A Research For Bridge-azobenzene Photoisomerization By Nonadiabatic Dynamic Simulation

This thesis has two main parts. The first part mainly introduce the background of bridge-azobenzene?b-Ab? and research methods. The second part, we performed on-the-fly trajectory surface hopping simulations to analyze the photoisomerization mechanism of b-Ab.In the first chapter we introduce applications of photochromic compound, and then summarize the b-Ab of previous research outcome.In the second chapter, the novel trajectory surface hopping method based on improved Zhu-Nakamura formula and internally contracted multi-reference configuration interaction method were described briefly.In the third chapter, with implementation of new Zhu-Nakamura theory based global nonadiabatic switching probability estimation algorithm, we performed on-the-fly trajectory surface hopping simulations at the CASSCF level to analyze the cis???trans photoisomerization mechanism of the bridged-azobenzene upon S1 excitation. In the S₁ states, the phtoisomerization proceed via different conical intersection regions?CI-trans and CI-cis?. The four CI-trans type conical intersections are enantiomers mirroring to the perpendicular and parallel molecular plane. The two type conical regions possess similar CNNC dihedral angles but the twisting angles of benzene rings toward the N=N bond are much different. We also observed chiral conversion pathway in cis-to-trans photoisomerization. As a fact of the initial stage oscillation in the cis Franck-Condon region, the trajectories follow this pathway possess a relative longer excited state lifetime. The S1 state population decay in trans-to-cis process show periodical distribution with interval of-16 fs. In our dynamic simulation process, within the 400 trajectories started at S1 cis, quantum yields converge to 0.57,12 trajectories through CI-trans type conical regions and 388 trajectories through CI-cis type conical regions. While, for 550 trajectories started at S1 trans, quantum yields converge to 0.44, all the trajectories hop to So state through CI-trans type conical region. The present results are in very good agreement with the experimental values.We have also simulated the S₂ states of photoisomerization. Simulated quantum yield is 0.16 ?0.31? for cis-to-trans ?trans-to-cis? photoisomerization with up to 100 sampling trajectories. Compared with the S1 states, the quantum yields is much lower, the chirality conversion channel is much smaller, trans-to-cis have a longer lifetime of excited state.