Study On Excited State Dynamics Of Several Complex Molecular Systems And Its Application

In this thesis,the dynamics behaviors of several complex molecular systems in ground state and excited state are studied by analyzing their special optical properties and the deactivation mechanism in excited states,also their applications in hydrogen storage materials and adsorbent materials.The theoretical methods of molecular dynamics,excited state potential surface hopping,minimum energy crossing point searching and wave function analysis are used in the thesis,and the time-dependent density functional theory is combined with the transition state theory in the excited state.The photo-excitation effect on the spectrum,reaction and material properties are discussed by more comprehensive,dynamical and more detailed with these methods.Firstly,we have studied the hydrogen-storage and dehydrogenation mechanism of borane-amines as hydrogen storage material.In order to clarify the dehydrogenation process of phenol and trimethylborane ammonia,we combine the transition state theory and the time-dependent density functional theory in excited state,and interpret the mechanism of dehydrogenation process through the transition state which is induced by dihydrogen bond interaction in excited state.Through the results of the potential energy scanning in the ground state,it is found that the ground state cannot have dehydrogenation process due to the existence of a large energy barrier.When excited to the first excited state,the intermolecular dihydrogen bond of the phenol-trimethylborane-ammonia complex is significantly enhanced along with the breakage of hydroxyl group.Based on the geometric configuration in the excited state,the transition state is found with the only imaginary frequency directing the formation of hydrogen molecule,and forms a new hydrogen molecule in the product.This work provides a complete theoretical model for the study of the dehydrogenation mechanism of borane-amines in the excited state,and provides theoretical support for studying the hydrogen storage and dehydrogenation properties of borane-amines.Secondly,the anti-ultraviolet mechanism of AS1(Aloesaponarin 1)is studied.By analyzing the dynamics and spectra behaviors of intramolecular proton transfer progress in the excited state,it is found that AS1 absorbs ultraviolet light and then convert them to innocuous long-wavelength fluorescence through the intramolecular proton transfer process in the excited state.In this thesis,the anti-ultraviolet mechanism of AS1 is explained completely,and the inducement and effecting factors of proton transfer process in excited state are discussed in detail,which provide more helps for efficiently and economically designing and synthesizing skin care products with better anti-UV properties.Thereafter,the synergistic effect of intramolecular and intermolecular hydrogen bonds on the fluorescence behavior of the derivatives of PRODAN is studied.The strengthening and synergistic effect of intra-HB and inter-HB induce partial quenching of PRODAN derivative in methanol solvent by turning on the TICT state and fluorescence red-shift.This thesis gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent,which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics.Thirdly,the photoexcitation effect on the surface adsorption properties of the adsorbent material is studied.The short-wavelength ultraviolet(100-290 nm)increases due to the destruction of the ozone layer,which will induce photoexcitation effect and have a significant impact on the adsorption properties of adsorbent materials.However,the photoexcitation effect on the adsorption properties of adsorbent materials has not been systematically studied.The adsorption of four harmful gases(sarin gas,methyl dichlorophosphate,trimethyl phosphate and hydrogen sulfide)on the surface of silica is provided as target sample.The results show that the adsorption intensity of the silica surface in the ground state is consistent with the hydrogen bonding strength between the silanol groups and the hazadous gas.The absorption intensity of the excited state is opposite to the strength of intermolecular hydrogen bond after transition to the excited state by absorbing the UV,which is consistent with the charge transfer type(intermolecular charge transfer or local excitation)of the complex.Hydrogen sulfide molecules are dissociated after photo-excitation to the first excited state.This thesis takes the photoexcitation effect as a new standard for the design of new adsorbent materials and the detection of adsorption properties,and proposes different environmental influencing factors of the adsorptive properties of adsorbent materials in ground state and excited state.Finally,the asymmetric effect on the nonradiative decay pathway of ?-diketones is studied.An effective nonradiative decay(ND)pathway of the chelated enol(CE)conformer of malonaldehyde(MA)and acetylacetone(AA)is provided:their second single excited(S2)states transfer to first single excited(S1)state by nonadiabatic surface hopping,and then transfers to first triplet(T1)state by intersystem crossing(ISC),after which decays to ground(S0)state through minimum energy crossing point(MECP).Furthermore,unlike MA and AA,the asymmetric effect of 4-hydroxybut-3-en-2-one induces the generation of proton transferred conformer with the lowest energy in the S1 state,exploiting a new ND pathway that the S1 state decays to the proton transferred T1 state and then undergoes reverse proton transfer to the S0 state.The asymmetric effect exploits a new,more effective inactivation path in the first excited state.This result is significantly different from the previous reports that excited state decays to ground state by conical intersection.Therefore,asymmetric effect should be taken as an essential factor in the study of photoinduced ultrafast dynamics.The study of excited state dynamics and its application extends the research scope of photoinduced excitation and provides a theoretical model for the study of materials,photo-induced reactions and special optical molecules,which has important scientific significance.