To investigate the nature of the long-lived species formed during photocatalysis, we employed continuous-wave electron spin resonance (ESR) spectroscopy. Therein, 1 mM samples of the dinuclear complexes were irradiated in the cavity of the ESRspectrometer using a blue LED mounted onto the spectrometer. After about five minutes of irradiation, a photostationary state was reached in the signal intensity, the radical traces in Figure show the 1 st derivative of the ESR signal of this stationary state. For the three photocatalysts prbimRuPt, fbpyRuPt, and tbbpyRuPt g-factor found are very similiar (2.004) and are in line with previous findings for phenazine containing metal complexes. This suggests, that for all the catalysts a stationary state with excess electron density on the phz-sphere of the bridging ligand is formed. While for prbimRuPt and tbbpyRuPt this is consistent with the insights obtained by TA spectroscopy, a long-lived state with excess electron density in the peripheral ligand sphere was found for fbpyRuPt by the same method. Circumspectly, this can be explained by structural and electronic changes occurring at the tpphz bridge during photocatalysis, i.e. stabilization of radical intermediates, such as protonation of the bridge -which is a plausible scenario for the complexes studied herein. Hydrogen production turnover. The catalytic performance of prbimRuPt has been screened under identical conditions and compared with the catalytic data of fbpyRuPt and tbbpyRuPt (re-measured under this standard, cf. experimental details). The respective catalysis results are summarized in Figure .