Identifying the Key Photosensitizing Factors over Metal–Organic Frameworks for Selective Control of 1O2 and O2⋅− Generation

Abstract

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 (¹O₂) and superoxide (O₂⋅⁻), generated via the sensitization of O₂ by photosensitizers. Studies on uncovering the role of photosensitizing factors on the selective control of ¹O₂ and O₂⋅⁻ 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 ¹O₂ and O₂⋅⁻ 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 O₂⋅⁻ and ¹O₂ pathway, respectively. Investigations reveal that UiO-4 with ligand localized excited state and long excited state lifetime contributed to triggering energy transfer to afford ¹O₂, whereas UiO-1 with charge-transfer state and negative reduction potential facilitates charge transfer to produce O₂⋅⁻. This work offers a novel insight into regulating ROS generation by modulating the photosensitizing factors at the molecular level.