| dc.description.abstract | Complexes or adducts containing boron difluoride (BF2) have been paid much attention during the past years. Many known boron difluoride complexes, widely investigated as fluorescent materials showed potential applications in many areas; such as biological imaging, molecular probes, electroluminescent devices, photosensitizers and others. However, only a few examples were reported among mesogenic applications.
In the first part, five new series of bis(boron difluoride) complexes 1-BF25-BF2 derived from substituted tetraketonates 1-5 were reported, and their mesomorphic and optical properties were also investigated. Results appeared that bis(BF2) complexes 1-BF2、2-BF2 were nonmesogenic and 3-BF25-BF2 (n = 10, 12, 14) exhibited enantiotropic columnar mesophases. A value of Ncell = 3.143.76 within a column slice of 9.0 Å thick was obtained for compound 3-BF25-BF2, indicating that a single discshaped molecule was stacked within columns in Colh phases. Bis(BF2) complexes 1-BF25-BF2 (n = 12) possess a pronounced greenyellow emission in solution at room temperature and possess a pronounced orangered emission in solid at room temperature. The luminescent emission also showed a strong dependence with structural moiety incorporated. To our best knowledge, there are rare examples of columnar bis(BF2) complexes.
Nowadays more and more liquid-crystalline compounds containing five-membered heterocycles are the subject of much investigation. These heterocyclic structures generally incorporated of such electronegative atoms (S, O or N atom) often resulted in a reduced or lowering symmetry for the overall molecules or/and a stronger polar induction. Quite a few examples, including pyrazoles, isoxazole, 1,3,4-oxaziazoles, and others have been prepared and investigated in our group. Most of them formed smectic phases whereas, only a few of them exhibited columnar phases.
In the second series, 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, changing the patern, and introducing a hydroxyl group. The results of POM and powder X-ray diffraction experiments indicate that compounds 2a, 3a, 4b and 5b show the Colh liquid crystals.And the presence of hydroxyl 6a has SmX phase found.In UV absorption spectra, the reddish shift of 5a is due to its longest conjugation length
In the third series,the heterocyclic derivative 7a, 7b with a benzene ring as the central hard core and three pyrazole and isoxazole compounds were successfully synthesized, and 7a clean point is higher than 7b, because 7a has strong intermolecular hydrogen bonding force.In the 7a, the SmX phase can be observed. With the variable temperature IR, the change of the hydrogen bonding force from the solid state to the liquid state can be found by the change of the peak. | en_US |