Time-temperature-solvent modulated Zn-Fe bimetallic MOFs: correlating structural dynamics with optical, redox, and dopamine sensing performance.

Engineering synergistic metal centres inside metal-organic frameworks (MOFs) provides an effective approach to simultaneously adjust structural, magnetic, and electronic properties within a single architecture. We present a multivariate solvothermal method that utilizes the time-temperature-solvent (T-T-S) synthesis space to fabricate zinc-iron bimetallic metal-organic frameworks (ZnFe-MOFs) based on the FeIII-MIL-88B (MIL - Materials of Institute Lavoisier) structure. The systematic alteration of reaction duration (12-48 hours), temperature (100-140 °C), and solvent polarity (N,N-dimethyl formamide (DMF)/ethanol) facilitates precise regulation of lattice expansion-contraction ("breathing"), metal-site distribution, and crystallographic orientation. Powder X-ray diffraction (PXRD) revealed that ZnII incorporation enhances structural stability and induces preferential growth along the (101) plane. Electronic modulation through Zn2+ substitution effectively inhibits Fe3+ mediated non-radiative decay processes, resulting in a significant increase in ligand-centered fluorescence. Meanwhile, glutathione depletion assays, electron paramagnetic resonance (EPR) spectroscopy, and magnetic force microscopy verify the retention of Fe-centered redox activity and the integrity of nanoscale magnetic domains. The designed optical-redox framework results in superior electrocatalytic efficacy: ZnFe-MOF-modified electrodes provide a detection limit of 0.043 µM, a linear range of 10-1000 µM, and a sensitivity of 66.24 µA µM-1 cm-2 for dopamine oxidation, exhibiting significant selectivity against prevalent interferents. These findings demonstrate that bimetallic synergy-driven structural modulation provides an effective design strategy for metal-organic frameworks, enabling enhanced optical emission, retention of magnetic functionality, and improved redox-active sensing performance.