Vibrationally resolved optical spectra and ultrafast electronic relaxation dynamics of diamantane.
Vibrationally resolved optical spectra and ultrafast electronic relaxation dynamics of diamantane.
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金刚烷的振动分辨光谱和超快电子弛豫动力学
DOI：
10.1039/c6cp00137h
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
J. Petersen
中科院分区：
文献类型：
--
作者：
M.I.S. Röhr;R. Mitrić;J. Petersen
我们对金刚烷的振动分辨光吸收和光电子能谱进行了理论模拟，并结合非绝热动力学模拟，以确定测量到的金刚烷光致发光的状态，并确定了电子态驰豫的机制和时间尺度。金刚烷是金刚烷类碳氢化合物的原型代表，由于其独特的电子性质，近年来引起了人们的极大兴趣。这种分子的特点是第一激发态几乎是暗的，因此不能直接激发。此外，计算的从几何驰豫的第一激发态到基态的垂直跃迁也没有强度。然而，最近的实验表明，观察到的光致发光起源于最低激发态。我们在Herzberg-Teller近似的框架下对振动跃迁进行了谱模拟，它超越了常数跃迁偶极矩的Franck-Condon近似，并考虑了它们对几何形变的线性依赖。通过这种方法，可以完全再现现有的实验光谱，解决了光致发光的起源问题。此外，第一激发态的光电子发射也意味着超快无辐射过程必须发生在亮电子态的初始激发之后。通过对S和p型里德堡激发态的非绝热动力学模拟，我们确定了这些弛豫过程的机制和时间尺度。模拟结果表明，在几百飞秒之后，金刚烷的最低激发电子态已经从较高的激发态获得了大量的布居。因此，我们的动力学模拟结合使用Herzberg-Teller近似计算的光谱，使我们能够完全解释观察到的金刚烷的光吸收和光电子发射性质。
We present theoretical simulations of the vibrationally resolved photoabsorption and photoemission spectra of diamantane combined with nonadiabatic dynamics simulations in order to identify the state responsible for the measured photoluminescence of diamantane and to determine the mechanism and the time-scales of the electronic state relaxation. Diamantane is a prototype representative of the diamondoid class of hydrocarbons which have recently gained significant interest due to their unique electronic properties. This molecule is characterised by an almost dark first excited state, which therefore cannot be directly excited. Moreover, the calculated vertical transition from the geometrically relaxed first excited state to the ground state also bears no intensity. However, recent experiments suggest that the observed photoluminescence originates from the lowest excited state. We have performed spectral simulations in the frame of the Herzberg–Teller approximation for vibronic transitions, which goes beyond the Franck–Condon approximation of constant transition dipole moments and takes into account their linear dependence on the geometrical deformations. In this way, the available experimental spectrum could be fully reproduced, resolving the issue about the origin of the photoluminescence. Moreover, the photoemission from the first excited state also implies that ultrafast nonradiative processes have to take place after the initial excitation of the bright electronic states. We have determined the mechanism and time-scales of these relaxation processes by performing nonadiabatic dynamics simulations in the manifold of s- and p-type Rydberg excited states. The simulations demonstrate that the lowest excited electronic state of diamantane gains significant population from higher-lying states already after several hundreds of femtoseconds. Thus, our dynamics simulations combined with spectra calculated using the Herzberg–Teller approximation allow us to fully explain the observed photoabsorption and photoemission properties of diamantane.
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