||Three series of mesogenic compounds were prepared and studied in this thesis. All compounds described were characterized via 1H-NMR, 13C-NMR, mass spectroscopy, and elemental analysis. The mesophases were studied polarized optical microscopy (POM) and differential scanning calorimeter (DSC), and the structures of the mesophases were also confirmed by variable temperature X-ray diffraction experiments.|
In the first series, a new type of mesogenic compounds derived from heterocyclic benzoxales were prepared and studied. All compounds exhibited nematic or/and smectic phases depending on the carbon length attached.
In the second series, numberous metal complexes including copper, palladium, cobalt, zinc and nickel ion coordinated with substituted benzoxales were prepared and their mesomorphic behavior studied. Their mesomorphic properties were dependent on the metal incorported. All Cu2+, Ni2+ and Pd2+ complexes exhibited nematic, or/and smectic plases, however, Zn and Co were crystalline phases. The mesomorphic properties were attributed to the geometries (tetrahedral or square planar) and electronic configuration (paramagnetic or diamagnetic) of the metal ions incorporated.
In the third series, the effect of substituent groups on the formation of the mesophases was invistigated. A variety of benzoxale derivatives with a substituent including CN, NO2, Cl, Br, OCF3, F, OCH3 were studied. The data indicated that the formation of the mesophase were strongly dependent on the electronic properties of the substituents. A SmA phase was observed for derivatives with a strong electrondrawing substituent, and a N phase was observed for the derivative with an electrondonating substituent. Electron cloud distribution between HOMH and LUMO precticted by theoretical calculation is studied, and the data showed that there is an energy gap of the electrondrawing and electrondonating substituent.
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