Abstract
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 (Ag12bpy-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. Ag12bpy-NH2 quantifies oxygen during hypoxia with the limit of detection of as low as 0.1 ppm and 0.3 s 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.
Highlights
Ratiometric luminescent oxygen sensing based on dual fluorescence and phosphorescence emission in a single matrix is highly desirable, yet the designed synthesis remains challenging
Far, designing such integrated luminophores has achieved limited success for the following reasons: first, achieving balanced Fl and Ph intensities originating from the same luminophore is challenging for a ratiometric O2 sensor because, as stated by Kasha’s rule, photon emissions occur from only the lowest excited state[14]; second, phosphors that have both long-lived Ph and a high quantum yield (QY) at room temperature are difficult to prepare due to the intrinsic competition between the Ph lifetime and efficiency[15]; third, this type of luminophore must have a high oxygen permeability for free gas diffusion[2,3,4,5,6,7,8]
Bpy-NH2 has an unchanged length and unaltered connectivity (Fig. 1c); introducing an amino group at the 3position of bpy greatly alters the reaction conditions: the synthesis method used for the Ag12bpy structures that are synthesized in mixed CH3CN and C2H5OH is no longer applicable for Ag12bpyNH2
Summary
Ratiometric luminescent oxygen sensing based on dual fluorescence and phosphorescence emission in a single matrix is highly desirable, yet the designed synthesis remains challenging. We rationally introduce −NH2 groups on the linkers of a silver-chalcogenolatecluster-based metal-organic framework (Ag12bpy-NH2) to tune the intersystem crossing, achieving a dual fluorescence-phosphorescence emission from the same linker chromophore. We hypothesize that, according to the interligand trans-metallic charge-transfer (ITCT) emission mechanism of Ag12bpy[33,36], the additional introduction of the organic ligand-centered Fl emission can achieve dual Fl-Ph emission centers in the host framework of a SCC-MOF, whose Ph component is supposed to be sensitive to oxygen; the functional modification of the MOF linker can modulate the Ph properties by changing the intersystem crossing (ISC) efficiency; ratiometric oxygen sensing could be achieved in a SCC-MOF with a higher sensitivity. The large gap of ~100 nm between the emission wavelengths and the increased lifetime difference a Ph 3O2 Qu b
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