63 results on '"L., Floreano"'
Search Results
2. The electronic properties of three popular high spin complexes [TM(acac)
- Author
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S, Carlotto, L, Floreano, A, Cossaro, M, Dominguez, M, Rancan, M, Sambi, and M, Casarin
- Abstract
The occupied and unoccupied electronic structures of three high spin TM(acac)
- Published
- 2017
3. Engineering 2D spin networks by on-surface encapsulation of azafullerene radicals in nanotemplates.
- Author
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Kladnik G, Schio L, Bavdek G, Tanuma Y, van Midden Mavrič M, Zupanič E, Anézo B, Sideri IK, Tagmatarchis N, Volkmann J, Wegner HA, Goldoni A, Ewels CP, Morgante A, Floreano L, Arčon D, and Cvetko D
- Abstract
We present an efficient strategy for on-surface engineering of organic metal-free supramolecular complexes with long-term spin protection. By vacuum deposition of azafullerene (C
59 N• ) monomers on a pre-deposited template layer of [10]cycloparaphenylene ([10]CPP) nanohoops on Au(111) surface we exploit the molecular shape matching between the C59 N• and [10]CPP for the azafullerene encapsulation with nanohoops in a guest-host complexation geometry. C59 N• ⊂[10]CPP supramolecular complexes self-assemble into an extended two-dimensional hexagonal lattice yielding a high density network of stable spin-1/2 radicals. We find compelling evidence for electronic coupling between the guest C59 N• and the host [10]CPP in supramolecular species. At the same time, [10]CPP effectively protects the radical state of encapsulated azafullerenes against dimerization and inhibits C59 N• coupling to the Au substrate. Azafullerene encapsulation by nanohoops represents a viable realization of molecular spin protection while simultaneously demonstrating exceptional self-assembling properties by which large-scale 2D architectures of molecular spins can be realized., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)- Published
- 2025
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4. Band Structure Engineering in 2D Metal-Organic Frameworks.
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Mearini S, Baranowski D, Brandstetter D, Windischbacher A, Cojocariu I, Gargiani P, Valvidares M, Schio L, Floreano L, Puschnig P, Feyer V, and Schneider CM
- Abstract
The design of 2D metal-organic frameworks (2D MOFs) takes advantage of the combination of the diverse electronic properties of simple organic ligands with different transition metal (TM) centers. The strong directional nature of the coordinative bonds is the basis for the structural stability and the periodic arrangement of the TM cores in these architectures. Here, direct and clear evidence that 2D MOFs exhibit intriguing energy-dispersive electronic bands with a hybrid character and distinct magnetic properties in the metal cores, resulting from the interactions between the TM electronic levels and the organic ligand π-molecular orbitals, is reported. Importantly, a method to effectively tune both the electronic structure of 2D MOFs and the magnetic properties of the metal cores by exploiting the electronic structure of distinct TMs is presented. Consequently, the ionization potential characteristic of selected TMs, particularly the relative energy position and symmetry of the 3d states, can be used to strategically engineer bands within specific metal-organic frameworks. These findings not only provide a rationale for band structure engineering in 2D MOFs but also offer promising opportunities for advanced material design., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)
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- 2024
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5. Oxygen-Promoted on-Surface Synthesis of Polyboroxine Molecules.
- Author
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Toffoli D, Turco E, Stredansky M, Costantini R, Dell'Angela M, Floreano L, Goldoni A, Morgante A, Kladnik G, Cvetko D, de Oteyza DG, Colazzo L, Mohammed MSG, Sala A, Comelli G, Africh C, Fronzoni G, Balducci G, Stener M, Ustunel H, and Cossaro A
- Abstract
We present a protocol for the on-surface synthesis of polyboroxine molecules derived from boroxine molecules precursors. This process is promoted by oxygen species present on the Au(111) surface: oxygen atoms facilitate the detachment of naphthalene units of trinaphthyl-boroxine molecules and bridge two unsaturated boroxine centers to form a boroxine-O-boroxine chemical motif. X-ray spectroscopic characterization shows that, as the synthesis process proceeds, it progressively tunes the electronic properties of the interface, thus providing a promising route to control the electron level alignment., (© 2024 Wiley-VCH GmbH.)
- Published
- 2024
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6. Stabilization versus competing de-metalation, trans-metalation and (cyclo)-dehydrogenation of Pd porphyrins at a copper surface.
- Author
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Baronio S, Bassotti M, Armillotta F, Frampton E, Vinogradov NA, Schio L, Floreano L, Verdini A, and Vesselli E
- Abstract
Metal-porphyrins are studied intensively due their potential applications, deriving from the variety of electronic and chemical properties, tunable by selecting metal centers and functional groups. Metalation, de- and trans-metalation processes are fundamental in this sense to investigate both the synthesis and the stability of these molecular building blocks. More specifically, Pd coordination in tetrapyrroles revealed to be potentially interesting in the fields of cancer therapy, drug delivery and light harvesting. Thus, we focused on the stability of palladium tetraphenyl porphyrins (PdTPPs) on a copper surface by means of combined spectroscopy and microscopy approaches. We find that PdTPPs undergo coverage-dependent trans-metalation accompanied by steric rearrangements already at room temperature, and fully trans-metalate to CuTPPs upon mild annealing. Side reactions such as (cyclo)-dehydrogenation and structural reorganization affect the molecular layer, with Pd-Cu alloying and segregation occurring at higher temperature. Instead, oxygen passivation of the Cu support prevents the metal-involving reactions, thus preserving the layer and increasing the chemical and temperature stability of the Pd porphyrins.
- Published
- 2024
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7. Emergence of Band Structure in a Two-Dimensional Metal-Organic Framework upon Hierarchical Self-Assembly.
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Baranowski D, Thaler M, Brandstetter D, Windischbacher A, Cojocariu I, Mearini S, Chesnyak V, Schio L, Floreano L, Gutiérrez Bolaños C, Puschnig P, Patera LL, Feyer V, and Schneider CM
- Abstract
Two-dimensional metal-organic frameworks (2D-MOFs) represent a category of atomically thin materials that combine the structural tunability of molecular systems with the crystalline structure characteristic of solids. The strong bonding between the organic linkers and transition metal centers is expected to result in delocalized electronic states. However, it remains largely unknown how the band structure in 2D-MOFs emerges through the coupling of electronic states in the building blocks. Here, we demonstrate the on-surface synthesis of a 2D-MOF exhibiting prominent π-conjugation. Through a combined experimental and theoretical approach, we provide direct evidence of band structure formation upon hierarchical self-assembly, going from metal-organic complexes to a conjugated two-dimensional framework. Additionally, we identify the robustly dispersive nature of the emerging hybrid states, irrespective of the metallic support type, highlighting the tunability of the band structure through charge transfer from the substrate. Our findings encourage the exploration of band-structure engineering in 2D-MOFs for potential applications in electronics and photonics.
- Published
- 2024
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8. Seeding the vertical growth of laterally coherent coordination polymers on the rutile-TiO 2 (110) surface.
