Scalable Synthesis and Characterization of Multilayer γ-Graphyne, New Carbon Crystals with a Small Direct Band Gap

Abstract

γ-Graphyne is the most symmetric sp 2 /sp 1 allotrope of carbon, which can be viewed as graphene uniformly expanded through the insertion of two-carbon acetylenic units between all the aromatic rings. To date, synthesis of bulk γ-graphyne has remained a challenge. We here report the synthesis of multilayer γ-graphyne through crystallization-assisted irreversible cross-coupling polymerization. A comprehensive characterization of this new carbon phase is described, including synchrotron powder X-ray diffraction, electron diffraction, lateral force microscopy, Raman spectroscopy, infrared spectroscopy, and cyclic voltammetry. Experiments indicate that γ-graphyne is a 0.48 eV band gap semiconductor, with a hexagonal a-axis spacing of 6.88 Å and an interlayer spacing of 3.48 Å, which is consistent with theoretical predictions. The observed crystal structure has an aperiodic sheet stacking. The material is thermally stable up to 240 °C but undergoes transformation at higher temperatures. While conventional 2D polymerization and reticular chemistry rely on error correction through reversibility, we demonstrate that a periodic covalent lattice can be synthesized under purely kinetic control. The reported methodology is scalable and inspires extension to other allotropes of the graphyne family.

Masked alkynes for synthesis of threaded carbon chains

“…This value of the predicted Raman frequency of infinite carbyne (1900 cm -1 ) is slightly higher than that deduced by Gao et al from the Meier fit of a series of shorter pyridine-terminated polyynes (ν∞ = 1886 cm -1 ) 22 . The frequency for the [5]rotaxane C68•(Mb)4 happens to equal the asymptotic limit, which illustrates that the Raman frequencies have already converged to that of carbyne. Carbyne chains inside double-walled carbon nanotube have lower Raman frequencies (1770-1850 cm -1 ; refs.…”

“…Unmasking of the [5]rotaxane mC68•(Mb)4 using MMPP (120 equiv.) gave the polyyne [5]rotaxane C68•(Mb)4 in 23% yield, after purification by silica gel chromatography and washing with ethanol, whereas this compound could not be prepared by unmasking mC68•(Mb)4 with mCPBA.…”

“…gave the polyyne [5]rotaxane C68•(Mb)4 in 23% yield, after purification by silica gel chromatography and washing with ethanol, whereas this compound could not be prepared by unmasking mC68•(Mb)4 with mCPBA. This polyyne [5]rotaxane is an orange-red solid, and it is stable in solution over several days on storing at -20 °C, but some decomposition is observed during chromatography. The C68 polyyne chain of this [5]rotaxane makes it longer than any previously reported polyyne 22 .…”

“…This polyyne [5]rotaxane is an orange-red solid, and it is stable in solution over several days on storing at -20 °C, but some decomposition is observed during chromatography. The C68 polyyne chain of this [5]rotaxane makes it longer than any previously reported polyyne 22 . It was fully characterized by 1 H NMR, UV-vis and Raman spectroscopy and high-resolution mass spectrometry.…”

“…It was fully characterized by 1 H NMR, UV-vis and Raman spectroscopy and high-resolution mass spectrometry. We also prepared C68•(Ma)4 but this [5]rotaxane is less stable than the version with the smaller macrocycle, which prevented characterization by NMR spectroscopy. UV-vis and Raman spectra.…”