Simple Air‐Stable [3] Radialene Anion Radicals as Environmentally Switchable Catholytes in Water
Date
2023-11-15
Authors
Hasan, Fuead
Gillen, Jonathan H.
Jayaweera, Amaya T.
McDearmon Jr., William D.
Bejger, Christopher M.
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A European Journal published by Wiley-VCH GmbH
Abstract
The hexacyano[3]radialene radical anion (1) is an attractive catholyte material for use in redox flow battery (RFB) applications. The substitution of cyano groups with ester moieties enhances solubility while maintaining redox reversibility and favorable redox potentials. Here we show that these ester-functionalized, hexasubstituted [3]radialene radical anions dimerize reversibly in water. The dimerization mode is substitution pattern dependent and can be switched in solution. Stimuli-responsive behavior is achieved by exploiting an unprecedented tristate switching mechanism, wherein the radical can be toggled between the free radical, a π-dimer, and a sigma-dimer -- each with dramatically different optical, magnetic, and redox properties -- by changing the solvent environment, temperature, or salinity. The symmetric, triester-tricyano[3]radialene (3) forms a solvent-responsive, σ-dimer in water that converts to the radical anion with the addition of organic solvents or to a π-dimer in brine solutions. Diester-tetracyano[3]radialene (2) exists primarily as a π-dimer in aqueous solutions and a radical anion in organic solvents. The dimerization behavior of both 2 and 3 is temperature dependent in solutions of methanol. Dimerization equilibrium has a direct impact on catholyte stability during galvanostatic charge-discharge cycling in static H-cells. Specifically, conditions that favor the free radical anion or π-dimer exhibit significantly enhanced cycling profiles.
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This article is published as Hasan, Fuead, Jonathan H. Gillen, Amaya T. Jayaweera, William D. McDearmon Jr, Arthur H. Winter, and Christopher Bejger. "Simple Air‐Stable [3] Radialene Anion Radicals as Environmentally Switchable Catholytes in Water." Chemistry–A European Journal (2023): e202302829. doi: https://doi.org/10.1002/chem.202302829. © 2023The Authors. This is an open access article under the terms of the Creative Commons Attribution.