Self-Assembly of Nanoporous Chiral Networks with Varying Symmetry from Sexiphenyl-dicarbonitrile on Ag(111)

The self-assembly of sexiphenyl-dicarbonitrile molecules on the Ag(111) surface is investigated using low-temperature scanning tunneling microscopy (STM) in ultrahigh vacuum. Several nanoporous networks with varying symmetry and pore size coexist on the surface after submonolayer deposition at room temperature. The different rectangular, rhombic, and kagom shaped phases are commensurate with the Ag(111) substrate and extend over micrometer-sized domains separated by step edges. All phases are chiral and have very similar formation energetics. We attribute this to common construction principles: the approximately flat-lying polyphenyl backbones following high-symmetry directions of the substrate, the epitaxial fit and the nodal motif composed of CN end groups laterally attracted by phenyl hydrogens. Close to saturation coverage, a single dense-packed phase prevails with all molecules aligned parallel within one domain. Our results demonstrate that porous networks of different complexity can evolve by the self-assembly of only one molecular species on a metal surface.