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

## TL;DR

This paper explores how different metal centers in MFM-300(M) materials affect their ability to detect sulfur dioxide through fluorescence.

## Contribution

The study introduces MFM-300(M) as a fluorescent platform for SO2 sensing and reveals how metal centers influence detection mechanisms.

## Key findings

- MFM-300(Al) shows the strongest fluorescence emission and quenching when exposed to SO2.
- Sc(III) and In(III) analogues exhibit moderate quenching via charge transfer at semi-open metal sites.
- DFT calculations clarify the role of metal centers in SO2 retention and electronic behavior.

## Abstract

The MFM‐300(M) series (M = Al(III), Sc(III), Cr(III), and In(III)) have previously demonstrated excellent sulfur dioxide (SO2) adsorption capabilities, however, their potential as fluorescent SO2 sensors remains unexplored. Here, this work presents a comparative study of their fluorescence response upon SO2 exposure, with a particular focus on the role of the metal centers. MFM‐300(Al) exhibits the strongest emission and highest quenching upon SO2 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 SO2 retention and to assess the semiconducting nature of these metal‐ organic frameworks (MOFs).

The MFM‐300(M) series is investigated as a fluorescent platform for SO2 detection, highlighting how the nature of metal centers modulates fluorescence emission. MFM‐300(Al) displays the brightest emission and strongest response. Experimental and computational studies reveal distinct quenching mechanisms depending on the metal center, highlighting the role of static versus dynamic host‐guest interactions in tuning fluorescence response.