| Summary: | 碩士 === 國立中央大學 === 化學學系 === 103 === In this thesis, we report the synthesis, characterization and mesomorphic properties of four novel series of new mesogenic derivates based on heterocyclic structures. All compounds were characterized by 1H, 13C-NMR spectroscopy and elemental analysis. The phase behavior of these mesogenic compounds was characterized and studied by differential scanning calorimeter (DSC) and polarization optical microscope.
In the first part, two new series of mesogenic bis-heterocyclic derivatives containing pyrazoles and isoxazoles 1a-b were reported. One single crystallographic structure of mesogenic 2a (n = 8) was determined by X-ray analysis, and it crystallizes in a triclinic space group P-1, with a = 7.0511(2), b = 7.6303(2) and c = 21.2143(5) Å, and Z = 2. The crystal was considered as slightly bent-shaped molecule with a molecular length of ca. ~24.9Å. A dimeric correlated structure induced by H-bonds was observed in the crystal lattice, which was favorable to the formation of mesophases. All compounds 1-2 exhibited N, SmA, N/SmC or SmA/SmC phases, as expected for linear-shaped molecules. All compounds 1 have higher clearing temperatures and wider ranges of mesophases than those of their precursors 2, which might be attributed to have higher dipoles polarized by two heterocyclic rings in 2.
In the second part, two new series of isomeric bis-pyrazoles 3a-b are prepared, characterized, and their mesomorphic properties investigated. These pyrazoyl derivatives were obtained from the condensation of α,β-diketones 4a-b with hydrazine monohydrate in refluxing THF. One single crystallographic structure of mesogenic 4b (n = 6) was determined by X-ray analysis, and it crystallizes in a triclinic space group P-1, with a = 4.7804(2), b = 16.5849(8) and c = 19.9328(10) Å, and Z = 2. Derivatives 3a exhibited smectic A/C mesophases, in contrast, derivatives 3b were all nonmesogenic. The difference in mesomorphic behavior was attributed to the between linear conformation and the coplanarity of the five rings over than in 3a. The correlation between the molecular structures and the mesomorphic properties is discussed.
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