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Structure Dependence of Kinetic and Thermodynamic Parameters in Singlet Fission Processes
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2020-10-29 , DOI: 10.1021/acs.jpclett.0c02505 Daphné Lubert-Perquel 1 , Anna A. Szumska 2 , Mohammed Azzouzi 2 , Enrico Salvadori 3 , Stefan Ruloff 4 , Christopher M. W. Kay 4, 5 , Jenny Nelson 2 , Sandrine Heutz 1
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2020-10-29 , DOI: 10.1021/acs.jpclett.0c02505 Daphné Lubert-Perquel 1 , Anna A. Szumska 2 , Mohammed Azzouzi 2 , Enrico Salvadori 3 , Stefan Ruloff 4 , Christopher M. W. Kay 4, 5 , Jenny Nelson 2 , Sandrine Heutz 1
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Singlet fission—whereby one absorbed photon generates two coupled triplet excitons—is a key process for increasing the efficiency of optoelectronic devices by overcoming the Shockley–Queisser limit. A crucial parameter is the rate of dissociation of the coupled triplets, as this limits the number of free triplets subsequently available for harvesting and ultimately the overall efficiency of the device. Here we present an analysis of the thermodynamic and kinetic parameters for this process in parallel and herringbone dimers measured by electron paramagnetic resonance spectroscopy in coevaporated films of pentacene in p-terphenyl. The rate of dissociation is higher for parallel dimers than for their herringbone counterparts, as is the rate of recombination to the ground state. DFT calculations, which provide the magnitude of the electronic coupling as well as the distribution of molecular orbitals for each geometry, suggest that weaker triplet coupling in the parallel dimer is the driving force for faster dissociation. Conversely, localization of the molecular orbitals and a stronger triplet–triplet interaction result in slower dissociation and recombination. The identification and understanding of how the intermolecular geometry promotes efficient triplet dissociation provide the basis for control of triplet coupling and thereby the optimization of one important parameter of device performance.
中文翻译：
单线态裂变过程中动力学和热力学参数的结构依赖性
单线态裂变（一个吸收的光子产生两个偶合的三线态激子）是克服肖克利-奎塞尔极限来提高光电器件效率的关键过程。一个关键参数是耦合三联体的解离速率，因为这限制了随后可用于收获的自由三联体的数量，并最终限制了设备的整体效率。在这里，我们在并五苯的共蒸发膜呈现用于通过电子顺磁共振光谱法测量平行和人字形二聚体这个过程中的热力学和动力学参数的分析p-三苯基。平行二聚体的解离速率比其人字形对应物的解离速率高，重组为基态的速率也更高。DFT计算可提供电子耦合的强度以及每种几何结构的分子轨道分布，这表明平行二聚体中较弱的三重态耦合是促进更快解离的驱动力。相反，分子轨道的定位和更强的三重态-三重态相互作用导致较慢的解离和重组。对分子间几何形状如何促进有效的三线态解离的识别和理解为控制三线态偶联并由此优化器件性能的一个重要参数提供了基础。
更新日期：2020-11-19
中文翻译：
单线态裂变过程中动力学和热力学参数的结构依赖性
单线态裂变（一个吸收的光子产生两个偶合的三线态激子）是克服肖克利-奎塞尔极限来提高光电器件效率的关键过程。一个关键参数是耦合三联体的解离速率，因为这限制了随后可用于收获的自由三联体的数量，并最终限制了设备的整体效率。在这里，我们在并五苯的共蒸发膜呈现用于通过电子顺磁共振光谱法测量平行和人字形二聚体这个过程中的热力学和动力学参数的分析p-三苯基。平行二聚体的解离速率比其人字形对应物的解离速率高，重组为基态的速率也更高。DFT计算可提供电子耦合的强度以及每种几何结构的分子轨道分布，这表明平行二聚体中较弱的三重态耦合是促进更快解离的驱动力。相反，分子轨道的定位和更强的三重态-三重态相互作用导致较慢的解离和重组。对分子间几何形状如何促进有效的三线态解离的识别和理解为控制三线态偶联并由此优化器件性能的一个重要参数提供了基础。
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