2,5-Furandicarboxylic acid (FDCA) is one of the top-12
value-added
chemicals from sugar. Besides the wide application in chemical industry,
here we found that solid FDCA polymerized to form an atomic-scale
ordered sp3-carbon nanothread (CNTh) upon compression.
With the help of perfectly aligned π–π stacked
molecules and strong intermolecular hydrogen bonds, crystalline poly-FDCA
CNTh with uniform syn-configuration was obtained
above 11 GPa, with the crystal structure determined by Rietveld refinement
of the X-ray diffraction (XRD). The in situ XRD and theoretical simulation
results show that the FDCA experienced continuous [4 + 2] Diels–Alder
reactions along the stacking direction at the threshold C···C
distance of ∼2.8 Å. Benefiting from the abundant carbonyl
groups, the poly-FDCA shows a high specific capacity of 375 mAh g–1 as an anode material of a lithium battery with excellent
Coulombic efficiency and rate performance. This is the first time
a three-dimensional crystalline CNTh is obtained, and we demonstrated
it is the hydrogen bonds that lead to the formation of the crystalline
material with a unique configuration. It also provides a new method
to move biomass compounds toward advanced functional carbon materials.
The
four-membered nitrogen ring (N4-ring) is predicted
to be a high-energy density moiety and has been the target of chemical
synthesis for quite a long time. Here, by compressing the 1:1 co-crystal
of trans-azobenzene and trans-perfluoroazobenzene
up to ∼40 GPa, the azo groups were restrained closely in parallel
in the crystal and underwent two competitive addition reactions. One
is [4 + 2] cycloaddition with the azo group as a part of diene and
phenyl as dienophile. The other is [2 + 2] cycloaddition between two
azo groups, which produced an unprecedented N4-ring structure
as evidenced by the metathesis product. The content of the N4-ring structure significantly increases under higher pressure, and
we found that it was the external pressure that decreased the kinetic
barrier and realized such a high-tensile moiety. Our work shows that
high pressure is an alternative synthetic strategy for these high-tensile
structures, which can be very effective under the cooperation of crystal
engineering.
The synergistic reaction between
alkyne and phenyl groups is a
promising pathway for decreasing the reaction pressures of aromatics
and enabling scalable high-pressure synthesis of carbon materials
via pressure-induced polymerization (PIP). Here by combining theoretical
calculations and experimental data, we demonstrate that a simultaneous
polymerization of alkynyl and phenyl groups occurred in phenylpropiolic
acid (PPA) with the threshold distance d
C···C = 3.3 Å, generating an extended structure consisting of sp2 and sp3 carbons. The reaction pressure of phenyl
was significantly decreased to ∼5 GPa, which can be applied
for large-scale synthesis. The product has a large π-electron
conjugated system, resulting in a band gap energy reduced to 1.65
eV and an electrical conductivity increasing to 1.24 × 10–6 S · cm–1. Our research confirmed
that conjugated polymers can be synthesized at lower pressures via
the high-pressure synergistic reaction route of phenylethynyl compounds
and can be used to further realize applications in organic photovoltaic
devices.
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