Effect of Structure on the Spin Switching and Magnetic Bistability of Solid-State Aryl Dicyanomethyl Monoradicals and Diradicals
Effect of Structure on the Spin Switching and Magnetic Bistability of Solid-State Aryl Dicyanomethyl Monoradicals and Diradicals
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DOI：
10.1021/acsomega.9b01658
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发表时间：
2019-08
期刊：
影响因子：
4.1
通讯作者：
Joshua P Peterson;Rui Zhang;Arthur H. Winter
中科院分区：
文献类型：
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作者：
Joshua P Peterson;Rui Zhang;Arthur H. Winter
具有可切换自旋态的稳定有机自由基在医学、生物学和材料科学中有广泛的应用。一类新兴的此类可自旋可切换的自由基是基于二氰甲基自由基的，这些自由基通常是热和空气稳定的物种，在较低温度下形成弱键(闭壳单重态)二聚体，在较高温度下断裂为电子顺磁共振活性的双自由基。然而，到目前为止，对这些二氰甲基自由基的研究主要集中在它们的溶液相行为上。对化学结构如何影响这些自由基的固态自旋转换行为的了解尚不清楚。在这里，我们研究了6个单环化合物和10个系留双自由基的固态自旋交叉行为，并证明了这些物种在固态中也经历了自旋转换。我们发现分子间二聚体的固态自旋转换磁化率与溶液相二聚化的吉布斯自由能有较弱的相关性，但分子内二聚体的溶液相自由能与固态行为之间没有明显的相关性。此外，与分子间二聚体相比，分子内双自由基二聚体具有更强的温度响应能力。具有相同基团的晶态和非晶态粉末具有相似的自旋转换行为，但晶态材料在较高的温度下具有较慢的键断裂动力学，这表明固态堆积效应是一个重要的动力学考虑因素。这些体系的一个有趣的特征是，在加热后冷却到室温时，一些自由基留在固体中，表明磁性双稳，而另一些则部分或完全返回到抗磁性二聚体。这项工作提供了关于化学结构如何影响这类新的空气稳定自由基的固态自旋交叉的见解，以及对构建动态响应固态材料和有机自旋交叉聚合物的重要性的知识。
Stable organic radicals with switchable spin states have applications in medicine, biology, and material science. An emerging class of such spin-switchable radicals is based on dicyanomethyl radicals, which are typically thermally and air-stable species that form weakly bonded (closed-shell singlet) dimers at a lower temperature that rupture into electron paramagnetic resonance-active diradicals at a higher temperature. However, thus far, the study of these dicyanomethyl radicals has focused on their solution-phase behavior. An understanding of how chemical structure affects the solid-state spin switching behavior for these radicals is unknown. Here, we examine the solid-state spin crossover behavior of 6 monoradicals and 10 tethered diradicals and demonstrate that these species also undergo spin switching in the solid state. We find that the susceptibility for solid-state spin switching for the intermolecular dimers is weakly correlated to the solution-phase Gibbs free energies of dimerization, but no apparent correlations are seen between the solution-state free energies for the intramolecular dimerization and the solid-state behavior. Furthermore, intramolecular diradical dimers have greatly enhanced temperature-responsive behavior compared to their intermolecular counterparts. Crystalline and amorphous powders of the same radicals feature similar spin switching behavior, but the crystalline materials have slower bond-rupture kinetics at higher temperatures, suggesting that solid-state packing effects are an important kinetic consideration. An interesting feature of these systems is that, upon cooling down to room temperature after heating, some radicals remain trapped in the solids, indicating magnetic bistability, while others partially or fully return to the diamagnetic dimers. This work provides insights into how chemical structure affects spin crossover in the solid state for this new class of air-stable radicals, the knowledge of importance for the construction of dynamically responsive solid-state materials, and organic spin crossover polymers.