ABSTRACT

A series of new compounds were synthesised by adding azo functional groups and chlorine substituent to the central bent-cores to form a 4-chloro-1,3-dizaophenylene bent-core. The structure, mesogenic properties, and photosensitivity of these compounds were characterised. The results show these synthesised compounds exhibit a broad temperature window up to 63.8°C for nematic phase and the rapid rate of trans – cis photoisomerisation. For instance, at 95°C, compound 4c in nematic phase became an isotropic liquid under UV-irradiation in 3 s and could be restored to nematic under natural visible light in 5 s. Quantum mechanics calculation confirms that using azos instead of esters as the central linkages can effectively reduce the molecular dipole moment, which appears to promote favourable mesogenic and photonic characteristics. Moreover, varying the carbon number in the terminal alkyl chains can alter molecular dipole moment and polarisability anisotropy, which are strongly correlated with the phase transition temperature and temperature range of the nematic phase. These findings suggest that 1) changing azo group position can effectively alter the intermolecular interactions by varying molecular polarity and polarisability; 2) reducing long-range electrostatic interactions can promote favourable mesogenic and possibly photonic properties of azobenzene bent-core liquid crystal.

摘要

通过在中心弯曲核上添加偶氮官能团和氯取代基以形成4-氯-1,3-二氮杂亚苯基弯曲核，合成了一系列新化合物。表征了这些化合物的结构、介晶特性和光敏性。结果表明，这些合成的化合物对向列相具有高达 63.8°C 的宽温度窗口和快速的反式 - 顺式光异构化速率。例如，在 95°C 时，化合物4c向列相在紫外光照射下 3 s 变为各向同性液体，在自然可见光下 5 s 即可恢复为向列相。量子力学计算证实，使用偶氮类代替酯类作为中心键可以有效降低分子偶极矩，这似乎促进了有利的介晶和光子特性。此外，改变末端烷基链中的碳数可以改变分子偶极矩和极化率各向异性，这与相变温度和向列相的温度范围密切相关。这些发现表明：1）改变偶氮基位置可以通过改变分子极性和极化率有效地改变分子间相互作用；