Identifying the Key Photosensitizing Factors over Metal-Organic Frameworks for Selective Control of O and O⋅ Generation.

The reaction pathway, product selectivity and catalytic efficiency of photo-oxidation are highly dependent on the specific reactive oxygen species (ROS), such as singlet oxygen (O) and superoxide (O⋅), generated via the sensitization of O by photosensitizers. Studies on uncovering the role of photosensitizing factors on the selective control of O and O⋅ generation are significant but remain underexplored. Here, we constructed a photosensitizing metal-organic framework molecular platform (UiO-1-UiO-4) by elaborately engineering Ir(III) complex ligands with pyrenyl group for modulating photosensitizing factors and elucidating their impact on ROS generation. Impressively, the ratios of O and O⋅ generation varied from 0 : 100 for UiO-1 to 94 : 6 for UiO-4 by modulating photosensitizing factors. UiO-2 and UiO-4 were respectively immobilized in a continuous-flow reactor, achieving gram-scale photosynthesis of phenol and juglone with high purity (>94 %) via O⋅ and O pathway, respectively. Investigations reveal that UiO-4 with ligand localized excited state and long excited state lifetime contributed to triggering energy transfer to afford O, whereas UiO-1 with charge-transfer state and negative reduction potential facilitates charge transfer to produce O⋅. This work offers a novel insight into regulating ROS generation by modulating the photosensitizing factors at the molecular level.