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Light-Induced Spin State Switching and Relaxation in Spin Pairs of Copper(II)–Nitroxide Based Molecular Magnets
Inorganic Chemistry ( IF 4.6 ) Pub Date : 2017-09-21 00:00:00 , DOI: 10.1021/acs.inorgchem.7b01689
Sergey V. Tumanov 1, 2 , Sergey L. Veber 1, 2 , Svyatoslav E. Tolstikov 1 , Natalia A. Artiukhova 1 , Galina V. Romanenko 1 , Victor I. Ovcharenko 1 , Matvey V. Fedin 1, 2
Affiliation  

Similar to spin-crossover (SCO) compounds, spin states of copper(II)–nitroxide based molecular magnets can be switched by various external stimuli including temperature and light. Although photoswitching and reverse relaxation of nitroxide–copper(II)–nitroxide triads were investigated in some detail, similar study for copper(II)–nitroxide spin pairs was still missing. In this work we address photoswitching and relaxation phenomena in exchange-coupled spin pairs of this family of molecular magnets. Using electron paramagnetic resonance (EPR) spectroscopy with photoexcitation, we demonstrate that compared to triad-containing compounds the photoinduced weakly coupled spin (WS) states of copper(II)–nitroxide pairs are remarkably more stable at cryogenic temperatures and relax to the ground strongly coupled spin (SS) states on the scale of days. The structural changes between SS and WS states, e.g., differences in Cu–Onitroxide distances, are much more pronounced for spin pairs than for spin triads in most of the studied copper(II)–nitroxide based molecular magnets. This results in higher energy barrier between WS and SS states of spin pairs and governs higher stability of their photoinduced WS states. Therefore, the longer-lived photoinduced states in copper(II)–nitroxide molecular magnets should be searched within the compounds experiencing largest structural changes upon thermal spin transition. This advancement in understanding of LIESST-like phenomena in copper(II)–nitroxide molecular magnets allows us to propose them as interesting playgrounds for benchmarking the basic factors governing the stability of photoinduced states in other SCO and SCO-like photoswitchable systems.

中文翻译:

铜(II)-一氧化氮基分子磁体的自旋对中的光诱导自旋态转换和弛豫

与自旋交叉(SCO)化合物相似,基于铜(II)–氮氧化物的分子磁体的自旋态可以通过各种外部刺激(包括温度和光)进行切换。尽管已详细研究了氮氧化物-铜(II)-氮氧化合物三联体的光开关和反向弛豫,但仍缺少关于铜(II)-氮氧化合物自旋对的类似研究。在这项工作中,我们解决了该分子磁体家族的交换耦合自旋对中的光开关和弛豫现象。使用电子顺磁共振(EPR)光谱和光激发,我们证明,与含三合化合物的化合物相比,铜(II)-氮氧化物对的光致弱耦合自旋(WS)状态在低温下显着更稳定,并强烈释放到地面耦合自旋(SS)状态,以天为单位。在大多数研究的基于铜(II)-氮氧化物的分子磁体中,自旋对的氮氧化物距离比自旋三重轴更明显。这导致自旋对的WS和SS状态之间具有更高的能垒,并控制了它们的光诱导WS状态的更高稳定性。因此,应该在热自旋跃迁经历最大结构变化的化合物中搜索寿命较长的铜(II)-氮氧化物分子磁体中的光诱导态。在理解铜(II)-氮氧化物分子磁体中的LIESST样现象方面的进步,使我们可以将它们作为有趣的游乐场,以对其他SCO和类似SCO的光开关系统中控制光致态稳定性的基本因素进行基准测试。
更新日期:2017-09-21
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