Covalent organic frameworks (COFs) are crystalline extended solids with permanent porosity constructed from organic building blocks. By virtue of the near infinite number of organic units and diversity of topologies formed, they are a powerful platform for synthetic tunablility for targeted functionality [1]. Recently, solid solutions of COFs have been synthesised where monomers of different lengths are distributed in a non-ordered fashion [2]. This study demonstrates the potential for monomer ratio to be used as a parameter to continuously tune the properties of these emerging materials [2]. The distribution of monomers on the lattice will no doubt influence the resulting properties of the COF, but as of yet it is unknown how the arrangement effects the properties, or whether it is controllable.<br/><br/>In this study we investigate how the distribution of a variety of monomer mixtures, differing in the ratio of their lengths, effects the pore distribution within COF solid solutions. We base our work on the hexagonal COF solid solution reported by Li et al. [2] (Fig 1a). As there are two linear monomers which can bond to the tritopic linker sitting on the vertices of the lattice, the linear linkers can distribute around each vertex in one of four ways (Fig 1b). However, to alleviate strain in the system, we hypothesise that linkers with very different lengths likely arrange themselves in a correlated fashion, only allowing two linkers of the same type around each vertex (Fig 1c). To gain insight on how the COF solid solutions can be utilised to target specific pore sizes, we employ Monte Carlo simulations to investigate the effect of both statistical (Fig 1b) and correlated (Fig 1c) distributions of the linkers on the average pore size of the COF.

Effect of monomer distribution on porosity in COF solid solutions

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