Containing Heterocyclic Groups At The End Of The Liquid Crystal Compound Preparation And Its Thermal Performance

The development and LCD application of the liquid crystal materials has brought significant economic benefits, however, the driving force based on the formation of liquid crystalline state has become a basic research direction in the liquid crystal molecules engineering. All these methods such as changing molecular geometry structure, rigidity of mesogen unit, polarity and introducing the heteroatoms into the molecule were considered as effective ways in modification research, which will help to deepen understanding of the structure-activity relationship about liquid crystal materials, as well as design high-performance liquid crystal materials.In this thesis, two kinds of liquid crystal compounds, with triazole and thiobarbituric acid as the terminal group were proposed and prepared. The effects of alkoxy chain and end group on the properity were also investigated. The detailed contents are as follows:1. Eight novel compounds, N-((4’-(alkoxy)-[1,1’-biphenyl]-4-yl)methylene)-1H-1,2,4-triazol-3-amine (APAT-n), were synthesized via three-step reactions, Suzuki coupling, nucleophilic substitution, and aldehyde amine condensation, with yields of15.4-40.5%and purity of99%. The structures were confirmed by1H NMR, IR and MS. Conditions of experimental studies showed that,(1)5%Pd/C was the best catalyst for the synthesis of intermediate dihydroxybiphenyl formaldehyde with high purity and easy processing.(2) For the preparation of schiff base compounds, the meltings method showed higher conversion and selectivity than the conventional heating and microwave radiation methods, where the product could be obtained with hingh purity of99%, in low cost, and easy processing. The thermal behavior of the APAT-n was measured by differential scanning calorimetry (DSC), hot stage polarized light microscopy (POM) and thermogravimetric (TGA). The results showed that the APAT-n had enantiotropic mesophases with temperature domains of7-22℃and13-34℃on heating and cooling processes, where the melting points of APAT-n decreased smoothly with ascending homologues, whereas the increase of carbon numbers resulted in a gradual increase and then a decrease of the clearing point. The decomposition temperature of compounds was found above313℃. Preliminary studies suggest that the formation of thermotropic smectic phase was mainly driven by triazole-based hydrogen bonding interaction.2. Seven compounds,5-((4’-(alkoxy-[1,1’-biphenyl]-4-yl)methylene)-2-thioxo-dihydropyrimidine-4,6(1H,5H)-dione (APMT-n), were designed and prepared via the Knoevenagel condensation reaction between4’-(alkoxy)-[1,1’-biphenyl]-4-carbaldehyde and thiobarbituric acid, with purity of98%, and yield of30.7-49.3%. Their structures were confirmed by1H NMR and IR. The liquid crystalline behaviors were studied.The resuits showed APMT-n had smectic phase. With the increase in the number of carbon atoms in the alkoxyl chain, the melting point of APMT-n decreased, and the stability of liquid crystal phase was improved slightly. Preliminary studies indicated that hydrogen bonding was one of the main driving forces for the formation of thermotropic smectic phase of APMT-n.