Synthesis And Properties Of Liquid Crystals Containing Ethylene Bridge And Fluorines

Synthesis of liquid crystals containing ethylene bridge and fluorines was studied. The relationship between liquid crystal properties and molecular structure was discussed.At the same time,the author designed liquid crystal compounds containing ethylene bridge and fluorines with different structure.Three liquid crystal compounds which have excellent properties had been synthesized by the intermediate 4-(2-(4-propylcyclohexyl)ethyl)cyclohexanone.The effects of functional groups on liquid crystal properties were studied and discussed through analyzing their physical performance parameters.This thesis consists of four parts:Part one,the relationship between liquid crystal properties and molecular structure was discussed.It includes the relationship between the physical and chemical stability, the phase transition temperature,the dielectric anisotropy,the birefringence and the liquid crystal molecular structure.Part two,the compound 4-(2-(4-tans-propylcyclohexyl)ethyl)cyclohexanone was synthesized from trans-4-propylcyclohexanecarboxylic acid and ethyl 4-oxocyclohexanecarboxylate via eight step reactions,namely carboxylic acid reduction,substitution of hydroxyl by bromine,carbonyl protection,ester reduction, Grignard reaction,hydrolysis,dehydration reaction,catalytic hydrogenation.This compound was identified by GC-MS,IR and ~1H NMR.Part three,4-(2-(4-tans-propylcyclohexyl)ethyl)cyclohexanone can be used to synthesize many liquid crystal monomers via Grignard reaction,dehydration reaction, catalytic hydrogenation.Three liquid crystal monomers have been synthesized: 1-ethoxy-2,3-difluoro-4-(4-(2-(4-propylcyclohexyl)ethyl)cyclohexyl)benzene, 1,2,3-trifluoro-5-(4-(2-(4-propylcyclohexyl)ethyl)cyclohexyl)benzene, 1,2-difluoro-4-(4-(2-(4-propylcyclohexyl)ethyl)cyclohexyl)benzene.The purity of all of the productes were analyzed by gas chromatography.The target compounds were identified by GC-MS and IR.Part four,testing the performance of the liquid crystal compounds and comparing with seven similar liquid crystal monomers get the following conclusions:(1) Effects of ethylene on liquid crystal performanceFor a negative dielectric anisotropy liquid crystal molecule,the introduction of ethylene into the molecular structure reduce its negative dielectric anisotropy.For a positive dielectric anisotropy of the molecule,the introduction of ethylene into the molecular structure reduce its positive dielectric anisotropy,so weaken the polarity of the molecular structure.Molecular structure and the location of ethylene impact the relationship between ethylene and clearing point.The introduction of ethylene reduces the birefringence of liquid crystal molecule.The introduction of ethylene lengthens the long axis of the molecule,increases the viscosity,slows the response speed.(2) Effects of fluorine on liquid crystal performanceFor positive dielectric anisotropy liquid crystal molecules with the same carbonic skeleton,the number of fluorine atoms impact clearing point,birefringence and dielectric anisotropy.The more fluorine atoms,the lower clearing point,the smaller dielectric anisotropy,the greater birefringence.In short,this thesis is useful for the synthesis of liquid crystals containing ethylene bridge,and is of great significance to study the relationship between fluorines and liquid crystal properties,and is of value for designning a more excellent liquid crystal molecule.