Synthesis And Properties Of Rod-like Magnetic Liquid Crystals

Liquid crystals, as a kind of functional materials with particular photoelectrical properties, have been widely used. Molecular magnetic materials are attractive research topic in material areas. A combination of magnetic property with liquid crystalline property is drawn a great attention from the material scientists If the magnetic property is put into flowing nematic liquid crystals (also called organic magnetic fluid or organic magnetic liquid crystals), liquid crystals will have the possibility to orderly arrange not only in electric field but also in magnetic field, and accordingly, they will carry out special application in wider and newer areas. The aim of this paper is to synthesize such new functional materials possessed double properties of liquid crystalline and magnetic. Main research work of this paper is shown below:1. Using a series of double ring acids substituted by n-propyl, n-pentyl with p-hydroxyl benzaldehyde as main reactants, six liquid crystal compounds of multi-ring monoesteryl aryl aldehydes were synthesized by reactions of chlorination and esterification. Their structures were identified by elemental analysis, IR, MS, and ¹H NMR. By DSC(Differential Scanning Calorimeter) and POM(Polarizing Optical Microscope) measurements, their mesophase was investigated. The results showed that chlorination under room temperature would restrain the transformation of configuration of trans-hexanes. They exhibited obvious nematic schlieren and streak textures during heating process. The temperature ranges of phase transition of these compounds were from 107 to 156℃2. A new method was described, which could be used to selectively oxidize aldehydes to corresponding acid in anhydrous acetone system with KMnO₄ as oxidant. Using a series of acids of double rings substituted by n-propyl, n-pentyl as main reactants, six liquid crystal compounds of multi-ring monoesteryl aromatic acids were synthesized by reactions of one step of esterifing and one step of oxidizing reactions(esterification and oxidization method). The total yields were more than 70%. Their structures were confirmed by IR, MS,¹HNMR and elemental analysis. DSC and POM measurements revealed their properties of thermotropic liquid crystals and their obvious nematic schlieren and streak textures.3. The oxidation method above was studied by using 4-(4-(trans-4-propyl cyclohexyl) benzoyloxy) benzaldehyde as substrate to produce 4-(4-(trans-4-propyl cyclohexyl) benzoyloxy) benzoic acid. The factors that affected the reaction were found by orthogonal experiments. The mechanism of the reaction was investigated by IR spectra. The structures of resulting products were confirmed by IR, MS, ¹HNMR and elemental analysis. The result showed that KMnO₄ possessed good reactivity and high selectivity to oxide aldehydes in anhydrous acetone system without the present of any catalyst when aldehydes and alkyls all located in aryl rings. The Selectivity of the process was 100%. The optimal conditions of the reaction confirmed by orthogonal test design was molar ratio of KMnO₄/reactant=2:1, the reaction time of 4h and acidifying time of 1.5h with the yield of 95%4. A new method of using oxidation and esterification was designed to synthesize compounds with double esters. By this method, six new liquid crystal compounds of multi-ring diester aryl aldehydes were synthesized with a series of acids of double rings substituted by n-propyl, n-pentyl and p-hydroxyl benzaldehyde as reactants. The target molecules have longer rigid groups. Their structures were identified by IR, MS, ¹H NMR and elemental analysis. DSC and POM measurement revealed their behaviors of mesophase. The results showed that the total yields were above 60%. The mesogenic ranges of resulting compounds were wider than 78℃and their textures belonged to nematic.5. By reaction of condensation, six novel rod-like monoester schiff base magnetic liquid crystals have been prepared in which trans-bicyclohexyl or trans-cyclohexyl phenyl and biphenyl carboxylic acid phenyl ester mesogenic cores with n-propyl and n-pentyl substituents were terminated by 4-amino-TEMPO (TEMPO=2, 2, 6, 6-tetramethylpiperidine-1-oxyl). Their purities were detected by HPLC and their structures were identified by MS, IR and elemental analysis. Their behaviors of liquid crystals were observed by DSC and POM. Of these compounds, the silk-like and schlieren textures were found from compounds with terminal group of pentyl under POM. DSC and POM measurements revealed that their mesophases exhibited from 3.9～6.5℃and their textures belonged to schlieren and streak. EPR spectra found their paramagnetic properties at room temperature. 6. By reactions of condensation, six novel rod-like diester schiff base magnetic liquid crystals were prepared in which four-ring diester mesogenic core with C₃ and C₅ alkyl substituents were incorporated with terminal TEMPO. Their purities were detected by HPLC and their structures were identified by MS, IR and elemental analysis. Mesophasic textures were observed in all the target compounds under POM. Their temperature ranges of phase transformation existed from 3.5 to 24.3℃. Their textures belonged to cholesteric, schlieren and streak. EPR spectra revealed their paramagnetic properties at room temperature.7. By reaction of chlorination and esterfication, six novel rod-like magnetic liquid crystals with double esters were prepared in which trans-bicyclohexyl or trans-cyclohexyl phenyl and biphenyl carboxylic acid phenyl ester mesogenic cores with n-propyl and n-pentyl substituents were terminated by 4-hydroxy-TEMPO. Their structures were confirmed with MS, IR and elemental analysis. Six compounds all exhibited mesophase and the temperature ranges of phase transformation existed from 15 to 24.8℃. The silk-like and schlieren textures were found from all these compounds under POM. EPR spectra revealed their paramagnetic properties at room temperature. A primary study was done which was about the influence on photoelectrical properties when magnetic liquid crystals were added to the liquid crystal materials.In this paper, there are 36 new compounds of 6 series were designed and synthesized. Among them, 18 are important intermediates. And their properties of liquid crystalline were studied systematically, Methods of chlorination at room temperature and selectively oxidizing in anhydrous system were put forward, which could restrain the transformation of the structure from trans to cis and keep the alkyls on aryl rings from being oxidized The method of synthesized asymmetry biester by using oxidation and esterification were advanced, which could improve the yield of this kind of reaction effectively.The other there series are 18 new magnetic molecules with the structures of mesophasic cores and radical groups. Among them, 15 possess the double properties of liquid crystalline and magnetic. The temperature range of their mesophase is over 24℃. Nowadays, all magnetic molecules made up of mesophasic cores and terminal TEMPO, reported by literature inside and outside have been not discovered any liquid crystalline properties. It was found for the first time that magnetic liquid crystals could increase the speed of response of liquid crystal materials.