新型弯曲形双偶氮苯类液晶合成及光致异构性能研究

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

弯曲形偶氮苯液晶由于其偶氮键独特的光致可逆异构化性能,已成为光电子信息材料研究的热门课题,但光响应速度慢已成为制约其发展的关键因素.目前报道的弯曲型偶氮类液晶化合物的偶氮键都距离中心核较远的位置,光致异构的响应时间较长,大都在分钟以上,不利于光敏器件应用研究.本工作试图以2-甲基-1,3-间苯二胺为中心核,将偶氮键紧挨中心核两边,末端为直链烷基,设计合成了一系列新型弯曲形双偶氮苯类液晶化合物,以期缩短光响应时间.通过IR, 1H NMR, 13C NMR和ICP-MS光谱鉴定这些化合物的分子结构,经差示扫描量热仪(DSC)和偏光显微镜(POM)测定其液晶相变温度和相态织构;并通过测定2-甲基-1,3-双(4-((4-庚基苯基)酯基)-1-(E)-偶氮苯基)苯(2c)的紫外-可见光的吸收光谱研究其光致异构化性能,通过UV-Vis光谱仪和偏光显微镜(POM)测定其液晶化合物以及掺杂向列相液晶材料的光致异构现象和响应时间.实验结果表明,所有设计合成的弯曲形双偶氮苯类液晶化合物均具有近晶相相态,且相态温度范围较宽,当近晶相态化合物2c掺杂到向列相混合液晶中时,其光致异构响应时间为2~3 s,在日光下液晶态恢复时间为3~4s,在乙酸乙酯稀溶液中时10s可达到光稳态.说明这类弯曲形双偶氮液晶化合物具有较快的光致异构响应速度.

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, 1H NMR, 13C 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(2 c) 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 2 c 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.