Synthesis And Characterization Of Chiral Biphenyl Oligomers

Currently, the oligomer has been studied extensively. With respect to the polymer, oligomer molecular has short molecular chain, its molecular weight is monodisperse, and its degree of polymerization is the same as the branching degree. It can dissolve, distill, and can form crystalline or amorphous substance. Its performance varies with different molecular weight. It is an polymer of incomplete polymerization.Linear oligomers have established molecular structure and molecular weight, easy to obtain materials of high purity and properties characterization. They are the ideal models to study molecular structure and photoelectric properties of polymer. Meanwhile, linear oligomer also can be used as an important component and the link of molecular devices, and plays an important role in the development of molecular electronics.Chirality is of great significance to the development of the life sciences, pharmaceutical chemistry, materials science and other related disciplines. The chiral dopant has been joined into the liquid crystal, which greatly promote the development and application of new liquid crystal materials and nonlinear optical materials. The chiral liquid crystal has splendid thermal colour effect, and its performance is stable. The chiral liquid crystal has been applied more and more in the thermal spectrum image. The molecule of chiral liquid crystal material forms helix structure due to the presence of asymmetric chiral center. Meanwhile, types of chiral crystal liquid are generally cholesteric and smectic phase.Chiral oligomer liquid crystal has characteristic properties of liquid crystal. It has better mechanical properties than other structural materials. Compared with other material, it has the unique superiority of some physical properties, such as photoelectric properties. It is a new materials of high performance.Herein,4’-hydroxy-4-biphenylcarboxylic acid mesogens and single and double substituted biphenyl mesogens were synthesized by classical chemical methods. Then a series of single and double substituted chiral biphenyl oligomers were synthesized through Mitsunobu reaction. The chemical formula is as follows: Single substituted biphenyl oligomers Double substituted biphenyl oligomerThe purity of the synthesized compound was confirmed by HPLC. The molecular structure was tested reasonably by HPLC(chiral column),1H NMR, FT-IR and X-ray single crystal diffraction, and then accurate molecular weights were obtained through LC-MS, consistent with the structure of the target molecule.The configuration of the compound is completely reverse after Mitsunobu reaction, from test results of the HPLC(chiral column) of HOPPO3*OH and X ray single crystal diffraction of HO*3OPPO3*OH. There is no racemization phenomenon obviously in the process of Mitsunobu reaction, which can confirm structure of chiral biphenyl monomer, namely S-HOPPO3*OH, S,S-HO*3OPPO3*OH, completely consistent with the expected design configuration. The subsequent reaction process does not involve chiral carbon atoms, so we can infer that molecular configuration of a series of biphenyl oligomers. And, all the inferred configuration matches designed molecular configurations.Polarized optical microscope (POM), differential scanning calorimetry (DSC), small angle X ray diffraction (SAXD) and wide angle X ray diffraction (WAXD) were used to study the optical texture of liquid crystal, thermodynamic properties and molecular ordering on the micro-level of mesogens and a series of the single and double substituted biphenyl oligomers. And the liquid crystal phase behavior of the compounds was studied.POM, DSC and XRD results indicated that4’-hydroxy-4-biphenylcarboxylic acid mesogens6OPPCOOMe and the single substituted oligomers6OPPO3*OOCPPO6,6OPPO3*OPPO3*OOCPPO6,6OPPO3*OPPO3*OPPO3*OOCPPO6, were smectic liquid crystals. The molecules of the three oligomer molecules display layered arrangement, and the molecules of layer is arranged in order. Typical birefringence whip, fan-shaped and focal conic texture could be observed through POM. But,60PPC003*OPP03*OOCPP06did not display birefringence texture of liquid crystal phase, without the properties of thermotropic liquid crystal.Polarimeter and circular dichroism spectroscopy (CD) was used to measure the optical rotation and circular dichroism of synthetic oligomers.From the polarimeter data, the answer was drawn that the optical rotation of synthetic oligomers liquid raised with increasing number of repeat biphenyl structure unit.Circular dichroism spectra express that the optical properties of synthetic oligomers thin solid films changed after annealing, but there was no regular variation. The optical activity of6OPPO3*OOCPPO6thin solid films annealed decreased greatly comparing with the unheated thin solid films; The optical rotation of6OPPO3*OPPO3*OOCPPO6and6OPPCOO3*OPPO3*OOCPPO6thin solid films annealed increased, and the maximum absorption wavelength took on blue shift.Recently, gels derived from low-molecular-mass compounds are attracting increasing interest owing to the simplicity of the gel molecules, their excellent physical properties, and great potential applications. A variety of gels based on hydrogen bonding, it stacking, van der Waals and so on interactions, has been reported to immobilize organic fluids or water to form swellable materials, even at extremely low concentrations.6OPPO3*OPPO3*OH can form gelator in THF and methanol mixed solvent in the synthetic mesogens and oligomers, indicating the formation of a three-dimensional network structure, which could be observed by polarized microscope. Whether the hydrogen bond was formed in the formation of the gel or not, using FT-IR study of the gel. SEM pictures displayed that the morphology of the gel was aggregate of fibrous material. The surface structure of the gel was researched by AFM.