Abstract:

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.

Key words: Conjugated porous polymers, Electronic structure matching, Donor-acceptor, Charge carrier separation, Hydrogen production