Scalable Synthesis of Crystalline One-Dimensional Carbon Nanothreads Through Modest-Pressure Polymerization of Furan

Abstract

<div><div><div><p>Carbon nanothreads, which are unique one-dimensional sp3-rich polymers, combine high tensile strength with flexibility owing to subnanometer widths and diamond-like cores. These extended carbon solids are constructed through pressure-induced polymerization of sp2 molecules such as benzene. Whereas a few examples of carbon nanothreads have been reported, the need for high onset pressures ( ≥ 17 GPa) to synthesize them precludes scalability and limits scope. Herein, we report the scalable synthesis of carbon nanothreads based on molecular furan, which can be achieved through ambient temperature pressure-induced polymerization with an onset reaction pressure of only 10 GPa due to its lessened aromaticity relative to other molecular precursors. When slowly compressed to 15 GPa and gradually decompressed to 1.5 GPa, a sharp six-fold diffraction pattern is observed in situ, indicating a well‐ordered crystalline material formed from liquid furan. Single-crystal X-ray diffraction of the reaction product exhibits three distinct d-spacings from 4.75 to 4.9 Å, whose size, angular spacing, and degree of anisotropy are consistent with our atomistic simulations for crystals of furan nanothreads. Further evidence for polymerization was obtained by powder XRD and Raman/IR spectroscopy. Comparison of the IR spectra with computed vibrational modes provides identification of spectral features characteristic of specific nanothreads, namely syn, anti, and syn/anti configurations. Furan therefore presents a strategic entry toward scalable carbon nanothreads.</p></div></div></div>

Perfect and Defective 13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13C NMR

“…In total, the data show that >95% of all carbons are bonded to one hydrogen, which is characteristic of nanothreads made from unsubstituted single aromatic rings. Due to an apparent OH band in the IR spectrum, 22,68 we searched for C-OH signals using hydroxyl-proton selection (HOPS) NMR, 51 but no such signals were recognized, see Figure S2, above the detection limit of ~2%. One-bond 2D NMR: Alkene identification.…”

“…Saturated carbon nanothreads, which fill the one-dimension/sp 3 entry in this matrix of dimensionality and hybridization, were first synthesized by high-pressure solid-state polymerization of benzene. 16,17 Since then, a wide variety of nanothreads consisting primarily of sp 3 -hybridized carbon have been synthesized by pressure-induced polymerization of aromatic molecules (e.g., pyridine, thiophene and aniline), [18][19][20][21][22] co-crystals (e.g., naphthalene-octafluoronaphthalene, phenol-pentafluorophenol), [23][24][25][26][27] and a strained saturated hydrocarbon, cubane. 28 Pressure-induced solid-state reaction thus appears to be a general means of obtaining ordered packings of one-dimensional, high-aspect ratio diamond-like backbones decorated with diverse heteroatoms and functional groups, living at the threshold of thickness where framework rigidity first emerges in solids, a regime rife with promise for novel chemical and physical properties.…”

“…28 Pressure-induced solid-state reaction thus appears to be a general means of obtaining ordered packings of one-dimensional, high-aspect ratio diamond-like backbones decorated with diverse heteroatoms and functional groups, living at the threshold of thickness where framework rigidity first emerges in solids, a regime rife with promise for novel chemical and physical properties. [29][30][31][32] Advances in our understanding of nanothread synthesisincluding the roles of temperature, 19,21 aromaticity, 22 molecular stacking geometry, [23][24][25][26] compression rate, 16,17,22,24 and uniaxiality of stress 16,17,20,22 have been accompanied by substantial reductions in synthesis pressure, convincing demonstrations of sp 3 character, 33,[18][19][20][21][22] and initial ascertainments of axial periodicity, 27 but not yet by a clear determination of the precise atomic structure of regular, periodic regions of saturated thread backbone.…”

“…For furan-derived nanothreads, mass spectrometry indicates molecular weights of about 6 kDa, consistent with ~100 furan units in the backbone, 22 but the detailed molecular structure has to date only been constrained by inferences as to the cross-sectional shape that follow from detailed analysis of their crystalline packing. 22 Three structures based on [4+2] cycloaddition pathways have been proposed, varying in the relative placement of oxygen atoms down the nanothread axis. These threads were termed syn, anti, and syn/anti, wherein syn has eclipsed oxygens and anti has oxygen atoms alternating across the thread backbone.…”

Perfect and Defective 13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13C NMR

“…In total, the data show that >95% of all carbons are bonded to one hydrogen, which is characteristic of nanothreads made from unsubstituted single aromatic rings. Due to an apparent OH band in the IR spectrum, 22,68 we searched for C-OH signals using hydroxyl-proton selection (HOPS) NMR, 51 but no such signals were recognized, see Figure S2, above the detection limit of ~2%. C spectrum can be assigned based on characteristic cross peaks in 2D 13 C- 13 C and 1 H- 13 C NMR spectra with mostly one-bond transfer.…”