Effect of COF linkage isomerism on photocatalytic hydrogen evolution performance†

Covalent organic frameworks (COFs) have attracted much attention recently as potential photocatalysts for the hydrogen evolution reaction (HER). Linkage isomerism in COFs usually has an important effect on their physicochemical properties. However, the effect of linkage isomerism on the photocatalytic HER performance has been rarely studied. Herein, a pair of COFs with isomeric imine bonds was synthesized, and thus a pair of isomeric amide materials was obtained by oxidation. The photocatalytic HER experiments demonstrated that the photocatalytic HER rates of the isomeric imine COFs were 110.6 and 4.8 μmol h⁻¹, respectively, while those of the amide materials were 2.1 μmol h⁻¹ and negligible, respectively. This indicates that linkage isomerism does have a significant impact on the photocatalytic HER performance. The main reason for this effect is that linkage isomerism leads to prominent differences in light absorption, charge carrier separation and transport, and interfacial reactivity of the two pairs of isomeric materials. Evidently, this work provides a new strategy for designing high-performance COF catalysts.