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

Journal name:
Nature Chemistry
Year published:
Published online


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


  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.


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


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Author information


  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


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.

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    Crystallographic data for compound 1

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    Crystallographic data for compound 1-partially polymerized

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    Crystallographic data for compound 1-polymer

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    Crystallographic data for compound 1-polymer-annealed

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    Crystallographic data for compound 1_depolymerized

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