While the Ni(I) signal was too weak to follow via ns-TA here, presumably due to the low molar absorptivity of Ni-OMebpy complexes (~1-15 M -1 cm -1 ), we observed a slow exponential decay of the signal at λ = 600 nm that is predominately due to Ir(IV) on a timescale spanning several hundred µs. Since the signal returns to zero, this decay can be assigned to a back electron transfer reaction (kBET = 5.4 * 10 3 s - 1 ) within the geminate ion pair where Ir(IV) oxidizes Ni(I) to regenerate the neutral pair of species (Fig. ). We propose that this [Ir(IV)][Ni(I)] complex remains as a tight ion pair during this step, resulting in the observed unimolecular decay kinetics. It is worth noting that the dominant Ni species here is [Ni(I)Br2(OMebpy)2] -which is well suited to ion pair with [Ir(ppy)3] + . If a bimolecular BET step is considered instead, a rate constant with a value above the diffusion limit in DMF would be required (See SI, Figure ).