Stepped spin crossover (SCO) complexes with three or more spin states have promising applications in high-order data storage, multi-switches and multi-sensors. Further synergy with other functionalities, such as luminescence and dielectric properties, will provide a good chance to develop novel multifunctional SCO materials. Here, a bent pillar ligand and luminescent pyrene guest are integrated into a three-dimensional (3D) Hofmann-type metal–organic framework (MOF) [Fe(dpoda){Au(CN)₂}₂]·pyrene (dpoda = 2,5-di-(pyridyl)-1,3,4-oxadiazole). The magnetic data show an incomplete and two-step SCO behavior with the sequence of 1 ↔ 1/2 ↔ 1/4. The rare bi-directional light-induced excited spin-state trapping (LIESST) effect and light-induced stepped thermal relaxation after LIESST are observed. The pyrene guests interact with dpoda ligands via offset face-to-face π⋯π interactions to form intermolecular exciplex emissions. The competition between thermal quenching and stepped SCO properties results in a complicated and stepped exciplex fluorescence. Moreover, the stepped dielectric property with higher dielectric permittivity at lower temperature may be related to the more frustrated octahedral distortion parameters in the intermediate spin states. Hence, a 3D Hofmann-type MOF with bent pillar ligands and fluorescent guests illustrates an effective way for the development of multifunctional switching materials.

中文翻译：

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自旋交叉霍夫曼型配位聚合物中的双向光磁、激基复合物荧光和介电异常


具有三种或更多自旋态的阶梯式自旋交叉（SCO）复合物在高阶数据存储、多开关和多传感器方面具有广阔的应用前景。与其他功能（例如发光和介电性能）的进一步协同将为开发新型多功能SCO材料提供良好的机会。在这里，弯曲的柱配体和发光芘客体被集成到三维（3D）霍夫曼型金属有机框架（MOF）[Fe(dpoda){Au(CN) ₂ } ₂ ]·芘（dpoda = 2,5-二-（吡啶基）-1,3,4-恶二唑）。磁数据显示出不完整的两步 SCO 行为，序列为 1 ↔ 1/2 ↔ 1/4。观察到罕见的双向光致激发自旋态俘获（LIESST）效应和 LIESST 后的光致阶梯热弛豫。芘客体通过抵消面对面的 π⋯π 相互作用与 dpoda 配体相互作用，形成分子间激基复合物发射。热猝灭和阶梯式 SCO 特性之间的竞争导致了复杂且阶梯式的激基复合物荧光。此外，在较低温度下具有较高介电常数的阶梯介电性能可能与中间自旋态中更受挫的八面体畸变参数有关。因此，具有弯曲柱配体和荧光客体的3D霍夫曼型MOF阐明了开发多功能开关材料的有效途径。