| 1. |
- Baran, Jakub D., et al.
(författare)
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A Case of Unusually Large Density of States Changes For Physisorption - TetraPhenyl-Porphyrins on Cu(111)
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Conformational changes caused by surface adsorption can dramatically affect a molecule’s properties. The conformational flexibility of the porphyrin family of molecules has been exploited particularly well in a number of contexts, including prototypical molecular switches. Despite this level of study, however, the exact mechanisms underpinning conformational switching are often unclear. We show that the conformation of the tetra(4-bromophenyl) porphyrin (Br4TPP) on Cu(111) depends critically on the precise adsorption site of the molecule, and that, remarkably, large conformational changes are driven entirely by van der Waals (vdW) interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, low temperature single molecule manipulation, dispersion-corrected density functional theory (DFT) and molecular dynamics (MD) simulations shows that van der Waals forces dominate the adsorption of TPP molecules, causing significant distortions of the molecular architecture so that the porphyrin can adopt one of two low energy conformations. In addition, scanning probe manipulation has been used to translate and switch the Br4TPP molecule between conformations via an intermediary, ‘hybrid’ structure. We have used the generalized gradient approximation (GGA) parameterization by Perdew—Burke—Ernzerhof (PBE), and the sparse-matter optBP86b-vdW20 (vdW-DFT) exchange and correlation functional to account for the missing dispersion forces. In order to check for the presence of chemical bonding we have analyzed the molecule-surface complexes using electron localization function (ELF) and Bader charges. We find that vdW-forces alone are capable of causing large shifts in the molecular density of states, despite the complete absence of chemical interactions.
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| 2. |
- Boström, Hanna L. B., et al.
(författare)
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How Reproducible is the Synthesis of Zr-Porphyrin Metal-Organic Frameworks? An Interlaboratory Study
- 2024
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Ingår i: Advanced Materials. - 0935-9648 .- 1521-4095. ; 36:15
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Tidskriftsartikel (refereegranskat)abstract
- Metal-organic frameworks (MOFs) are a rapidly growing class of materials that offer great promise in various applications. However, the synthesis remains challenging: for example, a range of crystal structures can often be accessed from the same building blocks, which complicates the phase selectivity. Likewise, the high sensitivity to slight changes in synthesis conditions may cause reproducibility issues. This is crucial, as it hampers the research and commercialization of affected MOFs. Here, it presents the first-ever interlaboratory study of the synthetic reproducibility of two Zr-porphyrin MOFs, PCN-222 and PCN-224, to investigate the scope of this problem. For PCN-222, only one sample out of ten was phase pure and of the correct symmetry, while for PCN-224, three are phase pure, although none of these show the spatial linker order characteristic of PCN-224. Instead, these samples resemble dPCN-224 (disordered PCN-224), which has recently been reported. The variability in thermal behavior, defect content, and surface area of the synthesised samples are also studied. The results have important ramifications for field of metal-organic frameworks and their crystallization, by highlighting the synthetic challenges associated with a multi-variable synthesis space and flat energy landscapes characteristic of MOFs. It performed an interlaboratory study of the synthesis of the metal-organic frameworks (MOFs) PCN-222 and PCN-224. Ten participants independently synthesized the two MOFs and the products are analyzed, primarily by X-ray diffraction. The success rates are low (one-three samples corresponding to a pure sample of the correct phase), thus highlighting the problems with irreproducibility in MOF synthesis. image
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| 3. |
- Jarvis, Samuel P., et al.
(författare)
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Measuring the mechanical properties of molecular conformers
- 2015
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules
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| 4. |
- Jarvis, Samuel P., et al.
(författare)
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Physisorption Controls the Conformation and Density of States of an Adsorbed Porphyrin
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:50, s. 27982-27994
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Tidskriftsartikel (refereegranskat)abstract
- Conformational changes caused by adsorption can dramatically affect a molecule's properties. Despite extensive study, however, the exact mechanisms underpinning conformational switching are often unclear. Here we show that the conformation of a prototypical flexible molecule, the free-base tetra(4-bromophenyl) porphyrin, adsorbed on Cu(111), depends critically on its precise adsorption site and that, remarkably, large conformational changes are dominated by van der Waals interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, single-molecule manipulation, DFT with dispersion density functional theory, and molecular dynamics simulations show that van der Waals forces drive significant distortions of the molecular architecture so that the porphyrin can adopt one of two low-energy conformations. We find that adsorption driven by van der Waals forces alone is capable of causing large shifts in the molecular density of states, despite the apparent absence of chemical interactions. These findings highlight the essential role that van der Waals forces play in determining key molecular properties.
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| 5. |
- Yang, Sihai, et al.
(författare)
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Pore with gate : modulating hydrogen storage in metal-organic framework materials via cation exchange
- 2011
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 151, s. 19-36
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Tidskriftsartikel (refereegranskat)abstract
- A range of anionic metal-organic framework (MOF) materials has been prepared by combination of In(III) with tetracarboxylate isophthalate-based ligands. These materials incorporate organic cations, either H(2)ppz(2+) (ppz = piperazine) or Me(2)NH(2)(+), that are hydrogen bonded to the pore wall. These cations act as a gate controlling entry of N(2) and H(2) gas into and out of the porous host. Thus, hysteretic adsorption/desorption for N(2) and H(2) is observed in these systems, reflecting the role of the bulky hydrogen bonded organic cations in controlling the kinetic trapping of substrates. Post-synthetic cation exchange with Li(+) leads to removal of the organic cation and the formation of the corresponding Li(+) salts. Replacement of the organic cation with smaller Li(+) leads to an increase in internal surface area and pore volume of the framework material, and in some cases to an increase in the isosteric heat of adsorption of H(2) at zero coverage, as predicted by theoretical modelling. The structures, characterisation and analysis of these charged porous materials as storage portals for H(2) are discussed. Inelastic neutron scattering experiments confirm interaction of H(2) with the carboxylate groups of the isophthalate ligands bound to In(III) centres.
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