Browsing by Author "Zhai, Gaohong"

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Methyl substitution enhanced photoisomerization of trans,trans-1,4-diphenyl-1,3-butadiene: direct ab initio trajectory surface hopping dynamic simulations
(2018-01-28)
Fan, Yueqian
;
Chen, Juan
;
Yu, Le
;
Li, Anyang
;
Zhai, Gaohong
Single methyl group substitution on the p-position of the phenyl ring (tt-DPB-me1) or the conjugated CQC bond (tt-DPB-me2) has been found to enhance the photoisomerization efficiency for two trans, trans-1,4-diphenyl-1,3-butadiene (tt-DPB) derivatives by performing direct ab initio trajectory surface hopping dynamics simulations. With implementation of the Zhu-Nakamura global switching algorithm, on-the-fly trajectory surface hopping dynamics simulations based on the ground state and first excited state potential energies and their gradients calculated by the two state averaged complete active space self-consistent field method with basis set 6-31G were propagated up to 3000 femtoseconds. Four-hundred sampling trajectories have been performed for both tt-DPB-me1 and tt-DPB-me2, and five distinctive photoisomerization pathways were observed for both of them. Among which, One Bond Flipping (OBF) and Hula-Twist (HT) are the dominant photoisomerization mechanisms. The lifetime of the S1 state is estimated to be 1423.0 fs (819.0 fs), and the photoisomerization quantum yields are 0.088 (0.378) in tt -> ct , 0.070 (0.015) in tt -> ct and 0.073 (0.065) in tt -> cc for tt-DPB-me1 (tt-DPB-me2). By analyzing the dynamics simulation data, it can be concluded that closer methyl substitution with respect to the central C=C double bond results in a higher percentage of the corresponding photoisomerization products. The present simulation results are in agreement with the ultrafast spectroscopy measurements, which unveil the photoisomerization mechanisms of tt-DPB derivatives and present useful physical insights on how to tune the photoisomerization of the substituted DPB.
Photo-induced 1,3-cyclohexadiene ring opening reaction: Ab initio on-the-fly nonadiabatic molecular dynamics simulation
(2016-02-15)
Lei, Yibo
;
Wu, Huiyu
;
Zheng, Xiaolei
;
Zhai, Gaohong
;
Zhu, Chaoyuan
By a newly developed algorithm to compute global nonadiabatic switching probability only using electronic adiabatic potential energy surfaces and its gradients, we could able to perform on-the-fly trajectory surface hopping molecular dynamics at the SA-CASSCF(14, 8)/6-31G* quantum level to investigate the photo-induced 1,3-cyclohexadiene ring opening reaction from 1,3-cyclohexadiene (CHD) to 1,3,5-hexatriene (HT). We found four conical intersection zones within three singlet low-lying electronic states, in which 1B/2A and 1A/2A are well known to be the most important conical intersection zones to govern dynamics of ring opening reaction. The present simulation gained insight into nonadiabatic dynamics in which 516 sampling trajectories out of 600 can switch back and forth between two involved potential energy surfaces not only at 1B/2A, but also at 1A/2A. This insight is the key to influence quantum yields and time scales of the ring opening reaction. We estimated time constants as 46 fs, 82 fs, and 120 fs, respectively for crossing 1B/2A and 1A/2A, and excited-state lifetime in comparison with corresponding experimental values 56 fs, 80 fs and 130 fs. We estimated quantum yield 0.47/0.53 to HT/CHD in comparison to experiment values 0.30/0.70 in the gas-phase and 0.41/0.59 in the condense-phase. Moreover, the present simulation within 600 sampling trajectories indicates that there is no five membered ring forming in agreement with experiment results and with prediction from the previous wave-packet simulation as a rare case. (C) 2015 Elsevier B.V. All rights reserved.
Photoisomerization mechanisms from trans, trans-1,4-diphenyl-1,3-butadiene: CASSCF on-the-fly trajectory surface hopping dynamic simulations
(2016-04-07)
Zheng, Xiaolei
;
Zhai, Gaohong
;
Gao, Wanqing
;
Lei, Yibo
;
Yu, Le
We have employed the SA2-CAS(4,4)/6-31G ab initio method together with an on-the-fly global-switching trajectory surface hopping algorithm to simulate photoisomerization reaction dynamics from reactant trans, trans-1,4-diphenyl-1,3-butadiene (DPB) to products cis,trans-DPB and cis,cis-DPB. This topic has been extensively studied experimentally and the present theoretical study is the first to simulate DPB photoisomerization reaction dynamics as far as we know. With total 600 sampling trajectories, 300 actively contribute to isomerization reaction via two conical intersections between the electronic ground and the first excited states. Simulated quantum yields of photoisomerization to cis, trans-DPB and cis, cis-DPB are 0.09 and 0.045, which are in good agreement with the experimental values of 0.07-0.25 and 0.02, respectively. The lifetime of the first excited state is estimated as 702 fs. The present simulation has shown two reactive photoisomerization mechanisms, namely one bond twist (OBT) and bicycle pedal (BP), and two non-reactive photoisomerization mechanisms, namely single bond torsion (SBT) and reverse torsion (RT) with respect to the central backbone CC bonds. We believe that the present theoretical work can benefit the experiments on photoisomerization of DPB derivates.