Fluorescent Sensing of SO₂ by MFM‐300(M) Metal–Organic Frameworks: Influence of Semi‐Open Metal Centres

The MFM‐300(M) series (M = Al(III), Sc(III), Cr(III), and In(III)) have previously demonstrated excellent sulfur dioxide (SO 2 ) adsorption capabilities, however, their potential as fluorescent SO 2 sensors remains unexplored. Here, this work presents a comparative study of their fluorescence response upon SO 2 exposure, with a particular focus on the role of the metal centers. MFM‐300(Al) exhibits the strongest emission and highest quenching upon SO 2 exposure, attributed to localized interactions with µ 2 ‐OH functional groups and aromatic sites. In contrast, Sc(III) and In(III) analogues show moderate quenching via charge transfer at the semi‐open metal sites, while Cr(III) remains weakly emissive. Density Functional Theory (DFT) calculations employing periodic boundary conditions are conducted to characterize the electronic structure of MFM‐300(M), to elucidate the role of metal centers in SO 2 retention and to assess the semiconducting nature of these metal‐ organic frameworks (MOFs).