On-Surface Bottom-Up Synthesis of Azine Derivatives Displaying Strong Acceptor Behavior

On-surface synthesis of metal-organic frameworks: the critical role of the reaction conditions

Two different metal-organic frameworks with either a honeycomb or Kagome structure were grown on Cu(111) using para-aminophenol molecules and native surface adatoms. Although both frameworks are made up from the same chemical species, they are structurally different emphasizing the critical role being played by the reaction conditions during their growth. This work highlights the importance of the balance between thermodynamics and kinetics in the final structure of surface-supported metal-organic networks.

On-Surface Thermal Stability of a Graphenic Structure Incorporating a Tropone Moiety

On-surface synthesis, complementary to wet chemistry, has been demonstrated to be a valid approach for the synthesis of tailored graphenic nanostructures with atomic precision. Among the different existing strategies used to tune the optoelectronic and magnetic properties of these nanostructures, the introduction of non-hexagonal rings inducing out-of-plane distortions is a promising pathway that has been scarcely explored on surfaces. Here, we demonstrate that non-hexagonal rings, in the form of tropone (cycloheptatrienone) moieties, are thermally transformed into phenyl or cyclopentadienone moieties upon an unprecedented surface-mediated retro–Buchner-type reaction involving a decarbonylation or an intramolecular rearrangement of the CO unit, respectively.

Polymerization of silanes through dehydrogenative Si-Si bond formation on metal surfaces

Element-element double bonds of group 14 elements can be formed in solution, but generally only by applying harsh reductive conditions using sterically highly shielded tetryl halides as precursors. The two-dimensional confinement in surface-assisted polymerization represents a valuable alternative to access such reactive compounds, as it allows shielding of the labile entities without requiring bulky residues and catalytic activation of the reactive groups. Here, we demonstrate Si-Si bond formation in on-surface chemistry. Polymerization upon multiple Si-H bond dissociation and subsequent Si-Si bond formation was achieved on Au(111) and Cu(111) surfaces by using two different monomers, each containing two silicon functional groups (CH₃SiH₂ or SiH₃) attached to an aromatic backbone, leading to polymeric disilenes that interact with the surface. A combination of experimental and theoretical studies corroborates the formation of covalent Si-Si bonds between the long, highly ordered polymer chains with high diastereoselectivity. The reactive Si=Si bonds formally generated via double dehydrogenative coupling are stabilized via covalent Si-surface interaction.

Azo bond formation on metal surfaces

The formation of azo compounds via redox cross‐coupling of nitroarenes and arylamines, challenging in solution phase chemistry, is achieved by on‐surface chemistry. Reaction products are analyzed with a cryogenic scanning tunneling microscope (STM) and X‐ray photoelectron spectroscopy (XPS). By using well‐designed precursors containing both an amino and a nitro functionality, azo polymers are prepared on surface via highly efficient nitro‐amino cross‐coupling. Experiments conducted on other substrates and surface orientations reveal that the metal surface has a significant effect on the reaction efficiency. The reaction was further found to proceed from partially oxidized/reduced precursors in dimerization reactions, shedding light on the mechanism that was studied by DFT calculations.

Copper-assisted oxidation of catechols into quinone derivatives

Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.

An antioxidant catechol transforms following intramolecular redox reactions into highly reactive oxygen species, a semiquinone and a quinone, on copper.

On-Surface Driven Formal Michael Addition Produces m-Polyaniline Oligomers on Pt(111)

On-surface synthesis is emerging as a highly rational bottom-up methodology for the synthesis of molecular structures that are unattainable or complex to obtain by wet chemistry. Here, oligomers of meta-polyaniline, a known ferromagnetic polymer, were synthesized from para-aminophenol building-blocks via an unexpected and highly specific on-surface formal 1,4 Michael-type addition at the meta position, driven by the reduction of the aminophenol molecule. We rationalize this dehydrogenation and coupling reaction mechanism with a combination of in situ scanning tunneling and non-contact atomic force microscopies, high-resolution synchrotron-based X-ray photoemission spectroscopy and first-principles calculations. This study demonstrates the capability of surfaces to selectively modify local molecular conditions to redirect well-established synthetic routes, such as Michael coupling, towards the rational synthesis of new covalent nanostructures.

