Stepwise assembly of Ni–N2S2 catalytic sites and porphyrin photosensitizers in a metal–organic framework for bioinspired photocatalysis†

Integrating biomimetic catalytic centers and photosensitizers into stable metal–organic frameworks (MOFs) holds great promise for efficient artificial photocatalysis. However, the direct incorporation of catalytic centers and photosensitizers are often hindered by the decomposition of biomimetic catalytic motifs under harsh solvothermal conditions typically required for synthesizing robust MOFs. In this work, we report a stepwise assembly strategy to incorporate biomimetic Ni–N₂S₂ catalytic sites and porphyrin-based photosensitizers into a stable Zr-based MOF for efficient photocatalysis. First, a Zr-MOF (Zr-NiTSC) bearing Ni-thiosemicarbazide (NiTSC) linkers was synthesized under mild conditions, preserving the structural integrity of the Ni–N₂S₂ sites. Subsequently, porphyrin-based linkers (DCPP) as photosensitizers were introduced via post-synthetic linker exchange, yielding a series of mixed-linker MOFs (Zr-NiTSC-Px, x = 1, 2, or 3). By fine-tuning the DCPP/NiTSC ratios, photocatalytic hydrogen evolution experiments revealed a non-monotonic dependence of photocatalytic hydrogen evolution activity on the DCPP/NiTSC ratio, with both insufficient and excessive photosensitizer content diminishing the activity. Zr-NiTSC-P2 achieved a balanced photosensitizer-to-catalyst ratio and the highest activity, with a 2.5-fold increase in turnover frequency compared to the parent MOF. This work demonstrates a stepwise synthetic strategy to integrate labile catalytic motifs into robust frameworks, offering a broadly applicable platform for constructing advanced photosensitized catalytic systems.