Fluorescence Modulation in UiO-66-NH₂ via Photooxidation and Selective Reduction

Metal-organic frameworks with emissive ligands offer tunable photophysical properties that are sensitive to their coordination environment and structural configuration. In this study, we demonstrate that the fluorescence of UiO-66-NH₂ can be modulated through photo-oxidation-induced quenching and subsequent solvent-mediated recovery. Upon visible-light irradiation, reactive oxygen species induce two distinct oxidation pathways: irreversible oxidation of the ligand and reversible oxidation of the metal-oxo cluster. These redox events lead to partial disruption of the coordination environment and result in fluorescence loss. Reduction using mild alcohols selectively removes adsorbed oxidative species from Zr₆O₄(OH)₄, leading to partial recovery of fluorescence and porosity. The extent of fluorescence restoration correlates with both the reducing strength and molecular size of the alcohol, reflecting its ability to penetrate internal pores and access to redox-active sites. Notably, some alcohol-treated samples exhibited nitrogen uptake beyond that of pristine UiO-66-NH₂, suggesting redux-induced structural reorganization and defect-assisted pore expansion. These results establish a structure-function relationship in MOFs governed by localized redox chemistry, providing a platform for designing reconfigurable optical materials with switchable photophysical and porous characteristics.