- Author
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Schio L, Bavdek G, Grazioli C, Obersnù C, Cossaro A, Goldoni A, Calloni A, Bossi A, Bussetti G, Orbelli Biroli A, Vittadini A, and Floreano L
- Abstract
Coordination polymers may be synthesized by linear bridging ligands to metal ions with conventional chemistry methods ( e.g. in solution). Such complexes can be hardly brought onto a substrate with the chemical, spatial and geometrical homogeneity required for device integration. Instead, we follow an in situ synthesis approach, where the anchoring points are provided by a monolayer of metal(II)-tetraphenylporphyrin (M-TPP, M = Cu, Zn, Co) grown in vacuum on the rutile-TiO
2 (110) surface. We probed the metal affinity to axial coordination by further deposition of symmetric dipyridyl-naphthalenediimide (DPNDI). By NEXAFS linear polarization dichroism, we show that DPNDI stands up on Zn- and Co-TPP thanks to axial coordination, whereas it lies down on the substrate for Cu-TPP. Calculations for a model pyridine ligand predict strong binding to Zn and Co cations, whose interaction with the O anions underneath is disrupted by surface trans effect. The weaker interactions between pyridine and Cu-TPP are then overcome by the strong attraction between TiO2 and DPNDI. The binding sites exposed by the homeotropic alignment of the ditopic DPNDI ligand on Zn- and Co-TPP are the foundations to grow coordination polymers preserving the lateral coherence of the basal layer.- Published
- 2024
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9. Mechanistic insights into on-surface reactions from isothermal temperature-programmed X-ray photoelectron spectroscopy.
- Author
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Grossmann L, Hocke M, Galeotti G, Contini G, Floreano L, Cossaro A, Ghosh A, Schmittel M, Rosen J, Heckl WM, Björk J, and Lackinger M
- Abstract
On-surface synthesis often proceeds under kinetic control due to the irreversibility of key reaction steps, rendering kinetic studies pivotal. The accurate quantification of reaction rates also bears potential for unveiling reaction mechanisms. Temperature-Programmed X-ray Photoelectron Spectroscopy (TP-XPS) has emerged as an analytical tool for kinetic studies with splendid chemical and sufficient temporal resolution. Here, we demonstrate that the common linear temperature ramps lead to fitting ambiguities. Moreover, pinpointing the reaction order remains intricate, although this key parameter entails information on atomistic mechanisms. Yet, TP-XPS experiments with a stepped temperature profile comprised of isothermal segments facilitate the direct quantification of rate constants from fitting time courses. Thereby, rate constants are obtained for a series of temperatures, which allows independent extraction of both activation energies and pre-exponentials from Arrhenius plots. By using two analogous doubly versus triply brominated aromatic model compounds, we found that their debromination on Ag(111) is best modeled by second-order kinetics and thus proceeds via the involvement of a second, non-obvious reactant. Accordingly, we propose that debromination is activated by surface supplied Ag adatoms. This hypothesis is supported by Density Functional Theory (DFT) calculations. We foresee auspicious prospects for this TP-XPS variant for further exploring the kinetics and mechanisms of on-surface reactions.
- Published
- 2024
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10. Enhancing Haloarene Coupling Reaction Efficiency on an Oxide Surface by Metal Atom Addition.
- Author
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Abadia M, Piquero-Zulaica I, Brede J, Verdini A, Floreano L, V Barth J, Lobo-Checa J, Corso M, and Rogero C
- Abstract
The bottom-up synthesis of carbon-based nanomaterials directly on semiconductor surfaces allows for the decoupling of their electronic and magnetic properties from the substrates. However, the typically reduced reactivity of such nonmetallic surfaces adversely affects the course of these reactions. Here, we achieve a high polymerization yield of halogenated polyphenyl molecular building blocks on the semiconducting TiO
2 (110) surface via concomitant surface decoration with cobalt atoms, which catalyze the Ullmann coupling reaction. Specifically, cobalt atoms trigger the debromination of 4,4″-dibromo- p -terphenyl molecules on TiO2 (110) and mediate the formation of an intermediate organometallic phase already at room temperature (RT). As the debromination temperature is drastically reduced, homocoupling and polymerization readily proceed, preventing presursor desorption from the substrate and entailing a drastic increase of the poly- para -phenylene polymerization yield. The general efficacy of this mechanism is shown with an iodinated terphenyl derivative, which exhibits similar dehalogenation and reaction yield.- Published
- 2024
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11. Noncontact Layer Stabilization of Azafullerene Radicals: Route toward High-Spin-Density Surfaces.
- Author
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Tanuma Y, Kladnik G, Schio L, van Midden Mavrič M, Anézo B, Zupanič E, Bavdek G, Canton-Vitoria R, Floreano L, Tagmatarchis N, Wegner HA, Morgante A, Ewels CP, Cvetko D, and Arčon D
- Abstract
We deposit azafullerene C
59 N• radicals in a vacuum on the Au(111) surface for layer thicknesses between 0.35 and 2.1 monolayers (ML). The layers are characterized using X-ray photoemission (XPS) and X-ray absorption fine structure (NEXAFS) spectroscopy, low-temperature scanning tunneling microscopy (STM), and by density functional calculations (DFT). The singly unoccupied C59 N orbital (SUMO) has been identified in the N 1s NEXAFS/XPS spectra of C59 N layers as a spectroscopic fingerprint of the molecular radical state. At low molecular coverages (up to 1 ML), films of monomeric C59 N are stabilized with the nonbonded carbon orbital neighboring the nitrogen oriented toward the Au substrate, whereas in-plane intermolecular coupling into diamagnetic (C59 N)2 dimers takes over toward the completion of the second layer. By following the C59 N• SUMO peak intensity with increasing molecular coverage, we identify an intermediate high-spin-density phase between 1 and 2 ML, where uncoupled C59 N• monomers in the second layer with pronounced radical character are formed. We argue that the C59 N• radical stabilization of this supramonolayer phase of monomers is achieved by suppressed coupling to the substrate. This results from molecular isolation on top of the passivating azafullerene contact layer, which can be explored for molecular radical state stabilization and positioning on solid substrates.- Published
- 2023
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12. Charge Transfer and Orbital Reconstruction at an Organic-Oxide Interface.
- Author
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Caputo M, Studniarek M, Guedes EB, Schio L, Baiseitov K, Daffé N, Bachellier N, Chikina A, Di Santo G, Verdini A, Goldoni A, Muntwiler M, Piamonteze C, Floreano L, Radovic M, and Dreiser J
- Abstract
The two-dimensional electron system (2DES) located at the surface of strontium titanate (STO) and at several other STO-based interfaces has been an established platform for the study of novel physical phenomena since its discovery. Here we report how the interfacing of STO and tetracyanoquinodimethane (TCNQ) results in a charge transfer that depletes the number of free carriers at the STO surface, with a strong impact on its electronic structure. Our study paves the way for efficient tuning of the electronic properties, which promises novel applications in the framework of oxide/organic-based electronics.
- Published
- 2023
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13. Self-Assembled Monolayers of N-Heterocyclic Olefins on Au(111).
- Author
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Berg I, Schio L, Reitz J, Molteni E, Lahav L, Bolaños CG, Goldoni A, Grazioli C, Fratesi G, Hansmann MM, Floreano L, and Gross E
- Abstract
Self-assembled monolayers (SAMs) of N-heterocyclic olefins (NHOs) have been prepared on Au(111) and their thermal stability, adsorption geometry, and molecular order were characterized by X-ray photoelectron spectroscopy, polarized X-ray absorption spectroscopy, scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The strong σ-bond character of NHO anchoring to Au induced high geometrical flexibility that enabled a flat-lying adsorption geometry via coordination to a gold adatom. The flat-lying adsorption geometry was utilized to further increase the surface interaction of the NHO monolayer by backbone functionalization with methyl groups that induced high thermal stability and a large impact on work-function values, which outperformed that of N-heterocyclic carbenes. STM measurements, supported by DFT modeling, identified that the NHOs were self-assembled in dimers, trimers, and tetramers constructed of two, three, and four complexes of NHO-Au-adatom. This self-assembly pattern was correlated to strong NHO-Au interactions and steric hindrance between adsorbates, demonstrating the crucial influence of the carbon-metal σ-bond on monolayer properties., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)
- Published
- 2023
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14. A local point of view of the Cu(100) → NiTPP charge transfer at the NiTPP/Cu(100) interface.
