C O M P L E X S Y S T E M S A N D B I O M E D I C A L S C I E N C E S

S C I E N T I F I C H I G H L I G H T S

6 6 H I G H L I G H T S 2 0 2 2 I

Fig 56: a) Conventional and de novo synthetic approaches of intercalating 2D materials. b) Conical fullerene amphiphile (CFA) with pseudo-C5 symmetry favours lateral growth via hydrogen bonding.

c) Intercalating nanofilm formation at the air/water interface via dissipative quenching of solvent.

De novo formation of non-crystalline fullerene bilayer on water surface

Octopus-shaped, conical fullerene amphiphile with five carboxylic acid legs spontaneously forms a densely packed nanofilm on water surface without compression. Specular X-ray reflectivity and grazing incidence wide-angle X-ray scattering revealed that the nanofilm consists of a non- crystalline CFA bilayer, confining a hydrogen- bonded network in between.

Two-dimensional (2D) intercalated materials have attracted increasing attention both for fundamental research on atoms and molecules confined in nanometric space and for a variety of applications in materials science, ranging from energy storage to charge transport. To date, the conventional top-down approaches (inserting intercalants into a layered material) and bottom- up approaches (assembling layers and intercalants together) have suffered from fundamental drawbacks. The top-down approach often lacks the control of long-range structural uniformity, while the bottom-up approach, relying on the self-assembly of molecular

building blocks, is intrinsically unsuited for the upscaled production of robust materials. Self-assembly driven by strong intermolecular forces tends to form a crystalline and brittle film.

As a new de novo strategy (Figure 56a), this study reports the formation of an intercalating nanofilm of a hydrogen-bonded network between two monolayers of conical fullerene amphiphile (CFA) (Figure 56b). The structure of the CFA drives the molecule to form a skewed dimer instead of a face-to-face dimer, and the near-C5 symmetry hampers the crystallisation of the forming 2D film. CFA dissolved in toluene/1-butanol spontaneously forms a uniform film on water over several tens of cm2 in a few hours under ambient conditions (Figure 56c). The CFA films can be transferred to flat or perforated substrates due to high mechanical stability.

The in-plane and out-of-plane structures of as-prepared CFA films at the water surface were studied with grazing incidence wide-angle X-ray scattering (GIWAXS) and specular X-ray reflectivity (XRR) measurements at beamline ID10 (Figure 57a). GIWAXS data showed no sign of periodic, long-range order, which seems