Molecular Design,Synthesis Of Triphenylene Discotic Liquid Crystals And Anchorage Of Columnar Mesophase

Discotic liquid crystals self-assemble to highly ordered hexagonal columnar mesophase (Colho), exhibit anisotropic high charge carrier mobility and show huge potential application as organic electronic materials. To obtain materials with improved charge carrier mobilities, the thrust of much research on triphenylene based liquid crystals has been to introduce structural modifications designed to increase the columnar ordering in terms of the average length of ordered stacking arrays along the column. Introducing fluorinated chain and hydrogen bonding are elegant method to enhance the attractive interactions between the discotic mesogens. This thesis reported the molecular designing, synthesis and mesomorphism of two series of triphenylene discotic liquid crystals with fluorinated chain or chains contain amide functional groups. 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 four chapters:1. Chapter one briefly introduced the fundamental knowledge about liquid crystal materials, then fluorinate discotic liquid crystals in latest years have been studied, and more attention of the thesis have been focused on hydrogen bond stabilized discotic liquid crystals.2. The fluorophobic effect of highly fluorinated alky terminal chain of rod-like molecular can efficiently promote the formation of semctic phase and improve the stability of mesophase. In order to investigate the influence of fluorinated chain on mesomorphism of disctoic molecules, a series of new triphenylene derivatives C₁₈H₆(OC_nH_2n+1)₅(OCOC₆H₄C₆F₁₃), with a perfluorohexylbenzoate side chain and their two series hydrocarbon analogues, C₁₈H₆(OC_nH_2n+1)₅(OCOC₆H₄OC₅H₁₁), C₁₈H₆(OC_nH_2n+1)₅(OCOC₆H₄C₆H13), n = 4 9, were synthesized in chapter two. Studies of DSC and POM texture observations revealed that these triphenylene derivatives showed enantiotropic hexagonal columnar mesophases (except C₁₈H₆(OC4H9)₅(OCOC₆H₄OC₅H₁₁)). Compared with the hydrocarbon ester chain, the fluorinated ester chain increased the melting points and clearing points, and stabilized the columnar mesophase of triphenylene discogens.3. An elegant method to enhance the attractive interactions between the discotic mesogens is by introducing hydrogen bonding. To obtain stabilized columnar phases amide groups have been used by several research groups. In chapter three, three series with total of eighteen triphenylene discotic liquid crystalline compounds possessing two different kinds of peripheral chains, which are abbreviated as C₁₈H₆(OC_nH_2n+1)₅(OCH₂COOEt), C₁₈H₆(OC_nH_2n+1)₅(OCH₂COOBu), and C₁₈H₆(OC_nH_2n+1)₅(OCH₂CONHBu), n = 4 9, were synthesized. Studies of DSC and texture observations by polarized microscope revealed that these triphenylenes show enantiotropic hexagonal columnar mesophase. The TGA showed that all these compounds had good thermal stability up to 300 oC. The results showed that, for compounds C₁₈H₆(OC_nH_2n+1)₅(OCH₂CONHBu) and C₁₈H₆(OC_nH_2n+1)₅(OCH₂COOBu), the former has higher melting and clearing points than the latter due to the intra-columnar intermolecular hydrogen bonding.4. In chapter four, triphenylene discotic liquid crystals with a tail contain function groups-amide or ester C₁₈H₆(OC₉H₁₉)₅[O(CH₂)_mCOXBu],X = O,NH,m = 1⁵, were synthesized. The influence of distance between function group and the triphenylene core on mesomorphism has been discussed. At the same time, the triphenylene derivatives with a tail contain amide and hydroxyl groups, C₁₈H₆(OC_nH_2n+1)₅(OCH₂CONHCH₂CH₂OH) , n = 4⁹ were synthesized. The terminal hydroxyl groups can also form hydrogen bond with each others, and the strong hydrogen bond impact on mesophase is also investigated. Organogels have attracted increasing interest in recent years due to their promising physical and morphological properties. In this thesis different organic solvents were tested for gelation by C₁₈H₆(OC₇H₁₅)₅(OCH₂CONHBu).5. Chapter 5 gives the summary and conclusion of the thesis.