A Flexible Zn-MOF: Gate-Opening Adsorption Behavior and Selective Fluorescence Detection of Ethylenediamine

A new flexible Zn(II)-based metal–organic framework, namely, [Zn2(2,6-ndc)2(pvq)]·4.5DMF·0.5H2O (Zn-MOF-α), was solvothermally synthesized using 2,6-naphthalenedicarboxylate acid (2,6-H2ndc) and 5-(2-(pyridin-4-yl)vinyl)quinoline (pvq) as coligands. Single-crystal X-ray diffraction analyses revealed that Zn-MOF-α features a 2-fold interpenetrated framework with a primitive cubic (pcu) topology. Upon activation, Zn-MOF-α with 3D porous channels transformed into Zn-MOF-β (0D voids), involving significant changes in the metal–carboxylate coordination geometry, rotation of organic linkers, and relative sliding of the interpenetrated nets. Gas adsorption tests indicated that Zn-MOF-β displays no affinity for N2 at 77 K but demonstrates a two-step CO2 adsorption at 195 K. Additionally, Zn-MOF-β shows a significantly higher adsorption capacity for benzene (Bz) compared to cyclohexane (Cy) at 298 K. Fluorescence sensing experiments demonstrated that Zn-MOF-α exhibits significant fluorescence quenching in the presence of ethylenediamine. Remarkably, the Stern–Volmer quenching constant (Ksv) for ethylenediamine reached 7.6 × 103 M–1, with a detection limit of 5.78 × 10–6 M and a rapid quenching response time (<15 s). The underlying quenching mechanism was investigated and elucidated through systematic experiments. Furthermore, ethylenediamine detection was visually realized using a smartphone platform, enabling rapid and practical detection.