| 摘要: | 研究期間：10108~10207;This proposal continues our original research in metallomesogen derived from heterocycles. This research is to propose a strategic approach for the formation of novel metallomesogenic materials with superstructures, which are expected to exhibit liquid crystalline behavior, magnetic and related electro-optical properties. These materials are associated with unique molecular assemblies in which metal centers as core group have geometries of square planar or pyramid with a coordination number of 4, 5 and 6. Four different types of heterocyclic structures are applied to generate the metallomesogenic materials; (a) pyrazoles (b) benzoxazoles (c), 1,2,4-triazzoles, and (d) 1,3,4-oxadiazes. A variety of transition metals will be incorporated to induce the microscopic dipole, and the choice of the metals incorporated will be generally dependent on the coordination geometry, oxidation state or electronic state of the metals. Metal complexes incorporated with a twisted square planar (Cu2+), square planar structure (Ni2+/Pd2+) are often easier to form mesophases, however, complexes with a tetrahedron (Co2+/Zn2+) is not easy to form a mesophase due to unfavorable packing. A coordination number of 4 (Cu2+/Ni2+/Zn2+/Pd2+), 5 (VO2+/TiO2+/Mn2+), and 6 (Cr/3+Al/3+Ru3+/Fe3+) will be applied to generate the metal complexes. Occasionally, complexes with a CN = 3 (Cu1+/Ag1+) might be also possible. A non centrosymmetric structure and the large resulting molecular dipoles are prerequisites in order to give rise to large bulk macroscopic polarization. The ability to reorient the polarization with electric field applied and to have this polarization persist after the field is removed will make these materials polar ordering. A major distinction between metallomesogens and organic mesogens is their greater tendency to exhibit intermolecular dative coordination in the mesophase, which makes these materials attractive candidates for poling into acentric states. In these systems a lower symmetry is promoted at the molecular level by the self-ordering properties of liquid crystalline materials, the complementary shape of the molecules and head-to-tail ordering imposed by the linear chain superstructures, and these methods are also widely employed to facilitate the formation of these mesogenic materials. Self-organizing properties of liquid crystalline materials, the geometric shape of the molecules, and weak intermolecular dative coordination will be employed to facilitate the formation of the proposed materials. Preparation, characterization and mesomorphic properties of these poly-metallic compounds will be studied in the initial stage, and future research will be focused on the physical studies. |
