Chiral Domains Achieved By Surface Adsorption Of Achiral Nickel Tetraphenyl- Or Octaethylporphyrin On Smooth And Locally Kinked Au(111)

The self-assembly of either nickel tetraphenylporphyrin (NiTPP) or nickel octaethylporphyrin (NiOEP) on a reconstructed Au(111) surface is studied using scanning tunneling microscopy in ultrahigh vacuum. Even though the porphyrins are achiral in the gas phase, they are shown to form racemic chiral domains on the surface. For NiTPP we observe the expected roughly "square" unit cell as well as a new "parallelogram" unit cell. For NiOEP we find a hexagonally packed structure in which alternating rows are rotated 15 with respect to each other. We discuss the forces responsible for the formation of chiral domains and find intermolecular interactions to be the dominant factor in the assembly when the porphyrins are on a flat surface. Moreover, we observe that it is possible to break the formation of racemic domains of NiTPP on Au(111) by using a kinked vicinal surface as a symmetry-breaking template to locally lift the structural equivalence of the racemic surface structures. This study shows that a delicate interplay of intermolecular forces and adsorbate surface interactions leads to the formation of complex structures and chiral phenomena.