Gram-scale synthesis of two-dimensional polymer crystals and their structure analysis by X-ray diffraction

Journal name:
Nature Chemistry
Volume:
6,
Pages:
779–784
Year published:
DOI:
doi:10.1038/nchem.2007
Received
Accepted
Published online

Abstract

The rise of graphene, a natural two-dimensional polymer (2DP) with topologically planar repeat units, has challenged synthetic chemistry, and has highlighted that accessing equivalent covalently bonded sheet-like macromolecules has, until recently, not been achieved. Here we show that non-centrosymmetric, enantiomorphic single crystals of a simple-to-make monomer can be photochemically converted into chiral 2DP crystals and cleanly reversed back to the monomer. X-ray diffraction established unequivocal structural proof for this synthetic 2DP, which has an all-carbon scaffold and can be synthesized on the gram scale. The monomer crystals are highly robust, can be easily grown to sizes greater than 1 mm and the resulting 2DP crystals exfoliated into nanometre-thin sheets. This unique combination of features suggests that these 2DPs could find use in membranes and nonlinear optics.

At a glance

Figures

  1. Rotor-shaped anthracene monomer 1 and the anthracene dimerization that enables 2DP growth.
    Figure 1: Rotor-shaped anthracene monomer 1 and the ​anthracene dimerization that enables 2DP growth.

    a, Molecular structure of the monomer utilized to synthesize 2DPs. The easily synthesizable double-decker compound is characterized by its C3h symmetry in which three 1,8-disubstituted ​anthracene blades that can undergo photodimerization are connected to two overlaying ​triazine cores. b, Well-known photochemical dimerization of 1,8-disubsituted ​anthracenes and their thermally or photochemically triggered back reaction. In this Article, the photochemical dimerization is employed for polymerization and the thermally triggered back reaction is used for depolymerization.

  2. Crystal structures of monomer and polymer crystals.
    Figure 2: Crystal structures of monomer and polymer crystals.

    a,b, Magnified part of the crystal structure before polymerization (a), showing two adjacent reactive monomer units in its centre, and after polymerization (b), showing the two connected ​anthracene blades of neighbouring monomers with the new bonds formed in yellow. Blue, nitrogen; red, oxygen; green, carbon. c,d, Top view of the monomer (c) and polymer (d) crystal structures. e,f, side view of the monomer (e) and polymer (f) crystal structures. cf, The colour code reflects whether the three-bladed compound 1 acts as monomer (green) or as part of the template (red). The template also contains three ​CPY molecules (black), which are oriented vertically to the main plane. For the specially annealed polymer crystal, the ​CPY molecules are oriented such that their nitrile groups face to the same side. In the non-irradiated case the individual layers are separated further by ​CPY molecules, which are located coplanar right on top of the template's ​triazine rings of 1 (not shown). The monomer units arrange themselves with only small alternating vertical offsets and are suited for polymerization to proceed strictly within each layer and only at the predetermined sites (the 9,10 positions of the opposing ​anthracenes).

  3. Products of swelling and exfoliation.
    Figure 3: Products of swelling and exfoliation.

    a, Polarized light microscopy image of a swollen polymer crystal after five days in ​perfluoroheptanoic acid at 50 °C. Residual acid is still present and partially covers the crystal. b, SEM image (2 kV) of swollen polymer crystal after five days in ​perfluoroheptanoic acid at 50 °C. The delamination into thinner crystal layers of submicrometre size is clearly visible. c, SEM overview image (2 kV) of polymerized crystals of varying degrees of exfoliation on a Quantifoil TEM grid after exposure to ​perfluorohexanoic acid for six days at 50 °C and gentle stirring. The crystal sizes are also retained for the thin sheets. d, SEM image (2 kV) of a sheet composed of a few 2DPs in which a vertex of the crystal that the sheet was exfoliated from can still be seen. The hole size of the Quantifoil TEM grid is 2.5 µm. e,f, AFM images of thin 2DP sheets on mica showing part of a ~30 µm sheet primarily composed of three 2DP sheets on top of each other (e) and the corresponding AFM profiles (for cross-sections 1 and 2 in e), which show the flat nature of the sheet with few elevations and the clear edge of the sheet (f). g, AFM image of a micrometre-sized feature. h, As can be seen from the AFM profiles (for cross-sections 1 and 2 in g) the different thicknesses resemble multiples of a single 2DP.

