| 1. |
- Kepčija, Nenad, et al.
(författare)
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Steering On-Surface Self-Assembly of High-Quality Hydrocarbon Networks with Terminal Alkynes
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:8, s. 3987-3995
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Tidskriftsartikel (refereegranskat)abstract
- The two-dimensional (2D) self-assembly of 1,3,5-triethynyl-benzene (TEB) and de novo synthesized 1,3,5-tris-(4-ethynylphenyl)benzene (Ext-TEB) on Ag(111) was investigated by means of scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. Both 3-fold symmetric molecules form long-range ordered nanoporous networks featuring organizational chirality, mediated by novel, planar 6-fold cyclic binding motifs. The key interaction for the expression of the motifs is identified as C–H···π bonding. For Ext-TEB, an additional open-porous phase exists with the 3-fold motif. The nature of the underlying noncovalent bonding schemes is thoroughly analyzed by density functional theory (DFT) calculations including van der Waals corrections. The comparison of calculations focusing on isolated 2D molecular sheets and those including the substrate reveals the delicate balance between the attractive molecule–molecule interaction, mediated by both the terminal alkyne and the phenyl groups, and the molecule–substrate interaction responsible for the commensurability and the regularity of the networks. Comparison with bulk structures of similar molecules suggests that these strictly planar cyclic binding motifs appear only in 2D environments.
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| 2. |
- Salinas, Borja Cirera, et al.
(författare)
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Synthesis of Extended Graphdiyne Wires by Vicinal Surface Templating
- 2014
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 14:4, s. 1891-1897
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Tidskriftsartikel (refereegranskat)abstract
- Surface-assisted covalent synthesis currently evolves into an important approach for the fabrication of functional nanostructures at interfaces. Here, we employ scanning tunneling microscopy to investigate the homo-coupling reaction of linear, terminal alkyne-functionalized polyphenylene building-blocks on noble metal surfaces under ultra-high vacuum. On the flat Ag(111) surface thermal activation triggers a variety of side-reactions resulting in irregularly-branched polymeric networks. Upon alignment along the step-edges of the Ag(877) vicinal surface drastically improves the chemoselectivity of the linking process permitting the controlled synthesis of extended-graphdiyne wires with lengths reaching 30 nm. The ideal hydrocarbon scaffold is characterized by density functional theory as a 1D, direct band gap semiconductor material with both HOMO and LUMO-derived bands promisingly isolated within the electronic structure. The templating approach should be applicable to related organic precursors and different reaction schemes thus bears general promise for the engineering of novel low-dimensional carbon-based materials.
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| 3. |
- Zhang, Yi-Qi, et al.
(författare)
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Homo-coupling of terminal alkynes on a noble metal surface
- 2012
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The covalent linking of acetylenes presents an important route for the fabrication of novel carbon-based scaffolds and two-dimensional materials distinct from graphene. To date few attempts have been reported to implement this strategy at well-defined interfaces or monolayer templates. Here we demonstrate through real space direct visualization and manipulation in combination with X-ray photoelectron spectroscopy and density functional theory calculations the Ag surface-mediated terminal alkyne Csp−H bond activation and concomitant homo-coupling in a process formally reminiscent of the classical Glaser–Hay type reaction. The alkyne homo-coupling takes place on the Ag(111) noble metal surface in ultrahigh vacuum under soft conditions in the absence of conventionally used transition metal catalysts and with volatile H2 as the only by-product. With the employed multitopic ethynyl species, we demonstrate a hierarchic reaction pathway that affords discrete compounds or polymeric networks featuring a conjugated backbone. This presents a new approach towards on-surface covalent chemistry and the realization of two-dimensional carbon-rich or all-carbon polymers.
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