Anti-Heavy-Atom Effect Of Tetraphenylethene With Aggregation-Induced Emission And Its Functional Probes In Sensing Applications

Because luminescent sensing has the advantages of high selectivity,fast response,and easy operation,it has been widely used in various fields.Traditional fluorescent molecules such as rhodamine,fluorescein,and coumarin have planar structures,and thus they will pile up and show aggregation-induced fluorescence quenching in the aggregated state.Traditional fluorescent dyes fluoresce only in solution and no emission can occur in solid state.Traditional fluorescent molecules have small Stokes shifts,poor signal-to-noise ratio,poor light stability,and thus can only be applicable to solution systems.So the application of traditional fluorescent molecules is greatly limited in practical applications.Tang discovered in 2001 that the propeller-like structure of hexaphenylthiazole molecules provides a non-radiative transition channel due to the free rotation of carbon-carbon single bonds in the solution state.Because the propeller-like structure can prevent?-?stacking and the radiative transition channel is opened in the aggregated state,its fluorescence emission becomes bright in the solid state,which is aggregation-induced emission phenomenon.Aggregation-induced emission molecules have excellent light stability,the large Stokes shifts and wide application range.Aggregation-induced emission molecules have received great attention and great advances have been made since the aggregation-induced emission phenomenon was discovered.In this thesis,a typical aggregation-inducing emission molecule tetraphenylethene was used as the molecular skeloton.Several groups of compounds with aggeregation-induced emission including tetracarboxylate tetraphenylethene,tetrahalogen tetraphenylethene and monohalogen tetraphenylethene,were synthesized based on tetraphenylethene-baed molecular skeleton.Taking advantage of the luminescence properties of these compounds in the aggregated state,they are respectively applied to ion detection,reusable writing paper,and anti-counterfeiting.The following are the main contents of this thesis:?1?Aggregation-inducing emission molecular probes have been reported in the literature for detecting ions,but most of them have the problem of poor water solubility.When applied to the detection of biological systems,they will self-aggregate and generate interference signals,which will greatly impact the sensitivity and accuracy.Moreover,most fluorescent probes have poor light stability and are not suitable for long-term cell imaging.In this thesis,we use tetraphenylethene as the emission group,four sodium carboxylate groups were introduced into the tetraphenylethene?TPE-4COONa?.The introduction of the sodium carboxylate group not only provided a recognition site for the probe,but also greatly increased water solubility.The probe dissolves in water to form carboxylic acid negative ions,because of the force between the ions,the probe and cations are combined,which causes the probe to aggregate and emission,thereby achieving the detection of ions in the water environment.Because both Al³⁺and Pb²⁺can make the probe aggregate and emission,we have found suitable masking agents glutathione and sodium tetrafluoroborate,with the help of the masking agent,we have achieved the detection of the difference between two ions,this is the first article about the differential detection of Al³⁺and Pb²⁺.The probe imaging of Al³⁺and Pb²⁺in root cells of Arabidopsis thaliana showed that the two types of ions can be distinguished in vivo without the need for a masking agent,and the probe has excellent photostability,which is useful in long-term imaging and have a broad vision of application.?2?Heavy atom effect refers to that the introduction of heavy atoms such as bromine and iodine into the fluorescent molecules can increase the spin-orbit coupling?SOC?and promote the transfer of excited state electrons from the singlet excited state to the triplet excited state,resulting in weakened fluorescence and enhanced phosphorescence or thermally activated delayed fluorescence.Therefore,the introduction of heavy atoms is usually used to design high-efficiency room-temperature phosphorescent materials or thermally activated delayed fluorescence emitters materials.In this thesis,four halogen atoms such as fluorine,chlorine,bromine,and iodine are introduced into tetraphenylethene respectively,and it is found that the fluorescence efficiencies of the four tetrahalogenated tetraphenylethene are much higher than that of tetraphenylethene in the solid state at room temperature.Bromine and iodine act as heavy atoms,but the fluorescence quantum efficiencies of brominated and iodinated tetraphenylethene are greatly enhanced,which is inconsistent with heavy atom effect.Through theoretical calculations,it was found that the introduction of heavy atoms did not greatly lead to spin-orbit coupling,which explains the reason why the introduction of heavy atoms did not lead to fluorescence quenching.Chlorinated,brominated,and iodinated tetraphenylethenes have mechanochromism properties.Among them,chlorinated and brominated tetraphenylethenes show self-reversible mechanochromisms within a short time.Taking advantage of the fast self-reversible properties of bromotetraphenylethene,a repeatable writing paper was designed.?3?In this thesis,five kinds of monohalogenated tetraphenylethene were synthesized,including1-?4-fluorophenyl?-1,2,2-triphenylethylene,1-?4-chlorophenyl?-1,2,2-triphenylethylene,1-?4-bromophenyl?-1,2,2-triphenylethylene,1-?4-iodophenyl?-1,2,2-triphenylethylene and 1-?4'-bromo-4-diphenyl?-1,2,2-triphenylethylene.The anti-heavy atom phenomenon were investigated in depth in terms of atomic numbers and increasing conjugate structures.The experimental results show that introducing heavy atoms can greatly improve the fluorescence quantum efficiencies of TPE-based AIEgens,independent of the atomic numbers and the size of the conjugate structures.The research work in this thesis provides guidance for future research on anti-heavy atom effects.Mechanochromism properties of 1-?4-bromophenyl?-1,2,2-triphenylethylene were applied to anti-counterfeiting applications.In summary,we used the aggregation-inducing emission molecule tetraphenylethene to design and synthesize a water-soluble ion probe for distinguishingly detecting Al³⁺and Pb²⁺and imaging of Al³⁺is achieved in root cells of Arabidopsis thaliana.Based on the molecular skeleton of tetraphenylethene,two groups of halogenated tetraphenylethene derivatives were synthesized,and it is revealed that the introduction of halogens into the skeletonal tetraphenylethene can greatly improve the emission efficiencies of the the resulting luminogens in the solid state.This unique anti-heavy-atom effect on fluorescence quatum yield provides a promising research direction to enhance the AIE brightness.The intrinsic mechanisms of anti-heavy-atom effect and mechanochromism of these halogenated TPE derivatives were examined,and the unique mechanochromic properties were applied in the rewritable paper and anti-counterfeiting applications.