The implementation of redox active organic molecules as catholytes in nonaqueous redox flow batteries requires the design of small molecules possessing a number of critical properties. These properties include high oxidation potential, stable electrochemical cycling, a low degree of membrane crossover, and molar levels of solubility. <i>Tris</i>(dialkylamino)cyclopropenium (CP) ions were recently reported as a promising catholyte class based on their high oxidation potential (&gt; 0.8 V vs. Fc/Fc<sup>+</sup>) and stable electrochemical cycling; however, these species are sparingly soluble in their oxidized radical dication state and readily crossover through the membrane to cause detrimental battery self-discharge. Oligomerization of CP ions overcomes the issue of crossover, but further limits their maximum solubility in acetonitrile. This presentation will focus on the parameterization of CP ions for the development of a predictive model for oxidized CP ion solubility in acetonitrile. Because solubility is an ensemble property and many of the CP ions in the data set are conformationally flexibile, a new workflow was designed for this study. A simple and interpretable, two-parameter model is developed and the robustness of the model is validated through a series of statistical techniques. Although the model is established based on properties of CP monomers, the extrapolative power of this model is demonstrated through accurate prediction of oligomer solubility. Ultimately, the model is employed to identify a novel CP dimer exhibiting molar solubility. This work provides important insight into the features critical for nonaqueous solubility of CP ions and showcases that the workflow can effectively translate monomer behavior to predict CP oligomer outputs, quantitatively. Notably, preparation of oligomeric CPs involves multi-step synthetic routes, whereas the monomers are accessed in just a few steps. This model now allows for the straightforward virtual screening of alternative structures to streamline identification of oligomers with enhanced properties.

Monomeric property transfer predicts oligomeric nonaqueous solubility

2019 Fall National Meeting

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