Role of the metal surface on the room temperature activation of the alcohol and amino groups of p-aminophenol

We present a comparative study of the room-temperature adsorption of p-aminophenol (p-AP) molecules on three metal surfaces, namely Cu(110), Cu(111) and Pt(111). We show that the chemical nature and the structural symmetry of the substrate control the activation of the terminal molecular groups, which result in different arrangements of the interfacial molecular layer. To this aim, we have used in-situ STM images combined with synchrotron radiation high resolution XPS and NEXAFS spectra, and the results were simulated by DFT calculations. On copper, the interaction between the molecules and the surface is weaker on the (111) surface crystal plane than on the (110) one, favouring molecular diffusion and leading to larger ordered domains. We demonstrate that the p-AP molecule undergoes spontaneous dehydrogenation of the alcohol group to form phenoxy species on all the studied surfaces, however, this process is not complete on the less reactive surface, Cu(111). The Pt(111) surface exhibits stronger molecule-surface interaction, inducing a short-range ordered molecular arrangement that increases overtime. In addition, on the highly reactive Pt(111) surface other chemical processes are evidenced, such as the dehydrogenation of the amine group.

Differential pulse voltammetric determination of the carcinogenic diamine 4,4'-oxydianiline by electrochemical preconcentration on a MoS2 based sensor

An electrochemical sensor for the carcinogen 4,4'-oxydianiline (Oxy) is described. The method is based on the ability of MoS₂ nanosheets to preconcentrate Oxy. A glassy carbon electrode (GCE) was covered, by drop-casting, with MoS₂ nanosheets that were obtained by exfoliation. X-Ray photoemission spectroscopy indicates that Oxy accumulates on the MoS₂ nanosheets through an electropolymerization process similar to that reported for aniline. Both electrochemical impedance spectroscopy and atomic force microscopy were used to characterize the electrode surface at the different stages of device fabrication. Employing the current measured at +0.27 V vs. Ag/AgCl after Oxy adsorption, the modified GCE enables the voltammetric detection of Oxy at 80 nM levels with relative errors and relative standard deviations of <8.3 and <5.6%, respectively, at all the concentrations studied. The method was applied to the selective determination of Oxy in spiked river water samples. Very good selectivity and recoveries of around 95% in average are found. Graphical abstractSchematic representation of 4,4-oxydianiline electrochemical polymerization and preconcentration onto molybdenum disulfide nanosheets for the diamine determination in river waters.

Boosting Rechargeable Batteries R&D by Multiscale Modeling: Myth or Reality?

This review addresses concepts, approaches, tools, and outcomes of multiscale modeling used to design and optimize the current and next generation rechargeable battery cells. Different kinds of multiscale models are discussed and demystified with a particular emphasis on methodological aspects. The outcome is compared both to results of other modeling strategies as well as to the vast pool of experimental data available. Finally, the main challenges remaining and future developments are discussed.

On-Surface Hydrogen-Induced Covalent Coupling of Polycyclic Aromatic Hydrocarbons via a Superhydrogenated Intermediate

The activation, hydrogenation, and covalent coupling of polycyclic aromatic hydrocarbons (PAHs) are processes of great importance in fields like chemistry, energy, biology, or health, among others. So far, they are based on the use of catalysts which drive and increase the efficiency of the thermally- or light-induced reaction. Here, we report on the catalyst-free covalent coupling of nonfunctionalized PAHs adsorbed on a relatively inert surface in the presence of atomic hydrogen. The underlying mechanism has been characterized by high-resolution scanning tunnelling microscopy and rationalized by density functional theory calculations. It is based on the formation of intermediate radical-like species upon hydrogen-induced molecular superhydrogenation which favors the covalent binding of PAHs in a thermally activated process, resulting in large coupled molecular nanostructures. The mechanism proposed in this work opens a door toward the direct formation of covalent, PAH-based, bottom-up synthesized nanoarchitectures on technologically relevant inert surfaces.