A Long-Lived Water-Soluble Phenazine Radical Cation.

Long-lived water-soluble organic radical species have long been desired for applications in bioimaging and aqueous energy storage technologies. In the present work, we report a phenazine radical cation sodium 3,3'-(phenazine-5,10-diyl)bis(propane-1-sulfonate) () with a high solubility of 1.4 M and high stability in water. Collaboratively demonstrated by experiments and theoretical calculations, is not prone to undergo dimerization or disproportionation reactions, and its appropriate electron density avoids reactions with oxygen or water, which contribute together to its long lifetime in water under air. With an open-shell configuration, shows interesting magnetic activity with a narrow linewidth in the electron paramagnetic resonance spectra and a magnetic circular dichroism response. exhibits an ambipolar redox activity in water. By pairing with a cheap zinc negative electrolyte, a high-performance aqueous organic redox flow battery based on as a positive electrolyte with an open-circuit voltage of 1.0 V is established, which shows no obvious capacity fade after cycling for 2500 cycles (∼27 days), demonstrating the great promise of for large-scale energy-storage technology.