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Circularly Polarized Luminescence Materials Based On Tetraphenylethylene Fluorogen:Preparation,structure And Performance

Posted on:2016-03-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q YeFull Text:PDF
GTID:1361330590490952Subject:Polymer Chemistry and Physics
Abstract/Summary:PDF Full Text Request
Circularly polarized luminescence material shows great application values in LCD,data storage,quantum communication,stereoscopic display,backlight record,color casting materials and other fields.At present,majority of circularly polarized luminescence materials are dyes-doped cholesteric phase liquid matrix,chiral group induced conjugated polymers and plane conjugate fluorophores connected with chiral substituent,etc.The present cicularly polarized luminescence materials exhibit low properties,but also pose great challenges:1)These materials use traditional fluorescent molecules or groups,which suffer from fluorescence quenching in aggregation state.Therefore,they can only be studied in solution or their solid fluorescence quantum yields are not high.2)The studies of circularly polarized luminescence materials with liquid crystal performance are mainly based on cholesteric liquid crystals.Although they have natural characteristic of self-assembling into liquid crystal phase with helical structures,this kind of liquid crystals is ordered only with1-dimensional?1-D?orientation.There has been no report about circularly polarized luminescence materials of chiral liquid crystal,which can not only response to stimuli but also demonstrate highly ordered dimension.3)According to previously report,fluorogen of organic circularly polarized luminescence materials are usually connected through covalent bonds with chiral groups rather than non-covalent bond interactions which have advantages of rapid,facile and efficient preparation and flexibility of substrates choosing,etc.Currently,the latter has very less reports.4)Since chirality was discovered,some theories have been put forward after continuous efforts.But the understanding of chirality producing,the relationship between chiral molecule structure,stacked structure and chirality is still not clear enough.There have always been a lot of controversies.Therefore,preparing circularly polarized luminescence materials with higher fluorescence quantum yield in solid state,regulating their chiral optical performance,and studying the relationship among chiral molecules,condensed structure and chirality are still full of challenges.In this thesis,we employed tetraphenylethylene?TPE?,a typical aggregation-induced emission?AIE?molecule,as fluorescence chromophores.Through covalent bonds or ionic assembly method,TPE was connected with chiral centers such as cholesterol,chiral amine or binaphthol which may induce chiral fluorescence.A variety of materials with characteristics of circularly polarized luminescence were prepared.The relationships of temperature,molecular chirality,macrostructure and circularly polarized luminescence properties were also investigated.Firstly,we introduced cholesteryl with an eleven-methylene spacer through covalent bond into tetraphenylethylene group,fabricating a circularly polarized luminescence material with characteristics of cholesteric liquid crystal.This compound,2CTPE,was characterized via UV-vis absorption,fluorescence spectra,DSC,polarized optical microscopy?POM?,circular dichroism,and circular polarization spectrum.It was found that the compound showed obvious properties of aggregation induced luminescence,cholesteric phase liquid crystal and chiral optical activity.It was further found that temperature can affect the pitch of cholesteric liquid crystal,thereby regulate circular dichroic absorption and circular polarization luminescnece performance.With the increase of temperature,the pitch of cholesteric liquid crystal increased,leading to the red-shift of light reflection band of the chiral structure,thereby giving rise to the decrease of circularly polarized luminescence and absorption.In addition,we also measured the solid fluorescence quantum yield of the compound?about 42%?.This research overcomes the shortcomings of low doping ratio?usually less than 0.5%?,weak luminescence intensity and aggregation-caused luminescence performance decrease,which existed in the doped circularly polarized luminescence systems.Secondly,the liquid crystal properties were regulated by changing the length and structure of spacers between TPE group and cholesteryl group.The compounds obtained by mono-or bis-substitution of TPE both possessed typical AIE property.However,the structure of spacers is critical to the formation of liquid crystal phase.When a phenyl group spacer was directly connected to TPE group,the steric hindrance increased,leading to only amorphous structure and the absence of chiral optical activity.When TPE group was directly connected with cholesteryl group or via a six-methylene spacer,the obtained products both exhibited typical cholesteric liquid crystal properties.Moreover,these two compounds also showed temperature-regulating circular polarization absorption and emission performance.Similar to 2CTPE compound,the circular polarization performances of the above two compounds decreased with the increase of temperature,and can't be recovered when temperature is back to ambient temperature.When TPE group is connected with cholesteryl group via a long spacer with eleven methylene group,the obtained product showed smectic c phase LC.This product showed higher circular dichroism and circularly polarized luminescence properties compared with products with shorter spacers.Furthermore,its CPL property is responsive to temperature and is recoverable.X-ray diffraction analysis revealed that the product with methylene or 6 methylene spacers both show double-molecule arrangement with one dimensional ordered structure.And the product with eleven methylene interval has strict layered arrangement.The molecules arranged parallel to each other within the layer.The layer spacing is less than the molecular length,and the molecule long axis is tend to the plane with a dgree of 44.8o.The XRD results are consistent with liquid crystal phase structure revealed by POM investigation.We also synthesized ionized TPE molecule and binaphthol with opposite charged ions each other.Through ionic self-assembly,enantiotopic complexes were obtained.The structure of the complexes were confirmed by NMR and FTIR investigations.Circular chroism and vibrating circular chroism studies demonstrated the successful chirality transfer from chiral binaphthol center to TPE fluorogen via ionic self-assembly.The chiral films of assemblies showed high dissymmetry factors at the absorption band of TPE moieties(gabs;+0.065 for the S configuration,and-0.063 for the R configuration)and high glum values of+3.8×10-2?S configuration?-4.2×10-2?R configuration?at 442 nm.Scanning electron microscopy?SEM?investigation revealed that these two enantiomer complexes can assembly and form a spiral fiber structure.X-ray diffraction?XRD?studies showed that both compounds had layer structure with a length of single molecule.On the basis of the above results,the assembled mechanism of the spiral fiber was proposed.In addition,we successfully prepared circularly polarized luminescence materials based on R-and S-chiral amine modified tetraphenylethylene.The products showed obvious aggregation induced luminescence properties and fluorescence quantum yield rate in solid state are high?43%?.In mixed solvents with different volume ratio of dichloroethane and n-hexane,assemblies with the morphology of R-and S-products,which are changing from clear screw pitch spiral fibers to smooth thin film,were obtained.The circular dichroism and circularly polarized luminescence studies showed that each product can exhibit two kinds of chiral signal.For example,the R-configuration product assembly obtained under different conditions can possess right-handed or left-handed absorption or circularly polarized luminescence?as well as the product of S-configuration?.These results suggested that the assembly products obtained under different assembly conditions have different molecular packing way,therefore leading to chirality inversion.X-ray diffraction analysis showed that the products with spiral fiber structure have very dense and well-ordered molecular arrangement,while the film obtained by annealing in methylene chloride is layer structure.
Keywords/Search Tags:Circularly Polarized Luminescence(CPL), Helical Structure, Chiral Liquid Crystal, Aggregation-Induced Emission(AIE), Ions Assembly
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