Future Industries Institute, University of South Australia, Mawson Lakes, SA, 5095, Australia.
Department of Chemistry and Physics, University of Adelaide, Adelaide, SA, 5000, Australia.
Sci Rep. 2022 Jul 14;12(1):11982. doi: 10.1038/s41598-022-15663-z.
Metal-organic frameworks (MOFs) with ratiometric sensing properties are desirable for many applications due to their intrinsic self-calibration. We report the re-assessment of the sensing properties of a MOF, originally reported as containing europium(III) and 2-hydroxyterephtalic acid, and having fluorescent ratiometric iron(III) sensing properties. Synchrotron single-crystal X-ray diffraction and proton nuclear magnetic resonance (H NMR) spectroscopy revealed that the MOF is composed of 2-methoxyterephthalate, not 2-hydroxyterephthalate as originally reported. We found that the MOF exhibits a sensor turn-off response towards Fe ion concentrations in the range 0.5-3.7 ppm (band 425 nm), and a turn-on response towards a decrease of pH from 5.4 to 3.0 (band 375 nm), both resulting from the addition of acidic Fe salt solution to a MOF suspension. Thus, the ratiometric sensing properties and the originally proposed mechanism no longer apply; our work reveals a dynamic quenching mechanism for the fluorescence turn-off response due to the presence of Fe ions, and a ligand protonation mechanism for the turn-on response to a decrease in pH. Our work highlights the importance of a thorough investigation of the structure of any newly synthesized MOF, and, in the case of potential sensors, their selectivity and any environmental effects on their sensing behavior.
具有比率感应性能的金属-有机骨架（MOFs）由于其固有自校准而在许多应用中是理想的。我们重新评估了最初报道的含有铕（III）和 2-羟基对苯二甲酸的 MOF 的感应性能，该 MOF 具有荧光比率感应铁（III）的性能。同步加速器单晶 X 射线衍射和质子核磁共振（H NMR）光谱表明，MOF 由 2-甲氧基对苯二甲酸组成，而不是最初报道的 2-羟基对苯二甲酸。我们发现，MOF 对 Fe 离子浓度在 0.5-3.7 ppm 范围内表现出传感器关闭响应（425 nm 波段），对 pH 值从 5.4 降低到 3.0 表现出开启响应（375 nm 波段），这两种响应都是通过向 MOF 悬浮液中添加酸性 Fe 盐溶液引起的。因此，比率感应性能和最初提出的机制不再适用；我们的工作揭示了荧光关闭响应的动态猝灭机制是由于存在 Fe 离子，以及对 pH 值降低的开启响应的配体质子化机制。我们的工作强调了对任何新合成的 MOF 的结构进行彻底调查的重要性，并且在潜在传感器的情况下，还需要调查其选择性和任何环境对其感应行为的影响。
