Pyrrolo[3,2- b ]pyrrole Dicarboxylate Linkers Enable Topological Diversity and Tunable Luminescence in Zr6-Based Metal–Organic Frameworks

Aryl-substituted pyrrolo[3,2-b]pyrrole dicarboxylate linkers with distinct substitution patterns were designed to construct Zr6-based metal–organic frameworks (SIFE-8–14) with controllable topology and photophysical properties. The 2,5-substituted linear linkers form conventional fcu-topology MOFs and exhibit aggregation-caused quenching (ACQ). In contrast, 1,4-substituted analogues display aggregation-induced emission (AIE), assembling into either disordered fcu frameworks or a rare 2,6-connected pcu net (SIFE-14). Modulator engineering triggers the fcu-to-pcu structural transition, confirmed by 3D microelectron diffraction. Remarkably, SIFE-14 achieves a photoluminescence quantum yield (PLQY) of 2%, representing up to a 4-fold enhancement relative to the fcu-type analogues (0.5–0.7%). Benefiting from its excellent water resistance and thermal stability, SIFE-14 can serve as a highly sensitive fluorescent probe for Cr3+ in aqueous media via a significant fluorescence quenching effect. It exhibits excellent reliability (R2 = 0.996) with a detectable Cr3+ concentration as low as 25 × 10–5 M. This work establishes pyrrolo[3,2-b]pyrrole as a versatile building block that enables simultaneous topological control and luminescence tuning in Zr-MOFs, offering a new design paradigm for high-performance luminescent framework materials.