Experimental And Theoretical Investigation On The Proton Transfer Process Of Organic Fluorescent Molecules By High-pressure Environment And Molecular Modification

The proton transfer process is a momentous and cutting-edge research topic in the field of atomic and molecular physics.The proton transfer process includes intermolecular proton transfer process and intramolecular proton transfer process.Intermolecular proton transfer plays a vital role in the realms of acid catalysis and biological enzyme catalysis;and intramolecular proton transfer is increasingly showing significant development prospects in luminescent materials,antioxidants,and drug delivery.By molecular modification of molecules with proton transfer properties,their proton transfer process can be regulated,thereby changing their physical and chemical properties.However,changing the external environment of these molecules by means of high pressure can trigger numerous new phenomena that cannot be achieved at atmospheric pressure conditions.In this thesis,the combination of density functional theory and in-situ high-pressure anvil technology as well as a variety of spectral detection methods were be used to explore the process of molecular modification and proton transfer of organic fluorescent molecules under high-pressure environments from both experimental and theoretical directions.The major research contents are as follows:(1)Using in-situ high pressure anvil technology combined with a variety of spectral detection methods(femtosecond transient absorption spectroscopy,confocal Raman fluorescence spectroscopy and steady-state absorption fluorescence spectroscopy)and DFT theory,experimentally and theoretically studied the effect of pressure on 8-Hydroxypyrene-1,3,6-trisulfonic acid trisodium(HPTS)intermolecular proton transfer process.Through the control experiment of changing the pressure with fixed p H value and changing the p H with fixed pressure,we confirmed that the pressure causes the proton transfer of HPTS in the ground state.In-situ high-pressure confocal Raman fluorescence spectroscopy and NCI calculation analysis also validated that HPTS is more prone to intermolecular proton transfer under high-pressure conditions.The femtosecond transient absorption spectroscopy shows that pressure can also promote the intermolecular proton transfer of HPTS in the excited state.(2)Femtosecond transient absorption spectroscopy technology combined with in-situ high pressure anvil technology was used to investigate the impact of pressure on the aggregation-induced emission(AIE)of Quercetin(QC)in distrinct proton transfer channels.The in-situ high-pressure steady-state fluorescence spectroscopy shows that the fluorescence of the QC molecules in both Keto₁*and Keto₂*state under pressure display the characteristic of AIE.When the solvent tetrahydrofuran(THF)undergoes a phase change,the fluorescence of the QC molecule all comes from the Keto₂*state at this time.The effect of pressure makes the original ESIPT channel from Enol*state to Keto₁*state to be gradually closed,and the channel from Enol*state to Keto₂*state is gradually opened.Fluorescence photographs and Commission Internationale de l'Eclairage(CIE)chromatic diagram also verify our results.That is,with the increase of pressure,the fluorescence of QC molecules gradually changes from the blue-white color dominated by the Keto₁*state to the yellow-white color fluorescence with the Keto₂*state as the main component.Until the solvent THF undergoes a phase transition,the QC molecule exhibits a pure yellow fluorescence that is completely emitted from the Keto₂*state.The results of ultrafast kinetics fitting also verify that the pressure promotes the Excited state intramolecular proton transfer(ESIPT)process of QC,the ESIPT rate from Enol*state to Kero₂*state also increases with the increase of pressure.(3)Through employing density functional theory(DFT)and time-dependent density functional theory(TD-DFT)methods,the impact of distrinct electron withdrawing groups on the forward and backward ESIPT process and white fluorescence emission of 1-hydroxy-9H-fluoren-9-one(HHF)has been investigated.The electron-withdrawing group can efficaciously lessen the forward ESIPT barrier of HHF,and restrain the backward ESIPT barrier,so as to achieve the effect of regulating the ESIPT process of HHF.By introducing electron withdrawing groups,the population of HHF in the E*state decreases and the population in the Keto*states increases,which in turn causes the HHF electron withdrawing group substituents to emit stronger Keto*state fluorescence.In addition,by calculating the fluorescence spectra of HHF and its substitutions with different electron-withdrawing groups,it can be seen that the introduction of electron-withdrawing groups makes the Keto*state fluorescence of HHF derivatives a large red shift.For example,the fluorescence of HHF in the Keto*state after the introduction of the-NO₂group is nearly 60 nm red-shifted and its fluorescence band range is extended from 420?550 nm to 450?610nm.Therefore,the introduction of electron-withdrawing groups can effectively control the HHF forward and reverse ESIPT process so that it can emit white fluorescence.(4)The DFT/TD-DFT theoretical calculation method was employed to investigate the influence of atoms with different electronegativity on the ESIPT process and antioxidant activity of Myricetin(MYR)molecules.The calculated results show that the reduction of atomic electronegativity can promote the ESIPT process of MYR molecules.By comparing the fluorescence spectra of MYR and its derivatives(MYR-S and MYR-Se),it can be seen that the fluorescence of MYR derivatives has undergone a large red shift,which will facilitate its fluorescence imaging in vivo.The calculated energy gap and ionization potential show that the energy gap and ionization potential of MYR and its derivatives gradually decrease as the electronegativity of the atom decreases.This phenomenon shows that the lower atom electronegativity can make MYR derivatives exhibit stronger antioxidant activity.Moreover,the Keto state antioxidant activity of MYR and its derivatives is stronger than their Enol state,and this phenomenon is more pronounced in MYR derivatives.