- Author
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Carlotto S, Verdini A, Zamborlini G, Cojocariu I, Feyer V, Floreano L, and Casarin M
- Abstract
A precise understanding, at the molecular level, of the massive substrate → adsorbate charge transfer at the NiTPP/Cu(100) interface has been gained through the application of elementary symmetry arguments to the structural determination of the NiTPP adsorption site by photoelectron diffraction (PED) measurements and Amsterdam density functional calculations of the free D
4h NiTPP electronic structure. In particular, the PED analysis precisely determines that, among the diverse NiTPP chemisorption sites herein considered (fourfold hollow, atop, and bridge), the fourfold hollow one is the most favorable, with the Ni atom located at 1.93 Å from the surface and at an internuclear distance of 2.66 Å from the nearest-neighbors of the substrate. The use of elementary symmetry considerations enabled us to provide a convincing modeling of the NiTPP-Cu(100) anchoring configuration and an atomistic view of the previously revealed interfacial charge transfer through the unambiguous identification of the adsorbate π* and σ* low-lying virtual orbitals, of the substrate surface atoms, and of the linear combinations of the Cu 4s atomic orbitals involved in the substrate → adsorbate charge transfer. In addition, the same considerations revealed that the experimentally reported Ni(II) → Ni(I) reduction at the interface corresponds to the fingerprint of the chemisorption site of the NiTPP on Cu(100).- Published
- 2023
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15. Surface-Mediated Spin Locking and Thermal Unlocking in a 2D Molecular Array.
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Cojocariu I, Windischbacher A, Baranowski D, Jugovac M, Ferreira RCC, Doležal J, Švec M, Zamalloa-Serrano JM, Tormen M, Schio L, Floreano L, Dreiser J, Puschnig P, Feyer V, and Schneider CM
- Abstract
Molecule-based functional devices may take advantage of surface-mediated spin state bistability. Whereas different spin states in conventional spin crossover complexes are only accessible at temperatures well below room temperature, and the lifetimes of the high-spin state are relatively short, a different behavior exhibited by prototypical nickel phthalocyanine is shown here. Direct interaction of the organometallic complex with a copper metal electrode mediates the coexistence of a high spin and a low spin state within the 2D molecular array. The spin state bistability is extremely non-volatile, since no external stimuli are required to preserve it. It originates from the surface-induced axial displacement of the functional nickel cores, which generates two stable local minima. Spin state unlocking and the full conversion to the low spin state are only possible by a high temperature stimulus. This spin state transition is accompanied by distinct changes in the molecular electronic structure that might facilitate the state readout at room temperature, as evidenced by valence spectroscopy. The non-volatility of the high spin state up to elevated temperatures and the controllable spin bistability render the system extremely intriguing for applications in molecule-based information storage devices., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)
- Published
- 2023
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16. Two-Dimensional Self-Assembly Driven by Intermolecular Hydrogen Bonding in Benzodi-7-azaindole Molecules on Au(111).
- Author
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Abad J, Martínez JI, Gómez P, Más-Montoya M, Rodríguez L, Cossaro A, Verdini A, Floreano L, Martín-Gago JA, Curiel D, and Méndez J
- Abstract
The control of molecular structures at the nanoscale plays a critical role in the development of materials and applications. The adsorption of a polyheteroaromatic molecule with hydrogen bond donor and acceptor sites integrated in the conjugated structure itself, namely, benzodi-7-azaindole ( BDAI ), has been studied on Au(111). Intermolecular hydrogen bonding determines the formation of highly organized linear structures where surface chirality, resulting from the 2D confinement of the centrosymmetric molecules, is observed. Moreover, the structural features of the BDAI molecule lead to the formation of two differentiated arrangements with extended brick-wall and herringbone packing. A comprehensive experimental study that combines scanning tunneling microscopy, high-resolution X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and density functional theory theoretical calculations has been performed to fully characterize the 2D hydrogen-bonded domains and the on-surface thermal stability of the physisorbed material., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)
- Published
- 2023
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17. On-surface synthesis of metal-organic frameworks: the critical role of the reaction conditions.
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Ruiz Del Árbol N, Sánchez-Sánchez C, Martínez JI, Rodríguez L, Serrate D, Verdini A, Floreano L, Jacobson P, Grill L, Martín-Gago JA, and López MF
- Abstract
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.
- Published
- 2023
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18. Conservation of Nickel Ion Single-Active Site Character in a Bottom-Up Constructed π-Conjugated Molecular Network.
- Author
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Baranowski D, Cojocariu I, Sala A, Africh C, Comelli G, Schio L, Tormen M, Floreano L, Feyer V, and Schneider CM
- Abstract
On-surface chemistry holds the potential for ultimate miniaturization of functional devices. Porphyrins are promising building-blocks in exploring advanced nanoarchitecture concepts. More stable molecular materials of practical interest with improved charge transfer properties can be achieved by covalently interconnecting molecular units. On-surface synthesis allows to construct extended covalent nanostructures at interfaces not conventionally available. Here, we address the synthesis and properties of covalent molecular network composed of interconnected constituents derived from halogenated nickel tetraphenylporphyrin on Au(111). We report that the π-extended two-dimensional material exhibits dispersive electronic features. Concomitantly, the functional Ni cores retain the same single-active site character of their single-molecule counterparts. This opens new pathways when exploiting the high robustness of transition metal cores provided by bottom-up constructed covalent nanomeshes., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)
- Published
- 2022
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19. The influence of adsorption geometry on the reduction affinity of nitroaromatics on Au(111).
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Berg I, Eisenberg H, Dery S, Shahar T, Cossaro A, Verdini A, Floreano L, Stein T, and Gross E
- Abstract
Chemoselective reduction of nitro groups in multifunctional nitroaromatics is a challenging catalytic process with high interest due to the importance of the resulting anilines for the chemical industry. Molecular-level understanding of the ways by which adsorption geometry of nitroaromatics influence their affinity toward nitro reduction will enable the development of highly selective reactions. Herein, taking advantage of the well-ordered self-assembly of para - and ortho -nitrothiophenol ( p -NTP and o -NTP, respectively) monolayers on Au(111), we examined the correlation between adsorption geometry and nitro reduction affinity. The anchoring geometry of NTPs and their nitro reduction affinity were determined by conducting polarized X-ray absorption spectroscopy while the influence of NTPs' adsorption geometry on the interaction with the Au surface was analyzed by density functional theory (DFT) calculations. Exposure of surface anchored p -NTPs to reducing conditions led to their reorientation from a tilt angle of 52° to 25°, which enabled strong interactions between the π system of the molecules and the Au surface. Direct correlation was identified between the surface proximity of the nitro group, its parallel position to the surface and the resulting reduction yield. The asymmetric structure of o -NTP led to a tilted adsorption geometry in which the nitro group was rotated away from the plane of the aromatic ring and therefore was positioned parallel and in high proximity to the Au surface. This positioning led to surface-bonding that involved the oxygen atoms of o -NTP. The higher surface proximity and stronger surface interactions of the nitro group in o -NTP enabled nitro reduction already at 180 °C, while in p -NTP nitro reduction was achieved only at 230 °C, due to the longer distance between the NO
2 group and the Au surface that led to weaker adsorbate-surface interactions. Thus, parallel positioning of the nitro group and high surface proximity were found as essential descriptors for nitro reduction affinity in both p -NTP and o -NTP on the Au surface. These findings provide explicit guidelines for tuning the reactant and surface properties in order to control the reactant's adsorption geometry for selective nitro reduction in multifunctional nitroaromatics.- Published
- 2022
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20. π-Orbital mediated charge transfer channels in a monolayer Gr-NiPc heterointerface unveiled by soft X-ray electron spectroscopies and DFT calculations.
