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

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{\deg}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.Comment: 9 pages, 6 figure

Investigation of Ultrathin Layers of Bis(phthalocyaninato)lutetium(III) on Graphite

We present a comprehensive study of the adsorption of bis­(phthalocyaninato)­lutetium­(III) (LuPc₂) on highly oriented pyrolytic graphite(0001) (HOPG). The growth and self-assembly of the molecular layers as well as the electronic structure has been investigated systematically using scanning tunneling microscopy and scanning tunneling spectroscopy combined with density functional theory (DFT) calculations and molecular mechanics simulations. We reveal that the adsorption of LuPc₂ leads to the formation of a square-like close-packed structure on the almost inert surface of HOPG, which is corroborated by simulations. Moreover, we observed a parallel orientation of the LuPc₂ molecules in the first monolayer, whereas in subsequent layers an increasing tilt out of the surface plane was found. Tip–sample distance-dependent tunneling spectroscopy measurements allowed us to detect a shift in the energy positions of the peaks assigned to the lowest unoccupied molecular orbital toward the Fermi energy with decreasing tip–sample separation