The Nonadiabatic Molecular Dynamic Study Of Methyl Group Substituted Diphenylbutadiene Photoisomerization Mechanism

In this dissertation,the effect of substituents on the photoisomerization of trans-,trans-1,4-diphenyl-1,3-butadiene(tt-DPB)was studied by surface hopping molecular dynamic simulation.All calculations were performed based on the improved Zhu-Nakamura formula.The whole paper is divided into three parts: The first part mainly introduces the effect of substituents on the molecular properties of olefins,which plays a role in analyzing the effect of substituents on the photoisomerization of molecules.The second part mainly introduces the theoretical method to study the photoisomerization reaction of substituted tt-DPB.In the third part,the mechanism of photoisomerization of methyl substituted tt-DPB and nitro substituted tt-DPB-me2 was studied by a new surface hopping method.The first chapter is the introduction part,in which the effect of substituents on the isomerization was introduced,and the theoretical methods were introduced in the latter part: the trajectory surface hopping method and dynamic simulation based on the improved Zhu-Nakamura formula.The electronic structure methods were used for energy and gradient analysis in the simulation,including the complete active space self-consistent field method(CASSCF),the internally contracted multi-reference configuration interaction method(ICMRCI)and recent development of size consistency modified static-dynamic-static second-order perturbation method(SDSPT2+Q).In the second chapter,the photoisomerization reaction of a single methyl group substitution on p-position of phenyl ring(tt-DPB-me1)or conjugated C=C bond(tt-DPB-me2)at SA2-CASSCF(4,4)/6-31 G level were discussed.Static electronic structure calculations show that photoexcitation makes tt-DPB-me1 and tt-DPB-me2 easily reach the S1 state of Frank-Condon region and the excited states can directly generate more stable isomerized products tc-DPB-me1/me2,ct-DPB-me1/me2 and cc-DPB-me1/me2,or return to the S0 tt-DPB-me1 and tt-DPB-me2,which is proceed via the energy-lowest point on the S1 state and two important conical intersections.The four-hundred sampling trajectories have been performed for both tt-DPB-me1 and tt-DPB-me2,and both have been shown with five distinctive photoisomerization pathways,among which one-bond-flipping(OBF)and Hula-Twist(HT)are the dominant photoisomerization mechanisms.The first excited state lifetime has been estimated to be 1423.0 fs(819.0 fs),and the photoisomerization quantum yields have been obtained as 0.088(0.378)in tt→ct photoisomerization,0.070(0.015)in tt→tc,0.073(0.065)in tt→cc for tt-DPB-me1(tt-DPB-me2).Both tt-DPB-me1 and tt-DPB-me2 have found two conical intersections in the static electronic structure calculations,it can be found that the photoisomerization of tt-DPB-me1 is dominated by the process through CI1,while CI2 other than CI1 also plays an important role in photoisomerization of tt-DPB-me2 in the dynamic simulation.In the third chapter,we have also conducted a preliminary study on the photoisomerization of nitro-substituted tt-DPB-me2 on the para-position of the benzene ring using the static electronic structure calculation method and molecular dynamic simulation,and summarized the computational investigations briefly.