| 1. |
- Fritton, Massimo, et al.
(författare)
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The Role of Kinetics versus Thermodynamics in Surface-Assisted Ullmann Coupling on Gold and Silver Surfaces
- 2019
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 141:12, s. 4824-4832
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Tidskriftsartikel (refereegranskat)abstract
- Surface-assisted Ullmann coupling is the workhorse of on-surface synthesis. Despite its obvious relevance, many fundamental and mechanistic aspects remain elusive. To shed light on individual reaction steps and their progression with temperature, temperature-programmed X-ray photoelectron spectroscopy (TP-XPS) experiments are performed for a prototypical model system. The activation of the coupling by initial dehalogenation is tracked by monitoring Br 3d core levels, whereas the C 1s signature is used to follow the emergence of metastable organometallic intermediates and their conversion to the final covalent products upon heating in real time. The employed 1,3,5-tris(4-bromophenyl)benzene precursor is comparatively studied on Ag(111) versus Au(111), whereby intermolecular bonds and network topologies are additionally characterized by scanning tunneling microscopy (STM). Besides the well-comprehended differences in activation temperatures for debromination, the thermal progression shows marked differences between the two surfaces. Debromination proceeds rapidly on Ag(111), but is relatively gradual on Au(111). While on Ag(111) debromination is well explained by first-order reaction kinetics, thermodynamics prevail on Au(111), underpinned by a close agreement between experimentally deduced and density functional theory (DFT) calculated reaction enthalpies. Thermodynamically controlled debromination on Au(111) over a large temperature range implies an unexpectedly long lifetime of surface-stabilized radicals prior to covalent coupling, as corroborated by TP-XPS of C is core levels. These insights are anticipated to play an important role regarding our ability to rationally synthesize atomically precise low-dimensional covalent nanostructures on surfaces.
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| 2. |
- Grossmann, Lukas, et al.
(författare)
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Steering Self-Assembly of Three-Dimensional Iptycenes on Au(111) by Tuning Molecule-Surface Interactions
- 2022
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Ingår i: Angewandte Chemie International Edition. - : Wiley-V C H Verlag GMBH. - 1433-7851 .- 1521-3773. ; 61:25
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembly of three-dimensional molecules is scarcely studied on surfaces. Their modes of adsorption can exhibit far greater variability compared to (nearly) planar molecules that adsorb mostly flat on surfaces. This additional degree of freedom can have decisive consequences for the expression of intermolecular binding motifs, hence the formation of supramolecular structures. The determining molecule-surface interactions can be widely tuned, thereby providing a new powerful lever for crystal engineering in two dimensions. Here, we study the self-assembly of triptycene derivatives with anthracene blades on Au(111) by Scanning Tunneling Microscopy, Near Edge X-ray Absorption Fine Structure and Density Functional Theory. The impact of molecule-surface interactions was experimentally tested by comparing pristine with iodine-passivated Au(111) surfaces. Thereby, we observed a fundamental change of the adsorption mode that triggered self-assembly of an entirely different structure.
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| 3. |
- Rastgoo Lahrood, Atena, et al.
(författare)
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1,3-Diiodobenzene on Cu(111) - an exceptional case of on-surface Ullmann coupling
- 2015
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Ingår i: Chemical Communications. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 51:68, s. 13301-13304
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Tidskriftsartikel (refereegranskat)abstract
- Ullmann coupling of 1,3-diiodobenzene is studied on Cu(111) surfaces in ultra-high vacuum (UHV). In situ Scanning Tunneling Microscopy (STM) at room temperature revealed an unexpected ordered arrangement of highly uniform reaction products adsorbed atop a closed iodine monolayer.
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| 4. |
- Rastgoo-Lahrood, Atena, et al.
(författare)
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Post-Synthetic Decoupling of On-Surface-Synthesized Covalent Nanostructures from Ag(111)
- 2016
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 55:27, s. 7650-7654
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Tidskriftsartikel (refereegranskat)abstract
- The on-surface synthesis of covalent organic nanosheets driven by reactive metal surfaces leads to strongly adsorbed organic nanostructures, which conceals their intrinsic properties. Hence, reducing the electronic coupling between the organic networks and commonly used metal surfaces is an important step towards characterization of the true material. We demonstrate that post-synthetic exposure to iodine vapor leads to the intercalation of an iodine monolayer between covalent polyphenylene networks and Ag(111) surfaces. The experimentally observed changes from surface-bound to detached nanosheets are reproduced by DFT simulations. These findings suggest that the intercalation of iodine provides a material that shows geometric and electronic properties substantially closer to those of the freestanding network.
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