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.