Synthesis of photocatalysts. Inspired by the role of constrained Ar 3 N species as hole transport materials in material science, we designed and prepared catalysts A and B (Figure ). Their key structural feature is the central and planar nitrogen atom, surrounded by three bridged aryl units, with para positions substituted with the aim to prevent their photo-degradation. These compounds were prepared from readily available starting materials in 5 simple and scalable synthetic steps (see SI for further details). To the best of our knowledge, they have not yet been used as photocatalysts.