- Author
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Casotto A, Drera G, Perilli D, Freddi S, Pagliara S, Zanotti M, Schio L, Verdini A, Floreano L, Di Valentin C, and Sangaletti L
- Abstract
With the aim to identify charge transfer channels underlying device development and operation, X-Ray Photoelectron Spectroscopy (XPS), Near-Edge X-Ray Absorption Fine Structure (NEXAFS), and Resonant Photoelectron Spectroscopy (ResPES) have been employed to characterize a novel heterointerface obtained by the controlled evaporation of a Nickel Phthalocyanine (NiPc) monolayer on a single layer of Graphene (Gr) on SiC substrate. Indeed, the Gr-NiPc interface could be a promising candidate for different applications in the field of photonics, optoelectronics, and sensing, provided that clear information on the charge transfer mechanisms at the Gr-NiPc interface can be obtained. The analysis of the spectroscopic data has shown the effective functionalization and the horizontally-flat disposition of the NiPc complexes over the Gr layer. With this geometry, the main intermolecular interaction experienced by the NiPc species is the coupling with the Gr substrate, through π-symmetry orbitals, as revealed by the different behaviour of the valence band photoemission at resonance with the N K-edge and Ni L
3 -edge. These results have been supported by the analysis of density functional theory (DFT) calculations, that allowed for a rationalization of the experimental data, showing that charge transfer at the interface occurs from the doubly degenerate eg LUMO orbital, involving mainly N and C (pyrrole ring) pz states, to the holes in the p-doped graphene layer.- Published
- 2022
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21. Ordered assembly of non-planar vanadyl-tetraphenylporphyrins on ultra-thin iron oxide.
- Author
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Albani G, Schio L, Goto F, Calloni A, Orbelli Biroli A, Bossi A, Melone F, Achilli S, Fratesi G, Zucchetti C, Floreano L, and Bussetti G
- Abstract
Stabilizing ordered assemblies of molecules represents the first step towards the construction of molecular devices featuring hybrid (organic-inorganic) interfaces where molecules can be easily functionalized in view of specific applications. Molecular layers of planar metal-tetraphenylporphyrins (MTPP) grown on an ultrathin iron oxide [namely Fe(001)- p (1 × 1)O] show indeed a high degree of structural order. The generality of such a picture is tested by exploiting non-planar porphyrins, such as vanadyl-TPP (VOTPP). These molecules feature a VO
2+ ion in their center, with the O atom protruding out of the plane of the porphyrin ring. In this work, by employing diffraction, photoemission and X-ray absorption, we prove that non-planar VOTPP can nevertheless form a square and ordered superstructure, where porphyrin molecules lie flat with respect to the underlying substrate. Ab initio density functional theory simulations are used to elucidate the VO bond orientation with respect to the iron substrate.- Published
- 2022
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22. On surface chemical reactions of free-base and titanyl porphyrins with r-TiO 2 (110): a unified picture.
- Author
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Schio L, Forrer D, Casarin M, Goldoni A, Rogero C, Vittadini A, and Floreano L
- Abstract
In this Perspective we present a comprehensive study of the multiple reaction products of metal-free porphyrins (2H-Ps) in contact with the rutile TiO
2 (110) surface. In the absence of peripheral functionalization with specific linkers, the porphyrin adsorption is driven by the coordination of the two pyrrolic nitrogen atoms of the macrocycle to two consecutive oxygen atoms of the protruding Obr rows via hydrogen bonding. This chemical interaction favours the iminic nitrogen uptake of hydrogen from near surface layers at room temperature, thus yielding a stable acidic porphyrin (4H-P). In addition, a mild annealing (∼100 °C) triggers the incorporation of a Ti atom in the porphyrin macrocycle (self-metalation). We recently demonstrated that such a low temperature reaction is driven by a Lewis base iminic attack, which lowers the energy barriers for the outdiffusion of Ti interstitial atoms (Tiint ) [Kremer et al., Appl. Surf. Sci. , 2021, 564 , 150403]. In the monolayer (ML) range, the porphyrin adsorption site, corresponding to a TiO-TPP configuration, is extremely stable and tetraphenyl-porphyrins (TPPs) may even undergo conformational distortion (flattening) by partial cyclo-dehydrogenation, while remaining anchored to the O rows up to 450 °C [Lovat et al. , Nanoscale , 2017, 9 , 11694]. Here we show that, upon self-metalation, isolated molecules at low coverage may jump atop the rows of five-fold coordinated Ti atoms (Ti5f ). This configuration is associated with the formation of a new coordination complex, Ti-O-Ti5f , as determined by comparison with the deposition of pristine titanyl-porphyrin (TiO-TPP) molecules. The newly established Ti-O-Ti5f anchoring configuration is found to be stable also beyond the TPP flattening reaction. The anchoring of TiO-TPP to the Ti5f rows is, however, susceptible to the cross-talk between phenyls of adjacent molecules, which ultimately drives the TiO-TPP temperature evolution in the ML range along the same pathway followed by 2H-TPP.- Published
- 2022
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23. Disproportionation of Nitric Oxide at a Surface-Bound Nickel Porphyrinoid.
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Stredansky M, Moro S, Corva M, Sturmeit H, Mischke V, Janas D, Cojocariu I, Jugovac M, Cossaro A, Verdini A, Floreano L, Feng Z, Sala A, Comelli G, Windischbacher A, Puschnig P, Hohner C, Kettner M, Libuda J, Cinchetti M, Schneider CM, Feyer V, Vesselli E, and Zamborlini G
- Abstract
Uncommon metal oxidation states in porphyrinoid cofactors are responsible for the activity of many enzymes. The F
430 and P450nor co-factors, with their reduced NiI - and FeIII -containing tetrapyrrolic cores, are prototypical examples of biological systems involved in methane formation and in the reduction of nitric oxide, respectively. Herein, using a comprehensive range of experimental and theoretical methods, we raise evidence that nickel tetraphenyl porphyrins deposited in vacuo on a copper surface are reactive towards nitric oxide disproportionation at room temperature. The interpretation of the measurements is far from being straightforward due to the high reactivity of the different nitrogen oxides species (eventually present in the residual gas background) and of the possible reaction intermediates. The picture is detailed in order to disentangle the challenging complexity of the system, where even a small fraction of contamination can change the scenario., Competing Interests: The authors declare no conflict of interest., (© 2022 The Authors. Angewandte Chemie published by Wiley-VCH GmbH.)- Published
- 2022
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24. Adsorption of glutamic acid on clean and hydroxylated rutile TiO 2 (110): an XPS and NEXAFS investigation.
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Carraro G, Smerieri M, Passaglia S, Bracco G, Vattuone L, Rocca M, Cossaro A, Verdini A, Floreano L, and Savio L
- Subjects
- Adsorption, Photoelectron Spectroscopy, Surface Properties, Titanium, Glutamic Acid
- Abstract
Due to its biocompatibility, TiO
2 is a relevant material for the study of bio-interfaces. Its electronic and chemical properties are influenced by defects, which mainly consist of oxygen vacancies or adsorbed OH groups and which affect, consequently, also the interaction with biological molecules. Here we report on an x-ray photoemission spectroscopy and near edge adsorption fine structure study of glutamic acid (Glu) adsorption on the rutile TiO2 (110) surface, either clean or partially hydroxylated. We show that Glu anchors to the surface through a carboxylate group and that the final adsorption state is influenced by the presence of hydroxyl groups on the surface prior to Glu deposition. Indeed, molecules adsorb both in the anionic and in the zwitterionic form, the former species being favored on the hydroxylated substrate., (© 2022 IOP Publishing Ltd.)- Published
- 2022
- Full Text
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25. Clarifying the Adsorption of Triphenylamine on Au(111): Filling the HOMO-LUMO Gap.
