While the two π-stacked materials do outperform the non-π-stacking TPhP-α, the blue-shifted optical gap (SI, Figure ), lower wettability (SI, Figure and) and smaller driving force (SI, Figure ) of TPhP-α relative to TPyP-α could also contribute to the differences in HER between these two materials. As such, we cannot conclude that TPyP-α outperforms TPhP-α solely due to more optimal π-stacking.