Reductive Quench. Our investigations began with a decarboxylative photo-Giese reaction. This process has previously been reported by Ji et al. for their comparison of the effectiveness of different acridinium photocatalysts and also by Speckmeier et al. for their comparison of the suitability of alternative D-A photocatalysts. In the latter study Speckmeier et al. found that when 4CzIPN was used, a superior isolated yield of 80% is achieved compared to the previously reported best acridinium photocatalyst, which produced an isolated yield of 73%. Using N-Cbz protected proline 1a as the carboxylic acid substrate and diethyl maleate 2 as the electron deficient alkene, both DiKTa and Mes3DiKTa gave comparable NMR yields to that of 4CzIPN (Table , therefore, the more challenging iso-butyric acid, 1b, and propanoic acid, 1c, were also investigated in order to differentiate the photooxidation ability of the PCs. With iso-butyric acid both DiKTa and Mes3DiKTa showed improved NMR yields of 78% and 79%, respectively (Table , entries 4 and 5), relative to the 64% achieved using 4CzIPN (Table , entry 6). Changing to the primary radical formed when using propanoic acid resulted in lower yields for all three PCs (Table , entries 7-9). This is likely due to the decreased nucleophilicity of primary radicals relative to secondary radicals, leading to alternative and undesired reaction pathways becoming competitive. Notwithstanding the lower yields, both DiKTa and Mes3DiKTa still outperformed 4CzIPN (Table , entries 7-9).