n-Butane Capture Accompanied by a Colorimetric Response in a Flexible Thiazolothiazole Metal-Organic Framework

Simultaneous capture and optical detection of flammable gases in enclosed environments are critical for operational safety. Herein, using two dynamic MOFs, UAM-1S and UAM-1O, which differ compositionally by a single atom, we demonstrate the crucial role of framework flexibility in enabling this dual function. The mechanistic, kinetic, and energetic landscape of n-butane-induced structural transformations is revealed by in situ UV-vis spectroscopy and static/time-resolved powder X-ray diffraction conducted during adsorption along calorimetric studies. The integration of these results with single-crystal X-ray diffraction data of UAM-1O loaded with hydrocarbons, together with grand canonical Monte Carlo simulations and DFT calculations, enables us to propose a diffusion mechanism. Furthermore, isothermal adsorption measurements show that UAM-1S adsorbs 1.5 mmol g-1 of n-butane at 298 K and 0.016 bar, below its explosive limit (1.9%), while exhibiting minimal water uptake. Complementary dynamic column breakthrough and temperature-programmed desorption experiments reveal the selective capture of n-butane from simulated air at concentrations below 1.9% under dry conditions and below 3% under humid conditions. Finally, the loading of n-butane leads to a distinct color change of the host material thereby enabling its use as a visual indicator. These results open a new research direction, highlighting the untapped potential of flexible MOFs for capturing and detecting flammable gases at low concentrations.