Synthesis And Properties Of Novel Azobenzene Liquid Crystals With Quick Controllable Photochromism

Azobenzene liquid crystal is a kind of typical photochromic materials that can occur reversible trans-cis-trans isomerization transformations with special properties of photosensitivity, liquid crystalline behaviors, optical information storage characteristics ect, which make it widely apply in various areas, such as holographic grating, optical information storage, optical switches, nonlinear optical materials and so on. It also attracts great attention by researchers in recent years. Thence, design and synthesis of azobenzene liquid crystals with novel structure and better performance have been a focal point in materials science area.In this paper, five kinds of novel azobenzene liquid crystal compounds were designed and synthesized. The result structures were in according with the pre-design, being confirmed by FT-IR and1H NMR. The liquid crystalline performances of azobenzene compounds were also characterized by polarized microscopy and differential scanning calorimetry.The unique photoresponsive behaviors of azobenzene liquid crystals were studied by UV-Vis absorption spectrum and fluorescent emission spectrum. The results showed that the photostationary state of4-nitro-2’-acryloxy-4’-chloromethylbenzoyl azobenzene,2-pyridyl-(2’-acryloyloxy-4’-chloromethylbenzoyloxy) azobenzene and (S)-(+)-2-pyridyl-(2-acryloyloxy-4-(4’-(2’-methylbutoxy) benzoyloxy)) azobenzene could be achieved in less than100seconds. Their thermal back relaxation time restoring the cis-structure took long time under room temperature, while it only cost seven seconds under455nm blue light. These features showed its potential applications as optical storage medium materials. Furthermore the changes of fluorescent spectrum upon irradiation with UV were also studied, the result further proved that intramolecular hydrogen bonds had been generated by adjacent hydroxy group and the nitrogen atom could stable the trans structure of azobenzene compounds.A simple image-storing device was prepared from4-nitro-2’-acryloxy-4’-chloromethylbenzoyl azobenzene/E7liquid crystalline mixture. The results showed that this image-storing device could store the picture through photo inducing N-I transition which had many excellent performances such as controlled with certain wavelength, fast response, low light energy, long storage time, high content ratio, erase easily, ect, which meant an idea optical storage device had been constructed.