Bimetallic metal–organic frameworks (MOFs) capable of sensing external stimuli will provide more possibilities for further regulating third-order nonlinear optical (NLO) properties. In this work, we synthesized bimetallic MOFs (ZnCu-MOF and ZnCd-MOF) through central metal exchange using a photoresponsive Zn-MOF as a precursor. Compared with Zn-MOF, both ZnCu-MOF and ZnCd-MOF exhibit significantly enhanced third-order NLO absorption properties. This is mainly attributed to the introduction of metal ions with different electron configurations that can adjust the bandgap of MOFs and enhance electron delocalization, thus promoting electron transfer. Interestingly, the bimetallic MOFs show a transition from reverse saturation absorption (RSA) to saturation absorption (SA) after exposure to ultraviolet irradiation, as they retain the properties of directional photogenerated electron transfer. Photoresponsive bimetallic MOFs not only have the effect of bimetallic modulation of electronic structures but also have the characteristics of photoinduced electron transfer, exhibiting diversified optical properties. These findings provide a novel method for the development of multifunctional NLO materials.

中文翻译：

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光响应双金属 MOF 的三阶非线性光调制行为

能够感知外部刺激的双金属金属有机框架（MOF）将为进一步调节三阶非线性光学（NLO）特性提供更​​多可能性。在这项工作中，我们使用光响应 Zn-MOF 作为前驱体，通过中心金属交换合成了双金属 MOF（ZnCu-MOF 和 ZnCd-MOF）。与Zn-MOF相比，ZnCu-MOF和ZnCd-MOF均表现出显着增强的三阶NLO吸收性能。这主要归因于引入具有不同电子构型的金属离子，可以调节MOF的带隙并增强电子离域，从而促进电子转移。有趣的是，双金属MOF在暴露于紫外线照射后表现出从反向饱和吸收（RSA）到饱和吸收（SA）的转变，因为它们保留了定向光生电子转移的特性。光响应双金属MOF不仅具有双金属调制电子结构的作用，还具有光致电子转移的特性，表现出多样化的光学性能。这些发现为多功能非线性光学材料的开发提供了一种新方法。