Bottom Up Fabrication of a Metal Supported Oxo Metal Porphyrin

International audienceIn situ preparation of oxotitanium tetraphenylporphyrin (TiO-TPP) on Ag(111) under ultra-high vacuum conditions was achieved in a multistep procedure starting from adsorbed free-base tetraphenylporphyrin (2H-TPP). The final product as well as the intermediate titanium tetraphenylporphyrin (Ti-TPP) was characterized by a suite of surface-sensitive spectroscopic tools combined with scanning tunnelling microscopy and density functional theory (DFT), and compared against the parent 2H-TPP species. Facile oxidation of Ti-TPP with molecular oxygen was observed at 300 K, with X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) from the Ti 2p core levels supporting a change in the oxidation state from Ti 2+ to Ti 4+ . N K-edge and Ti L-edge NEXAFS suggest that the tetrapyrrole macrocycle conformation is modified upon binding to oxygen, in agreement with DFT calculations that predict a marked change of the local environment of the Ti centres upon oxygen attachment. O K-edge NEXAFS and O 1s energy-scanned photoelectron diffraction from the resulting TiO-TPP monolayer provide strong evidence for the presence of a titanium−oxygen double bond, with the latter technique yielding a bond length of 1.56 ± 0.02 Å. The majority of adsorbed TiO-TPP species have the oxo group pointing away from the surface rather than toward it, and thus the oxygen atom can potentially interact with external species. Both the highly reactive, intermediate Ti-TPP species and the final product TiO-TPP are of great interest for catalytic applications

X ray Spectroscopy of Thin Film Free Base Corroles A Combined Theoretical and Experimental Characterization

Corrole compounds attract increasing interest due to their potential to stabilize high-valent metal states. X-ray spectroscopy is a powerful tool for the investigation and development of functional interfaces. For corrolic species, however, the required reference data are missing. Here, we employ a multitechnique X-ray investigation of thin films of the prototypical free-base 5,10,15-tris­(pentafluorophenyl)­corrole (3H-TpFPC) grown on the Ag(111) surface under ultrahigh vacuum conditions. Ultrapure corrole multilayer samples are prepared and characterized by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In parallel, the X-ray fingerprints are simulated using the continued-fraction approach within density functional theory (DFT) for extended, (quasi-)­periodic molecular structures. An excellent agreement between experimental and theoretical spectra enables a thorough interpretation of the detailed spectral features and proves an accurate description of the free-base corrole electronic structure within the present DFT approach. The present study provides X-ray spectroscopic references for all relevant core-level regions and absorption edges of intact molecular species and, thus, represents an ideal starting point for the comprehensive understanding of the complex chemistry of corroles in the adsorbed state toward the development of related functional interfaces

On Surface Site Selective Cyclization of Corrole Radicals

Radical cyclization is among the most powerful and versatile reactions for constructing mono- and polycyclic systems, but has, to date, remained unexplored in the context of on-surface synthesis. We report the controlled on-surface synthesis of stable corrole radicals on Ag(111) <i>via</i> site-specific dehydrogenation of a pyrrole N–H bond in the 5,10,15-tris­(pentafluoro-phenyl)-corrole triggered by annealing at 330 K under ultrahigh-vacuum conditions. We reveal a thermally induced regioselective cyclization reaction mediated by a radical cascade and resolve the reaction mechanism of the pertaining cyclodefluorination reaction at the single-molecule level. <i>Via</i> intramolecularly resolved probing of the radical-related Kondo signature, we achieve real space visualization of the distribution of the unpaired electron density over specific sites within the corrole radical. Annealing to 550 K initiates intermolecular coupling reactions, producing an extended π-conjugated corrole system