Substituent effect of conjugated microporous polymers on the photocatalytic hydrogen evolution activity

The construction of a donor–acceptor (D–A) organic photocatalyst is a facile approach to improve photocatalytic performances because of the efficient separation of light-generated electrons and holes. The rational design of molecular skeletons and the selection of functional groups are of great importance to an organic photocatalyst with a high photocatalytic activity. Herein, we designed two D–A conjugated microporous polymers (CMPs) with different substituent groups of fluorine atoms and methyl groups on the acceptor unit of dibenzothiophene-dioxide (DBTDO). This study reveals that the introduction of fluorine atoms with strong electron-withdrawing ability onto the acceptor unit can further enhance the electron acceptability of the DBTDO unit, leading to the efficient separation of light-generated electrons and holes, while the introduction of methyl with electron-pushing ability decreases the electron acceptability of the acceptor unit, suppressing the separation of light-generated charge carriers. As a result, the polymer PyDF with fluorine atoms shows an excellent photocatalytic activity compared to PyDM with methyl groups. Under UV/Vis light irradiation, PyDF shows an attractive photocatalytic hydrogen generation rate of 18.93 mmol h−1 g−1, which is much higher than that of PyDM (3.96 mmol h−1 g−1), implying that the functional group acts as a vital role in the catalytic activity of polymer semiconducting photocatalysts.