The spontaneous polarization (PS) of a ferroelectric liquid crystal is modulated reversibly by photocyclization (λ
= 313 nm) of dithienyl- and dibenzothienylperfluorocyclopentene dopants with relatively high aspect ratios. Photocyclization of these dopants causes a decrease of PS due to a photomechanical effect which may originate from a loss of conformational flexibility of the dopant upon photocyclization. The degree of PS photomodulation increases with dopant concentration up to the solubility limit of 3 mol%. The maximum polarization photomodulation, ΔPS
= 16.2 nC cm−2, is achieved at 6 K below the Curie point with the dopant 1,2-bis(5-(4-heptyloxyphenyl)-2-methylthien-3-yl)perfluorocyclopentene (3c, 3 mol%). The resulting PS photoswitch is fatigue resistant and photochemically bistable. Polarized spectroscopy experiments suggest that the dopants form homogeneous solutions with the FLC host and are integrated within the layer structure of the SmC* phase, with their molecular long axes approximately coincident with the director. To the best of our knowledge, this is the first example of a bistable ferroelectric liquid crystal photoswitch to be reported in the literature.
具有相对较高纵横比的二
噻吩基和
二苯并噻吩基
全氟化
环戊烯掺杂剂的光环化(λ = 313 nm)可逆地调节
铁电液晶的自发极化(PS)。由于光机械效应,这些掺杂剂的光环化会导致 PS 值下降,这种效应可能源于掺杂剂在光环化时构象灵活性的丧失。PS 光调节的程度随着掺杂剂浓度的增加而增加,最高可达 3 摩尔%的溶解极限。当掺杂剂为 1,2-双(5-(4-庚氧基苯基)-
2-甲基噻吩-3-基)
全氟环戊烯(3c,3 摩尔%)时,在低于居里点 6 K 的温度下可实现最大偏振光调制,即 ΔPS = 16.2 nC cm-2。由此产生的 PS 光开关具有抗疲劳性和光
化学双稳态性。偏振光谱实验表明,掺杂剂与 FLC 主成分形成均相溶液,并与 SmC* 相的层结构融为一体,其分子长轴与方向大致重合。据我们所知,这是文献中报道的第一个双稳态
铁电液晶光开关实例。