Mechanistic Insight into H₂S-Induced Fluorescence Quenching in a Robust Metal-Organic Framework

The development of chemically robust sorbents capable of integrating capture and optical sensing of toxic gas remains a major challenge. Herein, the ultramicroporous Zn(II)-based metal-organic framework, MFM-520, has been investigated for the adsorption and luminescent detection of H₂S. Breakthrough measurements at 298 K and 1 bar show a reversible H₂S uptake of 3.91 mmol g^-1, while powder X-ray diffraction confirms full retention of crystallinity after adsorption. Solid-state photoluminescence experiments reveal a pronounced, selective fluorescence turn-off response to H₂S in the gas phase, with a limit of detection of 6.13 ppm. Time-resolved spectroscopy shows a decrease in the excited-state lifetime upon H₂S adsorption, indicating enhanced non-radiative decay pathways. In situ DRIFTS measurements indicate that H₂S interacts with MFM-520 through supramolecular interactions. The combined adsorption, structural, and spectroscopic analyses establish that fluorescence quenching arises from reversible, confinement-amplified modulation of ligand-centered excited-state dynamics. These results highlight how coordinatively saturated Zn(II) nodes within ultramicroporous environments can couple chemical stability with selective luminescent gas sensing.