A particular important objective in the field of coordination polymers and metal-organic frameworks is the realization of porous structures providing spaces with a well-defined geometry and chemical environment. 1,2 However, in three dimensions, mainly due to interpenetration of the forming networks, it is challenging to achieve open spaces reaching the mesoporous regime, i.e., 20-500 Å, based on building principles rooted in coordination interactions or supramolecular engineering. 2 Porous molecular layers can also be stabilized by the presence of surfaces, where they represent versatile functional nanoarchitectures. Thus over the past years a series of bottom-up fabrication schemes has been developed to realize two-dimensional (2D) open molecular networks, frequently with limited domain size, using hydrogen-bonding, 3 metal-directed assembly, 4 the organization of flexible species, 5 or covalent chemical reactions. 6 Similar to the situation encountered with 3D systems, the engineering of extended pore sizes organized in mesoscopically regular single-phase domains is particularly demanding. A recent step forward in this direction was an anthraquinone honeycomb network achieved on a Cu(111) surface, with a rather large pore diameter of ∼50 Å. 7 Because its formation relies on the interference of substrate-mediated long-range interactions, which are rather weak and hard to control in a systematic manner, 8 it turned out to be stable only up to 200 K. On the other hand, using only easy-tocontrol parameters we developed an approach to fabricate open and robust metal-organic nanomeshes on the Ag(111) surface that allows tuning the cavity size in a straightforward fashion using dicarbonitrile-polyphenyl linkers with variable length (CN-Ph n -CN, whereby n is 3, 4, or 5) coordinated by cobalt centers. 9 However, the longest linkers produced networks of reduced quality and deviations from the threefold symmetry of the coordination node appeared therewith.Herein we report a scanning tunneling microscopy (STM) investigation of a highly regular 2D nanoporous metal-organic network with a large pore diameter of ∼67 Å. To this end we employed a de noVo synthesized para-hexaphenyl-dicarbonitrile linker 1 (depicted in Scheme 1) with a length of 29.6 Å (as calculated in the semiempirical AM1 framework). The resulting large 29 nm 2 cell size (corresponding to an ∼24 nm 2 van der Waals cavity), expressed in the Co-directed assembly of nanomeshes, allowed for atomic resolution imaging of the atomic silver lattice therein. Thus we can rationalize the high quality of the fabricated networks in terms of their epitaxial fit where coordination nodes reside preferentially at hollow sites and the linkers strictly follow high-symmetry crystallographic orientations on the employed Ag(111) substrate.The synthesis of the rod-like NC-Ph 6 -CN (1) molecule was developed on the basis of Suzuki coupling of 4,4′-bis-iodo-diphenyl 2 with 2 equiv of boronic acid 3 in the presence of catalytic amounts of Pd(0) (see the Supporting Information; for r...

The confinement of surface-state electrons by a complex supramolecular network is studied with low-temperature scanning tunneling microscopy and rationalized by electronic structure calculations using a boundary element method. We focus on the self-assembly of dicarbonitrile-sexiphenyl molecules on Ag(111) creating an open kagomé topology tessellating the surface into pores with different size and symmetry. This superlattice imposes a distinct surface electronic structure modulation, as observed by tunneling spectroscopy and thus acts as a dichotomous array of quantum corrals. The inhomogenous lateral electronic density distribution in the chiral cavities is reproduced by an effective pseudopotential model. Our results demonstrate the engineering of ensembles of elaborate quantum resonance states by molecular self-assembly at surfaces.

The confinement of Ag(111) surface state electrons by self-assembled, nanoporous metal-organic networks is studied using low-temperature scanning tunneling microscopy/spectroscopy and electronic structure calculations. The honeycomb networks of Co ligands and dicarbonitrile-oligophenyl linkers induce surface resonance states confined in the cavities with a tunable energy level alignment. We find that electron scattering on the molecules is repulsive and stronger than on the weakly attractive Co and that the networks represent periodic arrays of coupled quantum dots featuring uniform electronic levels.

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.