- Author
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Zhang T, Svensson PHW, Brumboiu IE, Lanzilotto V, Grazioli C, Guarnaccio A, Johansson FOL, Beranová K, Coreno M, de Simone M, Floreano L, Cossaro A, Brena B, and Puglia C
- Abstract
In this article, we analyze the electronic structure modifications of triphenylamine (TPA), a well-known electron donor molecule widely used in photovoltaics and optoelectronics, upon deposition on Au(111) at a monolayer coverage. A detailed study was carried out by synchrotron radiation-based photoelectron spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, scanning tunneling microscopy (STM), and ab initio calculations. We detect a new feature in the pre-edge energy region of the N K-edge NEXAFS spectrum that extends over 3 eV, which we assign to transitions involving new electronic states. According to our calculations, upon adsorption, a number of new unoccupied electronic states fill the energy region between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the free TPA molecule and give rise to the new feature in the pre-edge region of the NEXAFS spectrum. This finding highlights the occurrence of a considerable modification of the electronic structure of TPA. The appearance of new states in the HOMO-LUMO gap of TPA when adsorbed on Au(111) has crucial implications for the design of molecular nanoelectronic devices based on similar donor systems., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)
- Published
- 2022
- Full Text
- View/download PDF
26. On-surface products from de-fluorination of C 60 F 48 on Ag(111): C 60 , C 60 F x and silver fluoride formation.
- Author
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Barrena E, Palacios-Rivera R, Babuji A, Schio L, Tormen M, Floreano L, and Ocal C
- Abstract
By employing diverse surface sensitive synchrotron radiation spectroscopies we demonstrate that the fluorine content of initial C
60 F48 deposited at room temperature on Ag(111) varies with molecular coverage. At the very early stages of deposition, C60 F48 fully de-fluorinates and transforms into C60 . Strong indications of silver fluoride formation are provided. The chemical footprint of fluorinated fullerenes emerges at relatively low molecular coverage indicating that the degree of fullerene de-fluorination decreases (from total to partial de-fluorination) as molecules are deposited. Full de-fluorination stops well before the substrate surface is completely covered by fullerenes. At the molecular level, the fluorine loss observed by spectroscopic techniques is supported by scanning tunneling microscopy imaging. Both molecules and metal surface are importantly involved in the process.- Published
- 2022
- Full Text
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27. The Magnetic Behaviour of CoTPP Supported on Coinage Metal Surfaces in the Presence of Small Molecules: A Molecular Cluster Study of the Surface trans -Effect.
- Author
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Carlotto S, Cojocariu I, Feyer V, Floreano L, and Casarin M
- Abstract
Density functional theory, combined with the molecular cluster model, has been used to investigate the surface trans -effect induced by the coordination of small molecules L (L = CO, NH
3 , NO, NO2 and O2 ) on the cobalt electronic structure of cobalt tetraphenylporphyrinato (CoTPP) surface-supported on coinage metal surfaces (Cu, Ag, and Au). Regardless of whether L has a closed- or an open-shell electronic structure, its coordination to Co takes out the direct interaction between Co and the substrate eventually present. The CO and NH3 bonding to CoTPP does not influence the Co local electronic structure, while the NO (NO2 and O2 ) coordination induces a Co reduction (oxidation), generating a 3d8 CoI (3d6 CoIII ) magnetically silent closed-shell species. Theoretical outcomes herein reported demonstrate that simple and computationally inexpensive models can be used not only to rationalize but also to predict the effects of the Co-L bonding on the magnetic behaviour of CoTPP chemisorbed on coinage metals. The same model may be straightforwardly extended to other transition metals or coordinated molecules.- Published
- 2022
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28. Room-Temperature On-Spin-Switching and Tuning in a Porphyrin-Based Multifunctional Interface.
- Author
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Sturmeit HM, Cojocariu I, Windischbacher A, Puschnig P, Piamonteze C, Jugovac M, Sala A, Africh C, Comelli G, Cossaro A, Verdini A, Floreano L, Stredansky M, Vesselli E, Hohner C, Kettner M, Libuda J, Schneider CM, Zamborlini G, Cinchetti M, and Feyer V
- Subjects
- Copper, Metals, Nickel, Temperature, Porphyrins
- Abstract
Molecular interfaces formed between metals and molecular compounds offer a great potential as building blocks for future opto-electronics and spintronics devices. Here, a combined theoretical and experimental spectro-microscopy approach is used to show that the charge transfer occurring at the interface between nickel tetraphenyl porphyrins and copper changes both spin and oxidation states of the Ni ion from [Ni(II), S = 0] to [Ni(I), S = 1/2]. The chemically active Ni(I), even in a buried multilayer system, can be functionalized with nitrogen dioxide, allowing a selective tuning of the electronic properties of the Ni center that is switched to a [Ni(II), S = 1] state. While Ni acts as a reversible spin switch, it is found that the electronic structure of the macrocycle backbone, where the frontier orbitals are mainly localized, remains unaffected. These findings pave the way for using the present porphyrin-based system as a platform for the realization of multifunctional devices where the magnetism and the optical/transport properties can be controlled simultaneously by independent stimuli., (© 2021 The Authors. Small published by Wiley-VCH GmbH.)
- Published
- 2021
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29. Orbital Mapping of Semiconducting Perylenes on Cu(111).
- Author
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Di Santo G, Miletić T, Schwendt M, Zhou Y, Kariuki BM, Harris KDM, Floreano L, Goldoni A, Puschnig P, Petaccia L, and Bonifazi D
- Abstract
Semiconducting O-doped polycyclic aromatic hydrocarbons constitute a class of molecules whose optoelectronic properties can be tailored by acting on the π-extension of the carbon-based frameworks and on the oxygen linkages. Although much is known about their photophysical and electrochemical properties in solution, their self-assembly interfacial behavior on solid substrates has remained unexplored so far. In this paper, we have focused our attention on the on-surface self-assembly of O-doped bi-perylene derivatives. Their ability to assemble in ordered networks on Cu(111) single-crystalline surfaces allowed a combination of structural, morphological, and spectroscopic studies. In particular, the exploitation of the orbital mapping methodology based on angle-resolved photoemission spectroscopy, with the support of scanning tunneling microscopy and low-energy electron diffraction, allowed the identification of both the electronic structure of the adsorbates and their geometric arrangement. Our multi-technique experimental investigation includes the structure determination from powder X-ray diffraction data for a specific compound and demonstrates that the electronic structure of such large molecular self-assembled networks can be studied using the reconstruction methods of molecular orbitals from photoemission data even in the presence of segregated chiral domains., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)
- Published
- 2021
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30. Identification of Topotactic Surface-Confined Ullmann-Polymerization.
