Tuning the Porosity and Photocatalytic Performance of Triazine‐Based Graphdiyne Polymers through Polymorphism

Crystalline and amorphous organic materials are an emergent class of heterogeneous photocatalysts for the generation of hydrogen from water, but a direct correlation between their structures and the resulting properties has not been achieved so far. To make a meaningful comparison between structurally different, yet chemically similar porous polymers, two porous polymorphs of a triazine‐based graphdiyne (TzG) framework are synthesized by a simple, one‐pot homocoupling polymerization reaction using as catalysts Cu^I for TzG_Cu and Pd^II/Cu^I for TzG_Pd/Cu. The polymers form through irreversible coupling reactions and give rise to a crystalline (TzG_Cu) and an amorphous (TzG_Pd/Cu) polymorph. Notably, the crystalline and amorphous polymorphs are narrow‐gap semiconductors with permanent surface areas of 660 m² g⁻¹ and 392 m² g⁻¹, respectively. Hence, both polymers are ideal heterogeneous photocatalysts for water splitting with some of the highest hydrogen evolution rates reported to date (up to 972 μmol h⁻¹ g⁻¹ with and 276 μmol h⁻¹ g⁻¹ without Pt cocatalyst). Crystalline order is found to improve delocalization, whereas the amorphous polymorph requires a cocatalyst for efficient charge transfer. This will need to be considered in future rational design of polymer catalysts and organic electronics.