Synthesis and Photo-Induced Isomerization Performance for the Novel Bent Diazobenzene Liquid Crystals

Abstract

The photo-reversible isomerization property of the azo bend liquid crystal has become a hot topic in the research opt-electronic information materials, but its slow light response has become a key factor restricting its development. At present, the azo bond of the bent liquid crystal compound is far from the central nucleus, and the photo isomerization response time is long, mostly over minutes, which is not conducive to the application research of the photosensitive device. In this work, methyl-1,3-m-phenylenediamine was chosen the central nucleus. The azo bond is adjacent to both sides of the central ring and the terminal group is an alkyl chain. A series of novel curved bisazo benzene liquid crystal compounds were designed and synthesized, in order to shorten the light response time. The molecular structures of these compounds were identified by IR, 1 H NMR, 13 C NMR and ICP-MS spectroscopy. The phase transition temperature and phase texture of the liquid crystals were determined by differential scanning calorimeter (DSC) and polarized light microscopy (POM). The photo isomerization performance of 2-methyl-1,3-bis(4-((4-heptylphenyl)ester)-1-(E)-azophenyl)benzene (2c) was determined by UV-Vis absorption spectroscopy. The photo isomerism and response time of the liquid crystal compound and the doped nematic liquid crystal material were measured by UV-Vis spectrometer and polarizing microscope (POM). The experimental results show that all the curved bisazo benzene liquid crystal compounds designed and synthesized have the smectic phase and the phase temperature range is wide. The photo induced isomerization response time of compound 2c in the liquid crystal state of smectic phase and nematic phase is 2～3 s, and the recovery time of liquid crystal state in sunlight is 3～4 s, which can be reached in diluted ethyl acetate solution for 10 s. This type of bent bisazo liquid crystal compound has a relatively fast photo induced heterogeneous response speed.

Synthesis and Photo-responsive Self-Assembly of Azobenzene-Containing Molecular Brushes

“…偶氮苯衍生物作为一类重要的液晶与光响应材料, 具有良好的加工性、成膜性、快速响应性和取向固定性, 在光机械相转变、光控可逆性能转变和光控纳米材料等 领域存在巨大的应用前景 [19][20] . 偶氮苯材料的光响应性 主要体现于其光致顺反异构化的特性, 处于基态的反式 结构呈现平面棒状形态, 具有较强的 π-π 共轭作用, 聚 集态表现出液晶行为; 处于亚稳态的顺式结构为拐式形 状, 无液晶行为, 具有一定的亲水性.…”