Carbon nanostructures with zigzag edges exhibit unique properties—such as localized electronic states and spins—with exciting potential applications. Such nanostructures however are generally synthesized under vacuum because their zigzag edges are unstable under ambient conditions: a barrier that must be surmounted to achieve their scalable integration into devices for practical purposes. Here we show two chemical protection/deprotection strategies, demonstrated on labile, air-sensitive chiral graphene nanoribbons. Upon hydrogenation, the chiral graphene nanoribbons survive exposure to air, after which they are easily converted back to their original structure by annealing. We also approach the problem from another angle by synthesizing a form of the chiral graphene nanoribbons that is functionalized with ketone side groups. This oxidized form is chemically stable and can be converted to the pristine hydrocarbon form by hydrogenation and annealing. In both cases, the deprotected chiral graphene nanoribbons regain electronic properties similar to those of the pristine nanoribbons. We believe both approaches may be extended to other graphene nanoribbons and carbon-based nanostructures.
The development of
functional organic molecules requires structures
of increasing size and complexity, which are typically obtained by
the covalent coupling of smaller building blocks. Herein, with the
aid of high-resolution scanning tunneling microscopy/spectroscopy
and density functional theory, the coupling of a sterically demanded
pentacene derivative on Au(111) into fused dimers connected by non-benzenoid
rings was studied. The diradical character of the products was tuned
according to the coupling section. In particular, the antiaromaticity
of cyclobutadiene as the coupling motif and its position within the
structure play a decisive role in shifting the natural orbital occupancies
toward a stronger diradical electronic character. Understanding these
structure–property relations is desirable not only for fundamental
reasons but also for designing new complex and functional molecular
structures.
Activating the strong C–C σ-bond is a central
problem
in organic synthesis. Directly generating activated C centers by metalation
of structures containing strained four-membered rings is one maneuver
often employed in multistep syntheses. This usually requires high
temperatures and/or precious transition metals. In this paper, we
report an unprecedented C–C σ-bond activation at room
temperature on Cu(111). By using bond-resolving scanning probe microscopy,
we show the breaking of one of the C–C σ-bonds of a biphenylene
derivative, followed by insertion of Cu from the substrate. Chemical
characterization of the generated species was complemented by X-ray
photoemission spectroscopy, and their reactivity was explained by
density functional theory calculations. To gain further insight into
this unique reactivity on other coinage metals, the reaction pathway
on Ag(111) was also investigated and the results were compared with
those on Cu(111). This study offers new synthetic routes that may
be employed in the in situ generation of activated
species for the on-surface synthesis of novel C-based nanostructures.
In the version of this article initially published, a few double bonds were missing in Figs. 3a, 5a and 6i. Original and corrected panels are shown below (Figs. 1-4), and the HTML and PDF versions of the article have been updated.
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