Structural Variation and Switchable Nonlinear Optical Behavior of Metal-Organic Frameworks
Structural Variation and Switchable Nonlinear Optical Behavior of Metal-Organic Frameworks
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金属有机框架的结构变化和可切换非线性光学行为
DOI：
10.1002/smll.202006649
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发表时间：
2021
期刊：
影响因子：
13.3
通讯作者：
Qian Guodong
中科院分区：
文献类型：
--
作者：
Zhang Lin;Li Hongjun;He Huajun;Yang Yu;Cui Yuanjing;Qian Guodong
通过微调溶剂含量来调整配位模式，选择性地合成了两种基于相同配体的铕金属有机骨架（MOFs），分别命名为ZJU-23-Eu和ZJU-24-Eu。Eu原子在ZJU-23-Eu和ZJU-24-Eu中分别为八配位和九配位，其骨架在空间连接性和对称性上都有差异。该配体不仅具有多光子响应，而且具有合适的三重态能级（19 998 cm−1），可以敏化Eu 3+。因此，ZJU-23-Eu通过从双光子/三光子激发配体到Eu 3+的能量转移表现出Eu 3+的特征发射，峰值在614 nm，其二维层状结构有利于这一过程。相比之下，三维ZJU-24-Eu中改变的空间连接性缩小了相邻Eu 3+离子之间的距离并降低了密度，导致弱的双光子激发荧光。此外，非中心对称的ZJU-24-Eu具有二次谐波（SHG）响应，其强度是KH 2 PO 4（KDP）微晶粉末的约6.2倍，而中心对称的ZJU-23-Eu没有。这些结果建立了两种基于MOFs的非线性光学（NLO）模型，同步分析了两种结构变量对不同NLO行为的影响，为设计具有按需功能的基于MOFs的NLO器件提供了巧妙的方法。
Two europium metal–organic frameworks (MOFs) based on the same ligand, named as ZJU‐23‐Eu and ZJU‐24‐Eu, are selectively synthesized by fine‐tuning solvent contents to tailor the coordination modes. Eu atoms are eight‐coordinated and nine‐coordinated in ZJU‐23‐Eu and ZJU‐24‐Eu respectively, and their frameworks vary in both spatial connectivity and symmetry. The ligand not only has multiphoton response but also suitable triplet energy level (19 998 cm−1) to sensitize Eu3+. Thus ZJU‐23‐Eu exhibits characteristic emission of Eu3+peaking at 614 nm via the energy transfer from the two‐/three‐photon excited ligand to Eu3+, with its bidimensional layered structure benefiting this process. In contrast, the changed spatial connectivity in tridimensional ZJU‐24‐Eu narrows the distances between adjacent Eu3+ions and reduces the density, resulting in poor two‐photon excited fluorescence. Besides, noncentrosymmetric ZJU‐24‐Eu shows second harmonic generation (SHG) response with an intensity of≈6.2 times relative to KH2PO4(KDP) microcrystalline powder while centrosymmetric ZJU‐23‐Eu cannot. These results have established two nonlinear optical (NLO) models based on MOFs to synchronously analyze the effects of two structural variables on different NLO behaviors, and provide ingenious ways to design MOF‐based NLO devices with function on demand.