Synthesis of polyynes to model the sp-carbon allotrope carbyne

Abstract

Carbyne is an allotrope of carbon composed of sp-hybridized carbon atoms. Although its formation in the laboratory is suggested, no well-defined sample is described. Interest in carbyne and its potential properties remains intense because of, at least in part, technological breakthroughs offered by other carbon allotropes, such as fullerenes, carbon nanotubes and graphene. Here, we describe the synthesis of a series of conjugated polyynes as models for carbyne. The longest of the series consists of 44 contiguous acetylenic carbons, and it maintains a framework clearly composed of alternating single and triple bonds. Spectroscopic analyses for these polyynes reveal a distinct trend towards a finite gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital for carbyne, which is estimated to be ∼485 nm (∼2.56 eV). Even the longest members of this series of polyynes are not particularly sensitive to light, moisture or oxygen, and they can be handled and characterized under normal laboratory conditions.

Carbon-atom wires: 1-D systems with tunable properties

“…Stable samples in powder form have been produced, 115 as a chief example, Chalifoux and Tykwinski synthesized long wires (44 carbon atoms) stabilized by bulky endgroups. 36 Polyynes are typically easier to produce than cumulenes probably due to higher stability, and nowadays polyynes up to 20 carbon atoms and more can be produced in solution even as size-selected samples. 22,28,75 Step-wise syntheses offer the possibility of different terminating groups.…”

“…[22][23][24][25][26][27][28][29][30][31][32][33][34][35] In addition, synthetic strategies allow us to produce long and stable sp-carbon wires with controlled length and termination. 36 Theoretical investigations have predicted a number of interesting vibrational, electronic, and transport properties that can be tuned by controlling the wire length and endgroups. This includes carbon wires connecting metal leads, graphene, and nanotubes as device prototypes.…”

“…Extrapolation procedures have been discussed in some studies. 36,85 2.3 Finite length sp-carbon systems: molecular vibrations and Raman spectroscopy Parallel to the case of the electronic properties, where finite length CAWs can be placed in correspondence with an infinite chain model sharing the same BLA (see section 2.2), an analogous correlation should also be worked out for the vibrational properties of CAWs. The Raman spectra of hydrogen-endcapped polyynes show a similar pattern as polyenes, namely a very intense line that corresponds to the ECC mode, 75,86 and this has also been named as "α-line" in the literature.…”

Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s

“…5 fs. Compounds with such long chains have been synthesized for polyynes 40 and we hope that this should be possible for cumulenes as well.…”

Self-assembly mechanisms of short atomic chains on single-layer graphene and boron nitride

“…A short segment of carbon atomic chain containing n C atoms, indicated as CAC(n) hereafter, is a truly one-dimensional carbon allotrope, and has recently drawn attention due to its linear geometry, high strength, size-dependent quantum ballistic conductance, and interesting electronic properties. These properties of CACs were both theoretically [11][12][13][14][15][16][17][18][19][20] and experimentally [21][22][23] investigated. Theoretical studies revealed the Peierls distortion in CACs, 11,13,19 half-metallic and spintronic properties, [16][17][18] size-dependent quantum conductance, 12,14 and other geometrical structures.…”