Recently, a number of detailed mechanistic studies have been reported which use a wide range of techniques to elucidate catalytic cycles involving cationic iridium PCs which, as strong photo-oxidants, were reported to participate in reductive quenching cycles (Fig. ) or energy transfer. Although these reports are highly useful, they provide only limited insight into systems in which highly reducing PCs such as Ir(ppy)3 are used. In contrast, while oxidative quenching cycles (Fig. ) have been proposed in the literature occasionally with regards to Ni/PC dual catalytic C─C, C─O, C─N, or C─S bond forming systems, sometimes with computational support, experiments capable of distinguishing between oxidative quenching, reductive quenching, and energy transfer (see reviews for relevant spectroscopic and electrochemical methods) have not been performed in the study of these systems.