Single-Amino Group Counted Rotation-Restriction in Eu-BTB-NH₂ MOF for Accurate Detection of Methcathinone

To address the urgent need for rapid and selective detection of methcathinone, a luminescent europium(III)-based metal organic framework is rationally designed by integrating a single-amino-functionalized π-conjugated ligand, enabling the efficient recognition of methcathinone. The specific hydrogen bonding and π-π interactions between methcathinone and the H₃BTB-NH₂ ligand in the Eu-BTB-NH₂ MOF could restrict the intramolecular rotation of the aromatic moieties and modulate the metal-to-ligand energy transfer pathway, resulting in an efficient redistribution of the characteristic Eu³⁺ ions emission to the ligand emission. Consequently, the Eu-BTB-NH₂ MOF probe exhibits a pronounced fluorescence emission change from red to emerald green under UV excitation, together with a fast response (<1 s) and a desirable limit of detection (LOD) of 21 ng/mL, highlighting the sensing material's potential for methcathinone early-warning. Furthermore, a portable sensing chip and a custom-built Drugs Analyst device are introduced, which enabled rapid, on-site methcathinone detection in various complex matrices such as urine, sewage, alcohol, etc., as well as a seized item, thereby demonstrating strong practical applicability. This work provides a mechanistically guided sensing strategy for desirable illicit drug detection in complex real-world environments and offers valuable insights into the design of rotation-restricted luminescent MOFs for optical sensing.