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.