Phenanthroimidazole-Based Covalent Organic Frameworks with Enhanced Activity for the Photocatalytic Hydrogen Evolution Reaction

The rational design of organic semiconductors based on crystalline covalent organic frameworks (COFs) as efficient photocatalysts is highly desirable. In this study, the first example of phenanthroimidazole-based COFs is reported: PIm-COF1 with an imine linkage and PIm-COF2 with a β-ketoenamine-linkage. Both COF materials showed substantial optical properties. The average hydrogen evolution rate was 7417.5 μmolg–1 h–1 for PIm-COF2, which was 14 times higher than that of PIm-COF1 (528.5 μmolg–1 h–1). This can be attributed to the strong donor–acceptor effect of PIm-COF2 and the continuous separation and transfer of the photoexcited electron–hole pair from the phenanthro[9,10-d] imidazole moiety which are verified by time-dependent density functional theory and excitation state analysis.