Tuning the porosity and photocatalytic performance of triazinebased graphdiyene polymers via 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, we present two porous polymorphs of a
triazine-based graphdiyene (TzG) framework from a simple, one-pot
reaction using Cu(I) for TzG_Cu and Pd(II)/Cu(I) for TzG_Pd/Cu catalyzed
homocoupling polymerization. The polymers form via 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 thus far up to 972 μmol h^-1 g^-1 with and 276 μmol h^-1 g^-1
without Pt co-catalyst. We conclude, that crystalline order improves
delocalisation, while the amorphous polymorph requires a co-catalyst
for efficient charge transfer; this will need to be considered in future
rational design of polymer catalysts and organic electronics.