Building 2D quasicrystals from 5-fold symmetric corannulene molecules

A comparative study has been performed on the adsorption of structurally related but stereochemically different C₆₀ and C₂₀H₁₀ molecules on the 5-fold surface of the icosahedral i-Ag-In-Yb quasicrystal. Both molecules have similar lateral dimensions and have the same pentagonal carbon ring surrounded by five phenyls. However, while C₆₀ molecules have 2-, 3- and 5-fold rotational symmetries, C₂₀H₁₀ only have C_5v symmetry. Therefore both organic moieties can match the underlying surface symmetry, but the C₆₀ have more degrees of freedom regarding its adsorption geometry on such complex substrate compared to C₂₀H₁₀. As a result, it is found that the C₆₀ adsorption on 5-fold symmetry i-Ag-In-Yb surface did not yield any ordered molecular films as evidenced from LEED and STM studies. In contrast, the templating effect was successfully exploited in corannulene self-assembly, even at moderate deposition temperatures. Analysis of STM images and associated autocorrelation pattern clearly demonstrates that corannulenes adsorb with its convex side down preferentially at five-fold symmetric sites (RTH cluster centers and Yb pentagons), thus enforcing long-range quasiperiodic order in the film. Since corannulene can be viewed as a fragment of C₆₀ with only C_5v symmetry, it can be hypothesized that these molecules probably enhance the dominant role of molecule-substrate symmetry matching. As the NN distance of 1.3 nm on i-Ag-In-Yb substrate is rather large, it suggests sufficiently weak intermolecular interaction in the organic film. Therefore, the molecule-surface interactions had to play a major role in generating principally different patterns with related C₂₀H₁₀ and C₆₀ molecules, i.e. either quasiperiodic or disordered networks, respectively. The role of the symmetry matching should be investigated further, possibly through density functional calculations of the molecular adsorption energies for example.

There are many bowl-shaped corannulene derivatives with C₅ rotational axis with various functionalities. They represent a class of molecules which can potentially self-assemble into quasiperiodic patterns on quasicrystalline templates using the same mechanism. Also the saturated quasiperiodic monolayer could potentially be extended in the third dimension, by further piling of corannulenes with a bowl-in-bowl geometry. This has already been demonstrated for periodic molecular pattern and could be extended to form the equivalent of a decagonal molecular quasicrystal.

 

Nataliya Kalashnyk, Julian Ledieu, Émilie Gaudry, Can Cui, An-Pang Tsai, and Vincent Fournée; “Building 2D quasicrystals from 5-fold symmetric corannulene molecules”, Nano Research, (2017) https://doi.org/10.1007/s12274-017-1830-x