Photocatalytic Hydrogen Evolution Based on Nitrogen-Containing Donor–Acceptor (D–A) Organic Conjugated Small Molecules

Photocatalytic water splitting has attracted widespread attention as one of the eco-friendly technologies that can scalably produce low-cost renewable solar hydrogen. As a rare case, in this work, we apply organic conjugated small molecules to photocatalytic hydrogen evolution and compare the photocatalytic performance of CM1, CM2, and M1, whose number of N atoms is controlled by replacing the intramolecular electron donor unit with benzene, pyridine, and pyrazole, respectively. There is a clear correlation between the photocatalytic activity and the number of N atoms in the structure, as N atoms can be active sites for the photocatalytic interface reaction and help to improve the water dispersibility and contact of organic conjugated molecules through hydrogen-bonding interactions. In addition, we apply a single-atom substitution strategy (O, S, Se) to control the photoelectric properties of organic conjugated molecules. Among these molecules, M1 exhibits the best performance, even better than the previous series of polymers P2 and P4.