Carbyne, the linear chain of carbon, promises the strongest and toughest material but possesses a Peierls instability (alternating single-bonds and triple-bonds) that reduces its strength and toughness. Herein, we computationally found that the gravimetric strength, strain-to-failure, and gravimetric toughness can be improved from 74 GPa·g^-1·cm³, 18%, and 9.4 kJ·g^-1 for pristine carbyne to the highest values of 106 GPa·g^-1·cm³, 26%, and 19.0 kJ·g^-1 for carbyne upon hole injection of +0.07 e/atom, indicating the charged carbyne with record-breaking mechanical performance. Based on the analyses of the atomic and electronic structures, the underlying mechanism behind the record-breaking mechanical performance was revealed as the suppressed and even eliminated bond alternation of carbyne upon charge injection.

Carbyne is an infinitely long linear chain of carbon atoms with sp¹ hybridization and the truly one-dimensional allotrope of carbon. While obtaining freestanding carbyne is still an open challenge, the study of confined carbyne, linear chains of carbon encapsulated in carbon nanotubes, provides a pathway to explore carbyne and its remarkable properties in a well-defined environment. In this review, we discuss the basics and recent advances in studying single confined carbyne chains by Raman spectroscopy, which is their primary spectroscopic characterization method. We highlight where single carbyne chain studies are needed to advance our understanding of confined carbyne as a material system and provide an overview of the open questions that need to be addressed and of those aspects currently under debate.

This review provides a discussion of the current state of research on sp-carbon chains synthesized by pulsed laser ablation in liquid. In recent years, pulsed laser ablation in liquid (PLAL) has been widely employed for polyynes synthesis thanks to its flexibility with varying laser parameters, solvents, and targets. This allows the control of sp-carbon chains properties as yield, length, termination and stability. Although many reviews related to PLAL have been published, a comprehensive work reporting the current status and advances related to the synthesis of sp-carbon chains by PLAL is still missing. Here we first review the principle of PLAL and the mechanisms of formation of sp-carbon chains. Then we discuss the role of laser fluence (i.e. energy density), solvent, and target for sp-carbon chains synthesis. Lastly, we report the progress related to the prolonged stability of sp-carbon chains by PLAL encapsulated in polymeric matrices. This review will be a helpful guide for researchers interested in synthesizing sp-carbon chains by PLAL.

Most existing studies assign a polyynic and cumulenic character of chemical bonding in carbon-based chains relying on values of the bond lengths. Building on our recent work, in this paper we add further evidence on the limitations of such an analysis and demonstrate the significant insight gained via natural bond analysis. Presently reported results include atomic charges, natural bond order and valence indices obtained from ab initio computations for representative members of the astrophysically relevant neutral and charged HC_2k/2k+1H chain family. They unravel a series of counter-intuitive aspects and/or help naive intuition in properly understanding microscopic processes, e.g., electron removal from or electron attachment to a neutral chain. Demonstrating that the Wiberg indices adequately quantify the chemical bonding structure of the HC_2k/2k+1H chains—while the often heavily advertised Mayer indices do not—represents an important message conveyed by the present study.

Carbyne, as the truly one-dimensional carbon allotrope with sp-hybridization, has attracted significant interest in recent years, showing potential applications in next-generation molecular devices due to its ultimate one-atom thinness. Various excellent properties of carbyne have been predicted, however, free-standing carbyne sample is extremely unstable and the corresponding experimental researches and modifications are under-developed compared to other known carbon allotropes. The synthesis of carbyne has been slowly developed for the past decades. Recently, there have been several breakthroughs in in-situ synthesis and measurement of carbyne related materials, as well as the preparation of ultra-long carbon chains toward infinite carbyne. These progresses have aroused widespread discussion in the academic community. In this review, the latest approaches in the synthesis of sp carbon are summarized. We then discuss its extraordinary properties, including mechanical, electronic, magnetic, and optical properties, especially focusing on the regulations of these properties. Finally, we provide a perspective on the development of carbyne.

Controlling the spin transport at the single-molecule level, especially without the use of ferromagnetic contacts, becomes a focus of research in spintronics. Inspired by the progress on atomic-level molecular synthesis, through first-principles calculations, we investigate the spin-dependent electronic transport of graphene nanoflakes with side-bonded functional groups, contacted by atomic carbon chain electrodes. It is found that, by rotating the functional group, the spin polarization of the transmission at the Fermi level could be switched between completely polarized and unpolarized states. Moreover, the transition between spin-up and spin-down polarized states can also be achieved, operating as a dual-spin filter. Further analysis shows that, it is the spin-dependent shift of density of states, caused by the rotation, that triggers the shift of transmission peaks, and then results in the variation of spin polarization. Such a feature is found to be robust to the length of the nanoflake and the electrode material, showing great application potential. Those findings may throw light on the development of spintronic devices.

