| dc.description.abstract | In this thesis, we report the synthesis, characterization and mesomorphic properties of two novel series of new mesogenic derivatives based on benzoxazole structure.
In serie one , this synthesis, characterization, and mesomorphic properties of a new type of transition metal complexes 1a-1b derived from benzoxazoles 2 as core group are reported. These metal complexes were obtained by the reactions of 6-alkoxynaphthalene-2-carboxylic acid and 4-(6-dodecyloxy benzooxazol-2-yl)-3-hydroxyphenyl esters. The metal complexes were obtained by reaction of benzoxazoles 2 and copper (II) or palladium acetate in refluxing ethanol. 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.
All compounds with shorter chains (n = 0, 1, 4, 6, 7, 8, 10, 12) exhibited nematic (N) and/or smectic C (SmC) phases, as expected for rod-like molecules. For copper(II) compounds 1a with shorter chains (n = 0, 1, 4, 6, 7, 8, 10) nematic phase was observed only, whereas those compounds having longer carbon chains (n = 12) smectic C phase was also observed at lower temperatures. However, palladium(II) complexes formed nematic phases with short chains (n = 1, 4) only. The difference in the mesomorphic properties observed by compounds 1a and 1b was probably attributed to the geometry at the metal center. Although the Cu2+ ions and Pd2+ ions are both square planar geometries, but the difference of bond length between metal center and ligand is the major effect of mesomorphic behavior. The fluorescent properties of these compounds were also examined.
In serie two,we designed and characterized a series of new type of organic molecule 3 ~ 6 derived from two benzoxazoles with two to six side chains. These compounds were prepared by the ring closure reaction of 4,4’’-Bis[(3,4,5-trialkoxybenzylidene)amino]biphenyl-3,3’’-diol in the presence of lead(Ⅳ) acetate. 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.
All compounds with two(n = 16) to six side chain(n = 6 ~ 16) exhibited crystal phase, indicate that the interaction between molecules are more larger than the side chain flexibility, no matter how many side chain does the molecule have. The fluorescent properties of these compounds were also examined. | en_US |