Synthesis And Mesomorphism Of Unsymmetric Triphenylene Discotic Liquid Crystals With A Semi-fluorinated Chain

The thesis consists of three parts:1. Chapter One briefly introduced the elementary knowledge about liquid crystal materials, including the definition and classification of liquid crystals, then the synthetic methods for triphenylenes discotic liquid crystals were reviewed, and the research progress in fluorinate discotic liquid crystals in latest years have been summarized.2. The literature reported several long synthetic routes to 2-hydroxy-3,6,7,10,11-penta(alkoxy)triphenylenes, which are valuable precursor molecules for the synthesis of avariety of discotic dimers, oligomers, polymers, networks, and mixed tail derivatives. Chapter Two has been developed a new method for this compound. In our experiment, 1,2-dialkoxybenzene and 2-methoxyphenol as starting material in one pot was FeCl3 oxidized cyclotrimerization, and further alkylation, selective demethylation with reagent of LiPPh2 (prepared from PPh3 and Li) resulted in key intermediates 2-hydroxy-3,6,7,10,11-penta(alkoxy)triphenylenes. Compared with other methods, this route is short and convenient in columnar chromatograph purification.3. Fluoroalkyl chains show strong affinity to neighboring fluoroalkyl chains (fluorophilic effect), and are incompatible with hydrocarbon chains and aromatic cores (fluorophobic effect). The fluorophilic and fluorophobic effects of fluorinated liquid crystals produce a micro-segregation to increase smectic phase stability. Reducing molecular symmetry of triphenylenes can decrease melting points, or results in room-temperature liquid crystals, polymesomorphism and wider mesophase ranges. So, unsymmetric triphenylene discotic liquid crystals with a fluorinated chain attract our interests.In Chapter Three and Chapter Four, the molecular designing, synthesis and mesomorphism of two kinds of unsymmetric triphenylene discotic liquid crystals with different kinds of semi-fluorinated chains were reported. The purity and structure characterization of these compounds were carried out with 1H NMR and Mass. 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.Chapter Three, a series of new triphenylene derivatives C18H6(OCnH2n+1)4(OMe)(O2CC2H4C6F13), with a semi-fluorinated nonyl ester chain and their hydrocarbon analogues, C18H6(OCnH2n+1)4(OMe)(O2CC8H17), n = 4~8, were synthesized. And another triphenylene derivatives with a semi-fluorinate chain C18H6(OCnH2n+1)4(OMe)(O2CC6H4C6F13) ,n = 4~8 and its two hydrocarbon analogues C18H6(OC6H13)4(OMe)(O2CC6H4C6H13), C18H6(OC6H13)4(OMe)(O2CC6H4OC5H11) were synthesized in Chapter Four. The results showed that, 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. Changes of the molecular symmetry affect the liquid crystal character of the molecules, and the influence varies with the length of the surrounding alkoxy chain.