The space-confined synthesis method has been an efficient way for the preparation of linear carbon chains. However, the large-scale preparation of linear carbon chains still faces many challenges due to the lack of methods for the large-scale synthesis of precursors, such as short carbon chains (polyynes), and regulation technology for the transport of reactants in one-dimensional space. Here, we report a facile method for the rapid preparation of polyynes in large quantities using a commercial laser marking machine. Spectroscopic characterizations show that a large number of polyynes, such as C₈H₂, C₁₀H₂, C₁₂H₂, and C₁₄H₂, can be produced by ablating the graphite plate immersed in the organic liquid using a laser marking machine. The results of in situ Raman spectroscopy investigation of C_2nH₂-filled single-walled carbon nanotubes further confirm that a variety of polyyne molecules are synthesized. Meanwhile, in situ Raman spectroscopy also shows that the local heating treatment can accelerate the filling process of C_2nH₂ into one-dimensional channels. This work provides new insights into the study of linear carbon chains and space-confined synthesis methods.

Carbyne is an infinite one-dimensional carbon chain comprising of sp-hybridized carbons. Due to its high chemical reactivity and extreme instability, the synthesis and structural diversity of carbyne have been much less investigated in the past decades compared to carbon allotropes built with sp² hybridized carbons, such as fullerenes, carbon nanotubes, and graphene. The emerging on-surface synthesis strategy provides an extremely promising approach for the fabrication of novel carbyne-like nanostructures with atomic precision. Herein, we summarize recent exciting progress in the synthesis of carbyne-like nanostructures with one-dimensional sp-carbon on surfaces, including polyynes, cumulenes, and organometallic polyynes. We also point out the scientific challenges and prospects, encouraging scientists to explore the fabrication and characterization of single strands of carbyne in this young and promising research field.

Cyclocarbon fully consists of sp-hybridized carbon atoms, which shows quite unusual electronic and geometric structures compared to common molecules. In this work, we systematically studied strain energy (SE) of cyclocarbons of different sizes using regression analysis method based on electronic energies evaluated at the very accurate DLPNO-CCSD(T)/cc-pVTZ theoretical level. In addition, ring strain of two systems closely related to cyclocarbon, boron nitride (BN) ring, and cyclic polyacetylene (c-PA), is also explored. Very ideal relationships between SE and number of repeat units ($n)$ are built for cyclo[2$n$]carbon, B$_{n}$N$_{n}$, and [2$n$]c-PA as ${\rm SE} = 555.0\cdot n^{-1}$, 145.1$\cdot n^{-1}$, and 629.8$\cdot n^{-1}$ kcal$\cdot $mol$^{-1}$, respectively, and the underlying reasons of the difference and similarity in their SEs are discussed from electronic structure perspective. In addition, force constant of harmonic potential of C-C-C angles in cyclocarbon is derived based on SE values, the result is found to be 56.23 kcal$\cdot $mol$^{-1}\cdot $rad$^{-2}$. The possibility of constructing homodesmotic reactions to calculate SEs of cyclocarbons is also explored in this work, although this method is far less rigorous than the regression analysis method, its result is qualitatively correct and has the advantage of much lower computational cost. In addition, comparisons show that $\omega $B97XD/def2-TZVP is a good inexpensive alternative to the DLPNO-CCSD(T)/cc-pVTZ for evaluating energies used in deriving SE, while the popular and very cheap B3LYP/6-31G(d) level should be used with caution for systems with global electron conjugation such as c-PA.

Linear carbon chains as new one-dimensional (1D) nanomaterials attract attention for the predicted outstanding properties. However, the high reactivity of linear carbon chains hampers further experimental research. To date, different methods have been developed to synthesize new materials containing linear carbon chains. Among them, the arc-discharge method is a practical way to prepare both finite and infinite linear carbon chains. This review provides a brief discussion of the recent progress in the techniques to prepare carbon chain-based materials and then focuses on the arc-discharge method. The configuration of apparatus, optimal conditions, and the corresponding mechanism of arc-discharge method to prepare long linear carbon chain inside multi-walled carbon nanotubes are summarized in detail. The characterization techniques are introduced to evaluate the quality of products. Moreover, remaining challenges and perspectives are presented for further investigation of long linear carbon chains.

Polyyne, an sp¹-hybridized linear allotrope of carbon, has a tunable quasiparticle energy gap, which depends on the terminated chemical ending groups as well as the chain length. Previously, nitrogen doping was utilized to tailor the properties of different kinds of allotrope of carbon. However, how the nitrogen doping tailors the properties of the polyyne remains unexplored. Here, we applied the GW method to study the quasiparticle energy gaps of the N-doped polyynes with different lengths. When a C atom is substituted by an N atom in a polyyne, the quasiparticle energy gap varies with the substituted position in the polyyne. The modification is particularly pronounced when the second-nearest-neighboring carbon atom of a hydrogen atom is substituted. In addition, the nitrogen doping makes the Fermi level closer to the lowest unoccupied molecular orbital, resulting in an n-type semiconductor. Our results suggest another route to tailor the electronic properties of polyyne in addition to the length of polyyne and the terminated chemical ending groups.