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

Abstract

The self-assembly of sexiphenyl-dicarbonitrile molecules on the Ag(111) surface is investigated using lowtemperature 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 kagomé 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 flatlying 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.

Rotational and constitutional dynamics of caged supramolecules

“…Firstly, we note that the confined monomers are always attached to the network rim in a specific geometry, reflecting a surface templating effect and weak attractions between phenyl hydrogen and CN end groups. This arrangement is consistent with the structural motifs observed in pure organic lattices of linear dicarbonitrile linker molecules on the same surface (27,28). Secondly, we identify a frequent trimeric arrangement reflecting the self-assembly of three caged linkers.…”

“…Furthermore, Fig. 1B evidences that there are two mirror-symmetric configurations of the supramolecular trimer reflecting an organizational chirality (27,28). These enantiomorphous species are designated λ-and δ-rotator, respectively.…”

“…Secondly, we identify a frequent trimeric arrangement reflecting the self-assembly of three caged linkers. Here a different threefold nodal bonding motif is encountered at the center of the trimeric unit, which must be understood as a consequence of the spatial confinement, because in organic layers exclusively fourfold nodal motifs exist (27,28). Nevertheless, there is again a preferred registry of the supramolecular trimer with respect to the surface atomic lattice, i.e., the molecular backbones are oriented along close-packed h110i directions and the terminating nitrogen atoms reside at threefold hollow sites (28) (compare Fig.…”

“…The Co-coordinated assembly was cooled down and an additional 0.1 monolayer concentration of linker molecules were added at 144 K (coverages are given with respect to the saturated monolayer coverage of a purely organic layer as defined in ref. 28). Following the preparation, the sample was transferred in situ and STM data were acquired at T ¼ 8-150 K. During the measurements, the tunneling parameters were in the high-resistance regime of 20 GΩ to avoid tip-induced motions.…”

Two-dimensional molecular sieves: structure design by computer simulations

“…For those systems, a suitable choice of the building block results in the formation of networks with regular pores of different size and shape (Kudernac et al 2009), e.g. square (Kühne et al 2009), rhombic (Ahn et al 2009), hexagonal (Tahara et al 2009) and so on (Gutzler et al 2009), as ob-served in scanning tunneling microscopy (STM) imaging. The distinct advantage of the porous networks is the regular spatial arrangement of nanometer-sized cavities with uniform well-defined shape.…”