Adaptive Spirobifluorene Chromophore in Pillared‐Layer Zr‐MOFs for Record Electrochemiluminescence Efficiency and Femtomolar Tetracycline Detection

ABSTRACT The widespread contamination of tetracycline hydrochloride (TC) in aquatic environments poses serious risks to ecological balance and human health, necessitating highly sensitive detection methods. Herein, three isoreticular Zr‐MOFs (NKM‐611, NKM‐612, and NKM‐613) are rationally constructed via a pillared‐layer assembly strategy, employing spirobifluorene‐based tetracarboxylate ligands as both emissive chromophores and geometrically adaptive pillars. This design effectively suppresses topological diversification and interpenetration, enabling precise regulation of framework geometry. Notably, among the MOF‐based ECL emitters evaluated against the Ru(bpy) 3 2+ reference system, NKM‐612 delivers the highest reported relative ECL efficiency of 3512.86%. Leveraging ultrafast photoinduced electron transfer between TC and excited spirofluorene units, the NKM‐613‐based sensor achieves an ultralow detection limit of 0.339 fM over a wide linear range of 1 × 10 −16 to 1×10 −10 M, along with excellent selectivity. This work provides a novel strategy for designing high‐performance ECL‐active MOFs and an ultrasensitive platform for TC monitoring in complex environmental samples.