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Micrometre-long covalent organic fibres by photoinitiated chain-growth radical polymerization on an alkali-halide surface


On-surface polymerization is a promising technique to prepare organic functional nanomaterials that are challenging to synthesize in solution, but it is typically used on metal substrates, which play a catalytic role. Previous examples on insulating surfaces have involved intermediate self-assembled structures, which face high barriers to diffusion, or annealing to higher temperatures, which generally causes rapid dewetting and desorption of the monomers. Here we report the photoinitiated radical polymerization, initiated from a two-dimensional gas phase, of a dimaleimide monomer on an insulating KCl surface. Polymer fibres up to 1 μm long are formed through chain-like rather than step-like growth. Interactions between potassium cations and the dimaleimide’s oxygen atoms facilitate the propagation of the polymer fibres along a preferred axis of the substrate over long distances. Density functional theory calculations, non-contact atomic force microscopy imaging and manipulations at room temperature were used to explore the initiation and propagation processes, as well as the structure and stability of the resulting one-dimensional polymer fibres.

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The authors acknowledge financial support from the French National Research Agency through contracts ORGANI’SO (ANR-15-CE09-0017) and PhotoNet (ANR-16-JTIC-0002). Via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service ( S. Clair, F. Palmino, C. M. Thomas and A. L. Shluger are acknowledged for helpful discussions.

Author information

All the authors contributed to the scientific discussion and the writing of the manuscript, C.L., L.N. and F.P. performed the NCAFM experiments, M.F. and F.C. purified the molecules, and M.W., D.Z.G. and F.F.C. performed the DFT and MD calculations.

Correspondence to Christian Loppacher or Matthew B. Watkins.

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Supplementary Information

Additional details on the synthesis, characterization and computations; Supplementary Figures 1–7; Supplementary Reference 1

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Fig. 1: Calculated structure and charge-difference plot of a dimaleimide molecule adsorbed on the KCl (001) surface.
Fig. 2: Evaluation of the polymer structure obtained on polymerization without light.
Fig. 3: Influence of weak ultraviolet illumination on the growth of the polymer fibres.
Fig. 4: Proof of the mechanical stability of the fibres.