M A T T E R A T E X T R E M E S
S C I E N T I F I C H I G H L I G H T S
2 4 H I G H L I G H T S 2 0 2 1 I
The arene-perfluoroarene co-crystals exhibit a remarkable pressure stability and, hence, retention of their highly- ordered p-stacking arrangement up to the pressure of polymerisation onset at 20 25 GPa (Figure 11a). Although amorphisation has typically been reported to occur simultaneously with the polymerisation process, it was possible to observe single-crystal diffraction spots of the polymer samples still indicating highly ordered polymer structures. One of the most striking results was that the experimental single-crystal diffraction data allowed indexing of the polymer unit cells, thus confirming the formation of polymers along the p-stacks. The one-dimensional polymer growth was corroborated by complementary infrared spectroscopic studies on the kinetics of the high-pressure reaction, and polymer structures were proposed from ab-initio computations (Figure 10, right).
The polymers consist of highly ordered rods of hydrofluorocarbons. Depending on the starting molecules,
the lateral extension and the bonding scheme of these rods may vary. Pressure-induced polymerisation takes place via a one-dimensional zipper reaction, which is preceded by a Diels-Alder 4+2 cycloaddition reaction in naphthalene:perfluoronaphthalene. This compound forms a double-thread zipper polymer structure, while in anthra-cene:perfluoronaphthalene, the mismatch of polycyclic rings leads to a diamondoid polymer structure (Figure 11b).
These results provide a clear picture of the mechanisms of pressure-induced polymerisation of aromatic compounds, and show the potential of the arene-perfluoroarene interaction for the high-pressure stabilisation of the molecular arrangement prior to polymerisation. These findings may offer a route towards the tailored design of novel, thread-like, carbon-based nanomaterials by controlling the width and lateral extension of the threads by variation of the arene and perfluoroarene starting molecules.
Fig. 11: a) Compression of the interplanar separations between
arene (naphthalene or anthracene) and perfluoronaphthalene (PFN)
molecules to 2.7 2.8 Å before pressure-induced polymerisation
(PIP). b) Sketch of the proposed PIP mechanism leading to the
formation of C C s-bonds between the units.
PRINCIPAL PUBLICATION AND AUTHORS Pressure-Induced Polymerization of Polycyclic Arene−Perfluoroarene Cocrystals: Single Crystal X-ray Diffraction Studies, Reaction Kinetics, and Design of Columnar Hydrofluorocarbons, A. Friedrich (a), I.E. Collings (b), K.F. Dziubek (c), S. Fanetti (c, d), K. Radacki (a), J. Ruiz-Fuertes (e,f), J. Pellicer-Porres (e), M. Hanfland (b), D. Sieh (a), R. Bini (c,d,g), S.J. Clark (h), T.B. Marder (a), J. Am. Chem. Soc. 142, 18907- 18923 (2020); https:/dx.doi.org/10.1021/jacs.0c09021 (a) Institute of Inorganic Chemistry, Julius-Maximilians-Universität Würzburg (Germany) (b) ESRF (c) LENS, Sesto Fiorentino (Italy) (d) ICCOM-CNR, Sesto Fiorentino (Italy) (e) MALTA Consolider Team, Universitat de València, Burjassot (Spain) (f) DCITIMAC, MALTA Consolider Team, Universidad de Cantabria, Santander (Spain) (g) Dipartimento di Chimica, Università degli Studi di Firenze, Sesto Fiorentino (Italy) (h) Department of Physics, University of Durham (UK)
REFERENCES  T.C. Fitzgibbons et al., Nat. Mater. 14, 43-47 (2015).  S. Fanetti et al., Nanoscale 12, 5233-5242 (2020).  J.C. Collings et al., New J. Chem. 25, 1410-1417 (2001).