Conjugated microporous polymer frameworks for sustainable energy materials - elucidating the influence of solvents on the porosity properties for future design principles

Since 2010 the influence of reaction solvent choice on the porosity of conjugated microporous polymers (CMPs) has been known, but never fully understood. This means that the current approach to find the optimal conditions for CMP synthesis relies heavily on the empirical knowledge of the researcher and costly solvent screening processes. This approach risks overlooking CMP systems with exceptional properties due to not being synthesised using the optimal solvent. In this work, we have artificially synthesised CMP-1 as a model system in multiple solvents of varying polarities to assess the influence of the reaction solvent choice on the CMP-1 structure. The full synthetic conditions and catalytic pathway were modelled, and we hypothesise that the solvent choice has little to no impact on the micro-structure of the polymer core, but does influence the ratios of meso- to microporosity in the edge regions surrounding the core of the polymer particles due to differences in the phase separation of the polymer from the solvent depending on the solvent polarity. This offers a strategy to explore this structural tuning effect for future CMP materials pre-real-world synthesis, allowing us to identify the optimal conditions for a material with the best opportunity to perform for a target application. Here, we use atomic simulations to rationalise why using high polarity solvents to synthesise conjugated microporous polymers gives a high ratio of micro- to mesoporosity, and using low polarity solvents gives a lower ratio of micro- to mesoporosity.