The loss of endgroup effects in long pyridyl-endcapped oligoynes on the way to carbyne


The versatility of carbon is revealed in its all-carbon forms (allotropes), which feature unique properties (consider the differences between diamond, graphite, graphene and fullerenes). Beyond natural sources, there are many opportunities to expand the realm of carbon chemistry through the study of new carbon forms. In this work, the synthesis of oligo-/polyynes is used to model the elusive carbyne. The chemical stabilization of oligoynes by sterically encumbered endgroups, particularly the 3,5-bis(3,5-di-tert-butylphenyl)pyridyl group, is key to assemble an extended series of stable oligoynes. The final member of this series is the longest monodisperse polyyne isolated and characterized so far, featuring 24 contiguous alkyne units (48 carbons). Spectroscopic and X-ray crystallographic analysis show that endgroups influence the properties of oligoyne derivatives, but this effect diminishes as length increases toward the polyyne/carbyne limit. For instance, with ultraviolet–visible spectroscopy, molecular symmetry clearly documents the evolution of characteristics from oligoynes to polyynes (in which endgroup effects are absent). The combined experimental data are used to refine predictions for the D∞h structure of carbyne.

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Fig. 1: Molecular structure and symmetry of oligoynes, polyynes and carbyne.
Fig. 2: Synthesis of sterically encumbered di- and tetraynes Py**[2a–e] and Py**[4a–d].
Fig. 3: Synthesis of PEOs Py**[na].
Fig. 4: Ultraviolet–visible spectroscopic analysis of PEOs Py**[na] as well as extrapolations as a function of oligoyne length n using Meier’s equation.
Fig. 5: The solid-state structures of PEOs Py**[na] by X-ray crystallographic analysis as well as the extrapolation of bond length alternation (BLAavg) and Raman shifts as a function of oligoyne length n using Meier’s equation.

Data availability

All data generated or analysed during this study are included in this Article (and its Supplementary Information). The structures of tBu[5], tBu[6], Py**[2c], Py**[2e], Py**[2a], Py**[4a], Py**[6a] (P-1), Py**[6a] (P21/c) and Py**[8a]in the solid state were determined by single-crystal X-ray diffraction, and the crystallographic data have been deposited with the Cambridge Crystallographic Data Centre under CCDC numbers 1981170 (tBu[5]), 1981171 (tBu[6]), 1977432 (Py**[2c]), 1977434 (Py**[2e]), 1977437 (Py**[2a]), 1977437 (Py**[4a]), 1977438 (Py**[6a], P-1), 1977436 (Py**[6a], P21/c) and 1977435 (Py**[8a]). Copies of the data can be obtained free of charge on application to CCDC.


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This Article is dedicated to the memory of François Diederich. We are grateful for funding from the Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), and the Deutsche Forschungsgemeinschaft (SFB 953, Synthetic Carbon Allotropes). We thank S. Frankenburger for synthesis and F. Hampel for X-ray structural determination of tBu[5] and tBu[6], Y. Zhou and R. McDonald for help with acquisition of the X-ray diffraction data for Py**[2a], Py**[6a] and Py**[2e], and L. Chen for crystallization of Py**[6a] (P21/c). Y.H. and Y.G. acknowledge funding from the China Scholarship Council (CSC). J.C. acknowledges MINECO and Junta de Andalucía of Spain project references PGC2018-098533-B-I00 and UMA18FEDERJA057.

Author information




R.R.T. designed and oversaw the project. R.R.T and Y.G. designed the molecules, Y.G. and Y.H. synthesized and characterized the molecules. Y.G. carried out room temperature spectroscopy, thermal analyses and data analysis. J.C. and F.G.G. carried out low-temperature absorption and Raman spectroscopy. M.F. conducted X-ray crystallographic characterization, refinement and analysis. Y.G and R.R.T. wrote the paper with contributions from all authors. All authors analysed the results and commented on the manuscript.

Corresponding author

Correspondence to Rik R. Tykwinski.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figures 1–93 and Supplementary Tables 1–21

Supplementary Data 1

Crystallographic data (CIF) for compound tBu[5]; CCDC reference: 1981170

Supplementary Data 2

Crystallographic data (structure factors, FCF) for compound tBu[5]; CCDC reference: 1981170

Supplementary Data 3

Crystallographic data (CIF) for compound tBu[6]; CCDC reference: 1981171

Supplementary Data 4

Crystallographic data (structure factors, FCF) for compound tBu[6]; CCDC reference: 1981171

Supplementary Data 5

Crystallographic data (CIF) for compound Py**[2a]; CCDC reference: 1977437

Supplementary Data 6

Crystallographic data (CIF) for compound Py**[2c]; CCDC reference: 1977432

Supplementary Data 7

Crystallographic data (CIF) for compound Py**[2e]; CCDC reference: 1977434

Supplementary Data 8

Crystallographic data (CIF) for compound Py**[4a]; CCDC reference: 1977433

Supplementary Data 9

Crystallographic data (CIF) for compound Py**[6a] (P-1); CCDC reference: 1977438

Supplementary Data 10

Crystallographic data (CIF) for compound Py**[6a](P21/c); CCDC reference: 1977436

Supplementary Data 11

Crystallographic data (CIF) for compound Py**[8a]; CCDC reference: 1977435

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Gao, Y., Hou, Y., Gordillo Gámez, F. et al. The loss of endgroup effects in long pyridyl-endcapped oligoynes on the way to carbyne. Nat. Chem. 12, 1143–1149 (2020).

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