Akiyoshi Ryohei, Hirota Yuma, Kosumi Daisuke, Tsutsumi Mayu, Nakamura Masaaki, Lindoy Leonard F, Hayami Shinya
Department of Chemistry , Graduate School of Science and Technology , Kumamoto University , 2-39-1 Kurokami, Chuo-ku , Kumamoto , 860-8555 , Japan . Email:
Department of Physics , Graduate School of Science and Technology , Kumamoto University , 2-39-1 Kurokami, Chuo-ku , Kumamoto , 860-8555 , Japan.
Chem Sci. 2019 May 10;10(22):5843-5848. doi: 10.1039/c9sc01229j. eCollection 2019 Jun 14.
Ferroelectric liquid crystals (FLCs) are fascinating functional materials that have a remnant and electrically invertible polarization. To date, typical FLCs have been mainly realized by molecular design such as the incorporation of chirality into a given molecular structure. Here, we report for the first time ferroelectricity induced by spin transition associated with a crystal - liquid crystal phase transition in achiral molecules. Iron(ii) metallomesogens incorporating alkyl chains of type Fe(3C -bzimpy) ( = 8 (), 10 (), 12 (), 14 (), 16 () and 18 (); bzimpy = 2,6-bis(benzimidazol-2'-yl)pyridine) that exhibit spin crossover (SCO) phenomena have been synthesized. Compounds and were each demonstrated to show SCO behaviour along with the occurrence of a phase transition between the crystalline (Cr) state and corresponding chiral smectic C (SmC*) state. The distortion of the coordination sphere in the high spin state is seen to trigger the generation of the SmC* state. The liquid crystalline compounds do not display ferroelectric behaviour in their Cr state but do exhibit ferroelectric hysteresis loops in their SmC* state. Ferroelectric switching was clearly confirmed by second harmonic generation (SHG) experiments involving the respective phases. These findings will undoubtedly lead to new strategies for the design of new FLCs based on metal-centred spin transitions.
铁电液晶（FLCs）是一类迷人的功能材料，具有剩余极化且可电反转极化。迄今为止，典型的铁电液晶主要通过分子设计来实现，比如将手性引入特定分子结构中。在此，我们首次报道了在非手性分子中，与晶体 - 液晶相变相关的自旋转变诱导产生的铁电性。已合成了含有Fe(3C - bzimpy)（ = 8 (), 10 (), 12 (), 14 (), 16 () 和 18 (); bzimpy = 2,6 - 双（苯并咪唑 - 2'- 基）吡啶）型烷基链且呈现自旋交叉（SCO）现象的铁（II）金属液晶基元。化合物 和 各自被证明表现出自旋交叉行为，同时伴随着晶体（Cr）态与相应的手性近晶C（SmC*）态之间的相变。在高自旋态下配位球的畸变被认为触发了SmC态的产生。这些液晶化合物在Cr态时不表现出铁电行为，但在SmC态时确实表现出铁电滞回环。通过涉及各个相的二次谐波产生（SHG）实验清楚地证实了铁电开关效应。这些发现无疑将为基于金属中心自旋转变的新型铁电液晶的设计带来新策略。
