Adaptive Supramolecular Interactions Govern Redox-Active Molecules in Aqueous Redox Flow Batteries

Weak noncovalent interactions critically govern molecular behavior in solution, yet how they shape redox processes in aqueous electrochemical environments remains underexplored. Here, we demonstrate control over the solubility and redox stability of aromatic redox-active molecules in aqueous redox flow batteries (RFBs). Zwitterionic substitution of naphthalene diimide (NDI) bearing quaternary ammonium and sulfonate groups shows weak π-π cohesion through steric and electrostatic effects, rendering otherwise insoluble NDIs responsive to external anions. Hydrophobic and weakly hydrated anions such as iodide and bis(trifluoromethanesulfonyl)imide disrupt residual stacking through anion-π interactions, enabling dissolution to concentrations approaching 1.3 M. Upon electrochemical reduction, these anions dissociate, and the reduced NDI species are instead stabilized through spin pairing and cation-mediated intermolecular interactions, which suppress irreversible aggregation, slow self-discharge, and enable rapid redox reactions. Operando Raman spectroscopy, ¹H NMR, and EPR elucidate the redox-state-dependent evolution of these supramolecular assemblies. Together, these results establish zwitterionic molecular design for adaptive supramolecular redox chemistry in aqueous RFBs.