Synthesis of extended polyynes: Toward carbyne

Thermal formation of carbynes

We simulate the formation of sp carbon chains (carbynes) by thermal decomposition of sp(2) carbon heated by a hot discharge plasma, by means of tight-binding molecular dynamics. We obtain and analyze the total quantity of carbynes and their length distribution as a function of temperature and density.

Synthesis and properties of long [n]cumulenes (n ≥ 5)

This review highlights the synthesis and reactivity of longer [n]cumulenes (n ≥ 5) and summarizes their electronic and structural properties.

Synthesis, characterization, and solid-state polymerization of cross-conjugated octatetraynes

Two series of cross-conjugated 1,3,5,7-octatetraynes (1a–1l and 6a–6d) have been synthesized. UV–vis spectroscopic analysis shows that pendent groups connected to the cross-conjugated skeleton have little effect on the λmax energies, irrespective of whether the groups are electron withdrawing or donating. A number of the isolated products readily give crystals suitable for X-ray crystallography, and the solid-state structural properties of five derivatives (1k, 1l, 6a, 6c, and 6d) have been examined by X-ray crystallographic analysis. Parallel packing of the polyynes in the solid state indicates that four of the five samples are potentially suitable for topochemical polymerization, based on solid-state packing parameters θ, R, and d. Attempts to effect a solid-state reaction have been explored through UV–vis and γ-ray irradiation as well as thermal heating. The course of these reactions was monitored by differential scanning calorimetry (DSC) analysis, as well as UV–vis and solid-state 13C NMR spectroscopy (for 1d, 1j, 1k, and 6d), which offered evidence of polymer formation from these reactions. Structural determination of the product(s), however, remains elusive.

Carbon sp chains in graphene nanoholes

Nowadays sp carbon chains terminated by graphene or graphitic-like carbon are synthesized routinely in several nanotech labs. We propose an ab initio study of such carbon-only materials, by computing their structure and stability, as well as their electronic, vibrational and magnetic properties. We adopt a fair compromise of microscopic realism with a certain level of idealization in the model configurations, and predict a number of properties susceptible to comparison with experiment.

A one-dimensional extremely covalent material: monatomic carbon linear chain

Polyyne and cumulene of infinite length as the typical covalent one-dimensional (1D) monatomic linear chains of carbon have been demonstrated to be metallic and semiconductor (Eg = 1.859 eV), respectively, by first-principles calculations. Comparing with single-walled carbon nanotubes, the densities are evidently low and the thermodynamic properties are similar below room temperature but much different at the high temperature range. Polyyne possesses a Young's modulus as high as 1.304 TPa, which means it is even much stiffer than carbon nanotubes and to be the superlative strong 1D material along the axial direction. The Young's modulus of cumulene is estimated to be 760.78 GPa. In addition, polyyne is predicted to be as a one-dimensional electronic material with very high mobility.

The Fritsch-Buttenberg-Wiechell rearrangement: modern applications for an old reaction

The Fritsch-Buttenberg-Wiechell rearrangement of carbene/carbenoid intermediates has evolved into a valuable synthetic methodology for the preparation of polyyne structures. Various synthetic routes toward the formation of the corresponding precursors, alkynyl-substituted dibromoolefins, have been developed. Additionally, the scope of this methodology is expanded significantly by the development of functional group-tolerant one-pot procedures. The preparation of various polyynes up to the octa- and decaynes is, thus, possible on a scale that enables thorough physico-chemical characterization. Hence, series of polyynes have been investigated by, e.g., UV-vis, IR- and Raman spectroscopy, as well as X-ray crystallography. These investigations give unique insight into the structural characteristics of longer polyynes and hint to the structure of carbyne.

Conjugated oligoyne-bridged [60]fullerene molecular dumbbells: syntheses and thermal and morphological properties

A series of linear and star-shaped pi-conjugated oligomer hybrids (2-5) composed of an oligoyne core, ranging from 1,3-butadiyne to 1,3,5,7,9,11-dodecahexayne, and fullerenyl end-capping groups has been synthesized and studied. The molecular structures of these fullerene-oligoyne hybrids were assembled through three key reactions: Pd-catalyzed cross-coupling, Cu-catalyzed oxidative homocoupling, and an in situ alkynylation reaction on [60]fullerene. The properties of these compounds were investigated by UV-vis spectroscopy, differential scanning calorimetry (DSC), and atomic force microscopy (AFM) with the purpose of understanding the thermal reactivity arising from the oligoyne moieties as well as the morphological properties on surface. Our study shows that these fullerene-oligoyne hybrids tend to aggregate in different morphologies, including nanospheres, nanoflakes, and continuous thin films, while the morphological properties appear to be subject to the influence of molecular factors such as oligomer chain length, solubilizing alkylphenyl groups, and the thermal reactivity of the oligoyne unit. The correlation between molecular property and interfacial aggregation behavior evinced by these fullerene-oligoyne hybrids suggests a viable approach to exert bottom-up control over the structures and properties of fullerene based nanomaterials.

Naturally occurring and synthetic polyyne glycosides

Polyyne glycosides are a class of natural products that have been found in terrestrial plants, fungi, and marine algae. Many display interesting and potentially useful biological activities, which in some cases has initiated synthetic efforts toward their formation. This review provides a comprehensive report of polyyne glycosides isolated from natural sources, as well as the synthesis of these molecules and their analogues.

Synthesis of hybrid masked triyne-phenylene axial rods containing (E)-beta-chlorovinylsilanes in the pi-conjugated framework

A two-directional synthesis of a masked hexayne 7, in which two beta-chlorovinylsilanes protect two of the internal alkynes, is reported. The key step involves the Pd-catalyzed oxidative dimerization of alkyne 10 to provide diyne 12, which is elaborated into centrosymmetric masked hexayne 7 in four steps. Masked hexayne 7 is a constitutional isomer of masked hexayne 2, which has been used as a monomer unit for oligoyne assembly. Although masked hexayne 7 was not as convenient a building block as 2 for application in oligoyne assembly, one of its precursors, namely alkyne 10, could be used successfully in Sonogashira couplings, which allowed the incorporation of aromatic spacers and the formation of hybrid masked triyne-phenylenes 20 and 28. Compounds 20 and 28 both contain removable end-groups, which will permit their application as building blocks for the assembly of classes of long-chain, pi-conjugated rod-like molecules. Rod-like molecule 34, which possesses a similar conjugated scaffold as 28, was also prepared by using a similar strategy. Treatment of 34 with TBAF effected a 2-fold dechlorosilylation to provide a rigid rod molecule 35 in which two phenylene units interrupt an octayne scaffold.