Tailoring functionalized nanostructures
at the atomic scale is
of importance in nanotechnology. We report on the controllable fabrication
of linear polyphenyl wires by direct C–H activation and C–C
coupling of para-sexiphenyl (p-6P)
on an anisotropic Au(110) surface. Because of the one-dimensional
spatial constraint at the surface, the equivalent C–H bonds
of p-6P molecules were differentiated with various
reaction probabilities. Consequently, linear polymerization of p-6P was achieved via C–C bonding at the meta-sites, with the kink formation every 6 phenylene units.
On the other hand, branched polymerization was efficiently suppressed.
Among such kinked polyphenyl wires, the trans conformation
is predominant, compared with the cis conformation.
Furthermore, exclusive C–C bond formation at the p-6P para-sites has been promoted by the neighboring
terphenyl radicals, which possess reactive para-sites,
resulting in the formation of straight para-polyphenyl
wires instead of kinked ones. Our study demonstrates that the surface
steric effect can be applied to guide the pathway of on-surface synthesis
toward desired covalently bonded nanostructures.
Lowering the oxygen content in biofuels is of vital importance, since high oxygen level content leads to low stability, low heat value, and corruption in engines. Here we report on the thermally activated decarboxylation of fatty acids, raw materials for biofuel production, on an anisotropic Au(110) surface. Due to the one-dimensional (1D) geometrical constraint of the surface reconstruction, linear fatty acid molecules (C 30 H 60 O 2 ) are decarboxylated and polymerized at their terminal ends at mild temperatures, resulting in the formation of oxygen-free aliphatic hydrocarbons. Different reaction stages of the decarboxylation were monitored by high-resolution scanning tunneling microscopy and X-ray photoemission spectroscopy. On the basis of density functional theory calculations, a two-step process was proposed for the fatty acid decarboxylation. Our work demonstrates a novel strategy for deoxygenation of fatty acids on a 1D constrained surface as a model catalytic system for producing low oxygen content biofuels.
Graphene nanoribbons (GNRs) are promising building blocks for nanoelectronic and spintronic devices. As a bottom‐up approach, on‐surface synthesis from predefined precursor molecules is widely applied for the fabrication of GNRs with precisely controlled edge structure and width. In order to guide the on‐surface reaction in a desired style, most of the chosen precursor molecules are functionalized with halogen atoms, while halogen‐free strategy for GNR synthesis is still challenging so far. Here, the on‐surface synthesis of ultranarrow armchair GNRs with five carbons across the ribbon (5‐aGNRs) on Au(111) surfaces via direct dehydrogenative CC coupling is reported. As the precursor molecule, quaterrylene molecules undergo various pathways of cyclodehydrogenation at submonolayer coverage: Instead of straight GNRs, a large proportion of the reaction products are kinked with an angle of 150°. When increasing the coverage to nearly one monolayer, the selectivity toward the straight GNRs is significantly enhanced. The coverage‐dependent reaction preference is ascribed to the intermolecular steric effect, in which the reaction pathway is constrained by the orientation of the neighboring molecules. Such an intermolecular steric effect is considered a novel approach to guide the on‐surface synthesis toward desired nanostructures.
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