Evidence for Orientational Order in Nanothreads Derived from Thiophene

Abstract

Nanothreads are one-dimensional sp 3 hydrocarbons that pack within pseudohexagonal crystalline lattices. They are believed to lack long-range order along the thread axis and also lack interthread registry. Here we investigate the phase behavior of thiophene up to 35 GPa and establish a pressure-induced phase transition sequence that mirrors previous observations in low-temperature studies. Slow compression to 35 GPa results in the formation of a recoverable saturated product with a 2D monoclinic diffraction pattern along (0001) that agrees closely with atomistic simulations for single crystals of thiophene-derived nanothreads. Paradoxically, this lower-symmetry packing signals a higher degree of structural order since it must arise from constituents with a consistent azimuthal orientation about their shared axis. The simplicity of thiophene reaction pathways (with only four carbon atoms per ring) apparently yields the first nanothreads with orientational order, a striking outcome considering that a single point defect in a 1D system can disrupt long-range structural order.

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

“…These results can be compared to prior X-ray diffraction measurements of thiophene-derived nanothreads, which are well-described by a monoclinic anti or syn/anti packing. 13 In thiophenederived threads the steric penalty for syn is much larger than for anti or syn/anti, presumably due to sulfur being larger than oxygen.…”

Synthesis of double core chromophore-functionalized nanothreads by compressing azobenzene in a diamond anvil cell

“…The presence of unsaturation can also play an important role in tuning the electronic properties by changing the gap from the UV to the near infrared, but obviously decreasing both strength and stiffness with respect to fully saturated nanothreads. 23 Experimentally, nanothreads have been synthesized from substituted aromatics and heteroaromatics like pyridine, 24,25 aniline 26 and thiophene, 27 and recently also from arene-peruoroarene cocrystals 28,29 and highly strained fully saturated molecules like cubane. 30 In spite of the general similarity regarding the mechanism of the nanothread formation, consistent differences in the synthesis conditions, in the thread packing and in the reaction yield can characterize the different systems and are ascribable to the crystal arrangement of the starting monomer.…”

Theoretical Studies of Furan and Thiophene Nanothreads: Structures, Cycloaddition Barriers and Activation Volumes

“…Focusing on the relationships of neighboring chalcogens (O or S) in a thiophene thread structure-whether they are on the same side or opposite sides of the thread-a syn/anti nomenclature naturally comes to mind, and was originally used. 8 Based on the closeness of the match to experimentally observed d-spacings of the three Friedel pairs of the quasi six-fold diffraction pattern, simulations of packed nanothread crystals suggest that (for both furan and thiophene nanothreads) the anti and/or syn-anti structures, with more elliptical cross sectional thread shapes, are the ones observed. 8,11 The latest solid-state NMR analyses of a furan thread sample produced in a Paris-Edinburgh cell, along with chemical shift calculations (by DFT), identified the fully…”

“…Nanothreads were first synthesized from benzene under pressure in diamond anvil cells or Paris-Edinburgh cells, 3,4 but the high-pressure solid-state synthesis technique appears to be quite general for unsaturated hydrocarbons. To date, nanothreads have been synthesized from benzene, 3,4 pyridine, 5 aniline, 6 a naphthalene/octafluoronaphthalene cocrystal, 7 thiophene, 8 cubane, 9 and very recently a phenol/pentafluorophenol cocrystal, 10 and furan. 11 It is expected that more polymers of this kind are coming, and that sample sizes of certain threads will rapidly expand as synthesis pressures continue to fall.…”