Quantum Beats in Crystalline Tetracene Delayed Fluorescence Due to Triplet Pair Coherences Produced by Direct Singlet Fission
Quantum Beats in Crystalline Tetracene Delayed Fluorescence Due to Triplet Pair Coherences Produced by Direct Singlet Fission
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DOI：
10.1021/ja301683w
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发表时间：
2012-05-23
影响因子：
15
通讯作者：
Bardeen, Christopher J.
中科院分区：
文献类型：
--
作者：
Burdett, Jonathan J.;Bardeen, Christopher J.
为了研究单重态裂变的机理，对结晶并四苯的延迟荧光中的振荡现象进行了详细的分析。三个量子拍频1.06 +/- 0.05，1.82 +/- 0.05，和2.92 +/- 0.06 GHz的解决，这是阻尼的时间尺度为20 ns。样品形态，激发波长和温度的影响进行了研究。建立了单重态裂变的密度矩阵模型。它定量地描述了振动的频率，振幅和阻尼。该模型假设一个直接耦合的初始激发单重态激子的三重态：对歧管。在单重态和三重态对状态之间没有电子相干性，但是在溶液生长的单晶中类似于200 ps的快速单重态衰减时间提供了产生具有整体单重态特征的三个零场三重态对状态垂直条xx >、垂直条yy >和垂直条zz >的相干叠加所必需的脉冲布居转移。这三个态的叠加产生了实验中看到的三个量子拍频。阻尼的量子拍频的结果从两个三重态和单重态流形之间的人口交换和三重态对状态之间的纯退相。通过降低温度和减慢SF速率，振荡的可见性降低。没有证据表明产品三重态之间的磁偶极偶极耦合。我们的模型提供了良好的整体协议的数据，支持的结论，并四苯的单线态裂变收益通过“直接”的机制，没有强的单重态和三重态对之间的电子耦合。
A detailed analysis of the oscillations seen in the delayed fluorescence of crystalline tetracene is presented in order to study the mechanism of singlet fission. Three quantum beat frequencies of 1.06 +/- 0.05, 1.82 +/- 0.05, and 2.92 +/- 0.06 GHz are resolved, which are damped on a time scale of 20 ns. The effects of sample morphology, excitation wavelength, and temperature are 2 examined. A density matrix model for singlet fission is developed. that quantitatively describes the frequencies, amplitudes, and 2 3 4 damping of the oscillations. The model assumes a direct coupling of the initially excited singlet exciton to the triplet: pair manifold. There is no electronic coherence between the singlet and triplet pair states, but the rapid singlet decay time of similar to 200 ps in solution-grown single crystals provides the impulsive population transfer necessary to create a coherent superposition of three zero-field triplet pair states vertical bar xx >, vertical bar yy >, and vertical bar zz > with overall singlet character. This superposition of the three states gives rise to the three quantum beat frequencies seen in the experiment. Damping of the quantum beats results from both population exchange between triplet and singlet manifolds and pure dephasing between the triplet pair states. By lowering the temperature and slowing the SF rate, the visibility of the oscillations decreases. There is no evidence of magnetic dipole-dipole coupling between the product triplets. Our model provides good overall agreement with the data, supporting the conclusion that singlet fission in tetracene proceeds through the "direct" mechanism without strong electronic coupling between the singlet and triplet pair states.