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.

The controlled and reversible interconversion between the free-base and the doubly dehydrogenated form of a 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin molecule in an ordered array is demonstrated. This is achieved through voltage pulses by hydrogen transfer between the center of the porphyrin and the tip of a scanning tunneling microscope (STM). The local dehydrogenation leads to significant shifts in the energetic positions of the molecular orbitals. Density functional theory (DFT) calculations corroborate our conclusions and allow to gain more insight into the different energy level alignment before and after dehydrogenation. Due to the different conductance at a given voltage a clear distinction of both molecular species is possible, which also enables the application as a single-molecular switch.

The organic/metal interface formed upon adsorption of cobalt(II) phthalocyanine (CoPc) molecules on a flat Ag(111) single crystal was investigated using a combination of scanning tunneling microscopy (STM) and photoemission spectroscopy (PES). A flat-lying molecular adsorption with the π conjugated phthalocyanine ligand parallel to the substrate was found to lead to an effective molecule-substrate coupling which governs a template-guided molecular growth. A voltage polarity dependence at the cobalt ion site was emphasized and correlated with the Co 2p core level spectra evolution which sustains an interface-confined reduction effect of the cobalt oxidation state. The formation of interface dipoles was observed via monitoring the changes in the work function (WF) upon deposition. The observations are discussed on the basis of a site-dependent donation/backdonation charge transfer at the molecule-substrate interface.

The second part of the previous study (Toader, M. J. Phys. Chem. C 2010, 114 (8), 3537-3543) is presented in this work where the electronic properties at the interface between an ultrathin layer of cobalt(II) hexadecafluoro-phthalocyanine (F 16 CoPc) and a noble metal Ag (110) single crystal, are investigated by means of scanning tunneling microscopy (STM) and spectroscopy (STS). The tunneling voltage polarity dependent STM image reflects a tunneling process mediated by the cobalt ion resulting from the overlapping of the Co d z 2 orbital with the metal surface states. The voltage polarity dependence is discussed based on a charge transfer at the interface, well sustained by the adsorption-induced gap states detectable in the normalized differential conductivity (NDC) spectra. Density functional theory (DFT) calculations are employed for the entire family of symmetrically substituted cobalt phthalocyanines (CoPc, F 4 CoPc, F 8 CoPc, and F 16 CoPc) in order to elucidate the influence of the fluorine atoms on the energy levels as well as on the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap evolution. Tip-sample distancedependent NDC spectra denote a pinning of the energy levels as a result of the strong molecule-substrate interaction. The experimentally estimated level positions and gap value are compared with the DFT calculated ones in order to determine the energy level alignment at the organic/metal interface, responsible for the observed degeneracy lifting of the LUMO as well as its energy shift toward the Fermi level.

We report that metal-free phthalocyanine (H 2 Pc) molecules with a central cavity are able to incorporate Ag atoms from an Ag(110) surface thus creating silver-phthalocyanine (AgPc). The reaction was investigated by means of scanning tunneling microscopy (STM) under ultrahigh vacuum, and the metalation of H 2 Pc at the interface was confirmed with X-ray photoelectron spectroscopy. Three different kinds of molecules were found on the surface that are assigned to H 2 Pc, the corresponding dehydrogenated molecules (Pc) and AgPc. The relative amounts of Pc and AgPc increase with increasing annealing temperature. We suggest that the reaction with Ag atoms from the steps of the surface occurs favorably only for already dehydrogenated molecules; thus, the metalation of H 2 Pc is likely limited by the heat-induced dehydrogenation. Density functional theory simulations of the reaction path are presented to corroborate this hypothesis.

The formation of hydrogen-bonded organic nano-structures and the role of the substrate lattice thereby were investigated by scanning tunneling microscopy. The self-organization of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin (H 2 THPP) molecules leads to two molecular arrangements on Au(111). One of these is characterized by pair-wise hydrogen bonding between hydroxyl groups and a low packing density which enables a rotation of individual molecules in the structure. A different interaction with stronger chain-like hydrogen bonding and additional interactions of phenyl groups was observed for the second structure. The influence of the substrate on the epitaxial behavior is demonstrated by the adsorption of H 2 THPP on the highly anisotropic Ag(110) substrate. There, several balances between the occupation of favorable adsorption positions and the number of hydrogen bonds per molecule were found. The molecules form molecular chains on Ag(110) and also assemble into two-dimensional periodic arrangements of differently sized close-packed blocks similar to the second type of supramolecular ordering found on Au(111). Dispersion corrected Density Functional Theory calculations were applied to understand the adsorption and complex epitaxy of these molecules. It is shown that the azimuthal orientation of the saddle-shape deformed molecule plays an important role not only for the intermolecular but also for the molecule-substrate interaction.

We present a comprehensive study of the adsorption of bis(phthalocyaninato)lutetium(III) (LuPc 2 ) 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 tunnelling microscopy and scanning tunnelling spectroscopy combined with density functional theory (DFT) calculations and molecular mechanics simulations. We reveal that the adsorption of LuPc 2 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 LuPc 2 molecules in the first monolayer, whereas in subsequent layers an increasing tilt out of the surface plane was found. Tip−sample distance-dependent tunnelling 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.

We have investigated the Pb/ Si͑111͒ mosaic phases of the surface with 1 / 6 monolayer Pb coverage at room temperature by means of scanning tunneling microscopy and spectroscopy and first-principles calculations. The dependence of the topographic height and electronic structure of Pb adatoms on the number of surrounding Si and Pb adatoms has been identified.