The electronic structure of surface-supported organometallic networks with Ag-bis-acetylide bonds that are intermediate products in the bottom-up synthesis of graphdiyne and graphdiyne-like networks were studied. Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal a frontier, unoccupied electronic state that is delocalized along the entire organometallic network and proves the covalent nature of the Ag-bis-acetylide bonds. Density-functional theory (DFT) calculations corroborate the spatial distribution of the observed delocalized state and attribute it to band mixing of carbon and silver atoms combined with n-doping of the metal surface. The metal-bis-acetylide bonds are typical metal-organic bonds with mixed character containing covalent and strong ionic contributions. Moreover, the organometallic networks exhibit a characteristic graphene-like band structure with linear band dispersion at each K point.
The facile assembly of shell-by-shell (SbS)-coated nanoparticles [TiO2-PAC16]@shell 1-7 (PAC16 = hexadecylphosphonic acid), which are soluble in water and can be isolated as stable solids, is reported. In these functional architectures, an umpolung of dispersibility (organic apolar versus water) was accomplished by the noncovalent binding of ligands 1-7 to titania nanoparticles [TiO2-PAC16] containing a first covalent coating with PAC16. Ligands 1-7 are amphiphilic and form the outer second shell of [TiO2-PAC16]@shell 1-7. The tailor-designed dendritic building blocks 3-5 contain negative and positive charges in the same molecule, and ligands 6 and 7 contain a perylenetetracarboxylic acid dimide (PDI) core (6/7) as a photoactive reporter component. In the redox and photoactive system [TiO2-PAC16]@shell 7, electronic communication between the inorganic core to the PDI ligands was observed.
The synthesis and characterization of a new type of very large perylene‐based molecules 9 are reported. The extension of the conjugated π system was accomplished by the facile condensation of two bay‐functionalized perylene moieties with 1,2,4,5‐tetraaminobenzene. The resulting chromophore in 9 consists of 35 conjugated π‐electron pairs and, therefore, is comparable to pentarylenes and hexarylenes containing 31 and 36 conjugated π‐electron pairs, respectively. The unsubstituted imine N atoms of the benz‐bisimidazole bridges in 9 can be readily and reversibly protonated to give the dications 9aH22+. The twofold protonation of 9 is accompanied by a bathochromic shift of the main absorption band and pronounced fluorescence quenching. The experimental results were corroborated by quantum mechanical calculations.
Graphyne-based
two-dimensional (2D) carbon allotropes feature extraordinary physical
properties; however, their synthesis as crystalline single-layered
materials has remained challenging. We report on the fabrication of
large-area organometallic Ag−bis-acetylide networks and their
structural and electronic properties on Ag(111) using low-temperature
scanning tunneling microscopy combined with density functional theory
(DFT) calculations. The metalated graphyne-based networks are robust
at room temperature and assembled in a bottom-up approach via surface-assisted dehalogenative homocoupling of terminal
alkynyl bromides. Large-area networks of several hundred nanometers
with topological defects at domain boundaries are obtained due to
the Ag–acetylide bonds’ reversible nature. The thermodynamically
controlled growth mechanism is explained through the direct observation
of intermediates, which differ on Ag(111) and Au(111). Scanning tunneling
spectroscopy resolved unoccupied states delocalized across the network.
The energy of these states can be shifted locally by the attachment
of a different number of Br atoms within the network. DFT revealed that free-standing metal−bis-acetylide networks
are semimetals with a linear band dispersion around several high-symmetry
points, which suggest the presence of Weyl points. These results demonstrate
that the organometallic Ag−bis-acetylide networks feature the
typical 2D material properties, which make them of great interest
for fundamental studies and electronic materials in devices.
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