangulenium was functionalized with a rotatable pyridyl moiety (pyridyl-TOTA), which exhibits a large electrostatic dipole moment, and investigated on the Ag(111) surface using low-temperature scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM). The molecules arrange themselves in a complex, well-ordered long-range pattern, namely, a chiral hexagonal mesh of rings composed of six molecules. Submolecularly resolved STM images reveal the orientations of the molecular dipoles, which are confirmed by NC-AFM measurements. Density functional theory (DFT) calculations reproduce the STM images and their intriguing dependence on the junction bias and confirm that the experimental results allow us to fully determine the orientation of the functional units. Comparison with phenyl-TOTA reveals that the dipole-dipole interaction of the pyridyl unit is strong enough to change the structure from a hexagonal close-packed pattern to a chiral hexagonal mesh of supramolecular hexagons. These results show that dipole functionalization may serve to control the formation of molecular assemblies on the surfaces.