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Dettmann D, Galeotti G, MacLean O, Tomellini M, Di Giovannantonio M, Lipton-Duffin J, Verdini A, Floreano L, Fagot-Revurat Y, Perepichka DF, Rosei F, and Contini G
- Abstract
On-surface Ullmann coupling is an established method for the synthesis of 1D and 2D organic structures. A key limitation to obtaining ordered polymers is the uncertainty in the final structure for coupling via random diffusion of reactants over the substrate, which leads to polymorphism and defects. Here, a topotactic polymerization on Cu(110) in a series of differently-halogenated para-phenylenes is identified, where the self-assembled organometallic (OM) reactants of diiodobenzene couple directly into a single, deterministic product, whereas the other precursors follow a diffusion driven reaction. The topotactic mechanism is the result of the structure of the iodine on Cu(110), which controls the orientation of the OM reactants and intermediates to be the same as the final polymer chains. Temperature-programmed X-ray photoelectron spectroscopy and kinetic modeling reflect the differences in the polymerization regimes, and the effects of the OM chain alignments and halogens are disentangled by Nudged Elastic Band calculations. It is found that the repulsion or attraction between chains and halogens drive the polymerization to be either diffusive or topotactic. These results provide detailed insights into on-surface reaction mechanisms and prove the possibility of harnessing topotactic reactions in surface-confined Ullmann polymerization., (© 2021 Wiley-VCH GmbH.)
- Published
- 2021
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31. Influence of N-Substituents on the Adsorption Geometry of OH-Functionalized Chiral N-Heterocyclic Carbenes.
- Author
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Dery S, Bellotti P, Ben-Tzvi T, Freitag M, Shahar T, Cossaro A, Verdini A, Floreano L, Glorius F, and Gross E
- Abstract
Adsorption of chiral molecules on heterogeneous catalysts is a simple approach for inducing an asymmetric environment to enable enantioselective reactivity. Although the concept of chiral induction is straightforward, its practical utilization is far from simple, and only a few examples toward the successful chiral induction by surface anchoring of asymmetric modifiers have been demonstrated so far. Elucidating the factors that lead to successful chiral induction is therefore a crucial step for understanding the mechanism by which chirality is transferred. Herein, we identify the adsorption geometry of OH-functionalized N-heterocyclic carbenes (NHCs), which are chemical analogues to chiral modifiers that successfully promoted α-arylation reactions once anchored on Pd nanoparticles. Polarized near-edge X-ray absorption fine structure (NEXAFS) measurements on Pd(111) revealed that NHCs that were associated with low enantioselectivity were characterized with a well-ordered structure, in which the imidazole ring was vertically positioned and the OH-functionalized side arms were flat-lying. OH-functionalized NHCs that were associated with high enantioselectivity revealed a disordered/flexible adsorption geometry, which potentially enabled better interaction between the OH group and the prochiral reactant.
- Published
- 2021
- Full Text
- View/download PDF
32. Deciphering Electron Interplay at the Fullerene/Sputtered TiO x Interface: A Barrier-Free Electron Extraction for Organic Solar Cells.
- Author
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Amelot D, Ahmadpour M, Ros Q, Cruguel H, Casaretto N, Cossaro A, Floreano L, Madsen M, and Witkowski N
- Abstract
Organic photovoltaics (OPVs) technology now offers power conversion efficiency (PCE) of over 18% and is one of the main emerging photovoltaic technologies. In such devices, titanium dioxide (TiO
x ) has been vastly used as an electron extraction layer, typically showing unwanted charge-extraction barriers and the need for light-soaking. In the present work, using advanced photoemission spectroscopies, we investigate the electronic interplay at the interface between low-temperature-sputtered TiOx and C70 acceptor fullerene molecules. We show that defect states in the band gap of TiOx are quenched by C70 while an interfacial state appears. This new interfacial state is expected to support the favorable energy band alignment observed, showing a perfect match of transport levels, and thus barrier-free extraction of charges, making low-temperature-sputtered TiOx a good candidate for the next generation of organic solar cells.- Published
- 2021
- Full Text
- View/download PDF
33. Insight into intramolecular chemical structure modifications by on-surface reaction using photoemission tomography.
- Author
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Cojocariu I, Feyersinger F, Puschnig P, Schio L, Floreano L, Feyer V, and Schneider CM
- Abstract
The sensitivity of photoemission tomography (PT) to directly probe single molecule on-surface intramolecular reactions will be shown here. PT application in the study of molecules possessing peripheral ligands and structural flexibility is tested on the temperature-induced dehydrogenation intramolecular reaction on Ag(100), leading from CoOEP to the final product CoTBP. Along with the ring-closure reaction, the electronic occupancy and energy level alignment of the frontier orbitals, as well as the oxidation state of the metal ion, are elucidated for both the CoOEP and CoTBP systems.
- Published
- 2021
- Full Text
- View/download PDF
34. Tailoring surface-supported water-melamine complexes by cooperative H-bonding interactions.
- Author
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Lanzilotto V, Grazioli C, Stredansky M, Zhang T, Schio L, Goldoni A, Floreano L, Motta A, Cossaro A, and Puglia C
- Abstract
The water-splitting photo-catalysis by carbon nitride heterocycles has been the subject of recent theoretical investigations, revealing a proton-coupled electron transfer (PCET) reaction from the H-bonded water molecule to the CN-heterocycle. In this context, a detailed characterization of the water-catalyst binding configuration becomes mandatory in order to validate and possibly improve the theoretical modeling. To this aim, we built a well-defined surface-supported water/catalyst interface by adsorbing water under ultra-high vacuum (UHV) conditions on a monolayer of melamine grown on the Cu(111) surface. By combining X-ray photoemission (XPS) and absorption (NEXAFS) spectroscopy we observed that melamine adsorbed onto copper is strongly tilted off the surface, with one amino group dangling to the vacuum side. The binding energy (BE) of the corresponding N 1s component is significantly higher compared to other N 1s contributions and displays a clear shift to lower BE as water is adsorbed. This finding along with density functional theory (DFT) results reveals that two adjacent melamine molecules concurrently work for stabilizing the H-bonded water-catalyst complex: one melamine acting as a H-donor via the amino-N (NH⋯OHH) and another one as a H-acceptor via the triazine-N (C[double bond, length as m-dash]N⋯HOH)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)
- Published
- 2021
- Full Text
- View/download PDF
35. Ferrous to Ferric Transition in Fe-Phthalocyanine Driven by NO 2 Exposure.
- Author
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Cojocariu I, Carlotto S, Sturmeit HM, Zamborlini G, Cinchetti M, Cossaro A, Verdini A, Floreano L, Jugovac M, Puschnig P, Piamonteze C, Casarin M, Feyer V, and Schneider CM
- Abstract
Due to its unique magnetic properties offered by the open-shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d-states of FePc and the sp-band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion. The Fe
II ion is stabilized in the low singlet spin state (S=0), leading to the complete quenching of the molecule magnetic moment. By exploiting the FePc/Cu(100) interface, we demonstrate that NO2 dissociation can be used to gradually change the magnetic properties of the iron ion, by trimming the gas dosage. For lower doses, the FePc film is decoupled from the copper substrate, restoring the gas phase triplet spin state (S=1). A higher dose induces the transition from ferrous to ferric phthalocyanine, in its intermediate spin state, with enhanced magnetic moment due to the interaction with the atomic ligands. Remarkably, in this way, three different spin configurations have been observed within the same metalorganic/metal interface by exposing it to different doses of NO2 at room temperature., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)- Published
- 2021
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- View/download PDF
36. Copper-assisted oxidation of catechols into quinone derivatives.
- Author
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Gómez-Herrero AC, Sánchez-Sánchez C, Chérioux F, Martínez JI, Abad J, Floreano L, Verdini A, Cossaro A, Mazaleyrat E, Guisset V, David P, Lisi S, Martín Gago JA, and Coraux J
- Abstract
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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)
- Published
- 2020
- Full Text
- View/download PDF
37. Role of the metal surface on the room temperature activation of the alcohol and amino groups of p-aminophenol.
- Author
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Del Árbol NR, Palacio I, Sánchez-Sánchez C, Otero-Irurueta G, Martínez JI, Rodríguez L, Serrate D, Cossaro A, Lacovig P, Lizzit S, Verdini A, Floreano L, Martín-Gago JA, and López MF
- Abstract
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.
