Vaporesponsive Lanthanide Metal–Organic Frameworks as Selective Luminescent Spin Quantum Sensors for Biogenic Amines

Detecting biogenic amines (BAs) is a topic of particular interest for future technological applications of metal-organic frameworks (MOFs) in food quality control. Herein, we demonstrate that integrating lanthanide single-ion magnets (SIMs) into MOFs offers a convenient route for developing a new class of luminescent spin quantum sensors for BA sensing, termed Ln SIM-MOFs. This study focuses on the well-known family of lanthanide(III) sesquioxalate hydrates of general formula {[Ln^III₂(ox)₃(H₂O)₆]·<i>x</i>H₂O}_<i>n</i>, which feature a 2D hexagonal layer structure. Upon selective adsorption of methylamine over di- or trimethylamine vapors, these compounds exhibit either a partial quenching of the luminescence [Ln = Eu <b>1a</b> (<i>x</i> = 3) and Tb <b>2a</b> (<i>x</i> = 3)] or a dramatic change of the spin dynamics from a slower to a faster relaxing phase [Ln = Er <b>3a</b> (<i>x</i> = 2.5)]. The dual luminescent and magnetic vaposwitching behavior observed in this series of dynamic Ln SIM-MOFs offers new design principles to obtain multifunctional and multiresponsive molecular materials for the chemical sensing of volatile organic compounds (VOCs), resulting from industrial procedures or food degradation.