Ultrafast Nonradiative Decay of Electronically Excited States of Malachite Green: Ab Initio Calculations
Ultrafast Nonradiative Decay of Electronically Excited States of Malachite Green: Ab Initio Calculations
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DOI：
10.1021/jp203415m
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发表时间：
2011-08-18
影响因子：
2.9
通讯作者：
Taketsugu, Tetsuya
中科院分区：
文献类型：
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作者：
Nakayama, Akira;Taketsugu, Tetsuya
采用CASPT 2//CASCF方法，对孔雀石绿色在单重激发态S-1和S-2的非辐射失活过程进行了高水平从头算量子化学计算.确定了连接Franck-Condon区域和圆锥相交区域的失活途径。S-1态的初始布居是在一个平坦的表面上，弛豫涉及苯环的旋转，这导致分子到达S-1和S-0态之间的圆锥形交叉点，在那里它有效地衰减回到基态。在S-1势能面上，存在一个小势垒连接Franck-Condon区和圆锥相交区。S-2态的衰变机制也涉及苯环的扭曲运动。与激发到S-1态相反，初始布居是在一个下坡斜坡电位上，并且预期通过取代苯环的旋转的无势垒弛豫。在弛豫过程中，分子在S-2和S-1之间的圆锥相交处切换到S-1状态，然后通过S-1和S-0之间的相交处衰减回到基态。在S-1和S-2的弛豫过程中，苯环的大变形是超快无辐射衰变到基态所必需的。
We have investigated the nonradiative deactivation process of malachite green in the singlet excited states, S-1 and S-2 by high-level ab initio quantum chemical calculations using the CASPT2//CASCF approach. The deactivation pathways connecting the Franck-Condon region and conical intersection regions are identified. The initial population in the S-1 state is on a flat surface and the relaxation involves a rotation of phenyl rings, which leads the molecule to reach the conical intersection between the S-1 and S-0 states, where it efficiently decays back to the ground state. There exists a small barrier connecting the Franck-Condon and conical intersection regions on the S-1 potential energy surface. The decay mechanism from the S-2 state also involves the twisting motion of phenyl rings. In contrast to the excitation to the S-1 state, the initial population is on a downhill ramp potential and the barrierless relaxation through the rotation of substituted phenyl rings is expected. During the course of relaxation, the molecule switches to the S-1 state at the conical intersection between S-2 and S-1 and then it decays back to the ground state through the intersection between S-1 and S-0. In relaxation from both S-1 and S-2, large distortion of phenyl rings is required for the ultrafast nonradiative decay to the ground state.