  4. Reversibility of polymerization.
    Figure 4: Reversibility of polymerization.

    Infrared spectra showing the reversibility of the polymerization and depolymerization processes. From the top: monomer crystals before irradiation, after irradiation for five hours, after being exposed to thermal treatment in an oven (200 °C, four days), which causes a full back reaction, and after repolymerization. a.u., arbitrary units.

Compounds

1 compounds View all compounds
  1. 1,5,10-(1,8)Trianthracena-2,4,5,8,9,11-hexaoxa 3,7-(1,3,5) ditriazinabicyclo [3.3.3]undecaphane
    Compound 1 1,5,10-(1,8)Trianthracena-2,4,5,8,9,11-hexaoxa 3,7-(1,3,5) ditriazinabicyclo [3.3.3]undecaphane

References

  1. Schmidt, G. M. J. Photodimerization in the solid state. Pure Appl. Chem. 12, 647678 (1971).
  2. Wegner, G. Topochemical reactions of monomers with conjugated triple bonds. I. Polymerization of 2,4-hexadiyn-1,6-diol derivatives in crystalline state. Z. Naturforsch. 24B, 824832 (1969).
  3. Kissel, P. et al. A two-dimensional polymer prepared by organic synthesis. Nature Chem. 4, 287291 (2012).
  4. Bhola, R. et al. A two-dimensional polymer from the anthracene dimer and triptycene motifs. J. Am. Chem. Soc. 135, 1413414140 (2013).
  5. Sakamoto, J., van Heijst, J., Lukin, O. & Schlüter, A. D. Two-dimensional polymers: just a dream of synthetic chemists? Angew. Chem. Int. Ed. 48, 10301069 (2009).
  6. Colson, J. W. & Dichtel, W. R. Rationally synthesized two-dimensional polymers. Nature Chem. 5, 453465 (2013).
  7. Staudinger H. Concerning polymerization. Ber. Dtsch. Chem. Ges. 53, 10731085 (1920).
  8. Berlanga, I. et al. Delamination of layered covalent organic frameworks. Small 7, 12071211 (2011).
  9. Spitler, E. L. et al. A 2D covalent organic framework with 4.7-nm pores and insight into its interlayer stacking. J. Am. Chem. Soc. 133, 1941619421(2011).
  10. Amo-Ochoa, P. et al. Single layers of a multifunctional laminar Cu(I,II) coordination polymer. Chem. Commun. 46, 32623264 (2010).
  11. Li, P., Maeda, Y. & Xu, Q. Top-down fabrication of crystalline metal–organic framework nanosheets. Chem. Commun. 47, 84368438 (2011).
  12. Gallego, A. et al. Solvent-induced delamination of a multifunctional two dimensional coordination polymer. Adv. Mater. 25, 21412146 (2013).
  13. Bauer, T. et al. Synthesis of free-standing, monolayered organometallic sheets at the air/water interface. Angew. Chem. Int. Ed. 50, 78797884 (2011).
  14. Zheng, Z. et al. Square-micrometer-sized, free-standing organometallic sheets and their square-centimeter-sized multilayers on solid substrates. Macromol. Rapid Commun. 34, 16701680 (2013).
  15. Payamyar, P. et al. Synthesis of a covalent monolayer sheet by photochemical anthracene dimerization at the air/water interface and its mechanical characterization by AFM indentation. Adv. Mater. 26, 20522058 (2014).
  16. Bunck, D. N. & Dichtel, W. R. Bulk synthesis of exfoliated two-dimensional polymers using hydrazone-linked covalent organic frameworks. J. Am. Chem. Soc. 135, 1495214955 (2013).
  17. Colson, J. W. et al. Oriented 2D covalent organic framework thin films on single-layer graphene. Science 332, 228231 (2011).
  18. Bianco, E. et al. Stability and exfoliation of germanane: a germanium graphane analogue. ACS Nano 7, 44144421 (2013).
  19. Kuhn, A., Holzmann, T., Nuss, J. & Lotsch, B. V. A facile wet chemistry approach towards unilamellar tin sulfide nanosheets from Li4xSn1–xS2 solid solutions. J. Mater. Chem. A 2, 61006106 (2014).
  20. Xu, M., Liang, T., Shi, M. & Chen, H. Graphene-like two dimensional materials. Chem. Rev. 113, 37663798 (2013).
  21. Beaudoin, D., Maris, T. & Wuest, J. D. Constructing monocrystalline covalent organic networks by polymerization. Nature Chem. 5, 830834 (2013).
  22. Côte, A. P. et al. Porous, crystalline, covalent organic frameworks. Science 310, 11661170 (2005).
  23. Uribe-Romo, F. J. et al. Crystalline covalent organic frameworks with hydrazone linkages. J. Am. Chem. Soc. 133, 1147811481 (2011).
  24. Kuhn, P., Antonietti, M. & Thomas, A. Porous, covalent triazine-based frameworks prepared by ionothermal synthesis. Angew. Chem. Int. Ed. 47, 34503453 (2008).
  25. Kory, M. J., Bergeler, M., Reiher, M. & Schlüter, A. D. Facile synthesis and theoretical conformation analysis of a triazine-based double-decker rotor molecule with three anthracene blades. Chem. Eur. J. 20, 69346938 (2014).
  26. Thomas, J. M. Organic reactions in the solid state: accident and design. Pure Appl. Chem. 51, 19651082 (1979).
  27. Hernandez, Y. et al. High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotech. 3, 563568 (2008).
  28. Ernst, K. H. Molecular chirality in surface science. Surf. Sci. 613, 15 (2013).
  29. Bouas-Laurent, H., Castellan, A., Desvergne, J. P. & Lapouyade, R. Photodimerization of anthracenes in fluid solutions: (part 2) mechanistic aspects of the photocycloaddition and of the photochemical and thermal cleavage. Chem. Soc. Rev. 30, 248263 (2001).
  30. Tomlinson, W. J. et al. Reversible photodimerization: a new type of photochromism. Appl. Optics 11, 533548 (1972).

