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Mechanochemical synthesis of an elusive fluorinated polyacetylene

Abstract

Polymer mechanochemistry has traditionally been employed to study the effects of mechanical force on chemical bonds within a polymer backbone or to generate force-responsive materials. It is under-exploited for the scalable synthesis of wholly new materials by chemically transforming the polymers, especially products inaccessible by other means. Here we utilize polymer mechanochemistry to synthesize a fluorinated polyacetylene, a long-sought-after air-stable polyacetylene that has eluded synthesis by conventional means. We construct the monomer in four chemical steps on gram scale, which involves a rapid incorporation of fluorine atoms in an exotic photochemical cascade whose mechanism and exquisite stereoselectivity were informed by computation. After polymerization, force activation by ultrasonication produces a gold-coloured, semiconducting fluoropolymer. This work demonstrates that polymer mechanochemistry is a valuable synthetic tool for accessing materials on a preparative scale.

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Fig. 1: Accessing polyenes from ladderene polymers requires force activation and enables the synthesis of a fluorinated polyacetylene.
Fig. 2: Synthesis of a fluoroladderene monomer and a computational description of the fluoroladderene extension mechanism using a model system.
Fig. 3: Synthesis of gold-coloured F-PA 18 and characterization, showing a semiconducting polymer with improved air stability relative to PA.
Fig. 4: Mechanochemical activation of polymer 19 produces a pentaene fine structure.

Data availability

Experimental data and characterization data for all new compounds prepared in the course of these studies are provided in the Supplementary Information of this manuscript. The X-ray crystallographic coordinates for compounds 13, S3, S6 and 16 have been deposited at the Cambridge Crystallographic Data Center (CCDC) with accession codes 2036390 (13), 2036388 (S3), 2036389 (S6) and 2036391 (16). These data can be obtained free of charge from the Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/structures/. The computational geometries obtained and used in Fig. 2 and in Supplementary Sections 18 and 19 are provided as .xyz files in the Supplementary Data.

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Acknowledgements

This work was supported by the Defense Advanced Research Projects Agency (DARPA-SN-18-47), the Office of Naval Research (N00014-17-S-F006) and the Center for Molecular Analysis and Design at Stanford (graduate fellowship for B.R.B.). Part of this work was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation (ECCS-1542152). Y.X. acknowledges support from the US Army Research Office (W911NF-15-1-0525). L.C. acknowledges support from the National Science Foundation (Awards 453247 and 2001189). Y. Jiang and Z. Bao (Stanford University) are acknowledged for assistance with conductivity experiments.

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Authors

Contributions

B.R.B., Y.X. and N.Z.B. conceived the work and designed the experiments. B.R.B. and C.M.F.M. carried out the synthesis experiments. B.R.B. and K.P.L. carried out X-ray photoelectron spectroscopy studies. B.R.B. and Z.J. carried out cyclic voltammetry studies. J.A.H.R. and L.C. designed and carried out solid-state NMR experiments and analysed the data. J.M.C. and S.A.L. designed and performed computations and analysed the data. B.R.B., N.Z.B., J.M.C. and S.A.L. wrote the manuscript. C.M.F.M. and Y.X. assisted in writing and editing the manuscript.

Corresponding authors

Correspondence to Yan Xia, Steven A. Lopez or Noah Z. Burns.

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The authors declare no competing interests.

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Peer review information Nature Chemistry thanks the anonymous reviewers for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Synthetic details and material characterization, Supplementary Figs. 1–58 and Tables 1–3.

Supplementary Data 1

xyz files for computed structures in Fig. 2b.

Supplementary Data 2

xyz files for each point in the computed surface in Supplementary Fig. 57.

Supplementary Data 3

Crystallographic data (CIF) for compound S6; CCDC reference: 2036389.

Supplementary Data 4

Crystallographic data (CIF) for compound 16; CCDC reference: 2036391.

Supplementary Data 5

Crystallographic data (CIF) for compound 13; CCDC reference: 2036390.

Supplementary Data 6

Crystallographic data (CIF) for compound S3; CCDC reference: 2036388.

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Boswell, B.R., Mansson, C.M.F., Cox, J.M. et al. Mechanochemical synthesis of an elusive fluorinated polyacetylene. Nat. Chem. 13, 41–46 (2021). https://doi.org/10.1038/s41557-020-00608-8

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