Structural Transformation of Surface‐Confined Porphyrin Networks by Addition of Co Atoms

Abstract

The self‐assembly of a nickel‐porphyrin derivative (Ni‐DPPyP) containing two pyridyl coordinating sites and two pentyl chains at trans meso positions was studied with scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) on Au(111). Deposition of Ni‐DPPyP onto Au(111) gave rise to a close‐packed network for coverages smaller or equal to one monolayer as revealed by STM and LEED. The molecular arrangement of this two‐dimensional network is stabilized via hydrogen bonds formed between the pyridyl's nitrogen and hydrogen atoms from the pyrrole groups of neighboring molecules. Subsequent deposition of cobalt atoms onto the close‐packed network and post‐deposition annealing at 423 K led to the formation of a Co‐coordinated hexagonal porous network. As confirmed by XPS measurements, the porous network is stabilized by metal‐ligand interactions between one cobalt atom and three pyridyl ligands, each pyridyl ligand coming from a different Ni‐DPPyP molecule.

Simple lattice model of surface-confined metal–organic networks consisting of linear nitrogen-bearing molecules and transition metals

“…These observations are in qualitative agreement with the published experimental and theoretical data. 4,16,[24][25][26]29,31,32 The often-observed absence of metal-organic structures with reduced metal coordination at a high tendency of the metal to coordinate a larger number of molecules can be associated with the narrow range of partial pressures and temperatures in which these phases appear.…”

“…This question has been answered in terms of the ability to form the coordination bond at different angles relative to the axis of the molecule in recent studies by D. Nieckarz et al [19][20][21][22] Another key factor in the self-assembly of metal-organic structures is the type of coordinating metal center, which determines its electronic structure and, therefore, a preferred coordination number. Using the same porphyrin derivatives as an example above, it was shown that iron, 23 cobalt 24 and nickel 25 tend to coordinate a larger number of molecules than copper. 26,27 This results in self-assembly of denser metalorganic structures.…”

Structure and Stability of Metalloporphyrin Networks on Au(111)

“…We run calculations for free-standing SAMs of the S and P conformers of FeTPyP with structures involving various numbers of molecules per unit cell, similar to those reported in the literature for this one or similar molecules. ,− Because our calculations indicate that the isolated P conformer is only 20 meV less stable than the S conformer, it is important to investigate whether the intermolecular interactions in the SAM might make up for this little energy difference, favoring a conglomerate of P conformers. We consider a structure of the free-standing SAM, inspired by the CoTPP/Au(111) and Ni–DPPyP/Au(111) structures, − with just one molecule per (square) unit cell (hereafter termed 1 × 1­(X), with X = S, P), and the molecular axis containing two opposing pyrrole rings rotated by ∼30° with respect with respect to the horizontal lattice vector defining the unit cell (see Figure a,b). We also do simulations for a configuration similar to the recently discovered FeTPyP/Au(111) arrangement with two conformers per (rectangular) unit cell (see Figure S1).…”

Structural Influence on Exciton Migration and Singlet Oxygen Photosensitization in Porphyrinic Metal–Organic Coordination Networks

“…The node is generally a polymetallic zero-dimensional (0D)- or one-dimensional (1D) secondary building unit (SBU). In contrast, metal–organic coordination networks (MOCNs) are a subgroup of MOFs, where the node consists of a single metal atom, for which porphyrin-based ligands turn out to be ideal building blocks. − This versatile linker benefits from intense absorption bands in the visible region that allows porphyrin-based MOFs to perform well in fields such as photo-induced eradication of pollutants and toxins in water, photosensitization of singlet oxygen ( 1 O 2 ) for antibacterial and fungicidal purposes (in solution or in contact with air), photocatalytic transformation of organic molecules, and cancer therapy . Concurrently, porphyrin-based MOCNs also exhibit rich visible-light-driven properties such as degradation of organic molecules and pollutants, − organic synthesis, , generation of solar fuels, , and even solar cells. − These photocatalytic and photosensitizing behaviors are profoundly influenced by the morphology of the solid ,, and are also known to affect the nonlinear optical properties of solid samples. − For instance, a direct link between excitation energy migration and upconversion processes was recently established …”

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A hexagonal three-dimensional (3D) metal−organic coordination network (MOCN) [(ZnTPyP)•0.75 DMSO] n (3D Helix) and a one-dimensional (1D) coordination polymer [(ZnTPyP)•DMF] n (1D Ladder) (ZnTPyP = 5,10,15,porphyrinatozinc(II)) are prepared and their photophysical properties are investigated to assess their ability to promote efficient exciton energy migration through singlet−singlet annihilation processes and to photosensitize singlet oxygen ( 1 O 2(g) ). The presence and absence of annihilation in 3D Helix and 1D Ladder, respectively, are indicative of their ability to efficiently promote exciton migration.

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