Single‐Amino Group Counted Rotation‐Restriction in Eu‐BTB‐NH ₂ MOF for Accurate Detection of Methcathinone

ABSTRACT 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 H ₃ BTB‐NH ₂ ligand in the Eu‐BTB‐NH ₂ 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 Eu ³⁺ ions emission to the ligand emission. Consequently, the Eu‐BTB‐NH ₂ 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.