| dc.description.abstract | The 1,3,4-oxadiazoles, isoxazoles and pyrazoles are often considered as one of the most important structures among numerous heterocyclic compounds. These heterocyclic compounds were recently found to exhibit novel mesomorphism due to their varieties in structures and/or known chemistry. Better mesomorphic behavior was attributed to their unsaturation and/or more polarizable nature. 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 bisheterocyclic derivatives containing 1,3,4-oxadiazoles and isoxazoles 1ad were described. A dimeric correlated structure induced by Hbonds was observed in the crystal lattice, which was favorable to the formation of mesophases. All compounds 12 exhibited N/SmC, SmA phases, as expected for linearshaped 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, three new series of heterocyclic structures 3ac are prepared, characterized, and their mesomorphic properties investigated. Derivatives 3a exhibited N/ smectic C mesophases; 3b exhibited N/ smectic C mesophases; 3c exhibited smecticA/ C mesophases. The best mesomorphic behavior formed in 3c might be attributed to stronger intermolecular interactions and higher polarization induced in pyrazoles 3c. | en_US |