Synthesis And Properties Of Difluoroethylene Oxylated Liquid Crystal Diluents

Liquid crystal materials are widely used as optical modulation materials in the visible,infrared,millimeter wave and terahertz spectral regions.However,large dielectric anisotropy,low viscosity,high birefringence,low melting point,and wide liquid crystal phase region temperature are still the key indicators for measuring whether liquid crystal materials can be used and their application scope.With the development of liquid crystal optics and new display technologies,high birefringence hybrid liquid crystals mixtures have become a research hotspot.In order to improve the problems of high melting point and low dielectric anisotropy of high birefringence mixed liquid crystals,this paper will design and synthesize three types of liquid crystal diluents using difluoroethyleneoxy as the polar end group:difluoroethyleneoxy biphenyl,difluoroethyleneoxy tolans,and difluoroethyleneoxy biphenyl with the lateral fluonine,and the effects of alkyl chains,terminal substituents and molecular backbone on the liquid crystal properties of the compounds were studied.The specific contents are as follows:(1)Using trifluoroethyl methanesulfonate and 4-bromophenol as raw materials,8 trifluoroethoxy compounds and 8 difluoroethyleneoxy compounds were completed by etherification,palladium-catalyzed Suzuki cross-coupling,Sonogashira coupling,and LDA dehydrofluorination.The structure of the target products were confirmed by nuclear magnetic resonance spectroscopy(NMR)and gas-mass spectrometry(GC-MS).The purity of the samples(GC)are higher than 99%.(2)Trifluoroethoxy and difluoroethyleneoxy-based compounds were doped into the liquid crystal 100 mixture to test their liquid crystal performance.The effect of end groups,alkyl chains and molecular backbones on mixtures liquid crystals were investigated.The results show that difluoroethyleneoxy compounds have significant advantages,which can lower the melting point and viscosity,and increase the birefringence and dielectric anisotropy of the mixed liquid crystal.The lowest melting point can be dropped to-59?,and the dielectric anisotropy is as high as 4.27.(3)The density functional theory calculation(DFT)was performed on the synthesized compound.It was found that the dihedral angle of different molecular frameworks has the same trend as the size of ?n.At the same time,the photophysical properties of the target compound were tested.The results show that the maximum absorption peaks of the tolans UV-vis and FL are red-shifted,the lateral fluorine biphenyls are blue-shifted,and the biphenyls substituted with the lateral fluorine have the maximum emission intensity based on the biphenyl type.(4)The effect of difluoroethylene oxy-based liquid crystal diluent on the optical and electrical properties of highly birefringence liquid crystals mixtures was preliminarily studied.The target products are suitable for fluorinated phenylacetylence type high birefringence liquid crystal(MW-16),in which the lateral fluorine biphenyl difluoroethyleneoxy liquid crystal diluent 3PF(2)POF2 can reduce the melting point of the liquid crystal mixtures from-15? at-33?,the viscosity decreased from 239 mPa·s to 93 mPa·s,and the dielectric anisotropy increase from 2.84 to 3.54.It is the only liquid crystal diluent were known that can significantly improve multiple key liquid crystal parameters at the same time.