Theoretical Study On The Aggregation Inducrd Emission Mechanism Of Tetrastyrene And Its Derivatives

Since the concept of aggregation induced emission(AIE)was proposed by Benzhong Tang's research group in 2001,the exploration of the mechanism of AIE and the development of new high-performance AIE materials have been focused.In spite of tetrastyrene and its derivative have a significant AIE effect,the detail luminescence mechanism is still unclear.Thus,it is necessary to systemly study the aggregation induced emission mechanism of tetrastyrene(TPE)and its deravitive and the change trend of their aggregated polymer's fluorescence.This will be important to the design of new AIE materials.In the present thesis,time-dependent density functional theory method(TD)?B97XD/6-31G(d,p)and PCM solvent model were performed to cacuclate the electronic structures,the frontier molecular orbitals,excited energy and electron transition configuration of TPE and anthracenyl tetrastyrene(TPE-an)and their dimer(D-TPE and D-TPe-an)in gas,tetrahydrofuran(THF)solvent and aqueous solution.Besides,the absorption spectrum,the fluorescence spetrum and reorganization energy of TPE,TPE-an,D-TPE,and D-TPe-an were calculated to disclose the AIE mechanism of AIE materials.Compared to the propeller geometry of TPE and TPE-an,there is strong?-?interaction among the monomers of D-TPE and D-TPE-an,which planarized their geometry and increased the rigid of them,and made the electron delocalize among monomer even among the whole system,especially for the first sinlet excited state(S₁).Then the electron-coupling of the groud state(S₀)and the S₁ state,the transition moment,and the oscillator strength increased.Thus,the probability of their electron emited from S₁ to S₀ increased,and their fuorescence was enhanced.The intensity of D-TPE and D-TPE-an fluorescence in acqueous solution is stronger than that in THF.Both of them are stronger than that in gase phase,which agrees very well with the repoted experimental results.In comparison with TPE and TPE-an,the rotation energy barrier of the benzene rings joint to the core ethylene through C-C single bond in D-TPE and D-TPE-an increased obviously.It implys that the increasing rigid of D-TPE and D-TPE-an and?-?interaction hindered the intramoleccular benzene rotation and the release of the excited energy through such nonradiative processes.Relative to monomers,the total reorganization energy of the normal modes with the frequency less than 1800 cm^-1 significantly reduced.This demonstrated that the intramolecular vibrations were restricted and the intramolecular vibration relaxtion decreased.The reorganization energy reduced mainly contributed from the vibration mode with low frequency(<400 cm^-1),which are related to the rotation of benzene rings.In a word,the aggregation induced emission of TPE and TPE-an is induced by the enhanced electron-coupling between S₁ and S₀,and also the restricted intramolecular rotation and vibration.In addition,in the acqueous solution,which made the highest aggregation of TPE and TPE-an,the fluorescence of D-TPE-an shifted blue visible region from orange region of D-TPE.The detailed theoretical study of AIE mechanism will provide theoretical guidance for the design of new AIE materials through substitution.