The effect of electronic structure matching between building blocks in conjugated porous polymers on photocatalytic hydrogen evolution activity

Conjugated porous polymers have been extensively studied as photocatalysts for hydrogen generation. However, the photocatalytic efficiency is often hindered by the inefficient charge separation and rapid recombination of photo-induced charge carriers, both are strongly affected by the electronic structure of the co-monomers in polymer photocatalysts. In this study, we design three conjugated porous polymers with distinct electronic architectures by combining dibenzo[g,p]chrysene (DBC) and benzene with different substituted groups. The results demonstrate that the combination of DBC and the unsubstituted benzene forms a donor-donor (D-D) structure due to their similar energy levels, while the introduction of methoxy enhances the electron-donating ability of benzene ring, leading to a reinforced D-D structure between DBC and the methoxy-substituted benzene unit, which suppresses the charges separation. In contrast, the introduction of electron-withdrawing cyano group significantly enhances the electron receptivity of the benzene unit, leading to the formation of donor-acceptor (D-A) structure between DBC and the cyano-substituted benzene unit, promoting charges transfer and separation of light-induced electrons and holes. As a result, the D-A polymer DBC-BCN achieves an impressive hydrogen evolution rate (HER) of 20.67 mmol h^–1 g^–1 under UV-Vis light irradiation, outperforming the D-D polymers of DBC-BMO (2.13 mmol h^–1 g^–1) and DBC-B (13.10 mmol h^–1 g^–1). This study underscores the importance of the electronic structure matching of building blocks in polymer photocatalysts to enhance the photocatalytic activity.