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) (PSPR) with a high solubility of 1.4 M and high stability in water. Collaboratively demonstrated by experiments and theoretical calculations, PSPR 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, PSPR shows interesting magnetic activity with a narrow linewidth in the electron paramagnetic resonance spectra and a magnetic circular dichroism response. PSPR 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 PSPR 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 (similar to 27 days), demonstrating the great promise of PSPR for large-scale energy-storage technology.

Automated summary

In this work, a long-lived water-soluble organic radical species called PSPR was reported for bioimaging and aqueous energy storage technologies. PSPR has high solubility and stability in water, with a long lifetime due to its resistance to dimerization or disproportionation reactions and its appropriate electron density that prevents reactions with oxygen or water. PSPR also exhibits magnetic activity and ambipolar redox activity in water, making it promising for applications such as redox flow batteries.