The ordering and conformational properties of dicarbonitrile‐para‐oligophenyls are studied with complementary methods, namely X‐ray structure analysis, low‐temperature scanning tunneling microscopy, and near‐edge X‐ray absorption fine‐structure spectroscopy. The packing of the functionalized variants differs from their technologically interesting para‐oligophenyl counterparts, both in the bulk crystal phase and in thin films grown by organic molecular beam epitaxy (OMBE) under ultra‐high vacuum conditions on the Ag(111) surface. In the crystal phase, the conformation depends on the number n of phenyl rings, exhibiting an intriguing screw‐like structure in the case of n = 4 at room temperature as well as at 180 K. For OMBE‐grown thin films, the whole series acquires the same type of conformation, characterized by alternately twisted phenyl rings, similar to the pure oligophenyl species. However, for all tested molecules, the orientation of the molecular reference plane is uniform within the entire film and coincides with the surface plane. This contrasts with the herringbone ordering adopted by the phenyl backbones without the carbonitrile groups. Our results demonstrate how the functionalization of moieties with extended conjugated electron systems can help to improve the structural homogeneity in technologically relevant organic thin films.

This Feature Article reports on the controlled formation and structurefunctionality aspects of vacuum-deposited self-assembled organic and metal-organic networks at metal surfaces using ditopic linear and nonlinear molecular bricks, namely di-carbonitrile polyphenyls. Surface confi ned supramolecular organization of linear aromatic molecules leads to a fascinating variety of open networks. Moreover, cobalt-directed assembly of the same linear linkers reveals highly regular, open honeycomb networks with tunable pore sizes representing versatile templates for the organization of molecular guests or metal clusters and the control of supramolecular dynamers. In addition, the 2D nanopore organic networks act as arrays of quantum corrals exhibiting confi nement of the surface-electronic states of the metallic substrate. A reduction of the linker symmetry leads to the formation of disordered, glassy coordination networks, which represent a structural model for amorphous materials.

The confinement of molecular species in nanoscale environments leads to intriguing dynamic phenomena. Notably, the organization and rotational motions of individual molecules were controlled by carefully designed, fully supramolecular host architectures. Here we use an open 2D coordination network on a smooth metal surface to steer the self-assembly of discrete trimeric guest units, identified as noncovalently bound dynamers. Each caged chiral supramolecule performs concerted, chirality-preserving rotary motions within the template honeycomb pore, which are visualized and quantitatively analyzed using temperature-controlled scanning tunneling microscopy. Furthermore, with higher thermal energies, a constitutional system dynamics appears, which is revealed by monitoring repetitive switching events of the confined supramolecules' chirality signature, reflecting decay and reassembly of the caged units. supramolecular dynamics | nanochemistry | surface architecture T he dynamics of molecular species can be controlled by carefully designed, fully supramolecular host architectures, provided either as discrete capsules or extended nanoporous networks. It was recognized in particular that unique rotary motion phenomena of single molecular species can be encoded by such conditions (1-5). Moreover, with the restriction to surfaceconfined systems it became possible to investigate molecular rotation and noncovalent assembly processes of individual molecules adsorbed at surfaces by atomic-scale scanning tunneling microscopy (STM) (6-12). However, the direct observation of dynamic supramolecular entities in controlled environments remained elusive although this objective represents a key issue of supramolecular science and constitutional dynamic chemistry (13-16). Herein we report dynamic phenomena at the supramolecular level, resulting from the nanoscale confinement of a multicomponent aggregate in an open 2D coordination network on a smooth metal surface. The presented nanopores steer the assembly and cage the realized discrete 2D-chiral trimeric dynamers, whose behavior is directly monitored by temperaturecontrolled STM. We visualized and analyzed quantitatively their rotary motions, whereby the collective nature of the system dynamics is demonstrated by following chirality-preserving individual reorientation events. The findings reveal opportunities for the field of surface-mounted rotors, limited to single molecular units so far (17)(18)(19). Furthermore, we infer constitutional dynamics from the switching of the chirality signature for increased thermal energies, reflecting the repetitive decay and reassembly of the caged supramolecules. With our observations, a demonstrator for the intricate collective dynamics of caged supramolecular dynamers is provided.

Scanning tunneling spectroscopy (STS) enables the local, energy-resolved investigation of a samples surface density of states (DOS) by measuring the differential conductance (dI/dV) being approximately proportional to the DOS. It is popular to examine the electronic structure of elementary samples by acquiring dI/dV maps under constant current conditions. Here we demonstrate the intricacy of STS mapping of samples exhibiting a strong corrugation originating from electronic density and local work function changes. The confinement of the Ag(111) surface state by a porous organic network is studied with maps obtained under constant-current (CC) as well as open-feedback-loop (OFL) conditions. We show how the CC maps deviate markedly from the physically more meaningful OFL maps. By applying a renormalization procedure to the OFL data we can mimic the spurious effects of the CC mode and thereby rationalize the physical effects evoking the artefacts in the CC maps.