Pleasingly, pDTCz-DPmS photocatalyzed this reaction but again, despite ostensibly having a larger thermodynamically driving force, the NMR yield falls short of that obtained for 4CzIPN (Table ) when conducting the reaction for a period of two hours. This may be linked to the molar absorptivity, ε, of the two photocatalysts at 390 nm, of which the e for 4CzIPN is higher (14.9 × 10 3 M -1 cm -1 vs 12.8 × 10 3 M -1 cm -1 , for 4CzIPN and pDTCz-DPmS, respectively, see Figure ). Since ε is linked to the rate of reaction, 29 the low yield may be explained by slower reaction kinetics; note that the reaction time is only two hours, following the conditions of Wenger et al. Increasing the reaction time to 24 h resulted in a much larger reaction yield for pDTCz-DPmS whereas there was only a minor difference in yield when 4CzIPN was used as the PC (Table ), resulting in comparable yields for the two PCs. Under our conditions, the reaction was also found to proceed without the need for a photocatalyst, this is termed the background reaction. Although the background reaction does also increase with the longer time period (Table ), this cannot fully account for the increase in yield for pDTCz-DPmS. Notably, PCs such as [Ru(bpy)3](PF6)2 cannot turn over this transformation as documented in the literature 28,30 and reproduced with our set-up.