For CzBN, however, the absorption profiles under both inert and aerated atmospheres changed significantly after irradiation, implying that CzBN is unstable under these conditions. It is not evident why there is such a divergent photostability behavior between these two photocatalysts nor how this is correlated to reaction yield. CzBN is the best PC of the four for this transformation. There seems to be a correlation between the reaction yield and the ∆EST of the PC as CzBN has the smallest one at ∆EST of 0.09 eV (cf.