Ligand engineering to achieve enhanced ratiometric oxygen sensing in a silver cluster-based metal-organic framework

Ratiometric luminescent oxygen sensing based on dual fluorescence and phosphorescence emission in a single matrix is highly desirable, yet the designed synthesis remains challenging. Silver-chalcogenolate-cluster-based metal-organic frameworks that combine the advantages of silver clusters and metal-organic frameworks have displayed unique luminescent properties. Herein, we rationally introduce -NH2 groups on the linkers of a silver-chalcogenolate-cluster-based metal-organic framework (Ag(12)bpy-NH2) to tune the intersystem crossing, achieving a dual fluorescence-phosphorescence emission from the same linker chromophore. The blue fluorescence component has a 100-nm gap in wavelength and 8,500,000-fold difference in lifetime relative to a yellow phosphorescence component. Ag(12)bpy-NH2 quantifies oxygen during hypoxia with the limit of detection of as low as 0.1 ppm and 0.3s response time, which is visualized by the naked eye. Our work shows that metal cluster-based MOFs have great potential in luminescent sensing, and the longer-lived charge-separated states could find more photofunctional applications in solar energy transformation and photocatalysis. Incorporating dual fluorescence and phosphorescence into a single matrix is attractive for oxygen sensing, but material design is challenging. Here the authors achieve dual fluorescence-phosphorescence from a single linker chromophore in a silver chalcogenolate-cluster-based metal-organic framework.