利用激光实时频谱直接观测分子结构变化(英文)

Direct observation of molecular structural change during intersystem crossing by real-time spectroscopy with a few optical cycle lasers

利用脉宽小于5 fs的激光脉冲超快光谱同时研究了RuⅡ(TPP)(CO)的电子弛豫和振动动力学。研究认为,由1Qx(1,0)(π,π*)and1Qx(0,0)(π,π*)产生的信号按1Qx(1,0)(π,π*)→1Qx(0,0)(π,π*)→3(d,π*)→3(π,π*)和1Qx(0,0)(π,π*)→3(d,π*)→3(π,π*)的顺序从高能态衰减到低能态1。Qx(1,0)(π,π*),1Qx(0,0)(π,π*),3(d,π*),和3(π,π*)的电子寿命依次为(230±70)fs,(1 150±260)fs,(2 150±360)fs和极大于4.8 ps3。(d,π*)和3(π,π*)的寿命估计为(2150±360)fs和极大于4.8 ps。计算动态Stokes-shift过程中的能量衰减率,得到了从1Qx(1,0)(π,π*)到1Qx(0,0)(π,π*)的渡越时间为(190±40)fs,表明1Qx(1,0)(π,π*)的寿命与该渡越时间有相对较好的一致性。对频谱图的分析表明,依赖时间变化的振动光谱与自旋态变化有关,自旋态可以通过曲线交叉点或者单态和三重态之间的势能面的圆锥交面从激发单重态中的Franck-Condon态变化到三重态。研究发现,不能简单地使用单重态信号频谱的指数衰减形式和三重态振动信号频谱的指数增长形式来表示这种动态变化。相反,振动频谱的变化伴随着复杂的动态变化。首先,单重态振动频谱发生衰减,然后产生不同于单重态和三重态的新的振动频谱。新的振动频谱增长和衰减后,三重态的振动频谱开始增长。这种动态变化似乎与电子频谱的动态变化不同,将这种明显差异的原因解释为:振动频谱的变化可以敏感地检测处于平衡点和过渡状态或者接近锥形交集状态中的单重态和三重态的结构差异。

The ultrafast spectroscopy by a sub 5 fs pulse laser was applied to the simultaneous study of electronic relaxation and vibrational dynamics in Ru^Ⅱ（TPP）（CO）.The signals due to ^1Qx（1,0）（π,π^＊） and ^1Qx（0,0）（π,π^＊） are thought to decay in a sequential order from the higher energy states to the lower energy states in the sequences ^1Qx（1,0）（π,π^＊）→^1Qx（0,0）（π,π^＊）→^3（d,π^＊）→^3（π,π^＊） and ^1Qx（0,0）（π,π^＊）→^3（d,π^＊）→^3（π,π^＊）.The electronic lifetimes of ^1Qx（1,0）（π,π^＊）,^1Qx（0,0）（π,π^＊）,^3（d,π^＊）,and ^3（π,π^＊） are determined to be（230±70） fs,（1150±260） fs,（2150±360） fs and larger than 4.8 ps,respectively.The lifetimes of ^3（d,π^＊）,and ^3（π,π^＊） are estimated to be（2 150 ± 360） fs and larger than 4.8 ps,respectively.The lifetime of ^1Qx（1,0）（π,π^＊） determined to be（230 ± 70） fs,is in relatively good agreement with the step-down time of（190±40） fs for the transition time from ^1Qx（1,0）（π,π^＊） to ^1Qx（0,0）（π,π^＊） calculated from the energy decay rate in the dynamic Stokes-shift process.The spectrogram analysis shows that the time dependent changes in the vibrational spectrum is associated with the spin state change from the Franck-Condon state in the excited singlet state to the triplet state via the curve crossing point or conical intersection between the singlet and triplet potential surfaces.It is found that the dynamics is can not be expressed in terms of the simple single exponential decay of the spectrogram signal of singlet and exponential growth of the triplet vibration spectrogram signal.In stead,the vibrational spectral change takes place with more complex dynamics.At first,the decay of the singlet vibration spectrum takes place and then new vibrational spectrum which is different from singlet and triplet states appears.After the growth and decay of the new vibrational spectrum,the triplet state vibration spectrum starts to grow.The dynamics at first looks different from that of electronic spectra.The reason of the apparent difference can be explained in the following way.The vibrational spectral change could sensitively detect the structural difference among the singlet sate and triplet state in their equilibriums and that of transition state or state close to the conical intersection.