Study On The Preparation And Performance Of Benzofuran Liquid Crystal Compounds

Liquid crystals has achieved rapid development since its application of LCD in 1980s,although it was queried,disputed and inveastigated during about 80 years after the discovery.Nowadays,various liquid crystal devices have penetrated into all aspects of our life.Along with the continuous progress of the liquid crystals,the development of new structrures of liquid crystals becomes a tendency of the synthetic chemistry.The early liquid crystal compounds mainly include non-heterocyclic compounds such as cyano,azobenzene,cyclohexane,biphenyl,and terphenyl.In recent years,researchers have found that methods prepare heterocyclic liquid crystal compounds by introducing the larger polar hetero atoms into the structures which can effectively improve the phase transition temperature,birefringence,phase type and the like of the liquid crystal compound.The main reason is that the introduction of hetero atom can modify the dipole moment,dielectric properties,and the conjugated electrons on the molecular system.Among them,the benzofuran liquid crystals containing a five-membered heterocyclic ring have been widely recognized for its excellent structure such as structural stability,wide phase interval,large birefringence,absorption spectrum bandwidth,molar absorption coefficient,and high fluorescence quantum yield.Based on this,in order to prepare liquid crystal compounds with excellent properties,firstly,the pepper ring was used as raw material,and then the IBDOAC,an important intermediate for the preparation of benzofuran compounds,was synthesized by Friedel-Crafts acylation,Baeyer-Villiger oxidation and iodide.A series of liquid crystal compounds of a total of 11 alkoxybenzofurans,alkylbiphenylbenzofurans and alkoxytolylbenzofurans were successfully prepared by using IBDOAC as a raw material.Various tests show that the series of liquid crystal compounds prepared in this paper have good thermal stability,optical anisotropy and spectral properties,which have certain guiding significance to design and synthesize new liquid crystal compounds.The specific contents of this paper are as follows:1.The pepper ring is used as a raw material,and the synthesis of the intermediate product IBDOAC is completed by Friedel-Crafts acylation,Baeyer-Villiger oxidation,and iodination.The synthesized compounds and intermediates were monitored by gas chromatography,and the purity was higher than 99%.All the compounds in the synthesis process were confirmed by nuclear magnetic resonance,mass spectrometry and infrared spectroscopy.The optimization of the reaction conditions in the synthesis of IBDOAC was carried out.2.Using p-bromophenol and brominated hydrocarbon as raw materials,followed by Williamson etherification,palladium catalyst catalyzed Sonogashira coupling,and acetylene bond deprotection group under basic conditions to obtain 4-AB;IBDOAC and 4-AB are used as raw materials for a one-pot two-step reaction of Sonogashira coupling and ring closure to obtain a final alkoxybenzofuran series of liquid crystal compounds.The mechanism of one pot and two step reaction was also discussed.Performance tests of this series of compounds have shown that the introduction of a higher degree of conjugated heterocyclic structure into the compound can effectively promote the optical anisotropy and spectral properties,such as the benzofuran liquid crystal compound prepared in this chapter.The birefringence An is greater than 0.35,and the maximum absorption wavelength of ultraviolet-visible absorption and the maximum emission wavelength of fluorescence emission reach 330 nm and 374 nm,respectively.3.Using 4-alkylbenzeneboronic acid and p-bromobenzene iodide as raw materials,sequentially subjected to Suzuki coupling,palladium-catalyzed Sonogashira coupling,and acetylene bond deprotection under basic conditions to obtain n-ADB;IBDOAC and n-ADB are used as raw materials for a one-pot two-step reaction of Sonogashira coupling and ring closure to obtain the final alkylbiphenylbenzofuran series liquid crystal compounds n-BFDB.Due to the increased n-n conjugated biphenyl in the structure,this series of compounds showed better optical anisotropy and spectral properties than alkoxylbenzofurans.Theoretical calculations show that the birefringence An of the series of compounds is greater than 0.53,compared with compounds n-BFB:the maximum absorption wavelength of the ultraviolet-visible spectrum of n-BFDB are red-shifted by about 16 nm,and the maximum emission wavelength of the fluorescence emission spectrum are about 29 nm.4.First,brominated hydrocarbon and p-bromophenol are used as raw materials,followed by Williamson etherification,palladium-catalyzed Sonogashira coupling,acetylene bond deprotection under basic conditions to obtain n-AAMB,finally the IBDOAC and the n-AAMB are used as raw materials for a one-pot two-step reaction of Sonogashira coupling and ring closure to obtain the final alkoxyphenylacetylene benzofuran series liquid crystal compounds n-BFAMB.Tests by DSC,POM and UV-visible absorption indicate that the series of compounds mainly exhibit a nematic phase,the melting point of the series of compounds is significantly lower than that of the above two series of compounds,the clearing point is also on the decline,and the phase interval temperature is broadened.At the same time,since the acetylene bond can prolong the ?-electron conjugation in the molecule,the optical anisotropy of the series of compounds has also been greatly improved,and the An of the series of compounds is calculated to be greater than 0.68.UV-visible absorption spectroscopy showed that the liquid crystal compound has a higher absorption wavelength than the alkoxybenzofuran and the biphenyl benzofuran,and the maximum absorption wavelength of n-BFAMB is measured 361 nm.Fluorescence emission spectroscopy results are basically consistent with the UV-visible absorption spectrum.