Dual-emitting MOF materials have been widely explored in recent years for their potential applications as ratiometric luminescent probes. However, most of these dichromatic MOFs were constructed through encapsulation of dye molecules, and ones with intrinsic dual-emission from ligands and/or metal ions are still rare. Herein, we report a novel Eu-MOF (1) composed of trinuclear europium clusters and 2,6-naphthalenedicarboxylate (NDC) linkers. It exhibits ratiometric luminescence behavior within a pH range of 4.00 to 3.00. On the basis of an in situ single-crystal to single-crystal transformation study, a mechanism is proposed for this pH-regulated luminescence switching, in which the tiny variations in Eu-O bond lengths disturb the energy transfer from the ligand to the metal and therefore diminish the “antenna effect”. Specifically, the Eu–O_NDC bond length is elongated and the Eu–O_water bond length is shortened with increasing acidity, resulting in a gradually reduced luminescence intensity of Eu³⁺ and gradually enhanced luminescence intensity of the NDC ligand at the same time. This unique luminescence switching property of 1 allows for quantitative detection of 3-nitropropionic acid (3-NPA), a toxic mycotoxin in moldy sugarcane. Moreover, a rapid, highly sensitive, and visualizable response to 3-NPA is demonstrated by using MOF-based test paper.

中文翻译：

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pH调节比例发光Eu-MOF用于快速检测发霉甘蔗中的有毒真菌毒素

近年来，双发射MOF材料作为比例发光探针的潜在应用已得到广泛研究。但是，大多数这些二色MOF是通过染料分子的包封构建的，而从配体和/或金属离子中发生固有双发射的MOF仍然很少。本文中，我们报道了由三核euro簇和2,6-萘二甲酸（NDC）接头组成的新型Eu-MOF（1）。它在4.00至3.00的pH范围内显示出比例发光行为。在原地的基础上从单晶到单晶的转换研究，提出了一种用于这种pH调节的发光转换的机制，其中Eu-O键长的微小变化会干扰从配体到金属的能量转移，从而减少“天线效应” ”。具体来说，随着酸度的增加，Eu-O _NDC键的长度变长，Eu-O_水键的长度变短，导致Eu ^3+的发光强度逐渐降低，同时NDC配体的发光强度逐渐增强。这种独特的发光开关特性为1可以定量检测发霉的甘蔗中的一种有毒真菌毒素3-硝基丙酸（3-NPA）。此外，使用基于MOF的试纸证明了对3-NPA的快速，高度敏感和可视化的响应。