Solid-State Luminescence Turn-On Sensing Using MOF-Confined Reporter-Spacer-Receptor Architectures Facilitated by Quencher Displacement

The reporter-spacer-receptor (RSR) approach is prevalent to develop molecular turn-on sensors. However, the fluorescent RSR sensors barely operate in solid state, which hinders their fabrication into devices for practical applications. Herein, we present a novel strategy to achieve solid-state luminescence turn-on sensing by assembling RSR architectures within MOF frameworks. Unlike the regular RSR systems, the framework-confined fluorophore and receptor are well arranged and separated even in the solid state. This concept is illustrated by a multicomponent MOF (Fc@NU-1000), which contains organic linkers with a highly luminescent pyrene core as the reporter, Zr6 nodes with unsaturated sites as the receptor, and the incorporated Fc molecules as the quencher. The separate incorporation of pyrene core and Fc in the multicomponent MOF favors an efficient pseudointramolecular photoinduced electron transfer (PET) process, resulting in significant luminescence quenching. Interestingly, such PET process can be blocked via the quencher displacement initiated by the phosphate analyte, therefore recovering the solid-state luminescence of MOF microcrystals. We found that Fc@NU-1000 is shown as a sensitive solidstate luminescence turn-on probe for phosphate with the naked-eye response at a low content. What's more, this study is the first example of confining a quencher displacement-based RSR system in the MOF framework for solid-state luminescence turn-on sensing, thus also providing new opportunities for MOF materials to develop luminescence turn-on sensors.