Design Of Cyclotriphosphazene-Based Liquid Crystal Functional Materials, Gels And Cholesteric Light Shutter

Since the first report about cyclotriphosphazene-based liquid crystal, the main work in this field was focusing on the effect of the length of terminal alkyl chain on the liquid crystalline properties of cyclotriphosphazenes with azobenzene or biphenyl rigid groups. The high reactivity of P-Cl bond in hexachlorocyclotriphosphazene facilitates the introduction of novel functional group on the phosphazene ring. Therefore, the introduced functional group not only could act as a rigid group but also could functionalize the corresponding cyclotriphosphazene derivative. More opportunities for the application of cyclotriphosphazene-based liquid crystal, especially the disk-like liquid crystal are anticipated due to the rapid development of organophotonics and liquid crystals.In this thesis, a series of cyanostilbene-containing cyclotriphosphazene derivatives with different lengths of terminal alkyl chains were synthesized. The effects of the length of alkyl chain, cyano-substituted position, the number of terminal alkyl chain and different kinds of terminal group on the liquid crystalline properties of the cyclotriphosphazene derivatives were studied. The molecular structures and purity of the products were characterized by 1H,13C,31P-NMR and elemental analysis. The liquid crystalline properties of cyclotriphosphazene derivatives were studied by the means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM).It was found that all the compounds with one terminal substituent exhibited nematic phases, and all the compounds with two terminal alkyl chains exhibited columnar phases. The number of the terminal substituent has great effect on the alignment of the cyclotriphosphazene molecule. Mesogenic units that contain only one terminal group give rise to calamitic alignment with three arms pointing upward and three other arms pointing downward. On the other hand, mesogenic units that contain two terminal alkyl chains give rise to disk-like alignment. As the length of the terminal alkyl chain was increased, the clear temperatures of cyclotriphosphazene-based liquid crystals increased. The cyclotriphosphazene derivatives with different substituted position of the cyano group exhibited different enthalpies of phase transition. The terminal subtituent has obvious effect on the liquid crystalline properties of cyclotriphosphazene derivatives. Compound without terminal substituent didn't exhibit liquid crystalline properties both on heating and cooling run. Compounds with different terminal substituents exhibited monotropic or enantiotropic nematic phases. The results mean that the terminal substituent is essential to the formation of liquid crystallinity in cyclotriphosphazene derivatives. Moreover, the rigidity of the cyclotriphosphazene molecule was reduced with increasing number of soft alkyl chains, therefore, the clear temperature of the cyclotriphosphazene-based liquid crystal was also reduced. Compounds with relatively large number of alkyl chains exhibited lower clear temperatures than those of compounds with one terminal alkyl chain. At the same time, the increase of number of terminal alkyl chains facilitated holding the liquid crystalline textures on cooling.The organogels formed by cyclotriphosphazene derivatives were prepared through heating-cooling method. The gelation properties and effect of length of alkyl chain on the fluorescent enhanced emission phenomenon were studied. It was found that cyclotriphosphazene derivatives could form stable organogels in THF/methanol mixed solvents, but could not form stable gels in single solvents. Fibrous aggregates were observed in the dried gels of cyclotriphosphazene derivatives. All the studied compounds could exhibit the aggregation-induced enhanced emission (AIEE) phenomenon in diluted THF/water mixed solution due to the formation of nanoparticles' suspension. Compounds with increasing length of terminal alkyl chains showed increasing fluorescence intensities in the nanoparticles' suspension. The size of nanoparticles (H2O/THF=4/1, v/v) decreased with increasing length of terminal alkyl chains. Small size of nanoparticle and large content of nanoparticle in nanoparticles'suspension facilitated the strong fluorescent emission.The development of polymer stabilized cholesteric texture (PSCT) light shutter is limited by its high energy consumption, novel PSCT light shutter with low energy consumption is required to meet the requirement of developing market. In order to reduce the energy used to stabilize the PSCT light shutter, bistable PSCT light shutters were developed by increasing the polymer concentration. The thermal properties of the PSCT light shutters were studied. It was found that the liquid crystal light shutter with the relatively highest polymer concentration exhibited the best thermal stability. The light shutter with 5.10% of monomer concentration was switched to scattering state when the temperature was higher than 41℃. The scattering state was switched to transparent state when the light shutter was applied a short voltage pulse. This thermally written and electrically erased light shutter could be used as smart windows in high buildings.The photo-polymerization of liquid crystalline monomer 4-cyanophenyl-4'-(6-acryloyloxyhexyloxy)benzoate (RM23) was studied both in reverse and normal mode liquid crystal cells. The results indicated that the low PDI was obtained in the reverse and normal modes at the monomer concentration of 3%. The PDI and molecular weight increased with monomer concentration. In the reverse mode cells, uniform dark red textures were observed after photo-polymerization. In the normal mode cells, textures attributed to the nematic phase disappered gradually with monomer concentration.