Photochemical reactions hold promise to develop energy-efficient mitigation strategies for (water) contamination. In general, contaminants can be photochemically destroyed/detoxified in two ways under the ambient condition: one, through generating reactive singlet oxygen -for this, the photocatalysts works in the triplet manifold, and the other is photoredox route where targeted organic molecules or heavy metal ions can be decomposed/detoxified. The former strategy has been shown to work well with solid porous systems, even in amorphous compounds where the excitons are expected to be more localized with poor mobility. Photoredox method, as a complementary strategy, should expand the range of the targeted contaminants significantly. However, solid-state photoredox catalysts in ambient conditions are challenging as substrate activation must occur within the nano-(sub-nano-)second lifetime of the excited photosensitizer (PS*). Therefore, in an attempt to develop generalized heterogeneous photoredox catalysts, we focus on efficient exciton migration within metal-organic frameworks instead of the molecular diffusion of excited photosensitizer (PS*). Such critical photochemistry is based on our recent photophysical developments on artificial molecular light-harvesting assemblies within crystalline metal–organic frameworks (MOFs) where tens of photoactive linkers serve as light-absorbing antenna forming spatially dispersed molecular excitons. The next requirement is matching with the required ground and excited-state redox potentials to facilitate the reductive or oxidative quenching of the excitons within the frameworks by the targeted contaminants. MOF-based photoredox chemistry offers a unique opportunity for organic photochemical processes, and therefore, will be used as a model reaction to showcase the potential at this early stage of development.

Designing efficient heterogeneous photo-redox catalysts

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ACS Fall 2022

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