Coarse-grained modelling for materials design Emma Wolpert and Kim Jelfs Department of Chemistry, Imperial College London, Molecular Science Research Hub, White City Campus, London, W12 0BZ, UK Coarse-grained models are widely used to simulate molecular and biomolecular systems as a way of reducing the computational cost of calculations but retaining the main chemical and physical degrees of freedom. Whilst common in biological materials 1-5 , using coarse-grained models to develop an understanding of the molecular interactions responsible for the solid-state phase behaviour of organic molecules remains largely unexplored. Here we show how coarse-grained models can be used for materials design by investigating the supramolecular assembly of porous organic cages. In this study, we develop a coarse-grained model to predict the packing of porous organic cages by relating the underlying geometry of the cage to a hard polyhedra with directional interactions through ``patches" between favoured motifs [Fig.1(a)] 6 . Our results show that by manipulating the parameters of our coarse-grained model, we can reproduce the phase space spanned by porous organic cages found within the literature. By mapping the coarse-grained phase space back onto intermolecular interaction strengths determined by a combination of DFT calculations and force field models, we can directly relate each cage to its likely crystal packing structure, highlighting the potential for this model to predict the packing of new, or uncharacterised, cages. Through this, we can examine the interactions necessary to target specific phase formation, informing materials design.
Figure 1: (Left) Atomistic and (right) coarse-grained representation of (a) the porous organic cage CC3 where the orange and blue patchesrepresent the different chemical nature of the cages facets (i.e.window and arene faces), (b) the organic semiconductor [6]helicene where each aromatic ring is represented as a hard sphere with red patches that represent the directional interactions of theπ system, (c) a covalent organic framework where the atoms in the coarse-grained model represent the different nodes/linkers. The principle used in this study is not unique to porous organic cages and we highlight examples of how coarse- grained modelling can be used for materials design in other molecular materials such as organic semiconductors [Fig.1(b)]and covalent organic frameworks[Fig.1(c)] 7 . References 1. I. A. Vakser, Curr. Opin. Struct. Biol. 23, 198 (2013).
2. N. S. Bieler, et al., PLoS Comput. Biol.8, e1002692 (2012). 3. L. Di Michele, et al., J. Phys. Chem. Lett. 4, 3158 (2013) 4. A. Šarić, et al., Nat. Phys. 12, 874 (2016). 5. S. Ranganathan, et al., J. Am. Chem. Soc. 138, 13911 (2016). 6. E. H. Wolpert, et al., Chem. Sci. 13, 13588 (2022). 7. E. H. Wolpert, et al., doi.org/10.21203/rs.3.rs-2361409/v1
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