Thermally and Magnetically Robust Triplet Ground State Diradical
Thermally and Magnetically Robust Triplet Ground State Diradical
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DOI：
10.1021/jacs.9b00558
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发表时间：
2019-03-20
影响因子：
15
通讯作者：
Rajca, Andrzej
中科院分区：
文献类型：
--
作者：
Gallagher, Nolan;Zhang, Hui;Rajca, Andrzej
高自旋（S = 1）有机双自由基可以提供相对于几种新兴技术的增强的性质，但通常表现出低的单重态三重态能隙并且具有有限的热稳定性。我们报道了具有大的单重态-三重态能隙的三重态基态双自由基2，Δ E-ST >= 1.7 kcal mol（-1），导致在室温下三重态基态的几乎唯一的布居，以及在惰性气氛下在类似于160 ℃下开始分解的良好的热稳定性。磁性的2和先前制备的双自由基1的特征在于多晶粉末，在聚苯乙烯玻璃，和在其他矩阵的SQUID磁力。多晶双自由基2形成了一个新的一维（1D）自旋为1（S = 1）的有机自由基链，其链内反铁磁耦合J ′/k =-14K，这与N中心点中心点中心点N和N中心点中心点中心点O分子间接触有关。链内反铁磁耦合2是迄今为止最强的所有研究的一维S = 1链的有机自由基，这也使得ID S = 1链2最各向同性，因此是一个很好的系统，用于研究低维磁性。在聚苯乙烯玻璃和冷冻的苯或邻苯二甲酸二丁酯溶液中，1和2都是单体。双自由基2是热鲁棒性的，并且在真空下蒸发以在硅衬底上形成完整的双自由基的薄膜，如通过X射线光电子能谱所证明的。基于C-K NEXAFS光谱和AFM图像的类似于1.5 nm厚的膜，双自由基分子在衬底上形成岛，分子大约沿着晶体学α轴堆叠。该膜在高真空下至少60 h是稳定的，但当暴露于环境条件下7 h时显示出分解的迹象。
High spin (S = 1) organic diradicals may offer enhanced properties with respect to several emerging technologies, but typically exhibit low singlet triplet energy gaps and possess limited thermal stability. We report triplet ground state diradical 2 with a large singlet-triplet energy gap, Delta E-ST >= 1.7 kcal mol(-1), leading to nearly exclusive population of triplet ground state at room temperature, and good thermal stability with onset of decomposition at similar to 160 degrees C under inert atmosphere. Magnetic properties of 2 and the previously prepared diradical 1 are characterized by SQUID magnetometry of polycrystalline powders, in polystyrene glass, and in other matrices. Polycrystalline diradical 2 forms a novel one-dimensional (1D) spin-1 (S = 1) chain of organic radicals with intrachain antiferromagnetic coupling of J'/k = -14 K, which is associated with the N center dot center dot center dot N and N center dot center dot center dot O intermolecular contacts. The intrachain antiferromagnetic coupling in 2 is by far strongest among all studied 1D S = 1 chains of organic radicals, which also makes ID S = 1 chains of 2 most isotropic, and therefore an excellent system for studies of low-dimensional magnetism. In polystyrene glass and in frozen benzene or dibutyl phthalate solution, both 1 and 2 are monomeric. Diradical 2 is thermally robust and is evaporated under ultrahigh vacuum to form thin films of intact diradicals on silicon substrate, as demonstrated by X-ray photoelectron spectroscopy. Based on C-K NEXAFS spectra and AFM images of the similar to 1.5 nm thick films, the diradical molecules form islands on the substrate with molecules stacked approximately along the crystallographic alpha-axis. The films are stable under ultrahigh vacuum for at least 60 h but show signs of decomposition when exposed to ambient conditions for 7 h.