j.chempr.2019.01.004
Article
Synthesis of Armchair
and Chiral Carbon Nanobelts
Kwan Yin Cheung,1 Shaojun Gui,1 Chenfang Deng,2 Huifang Liang,2 Zeming Xia,1 Zhifeng Liu,1
Lifeng Chi,2, and Qian Miao
*
SUMMARY
The Bigger Picture
Chirality-specific synthesis of
single-walled carbon nanotubes
remains the top challenge in the
science of carbon nanotubes as
well as a bottleneck limiting their
applications. A key in the bottom-
up approach to meeting this
challenge is the precise synthesis
of hoop-shaped segments of
carbon nanotubes, such as carbon
nanobelts, which have been long-
standing targets of synthesis for
organic chemists. Herein, we
report an unprecedented
Carbon nanobelts that consist of a loop of fully fused benzene rings are long-
standing and challenging targets of organic synthesis and are key steps toward
the ultimate synthesis of uniform carbon nanotubes (CNTs) of single chirality
and predefined diameter. Herein, we report the synthesis of an unprecedented
armchair carbon nanobelt and the first chiral carbon nanobelt, which represent
sidewall segments of armchair and chiral CNTs, (12,12)CNT and (18,12)CNT,
respectively. These carbon nanobelts were synthesized from 2,5-di(benzy-
loxy)-1,4-benzoquinone in six steps by p-expansion of the corresponding
polyarylated carbon nanorings through Scholl reactions. Scanning tunneling
microscopy revealed these nanobelts to be nanoparticles of roughly uniform
size. In contrast to earlier unsuccessful attempts to synthesize carbon nanobelts
from the corresponding carbon nanorings, the belt-forming step reported here-
in is accompanied by either a small increase or even a decrease in strain energy,
as found from the theoretical calculations.
armchair carbon nanobelt and the
first chiral carbon nanobelt, which
were efficiently synthesized by p-
expansion of the corresponding
polyarylated carbon nanorings
through Scholl reactions
INTRODUCTION
Most of the physical properties of single-walled carbon nanotubes (SWCNTs), such
as electrical conductivity and band gap, are dependent on the chiral indices (n,m),
which determine the diameter and chirality of SWCNTs.1 Chirality-specific synthesis
of SWCNTs remains the top challenge in the science of carbon nanotubes (CNTs)
and a bottleneck limiting their applications,2 although progress was recently
made in chirality-controlled synthesis of SWCNTs, such as highly selective growth
of (12,6) SWCNT with an abundance higher than 92% by using solid alloy catalysts.3
Organic synthesis was proposed as a bottom-up approach to meet this challenge.
Bowl-shaped4–6 and hoop-shaped7–9 polycyclic aromatics that represent cap and
sidewall segments of SWCNTs, respectively, can in principle serve as templates or
precursors for the synthesis of SWCNTs. The recent decade has witnessed significant
progress in the chemistry of [n]cycloparaphenylenes (CPPs) and CPP-related carbon
nanorings (CNRs), which were synthesized by Jasti,10,11 Itami,12,13 Yamago,14,15
accompanied by either only a
small increase or even a decrease
in strain energy, as found from the
theoretical calculations. The
carbon nanobelts could not only
find applications as novel
molecular hosts and organic
semiconductors but also
ultimately lead to the
programmable synthesis of
uniform carbon nanotubes of
single chirality and predefined
diameter.
Isobe,16,17 Mullen,18,19 and many others.20–23 As suggested by the successful syn-
¨
thesis of these CNRs and Scott’s proof-of-concept approach to the growth of
CNTs through Diels-Alder reactions,24,25 uniform CNTs of single chirality and prede-
fined diameter could become a reachable target of organic synthesis.26,27 The next
challenging step toward the ultimate synthesis of uniform SWCNTs is the synthesis of
carbon nanobelts (CNBs), which, unlike CNRs, have a loop of fully fused benzene
rings and require cleavage of at least two CÀC bonds in order to open their cyclic
structures according to the definition by Itami.28 CNBs have been long-standing tar-
gets of synthesis for organic chemists, and the earliest attempts to synthesize zigzag
CNBs by Stoddart29 and armchair CNBs by Vogtle30 were documented even before
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Chem 5, 1–10, April 11, 2019 ª 2019 Elsevier Inc.
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