The Nonadiabatic Molecular Dynamic Study Of Diphenylbutadiene Cis-trans Photoisomerization With Electron Transfer And Hindering Effect Mechanism

In this dissertation,the effects of different substituents on the photoisomerization of trans,trans-1,4-diphenyl-1,3-butadiene?tt-DPB?were studied by static electronic structure calculation and trajectory surface hopping dynamic simulations.The whole dissertation was divided into three parts:The first part mainly introduced the research progress on isomerization of diphenylbutadiene derivatives,and briefly explained the theoretical calculation methods used in this work.In the second part,the theoretical study of the photoisomerization reaction of various substituted tt-DPB are carried out mainly through the calculation of static electronic structure.In the third part,the molecular dynamics simulation of p-NO₂-tt-DPB-CH₃ was performed using the surface hopping method,and the related information such as the reaction mechanism,quantum yield and product branching ratio were discussed in detail.In Chapter 1,we mainly introduced the effect of the substituents on the structure and properties of the compounds,as well as the previous research progress on the isomerization of diphenylbutadiene derivatives,and explained the theoretical calculation methods in this work.In Chapter 2,we introduced the effect of the substituents on the photoisomerization reaction by adding different substituents to tt-DPB at the computational level of SA2-CASSCF?8,8?/6-31G?N,O=6-31G*?.The compounds we studied include a single methoxy group or nitro group substitution on p-position of phenyl ring?tt-DPB-OCH₃,tt-DPB-NO₂?,a single nitro group substitution on p-position of phenyl ring and a single methyl group substitution on conjugated C=C bond,where the methyl group is on the side of the phenyl ring with a nitro substitution?p-NO₂-tt-DPB-CH₃?.Through the static electronic structure calculations,we have got two important conical intersections for different systems,and the energies at the CIs relative to energy minimum of DPB species has been significantly reduced due to the addition of substituents.The possible photoreaction mechanism of such compounds is calculated as follows:the reactant is excited vertically to the S₁ state,and two types of possible paths appear after passing through the lowest energy point of the S₁ state and the two conical intersections,generating more stable isomerized products or going back to the reactants.We have also found that during the process of tt-DPB-NO₂ towards the product,the potential energy curve of the S₁ state has an obvious potential well,which leads to an almost ineffective isomerization process.However,after the methyl group is added,because its steric hindrance effect reduces the electron-withdrawing effect of the nitro group,the photoisomerization has a good regioselectivity,and it is more inclined to produce ct-type products.In Chapter 3,we have performed photoisomerization molecular dynamics simulation of p-NO₂-tt-DPB-CH₃.The 300 sampling trajectories have been calculated.The results show that the isomerization reaction proceeds with one reactive path and one nonreactive path.5.0%of the trajectories from initial excited p-NO₂-tt-DPB-CH₃passes through the Hula-Twist?HT?mechanism to generate p-NO₂-ct-DPB-CH₃,while 7.3%of the trajectories decays through the reverse torsion?RT?mechanism returns to p-NO₂-tt-DPB-CH₃,and the remaining 262trajectories stay on S₁ state as resonance trajectories within the limited run time.The photoisomerization quantum yields have been obtained as 0.053 in tt?ct photoisomerization,which is in agreement with experiments,and the first excited state lifetime has been estimated to be 1614.2 fs.