Any subtle changes in the UV-Vis absorption spectra will ultimately have an impact on the ε value, meaning that aside from the thermodynamic driving force that may change with solvent (such as redox potentials), the kinetics of the reaction will also be impacted by the polarity of the solvent. To allow for a fair cross-comparison of the PCs, the same optical density of the excited PC should be present in the reaction mixture. This in practice is not done (and would not be something that most synthetic photochemists would take into account) and we can only comment on the variation of the ε values at the excitation wavelengths chosen for the photocatalysis reactions (456 nm and 390 nm) and assess how this may correlate with the yield of the reaction.