We attribute the induction period to the slow and photon-inefficient EDA fragmentation, resulting in a slow generation of product (P). However, if photolytic EDA fragmentation was the rate-determining step through the reaction, one would expect the reaction rate to decline as the concentration of RAE decreases. Instead, an increasing rate was observed in the second phase, indicating a chain-propagative radical mechanism, which is consistent with previous EDA methodologies. The chain propagation in our proposed mechanism, as modelled by DFT, depends on a base to deprotonate the aryl radical adduct (I1 in Fig. ). This step would be rate-limiting in the initial phase of the reaction, as the phthalimide anion has not yet accumulated in solution from RAE fragmentation.