- Published
- 2020
- Full Text
- View/download PDF
38. Keto-enol tautomerization drives the self-assembly of leucoquinizarin on Au(111).
- Author
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Costantini R, Colazzo L, Batini L, Stredansky M, Mohammed MSG, Achilli S, Floreano L, Fratesi G, de Oteyza DG, and Cossaro A
- Abstract
The self-assembly of leucoquinizarin molecules on Au(111) surfaces is shown to be characterized by the molecules mostly being in their keto-enolic tautomeric form, with evidence of their temporary switching to other tautomeric forms. This reveals a metastable chemistry of the assembled molecules, to be considered for their possible employment in the formation of more complex hetero-organic interfaces.
- Published
- 2020
- Full Text
- View/download PDF
39. Strong Metal-Adsorbate Interactions Increase the Reactivity and Decrease the Orientational Order of OH-Functionalized N-Heterocyclic Carbene Monolayers.
- Author
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Dery S, Berg I, Kim S, Cossaro A, Verdini A, Floreano L, Toste FD, and Gross E
- Abstract
Fundamental understanding of the correlation between the structure and reactivity of chemically addressable N-heterocyclic carbene (NHC) molecules on various surfaces is essential for the design of functional NHC-based self-assembled monolayers. In this work, we identified the ways by which the deposition of chemically addressable OH-NHCs on Au(111) or Pt(111) surfaces modified the anchoring geometry and chemical reactivity of surface-anchored NHCs. The properties of surface-anchored NHCs were probed by conducting X-ray photoelectron spectroscopy and polarized near-edge X-ray absorption fine structure measurements. While no preferred orientation was identified for OH-NHCs on Pt(111), the anchored molecules adopted a preferred flat-lying position on Au(111). Dehydrogenation and aromatization of the imidazoline ring along with partial hydroxyl oxidation were detected in OH-NHCs that were anchored on Au(111). The dehydrogenation and aromatization reactions were facilitated, along with partial decomposition, for OH-NHCs that were anchored on Pt(111). The spectroscopic results reveal that stronger metal-adsorbate interactions increase the reactivity of surface-anchored OH-NHCs while decreasing their molecular orientational order.
- Published
- 2020
- Full Text
- View/download PDF
40. Flexible NO 2 -Functionalized N-Heterocyclic Carbene Monolayers on Au (111) Surface.
- Author
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Dery S, Kim S, Tomaschun G, Haddad D, Cossaro A, Verdini A, Floreano L, Klüner T, Toste FD, and Gross E
- Abstract
The formation of flexible self-assembled monolayers (SAMs) in which an external trigger modifies the geometry of surface-anchored molecules is essential for the development of functional materials with tunable properties. In this work, it is demonstrated that NO
2 -functionalized N-heterocyclic carbene molecules (NHCs), which were anchored on Au (111) surface, change their orientation from tilted into flat-lying position following trigger-induced reduction of their nitro groups. DFT calculations identified that the energetic driving force for reorientation was the lower steric hindrance and stronger interactions between the chemically reduced NHCs and the Au surface. The trigger-induced changes in the NHCs' anchoring geometry and chemical functionality modified the work function and the hydrophobicity of the NHC-decorated Au surface, demonstrating the impact of a chemically tunable NHC-based SAM on the properties of the metal surface., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)- Published
- 2019
- Full Text
- View/download PDF
41. Flexible NO 2 -Functionalized N-Heterocyclic Carbene Monolayers on Au(111) Surface.
- Author
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Dery S, Kim S, Tomaschun G, Haddad D, Cossaro A, Verdini A, Floreano L, Klüner T, Toste FD, and Gross E
- Abstract
Invited for the cover of this issue are Elad Gross, F. Dean Toste, and co-workers at The Hebrew University and UC Berkeley. The image depicts the flexible anchoring geometry of addressable carbene molecules on Au surface, which upon exposure to reducing conditions changed their orientation from a standing into a flat-lying position. Read the full text of the article at 10.1002/chem.201903434., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)
- Published
- 2019
- Full Text
- View/download PDF
42. Magnetic properties of on-surface synthesized single-ion molecular magnets.
- Author
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Diller K, Singha A, Pivetta M, Wäckerlin C, Hellwig R, Verdini A, Cossaro A, Floreano L, Vélez-Fort E, Dreiser J, Rusponi S, and Brune H
- Abstract
We perform on-surface synthesis of single-ion molecular magnets on an Ag(111) surface and characterize their morphology, chemistry, and magnetism. The first molecule we synthesize is TbPc
2 to enable comparison with chemically synthesized and subsequently surface adsorbed species. We demonstrate the formation of TbPc2 with a yield close to 100% and show that on-surface synthesis leads to identical magnetic and morphological properties compared to the previously studied chemically synthesized species. Moreover, exposure of the surface adsorbed TbPc2 molecules to air does not modify their magnetic and morphological properties. To demonstrate the versatility of our approach, we synthesize novel Tb double deckers using tert -butyl-substituted phthalocyanine (tbu-2H-Pc). The Tb(tbu-Pc)2 molecules exhibit magnetic hysteresis and therefore are the first purely on-surface synthesized single ion magnet., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2019
- Full Text
- View/download PDF
43. Elucidating the Influence of Anchoring Geometry on the Reactivity of NO 2 -Functionalized N-Heterocyclic Carbene Monolayers.
- Author
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Dery S, Kim S, Tomaschun G, Berg I, Feferman D, Cossaro A, Verdini A, Floreano L, Klüner T, Toste FD, and Gross E
- Abstract
The development of chemically addressable N-heterocyclic carbene (NHC) based self-assembled monolayers (SAMs) requires in-depth understanding of the influence of NHC's anchoring geometry on its chemical functionality. Herein, it is demonstrated that the chemical reactivity of surface-anchored NO
2 -functionalized NHCs (NO2 -NHCs) can be tuned by modifying the distance between the functional group and the reactive surface, which is governed by the deposition technique. Liquid deposition of NO2 -NHCs on Pt(111) induced a SAM in which the NO2 -aryl groups were flat-lying on the surface. The high proximity between the NO2 groups and the Pt surface led to high reactivity, and 85% of the NO2 groups were reduced at room temperature. Lower reactivity was obtained with vapor-deposited NO2 -NHCs that assumed a preferred upright geometry. The separation between the NO2 groups in the vapor-deposited NO2 -NHCs and the reactive surface circumvented their surface-induced reduction, which was facilitated only after exposure to harsher reducing conditions.- Published
- 2019
- Full Text
- View/download PDF
44. On-surface trapping of alkali atoms by crown ethers in ultra high vacuum.
- Author
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Stredansky M, Turco E, Feng Z, Costantini R, Comelli G, Verdini A, Floreano L, Morgante A, Dri C, and Cossaro A
- Abstract
Crown ethers, assembled into a regular 2D array via a chemical guest-host recognition process, have been successfully employed to trap sodium atoms on a surface, under ultra-high vacuum conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)
- Published
- 2019
- Full Text
- View/download PDF
45. On-surface nickel porphyrin mimics the reactive center of an enzyme cofactor.
- Author
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Zamborlini G, Jugovac M, Cossaro A, Verdini A, Floreano L, Lüftner D, Puschnig P, Feyer V, and Schneider CM
- Subjects
- Adsorption, Catalysis, Coenzymes chemistry, Copper chemistry, Metalloporphyrins chemistry, Molecular Structure, Particle Size, Surface Properties, Coenzymes metabolism, Metalloporphyrins metabolism
- Abstract
Metal-containing enzyme cofactors achieve their unusual reactivity by stabilizing uncommon metal oxidation states with structurally complex ligands. In particular, the specific cofactor promoting both methanogenesis and anaerobic methane oxidation is a porphyrinoid chelated to a nickel(i) atom via a multi-step biosynthetic path, where nickel reduction is achieved through extensive molecular hydrogenation. Here, we demonstrate an alternative route to porphyrin reduction by charge transfer from a selected copper substrate to commercially available 5,10,15,20-tetraphenyl-porphyrin nickel(ii). X-ray absorption measurements at the Ni L3-edge unequivocally show that NiTPP species adsorbed on Cu(100) are stabilized in the highly reactive Ni(i) oxidation state by electron transfer to the molecular orbitals. Our approach highlights how some fundamental properties of synthetically inaccessible biological cofactors may be reproduced by hybridization of simple metalloporphyrins with metal surfaces, with implications towards novel approaches to heterogenous catalysis.
