Arakawa Yuki, Arai Yuto
Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580, Aichi, Japan.
Materials (Basel). 2024 Jul 3;17(13):3278. doi: 10.3390/ma17133278.
Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report the thermal and photoinduced phase-transition behaviors of photoisomerizable imine-based LC dimers with twist-bend nematic (N) phases. We synthesize two homologous series of ester- and thioether-linked -(4-cyanobenzylidene)aniline-based bent-shaped LC dimers with an even number of carbon atoms ( = 2, 4, 6, 8, and 10) in the central alkylene spacers, namely, CBCOOSBA(CN) and CBOCOSBA(CN), possessing oppositely directed ester linkages, C=OO and OC=O, respectively. Their thermal phase-transition behavior is examined using polarizing optical microscopy and differential scanning calorimetry. All dimers form a monotropic N phase below the temperature of the conventional nematic (N) phase upon cooling. Remarkably, the N phases of CBCOOSBA(CN) ( = 2, 4, 6, and 8) and CBOCOSBA(CN) ( = 6 and 8) supercool to room temperature and vitrify without crystallization. In addition, the phase-transition temperatures and entropy changes of CBCOOSBA(CN) are lower than those of CBOCOSBA(CN) at the same . Under UV light irradiation, the N and N phases transition to the N and isotropic phases, respectively, and reversibly return to their initial LC phases when the UV light is turned off.
液晶（LC）中的光致异构分子可实现光致相变，推动了其在多种光响应材料中的应用。与被广泛研究的偶氮苯结构不同，基于亚胺的液晶的光致相变行为的研究相当有限。我们在此报告具有扭曲向列相（N）的光致异构亚胺基液晶二聚体的热致和光致相变行为。我们合成了两个同系物系列的基于酯和硫醚连接的 -（4-氰基亚苄基）苯胺的弯曲形液晶二聚体，其中心亚烷基间隔基中碳原子数为偶数（ = 2、4、6、8和10），即分别具有相反方向酯键C=OO和OC=O的CBCOOSBA(CN)和CBOCOSBA(CN)。使用偏光显微镜和差示扫描量热法研究了它们的热相变行为。所有二聚体在冷却时在传统向列相（N）温度以下形成单向性N相。值得注意的是，CBCOOSBA(CN)（ = 2、4、6和8）和CBOCOSBA(CN)（ = 6和8）的N相过冷至室温并玻璃化而不结晶。此外，在相同的 时，CBCOOSBA(CN)的相变温度和熵变低于CBOCOSBA(CN)。在紫外光照射下，N相和N相分别转变为N相和各向同性相，并且在紫外光关闭时可逆地回到其初始液晶相。
