Measurements of the UC decay kinetics at different IEX were performed and was followed by a global fitting procedure in which tT was fitted to a global constant value while allowing b to vary (Figure , see Supporting Information section 2.4 for more details). The results show that PPO has a lifetime of 1.3 ms, which is substantially longer than that previously reported for UC systems employing PPO, but close to that obtained from flash photolysis experiments. The longest lifetime was found for TIPS-Naph at 2.2 ms, resonating well with its impressive performance in terms of FUC,g. The remaining lifetimes span from 0.075 to 0.75 ms (Table ), which is much shorter than those often found in visible emitters based on anthracene, where lifetimes on the order of several milliseconds are common. At high IEX most annihilators still show b values relatively close to unity, indicating that the TTA pathway dominates at high IEX (Figure ).