Materials and methods. All chemicals and solvents were purchased from commercial suppliers and used without further purification unless otherwise noted. H NMR spectra were collected using a Bruker Avance III HD operating at 11.74 T, 500 MHz. Mass spectra were collected via electrospray ionization mass spectrometry using a Waters Synapt G2-Si ESI mass spectrometer. Ru-bpm was synthesized according to the previously published procedure. Electrochemistry. Cyclic voltammetry (CV) measurements of the Ru-bpm were performed in a standard three-electrode cell consisting of a glassy carbon (GC, MF-2012, Bioanalytical systems, 0.075 cm 2 surface area) working electrode, 3M Ag/AgCl aqueous reference electrode (MF-2052, Bioanalytical systems) and Pt wire counter electrode (MW-4130, Bioanalytical systems). The CV measurements were performed at 1 mM Ru-bpm concentrations in aqueous 1 M phosphate solutions in the pH 2-12 region. At highly acidic (pH ≤ 1) and basic (pH ≥ 13) pHs, solutions were made with HClO4 and NaOH, respectively. Each working electrode was polished before each measurement with alumina (CF-1050, Bioanalytical systems) and diamond (MF-2054, Bioanalytical systems) slurry. All the potentials shown are referenced against the normal hydrogen electrode (NHE).