Observation of positive and negative magneto-LC effects in all-organic nitroxide radical liquid crystals by EPR spectroscopy
Observation of positive and negative magneto-LC effects in all-organic nitroxide radical liquid crystals by EPR spectroscopy
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EPR光谱观察全有机硝基氧自由基液晶的正负磁液晶效应
DOI：
10.1039/c2jm16278d
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发表时间：
2012
影响因子：
--
通讯作者：
鈴木克明(共著)
中科院分区：
文献类型：
--
作者：
H. Yuzawa;M.Nagasaka;N. Kosugi;鈴木克明(共著)
在弱磁场下，在具有正介电各向异性（Δε > 0）的手性全有机自由基化合物 2 的块状液晶（LC）相中观察到了自旋玻璃状非均匀磁相互作用（平均自旋-自旋相互作用常数：> 0或< 0）的产生，我们分别将其称为正或负“磁LC效应”。的符号和大小取决于LC相或上层结构的类型； (2S,5S)-2b (89% ee) 的手性近晶 A (SmA*) 相 (89% ee) 中存在比 (2S,5S)-2a (96% ee) 的手性向列 (N*) 相更强的正相互作用 ( > 0)，而 (±)-2a 的非手性向列 (N) 相中观察到较弱的负相互作用 ( < 0)。 SmA*和N*相中正磁LC效应的起源被解释为铁磁头尾自旋-自旋偶极子相互作用的产生，而RS磁偶极相互作用形成所产生的反铁磁相互作用是N相中负磁LC效应的原因。
The generation of spin glass-like inhomogeneous magnetic interactions (the average spin–spin interaction constant: > 0 or < 0), which we refer to as positive or negative “magneto-LC effects”, respectively, was observed in the bulk liquid crystalline (LC) phases of chiral all-organic radical compounds 2 with a positive dielectric anisotropy (Δε > 0) under weak magnetic fields. The sign and magnitude of depended on the type of LC phase or superstructure; stronger positive interactions ( > 0) operated in the chiral smectic A (SmA*) phase of (2S,5S)-2b (89% ee) than in the chiral nematic (N*) phase of (2S,5S)-2a (96% ee), whereas weak negative interactions ( < 0) were observed in the achiral nematic (N) phase of (±)-2a. The origin of the positive magneto-LC effects operating in the SmA* and N* phases was interpreted in terms of the generation of ferromagnetic head-to-tail spin–spin dipole interactions, whereas antiferromagnetic interactions arising from the formation of the RS magnetic dipolar interaction were responsible for the negative magneto-LC effects in the N phase.