To check whether the PCs were degrading into the same species, irrespective of reaction conditions, the post-irradiation absorption spectra were overlayed for [Ir(ppy)2(dtbbpy)]PF6, [Ir(dF(CF3)ppy)2(dtbbpy)]PF6, [Cu(dmp)(xantphos)]PF6 and 4CzIPN (Figure ), since these PCs were shown to produce the desired product in at least two of the three photoredox reactions considered. For the metal complexes, no trend could be discerned; however, for 4CzIPN, the post-irradiation absorption spectra obtained in both the pinacol coupling reaction and the Giese type addition reaction are almost identical (Figure ), implying that for this PC, the photodegradation product is similar. This is very likely linked to the photosubstitution of the nitrile group of 4CzIPN for an alkyl group from DIPEA in the pinacol coupling, as shown by Kwon et al., and for an alkyl group from the decarboxylated N-Cbz-Pro, as shown by the work of König and co-workers. The photostability experiments from the ATRA and the Giese type addition reactions indicated that photodegradation of the PCs is not limited to reactions containing sacrificial amine donors, but instead is observed more widely in these other representative photoredox reactions. As such, it is clear that the photostability of the PC should be assessed as a required experiment by the photocatalysis community. Recently, a few reports have explored the complex issue of photostability, for example Wenger et al. noted that functionalised isoacridone dyes tended to decompose upon irradiation in solution; 63 the predominant photodecomposition pathway was proposed to involve the T1 state, which is sensitized in the presence of anthracene. The photodegradation of the PC may be a reason why some PCs perform poorer than expected in certain reactions, despite having suitable thermodynamic properties, which may explain why trends in PC yields cannot always be rationalized by factors such as redox potentials. The photodegradation of the PC means that it becomes difficult to ascertain whether the parent compound and/or its photodegraded version is/are the active PC(s) in the reaction.