Geminal Cross-coupling Synthesis And Applications Of Aggregation-induced Emission Molecules

Tetraphenylethylene?TPE?has many predominances including relatively simple structure,high fluorescence quantum yield,being apt to synthesize and modify etc,which is a"star molecule"in Aggregation-induced Emission?AIE?materials.Therefore,it is widely applied in fluorescence sensing,fluorescence imaging,optoelectronic devices and other fields.Replacing one or more phenyl rings of TPE with ACQphores might be able to afford new tetraarylethenes?TAEs?,which eliminates their ACQ effect and retains the AIE activity,thus becoming the focus of current research.However,the traditional synthesis methods such as the McMurry reaction or the Rathore's protocol have their own defects,and can hardly meet the increasing demand for diverse structural modifications.In order to enrich the types of tetraarylethene molecules,our research group has designed and synthesized a series of tetraarylethene chromophores using Geminal Cross-Couplings?GCC?.Based on this synthetic method,a series of dendrimers containing tetraarylethene topological units were designed and synthesized on the one hand,on the other hand,various bioactivity groups were introduced into the tetraarylethene molecule efficiently.Besides,a detailed study of their fluorescent properties and applications was carried out.The details of the dissertation are summarized as follows:?1?For the first time,a series of conjugated dendrimers containing tetraarylethene topological units were synthesized via the approach of geminal cross-couplings of1,1-dibromoolefins,which extends this method from the synthesis of small molecules to the dendrimers.By changing the core of the dendrimers,AB₂-tyepe dendrimers centered on fluorene or diphenylmethane and AB₄-tyep dendrimers centered on9,10-dihydroanthracene were successfully synthesized.Besides,it can increase the solubility and fluorescent properties of dendrimers by changing their peripheral groups.All the conjugated dendrimers exhibit AIE activity and higher thermal stability,which lays the foundation for further applications in optoelectronic devices and biosensing.In addition,the dendrimer 3-I has a twisted propeller-like structure compared with 2-I,which shows the dual effects of intramolecular charge transfer?ICT?and aggregation-induced emission?AIE?.Benefiting from this characteristic,3-I are found to be useful as fluorescent indicators for the qualitative and quantitative detection of low-level water content in organic solvents,and the detection limit can be as low as 0.0032%.?2?To meet the growing demand in biological detection and fluorescence imaging,a series of hydrophilic tetraarylethene molecules were designed and synthesized via the approach of geminal cross-coupling.All the molecules exhibit typical AIE behaviors,which is non-emissive in the solution state but show intense fluorescence in the aggregate state.It is noteworthy that all the probes contain two N,N-dimethylamino groups or piperidine groups as a pH-sensitive functionality,which can bind two protons and become soluble and non-fluorescent in the acidic medium.The fluorescence responses of these hydrophilic probes to HEWL fibrils were investigated by the titration experiment of HEWL.It was found that all the probes show the stepwise fluorescence enhancement responses to the HEWL fibrils,in which the probe 6a shows the highest sensitivity to HEWL and possesses the lowest detection limit of 0.6 nM.Therefore,we demonstrate the super-resolution fluorescence imaging of amyloid fibrils with hydrophilic AIE-active probe 6a and obtain the detailed nanostructures of amyloid aggregate with a resolution of42 nm,breaking the optical diffraction limit of traditional fluorescence imaging.?3?Two or four naphthalimide moieties were introduced into the xanthene and6,13-dihydropentacene structures using geminal cross-coupling of 1,1-dibromoolefins,respectively,which were first discovered to have two distinct oxidation-cyclization products.Through the photooxidation reaction,the 2-position naphthalimide group in the Xan-NI structure and the xanthene are selectively closed via cyclodehydrogenation reaction.While the attached naphthalimide of P-NI does not rotate freely due to the huge steric hindrance of 6,13-dihydropentacene,thus only the 4-position naphthalimide group can participate in the cyclodehydrogenation reaction with 6,13-dihydropentacene.Before the photo-oxidation,the naphthalimide groups in the Xan-NI and P-NI structures are free to rotate in the solution and weak fluorescence is observed.While after the photo-oxidation,the cyclization reaction suppress the rotational motions of naphthalimide.The exciton energy cannot be depleted by the radiationless decay,thus making the molecule emissive even in isolated state.The change of fluorescence properties before and after oxidation can be utilised for directly validating the mechanism of AIE:restriction of intramolecular rotation?RIR?.However for the chemical oxidation method,xanthene or6,13-dihydropentacene does not participate in the cyclization reaction and the oxidative products exhibit non-fluorescent in both the solution and solid state.?4?For the first time,two benzimidazole groups were introduced into the tetraarylethene structure by the approach of geminal cross-coupling,and their fluorescent spectra can be adjusted by changing the dibromoolefin precursor.The benzimidazole group has two nitrogen atoms in the structure,which is easy to form non-covalent bonds such as hydrogen bonds and coordination bonds.Benefiting from this characteristic,it can be widely used for the detection of biomolecules and metal ions.The fluorescence responses of these probes to metal ions was systematically studied.All probes were found to exhibit fluorescence enhancement responses to zinc ions and silver ions.Wherein,the emission of probe Ph-BI is found to be linearly proportional to the amount of zinc ion in the range of 1.25-5?M,which can be used for the quantitative detection of zinc ions.