Engineering of Metal–Organic Frameworks as Ratiometric Sensors

In the last two decades, metal–organic frameworks (MOFs) have appeared as new multifunctional materials that show a variety of framework architectures depending on the choice of metal ions and ligands. Among several features that have been displayed by MOF, one of the important properties is its luminescent behavior that can arise from the ligand unit, metal ions, or the cavity guest molecules. Ratiometric fluorescence (RF) sensors can be made by changing the fluorescence intensity of emission peaks associated with multi-emission probes, but the synthesis of such materials is always a challenge, as it requires multifluorescence groups having the same excitation with diverse emission wavelengths. In the case of MOFs, such features can be included by modifying the ligand unit and selecting the suitable metal ions or by using a desired guest molecule. As a result, MOF can act as a promising candidate for the construction of ratiometric fluorescence (RF) sensors. Thus, our aim in this review is to summarize some of the recent development that has been done in terms of synthesis, mechanism, and applications of ratiometric sensors by using MOF materials.