Synthesis,Self-assembly And CPL Performance Enhancement Of Helical Tetraphenylethylene

Circularly polarized luminescence（CPL）is referred to as the phenomenon that chiral luminescent substances are excited to emit different left-handed or right-handed circularly polarized light,which is usually expressed by the CPL dissymmetry factor g_lum.The theoretical g_lum value is 2.However,the CPL dissymmetry factor of pure chiral organic molecules is generally only 10^-5 to 10^-2,which is far less than the theoretical value,limiting their practical applications.In this thesis,tetraphenylethylene with AIE effect and propeller-like structure was used as building block to synthesize tetraphenylethylene（TPE）macrocyclic compounds with AIE properties and helical chirality.Self-assembly of these tetraphenylethylene（TPE）macrocycles is used to increase the fluorescence intensity and fluorescence asymmetry,which greatly improves the CPL asymmetry factor,solving the problem of low g_lum of organic fluorescent molecules.The following results have been achieved:1.The tetraphenylethylene tetracycle tetramine TPETA with propeller-like conformation was completely fixed.The racemic TPETA is resolved into M and P-TPETA enantiomers by chiral high pressure liquid chromatography column.Due to the intramolecular cycle formation,the rotation of the benzene ring was restricted.This helical tetraphenylethylene has fluorescence quantum yield more than 90%not only in solution but also in solid state.The two helical enantiomers show strong circular dichroism（CD）signals and CPL signals in 1,2-dichloroethane.The CPL dissymmetry factors g_lum of M and P-enantiomers are 0.0025 and-0.0028,respectively.After adding dodecylbenzenesulfonic acid DSA,it can self-assemble with TPE helical monomer to generate helical nanofibers.In the film state,M-helical monomer induces P-helical nanofibers,and P-helical monomer induces M-helical nanofibers.The g_lum is-0.17 and+0.16,respectively,which is enhanced by 76 times.Interestingly,when D-tartaric acid is added to the solution of M-supramolecular chiral complex,the g_lum value can be increased to 0.61,but L-tartaric acid is added,the g_lum value does not change.Using P-supramolecular chiral complex,the g_lum value with adding the D-tartaric acid is unchanged,but the g_lum value of addition of L-tartaric acid reaches-0.61,the g_lum value is enhanced by 243 times,indicating that the self-assembled supramolecular chiral system not only has excellent CPL performance but also can be used for chiral recognition.This provides a new method for the design and development of AIE-based CPL materials.2.TPE dodecylamine carboxamide M/P-TPETADA was obtained by the reaction of dodecyl isocyanate and M/P-TPETA helical enantiomers,which was as high as 89%of fluorescence quantum yield,and could emit strong CPL signals.The CPL g_lum value reaches 0.0043,which was two times than M/P-TPETA.In addition,the Langmuir monolayer was formed by M/P-TPETADA at the interface between air and water,which has chiral structure and can detect obvious chiral SHG signals,and the DCE value（the degree of chiral excess）reaches 0.684.It shows that chiral AIEgens can detect the weak chirality at the interface in situ and has the research and development potential in nonlinear optical technology.3.The TPE dicycle tetracholesterol was synthesized by forming dicycle at the gem position of TPE to enhance the ability to form helix and connecting the cholesterol unit to the benzene ring to increase the self-assembly ability.For comparison,TPE tetracholesterol without intramolecular cyclization was also synthesized.It was found that TPE dicycle tetracholesterol can self-assemble into nanorods in 1,2-dichloroethane（DCE）.After the suspension was standing for a period of time,the nanorods can be slowly transformed into a double molecule layer of shell by solvent etching from the middle of the nanorods,it shows more than 76%fluorescence quantum yield.The suspension of nanotubes displays the first negative Cotton effect and emits a negative CPL signal;but the thin film composed of nanotubes shows the first positive Cotton effect and emits a strong positive CPL signal with a large g_lum of 3.0×10^-3.For the TPE tetracholesterol without intramolecular cyclization,it can self-assemble into curved noodle-like aggregates in DCE,and shows very weak CD and CPL signals.It demonstrates that the TPE intramolecular cyclization formation facilitates self-assembly into rigid aggregates,and more single helical chirality is induced to enhance CD and CPL performance.4.The chiral R/S-TPE-binaphthalene[2+2]macrocyclic compounds,composed of two TPE units and two binaphthalene units,were obtained in high yield through the condensation of TPE diacetonitrile and optically pure binaphthalene dialdehyde.The macrocycles can display different fluorescent colors in different solvents,forming multi-color adjustable chiral AIEgens,and show a strong CD signal.Due to the large internal cavity of the macrocycles,the fullerene can be encapsulated by the host-guest binding to quench the fluorescence.It was found that the quenching constant of C₇₀ for macrocycles is 10⁵ orders of magnitude,while C₆₀ is only on the order of 10⁴.The fluorescence intensity is linearly related to the concentration in the range of 10^-7 M,indicating that the macrocycle can be used for high sensitivity determination of fullerenes.5.The cis-and gem-TPE crown ether macrocycle diquaternary ammoniums,formed cycle between two benzene cycles at the cis and gem position of TPE by polyethylene glycol ether chain,introduced two quaternary ammonium salt groups,were synthesized.When its two quaternary ammonium salt groups are combined with the DNA chain,the rotation of the cis-isomer double bond in the excited state can be further restricted,and the fluorescence is greatly enhanced,making its detection limit for DNA reaches 0.29 ng/m L,becoming one of the best fluorescent receptors for DNA detection.At the same time,due to the limitation of the double bond rotation in the excited state,the cis-TPE diammonium salts exhibits enhanced CD and CPL performance after interacting with DNA.The CPL dissymmetry factor reaches 0.028,which is the highest of CPL dissymmetry factor by the combination of AIEgens and DNA.However,the gem-TPE diammonium salts does not emit CPL signal,indicating that the restricted double bond rotation in the excited state is the key role of CPL enhancement.It is also the first example of the use of AIE double bond rotation limitation mechanism to enhance sensing performance and CPL performance.