| Liquid crystals with fluorinated chains produce a micro-segregation at the molecular level for the difference of structure and chemical properties of perfluorinated and hydrocarbon alkane segments within the same molecule. Fluorocarbon chains are miscible with fluorocarbon chains but incompatible with corresponding hydrocarbon chains to form the layers of fluorocarbon chains and hydrocarbon chains respectively. Fluorinated liquid crystals have focused most attentions for its excellent feature, such as higher clearing points, wider mesophase temperature range, higher thermal stability than corresponding hydrocarbon ones. In general, nematic phases are depressed while segregated phases, such as smectic phases are favoured and sometimes even new mesophase types are generated.Discotic liquid crystals possess high charge carrier mobility and show huge potential application as organic semiconductor materials. High speed of electric charge transition in column is needed for its application as organic semiconductor materials, and the speed can increase as the stability of columnar increase. So it's a useful means to fix the column by fluorophilic effect within perfluorinated chains and fluorophobic effect between perfluorinated chains and hydrogenated chains. But up to the present only few study on this means, more researches are needed.This thesis reported the molecular designing, synthesis and mesomorphism of three kinds of triphenylene discotic liquid crystals with different number of semi-fluorinated chains. The purity and structure characterization of these compounds were carried out with 1H NMR, EA. Thermal gravimetry analysis (TGA) showed these compounds have good thermal stability. The thermotropic liquid crystal properties were studied through polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The structure-property relationship of these molecules was proposed, and it is hopefully to contribute to the molecular designing and practical application of these liquid crystals as new materials. The thesis consists of three main parts:1. Firstly, chapter one briefly introduced the elementary knowledge about liquid crystal materials, including the definition and classification of liquid crystals. Then mostly introduce the study on liquid crystals with fluorinated chains. It showed that the more attention has been focused on the traditional rod-like and some unconventional liquid crystals but only a few on the discotic ones.2. A series of new triphenylene derivatives F-a-n C18H6(OCnH2n+1)5 (OCOC2H4C6F13), with a semi-fluorinated chain and their hydrocarbon analogues, H-a-n C18H6(OCnH2n+1)5(OCOC8H17), n = 49, were synthesized in chapter two. Studies of DSC and POM texture observations revealed that these triphenylene derivatives showed enantiotropic hexagonal columnar mesophases. Compared with the hydrocarbon ester chain, the semi-fluorinated ester chain increased the melting points and clearing points, and stabilized the columnar mesophase of triphenylene discogens.3. In chapter three, triphenylene derivatives with two semi-fluorinate chains 2,7-C18H6(OC5H11)4(OCOC2H4C6F13)2 (F-b-5) and its hydrocarbon analogues 2,7-C18H6(OC5H11)4(OCOC8H17)2 (H-b-5) were synthesized. A series of triphenylene derivatives with three semi-fluorinated chains C18H6(OCnH2n+1)3 (OCOC2H4C6F13)3 (F-c-n) and the typical hydrocarbon analogues C18H6(OC9H19)3(OCOC8H17)3 (H-c-sym-9 and H-c-asym-9) were also synthesized in this chapter. Studies of differential scanning calorimetry (DSC) and texture observations by polarized microscope revealed that these triphenylenes show enantiotropic hexagonal columnar mesophase. The thermal gravimetry analysis results showed that compounds F-c-n series have good thermal stability up to 300℃.In F-c-n series symmetrical compounds have lower clearing points compared with their corresponding asymmetrical ones. The columnar mesophase was greatly affected by both the length of fluorinated chains compared with alkoxy chains and the position of ester groups.Compared with the three kinds of triphenylene derivatives with different number of semi-fluorinated chains, it showed that with the increasing number of semi-fluorinated chains, the range of mesophase does not enlarged but the stability of that increase in rules. In these three kinds of discotic triphenylene derivatives, compounds with three semi-fluorinated chains is superiority and have the potential value for application. |
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