| dc.description.abstract | In the first part, one new series of bis(boron difluoride) complexes 1ad derived from substituted -enaminoketonates 2ad were successfully synthesized, in which both 1a and 2a exhibit rod-like mesogen behavior. Increasing the number of terminal alkyl chains, compounds 1ac and 2ac exhibit columnar mesogen behaviour. Compounds 1d and 2d did not exhibit liquid crystal behaviour because of their bent stuctures. One single crystal and molecular structure of nonmesogenic BF2 complex 1b (n = 8) was resolved and the geometry of the central boron atom was tetrahedron. A larger dihedral angle of 45.141 between the phenyl rings and coordination structure ring observed in crystal lattice and excessive intermolecular hydrogen bonds were contributed to the lack of liquid crystallinity. The maximum absorption and the maximum luminescent emission of the compound 1ac were red-shifted compared to the compound 2ac. The luminescent emission of the compound 1ac in the solid state (λmax = 604653 nm) were red-shifted compared to in the solution (λmax = 591644 nm) because of the J-aggregate.
In the second part, a system of twin mesogens containing pyrazoles and isoxazoles was synthesized and characterized by 1H NMR, 13C NMR, Mass spectrometry and Elementary anaylysis. In this experiment, the effect of the above factors on the liquid crystal behavior of the compound was observed by introducing a heterocyclic system, changing the ratio of the hard and soft terminals and introducing a hydroxyl group. The results of POM and powder X-ray diffraction experiments indicate that the compound 4 exhibit SmC and N phase and the compound 3a exhibit SmA phase. Compound 3b did not exhibit liquid crystal behavior.
In the third part, a system of twin mesogens containing pyrazoles and 1,3,4-oxadiazoles was successfully synthesized. In this experiment, the effect of the above factors on the liquid crystal behavior of the compound was observed by introducing a heterocyclic system and changing the ratio of the hard and soft terminals. The results of POM and powder X-ray diffraction experiments indicate that the compound 5a exhibit SmA phase and the compound 5b exhibit SmC and N phase. Compound 5b emitted a pronounced violet emission at λmax = 427 nm in solution at room temperature
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