SummaryHere, we present a protocol for the determination of cage-escape yields following excited-state electron transfer between a photosensitizer and a quencher. We describe steps for determining changes in molar absorption coefficient of the different oxidation states via photolysis experiments and the percentage of reacted species via steady-state or time-resolved spectroscopy. We then detail measurement of the amount of formed product via nanosecond transient absorption spectroscopy.For complete details on the use and execution of this protocol, please refer to Ripak et al. (2023).1