Firstly, we take a closer look at each photocatalytic DFT descriptor. To aid the evaluation of structure-property relationships for our descriptors, we determined a set of 26 substructures (see SI for the complete list) based on chemical intuition and on their occurrence as building blocks (linkages and linkers) and functional groups in COFs. Searching for the presence of those substructures in the CURATED COFs allows for methodical pattern-seeking when it comes to the structure-property relationships. Such a pattern has been shown previously, indicating benzene-based functional groups with C 3v symmetry and nitrogen-based functional groups as potential catalytic active sites for OER and HER, respectively. Among the defined substructures, we proceed to discuss the ones that presented statistically significant effects on our photocatalytic DFT descriptors, not considering the ones with only a few data points or that showed no effect.