Surface-confined 2D polymerization of a brominated copper-tetraphenylporphyrin on Au(111)

Abstract

A coupling-limited approach for the Ullmann reaction-like on-surface synthesis of a two-dimensional covalent organic network starting from a halogenated metallo-porphyrin is demonstrated. Copper-octabromo-tetraphenylporphyrin molecules can diffuse and self-assemble when adsorbed on the inert Au(111) surface. Splitting-off of bromine atoms bonded at the macrocyclic core of the porphyrin starts at room temperature after the deposition and is monitored by X-ray photoelectron spectroscopy for different annealing steps. Direct coupling between the reactive carbon sites of the molecules is, however, hindered by the molecular shape. This leads initially to an ordered non-covalently interconnected supramolecular structure. Further heating to 300 °C and an additional hydrogen dissociation step is required to link the molecular macrocycles via a phenyl group and form large ordered polymeric networks. This approach leads to a close-packed covalently bonded network of overall good quality. The structures are characterized using scanning tunneling microscopy. Different kinds of lattice defects and, furthermore, the impact of polymerization on the HOMO-LUMO gap are discussed. Density functional theory calculations corroborate the interpretations and give further insight into the adsorption of the debrominated molecule on the surface and the geometry and coupling reaction of the polymeric structure.

Surface chemistry of porphyrins and phthalocyanines

“…Due to sterical hindrance, the reaction did not result in C-C bonds between the β-positions of the porphyrin cores. Instead, C-C bonds were formed between the β-positions and C atoms of the phenyl rings after annealing to 573 K, indicating that also partial dehydrogenation of the phenyl rings occurred [489]. Note that C-C bond formation on the basis of surface-assisted dehalogenation of aromatic bromo-or iodocompounds (also referred to as Ullmann coupling) has also been studied with numerous non-porphyrinic compounds [485][486][487][488].…”

Gram‐Scale Bottom‐Up Synthesis of Macrographene

“…In our study C1 is observed at 284.5 eV and C2 at 285.6 eV and similar values were reported previously . Further, going from CAP to MG the binding energy increases from 284.3 eV to 284.5 eV, which confirms the formation of large carbon networks …”

“…The CAP was subjected to Scholl oxidation in 2:1 AlCl 3 ‐NaCl melt at 165 °C for 6 h. The reaction mixture was quenched with water and worked up to get MG in good yields (see supporting information (SI) for details of synthesis). We have applied a variety of techniques (FTIR, UV‐Vis, XPS, Raman, XRD, TEM and AFM) for characterization of the product, and the data obtained were compared with literature to confirm our assignment of the product as graphene sheets.…”

Nanocrystalline MoO3/Polymerized Dibromo‐EDOT as Hybrid Nanocomposite: Efficient Hole Transport Material for Solid‐State Dye‐Sensitized Solar Cells

“…Four major binding energy peaks were detected at approximately 71, 233, 284, and 533 eV, which were attributed to the Br 3d, Mo 3d, C 1s, and O 1s core levels, respectively. A high‐resolution Br 3d XPS spectrum (Figure b) shows peaks at 68.5, 69.7, and 70.5 eV, which represent covalent bonding (C−Br 3d 3/2 , 56.8%), ionic bonding (C−Br + −C 3d 5/2 , 6.5%), and covalent bonding (C−Br 3d 5/2 , 37.7%), respectively . The existence of ionic bonds could be an important feature for enhancing the electroactivity because these bonds play a vital role as electron donors or acceptors in charge transfer between carbon atoms.…”

“…The data clearly show that the series resistance of the devices increases continuously with increasing MoO 3 concentration. The reason is the insulating nature of MoO 3 , which tends to reduce the device efficiency . However, the device with a hybrid HTM having a MoO 3 concentration of 0.2 wt% shows the best efficiency because of the small MoO 3 concentration.…”