Pelzl G, Schröder M W, Eremin A, Diele S, Das B, Grande S, Kresse H, Weissflog W
Institut für Physikalische Chemie, Martin-Luther-Universität Halle-Wittenberg, Mühlpforte 1, 06108, Halle (Saale), Germany.
Eur Phys J E Soft Matter. 2006 Dec;21(4):293-303. doi: 10.1140/epje/i2006-10068-2. Epub 2007 Feb 12.
Three homologous achiral five-ring bent-core mesogens are presented where 4-chlororesorcinol is the central core and the aromatic rings are linked by ester groups. These compounds form smectic phases with a tilted arrangement of the molecules (tilt angle approximately 45 degrees). On cooling the isotropic liquid this phase adopts a fan-like texture which shows for two homologues at relatively high electric fields ( 25-35 V microm(-1)) an antiferroelectric electro-optical response based on the collective rotation of the molecules around their long axes. At lower temperature the application of a sufficiently high electric field leads to a continuous transition into a non-birefringent texture which exhibits randomly distributed domains of opposite handedness. These domains can be reversibly switched into a state of opposite chirality by reversal of the field polarity. This switching is bistable and shows a current response typical for a ferroelectric ground state. The possible mechanism of the field-induced phase transition, of the ferroelectric switching and of the field-induced inversion of the chirality is discussed on the base of XRD, 13C- and 1H-NMR investigations, dielectric and electro-optical measurements.
本文介绍了三种同系的非手性五环弯曲核液晶基元，其中间核心为4-氯间苯二酚，芳环通过酯基相连。这些化合物形成了分子呈倾斜排列（倾斜角约为45度）的近晶相。在冷却各向同性液体时，该相呈现出扇形织构，对于两种同系物，在相对较高的电场（25 - 35 V μm⁻¹）下，基于分子围绕其长轴的集体旋转，呈现反铁电电光响应。在较低温度下，施加足够高的电场会导致连续转变为非双折射织构，该织构呈现出手性相反的随机分布畴。通过反转场极性，这些畴可以可逆地切换到手性相反的状态。这种切换是双稳态的，并显示出铁电基态典型的电流响应。基于XRD、¹³C - 和¹H - NMR研究、介电和电光测量，讨论了场诱导相变、铁电切换和场诱导手性反转的可能机制。