- Published
- 2018
- Full Text
- View/download PDF
46. On-Surface Bottom-Up Synthesis of Azine Derivatives Displaying Strong Acceptor Behavior.
- Author
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Ruiz Del Árbol N, Palacio I, Otero-Irurueta G, Martínez JI, de Andrés PL, Stetsovych O, Moro-Lagares M, Mutombo P, Svec M, Jelínek P, Cossaro A, Floreano L, Ellis GJ, López MF, and Martín-Gago JA
- Abstract
On-surface synthesis is an emerging approach to obtain, in a single step, precisely defined chemical species that cannot be obtained by other synthetic routes. The control of the electronic structure of organic/metal interfaces is crucial for defining the performance of many optoelectronic devices. A facile on-surface chemistry route has now been used to synthesize the strong electron-acceptor organic molecule quinoneazine directly on a Cu(110) surface, via thermally activated covalent coupling of para-aminophenol precursors. The mechanism is described using a combination of in situ surface characterization techniques and theoretical methods. Owing to a strong surface-molecule interaction, the quinoneazine molecule accommodates 1.2 electrons at its carbonyl ends, inducing an intramolecular charge redistribution and leading to partial conjugation of the rings, conferring azo-character at the nitrogen sites., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)
- Published
- 2018
- Full Text
- View/download PDF
47. Identifying site-dependent reactivity in oxidation reactions on single Pt particles.
- Author
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Dery S, Kim S, Haddad D, Cossaro A, Verdini A, Floreano L, Toste FD, and Gross E
- Abstract
Catalytic nanoparticles are heterogeneous in their nature and even within the simplest particle various surface sites exist and influence the catalytic reactivity. Thus, detailed chemical information at the nanoscale is essential for understanding how surface properties and reaction conditions direct the reactivity of different surface sites of catalytic nanoparticles. In this work, hydroxyl-functionalized N-heterocyclic carbene molecules (NHCs) were anchored to the surface of Pt particles and utilized as chemical markers to detect reactivity variations between different surface sites under liquid and gas phase oxidizing conditions. Differences in the chemical reactivity of surface-anchored NHCs were identified using synchrotron-radiation-based infrared nanospectroscopy with a spatial resolution of 20 nanometers. By conducting IR nanospectroscopy measurements, along with complementary spatially averaged IR and X-ray spectroscopy measurements, we identified that enhanced reactivity occurred on the particles' periphery under both gas and liquid phase oxidizing conditions. Under gas phase reaction conditions the NHCs' hydroxyl functional groups underwent preferential oxidization to the acid along the perimeter of the particle. Exposure of the sample to harsher, liquid phase oxidizing conditions induced modification of the NHCs, which was mostly identified at the particle's periphery. Analysis of X-ray absorption spectroscopy measurements revealed that exposure of the sample to oxidizing conditions induced aromatization of the NHCs, presumably due to oxidative dehydrogenation reaction, along with reorientation of the NHCs from perpendicular to parallel to the Pt surface. These results, based on single particle measurements, demonstrate the high reactivity of surface sites that are located at the nanoparticle's periphery and the influence of reaction conditions on site-dependent reactivity.
- Published
- 2018
- Full Text
- View/download PDF
48. On-surface synthesis of a 2D boroxine framework: a route to a novel 2D material?
- Author
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Stredansky M, Sala A, Fontanot T, Costantini R, Africh C, Comelli G, Floreano L, Morgante A, and Cossaro A
- Abstract
The synthesis and preliminary characterization of a boron-based 2D framework are presented. The peculiar electronic and morphological properties of this compound, together with its facile formation process, enable it to be used as a novel smart material for the design of electronic devices.
- Published
- 2018
- Full Text
- View/download PDF
49. Ubiquitous deprotonation of terephthalic acid in the self-assembled phases on Cu(100).
- Author
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Quiroga Argañaraz B, Cristina LJ, Rodríguez LM, Cossaro A, Verdini A, Floreano L, Fuhr JD, Gayone JE, and Ascolani H
- Abstract
We performed an exhaustive study of terephthalic acid (TPA) self-assembly on a Cu(100) surface, where first-layer molecules display two sequential phase transitions in the 200-400 K temperature range, corresponding to different stages of molecular deprotonation. We followed the chemical and structural changes by means of high-resolution X-ray photoelectron spectroscopy (XPS) and variable-temperature scanning tunneling microscopy (STM), which were interpreted on the basis of density functional theory (DFT) calculations and photoemission simulations. In order to reveal the spectroscopic contributions of the molecules in different states of deprotonation, we modified the substrate reactivity by deposition of a small amount of Sn, which hampers the deprotonation reaction. We found that the characteristic molecular ribbons of the TPA/Cu(100) α-phase at a low temperature contain a significant fraction of partially deprotonated molecules, in contrast to the expectation of a fully protonated phase, where the self-assembly was claimed to be simply driven by the intermolecular double hydrogen bonds [OHO]. On the basis of our simulations, we propose a model where the carboxylate groups of the partially deprotonated molecules form single hydrogen bonds with the carboxylic groups of the fully protonated molecules. Using real time XPS, we also monitored the kinetics of the deprotonation reaction. We show that the network of mixed single and double hydrogen bonds inhibits further deprotonation up to ∼270 K, whereas the isolated molecules display a much lower deprotonation barrier.
- Published
- 2018
- Full Text
- View/download PDF
50. The role of halogens in on-surface Ullmann polymerization.
- Author
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Galeotti G, Di Giovannantonio M, Lipton-Duffin J, Ebrahimi M, Tebi S, Verdini A, Floreano L, Fagot-Revurat Y, Perepichka DF, Rosei F, and Contini G
- Abstract
Ullmann coupling is the most common approach to form surface-confined one- and two-dimensional conjugated structures from haloaryl derivatives. The dimensions of the formed nanostructures can be controlled by the number and location of halogens within the molecular precursors. Our study illustrates that the type of halogen plays an essential role in the design, orientation, and extent of the surface-confined organometallic and polymeric nanostructures. We performed a comparative analysis of five 1,4-dihalobenzene molecules containing chlorine, bromine, and iodine on Cu(110) using scanning tunneling microscopy, fast-X-ray photoelectron and near edge X-ray absorption fine structure spectroscopies. Our experimental data identify different molecular structures, reaction temperatures and kinetics depending on the halogen type. Climbing image nudged elastic band simulations further clarify these observations by providing distinct diffusion paths for each halogen species. We show that in addition to the structure of the building blocks, the halogen type has a direct influence on the morphology of surface-confined polymeric structures based on Ullmann coupling.
- Published
- 2017
- Full Text
- View/download PDF
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