Design of donor–acceptor covalent organic frameworks for photocatalytic hydrogen generation†

Abstract

The well-ordered π-conjugated backbone facilitates efficient light absorption, enhancing carrier mobility, while the tensile molecular structure allows precise tailoring of optoelectronic properties. In addition, the alternating arrangement of donor (D) and acceptor (A) segments in the well-ordered π-conjugated framework provides pathways and channels for intermolecular charge transfer (ICT). Therefore, the precise integration of the D and A moieties into the long-range ordered backbone of the COFs accelerates carrier mobilities and reduces the possibility of electron–hole recombination. COFs with a D–A system have made great progress in the related research of photocatalytic applications. It is anticipated that COFs consisting of polar hydrophilic electron-withdrawing groups (e.g., COOH) can promote the efficient migration of photogenerated electrons to the Pt cocatalyst for the reduction of water protons to produce hydrogen. Herein, we demonstrate the tuning of hydrogen evolution activity by tailoring the functionality of pyrene-based COFs by introducing donor (D) and acceptor (A) functionalities to facilitate the effective charge separation through the push–pull effect. Further, in order to systematically study the photocatalytic performances, a series of D–A COFs with different linkages and electron-donating/withdrawing groups have been synthesized. This difference in photocatalytic hydrogen generation activity is further supported by different optical and electrochemical studies. This work highlights the rational tuning of the hydrogen generation activity of COFs by strategic incorporation of appropriate functionality.