Download references

Author information

Affiliations

  1. Laboratory of Polymer Chemistry, Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 5, 8093 Zürich, Switzerland

    • Max J. Kory,
    • Payam Payamyar,
    • Stan W. van de Poll &
    • A. Dieter Schlüter
  2. Laboratory of Inorganic Chemistry, Small Molecule Crystallography Center, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, 8093 Zürich, Switzerland

    • Michael Wörle &
    • Nils Trapp
  3. Laboratory of Crystallography, Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 5, 8093 Zürich, Switzerland

    • Thomas Weber &
    • Julia Dshemuchadse

Contributions

M.J.K. designed and performed most of the experiments. T.W., M.W. and N.T. carried out the X-ray crystal structure measurements, and analysed and interpreted the data. P.P. performed the AFM height analyses and helped with the acquisition of SEM images. S.W.v.d.P. carried out some of the exfoliation experiments under the supervision of M.J.K. J.D. performed the X-ray powder diffraction measurements and created the X-ray structure illustrations presented in this paper. A.D.S. initiated the activities for 2DP synthesis, designed the monomer and coordinated the research. A.D.S and M.J.K. wrote the paper.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Supplementary information

PDF files

  1. Supplementary information (5,859 KB)

    Supplementary information

Crystallographic information files

  1. Supplementary information (1,671 KB)

    Crystallographic data for compound 1

  2. Supplementary information (35 KB)

    Crystallographic data for compound 1-partially polymerized

  3. Supplementary information (674 KB)

    Crystallographic data for compound 1-polymer

  4. Supplementary information (4,148 KB)

    Crystallographic data for compound 1-polymer-annealed

  5. Supplementary information (35 KB)

    Crystallographic data for compound 1_depolymerized

Additional data