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Striking the right balance of intermolecular coupling for high-efficiency singlet fission†
Chemical Science ( IF 7.6 ) Pub Date : 2018-06-01 00:00:00 , DOI: 10.1039/c8sc00293b Ryan D Pensack 1 , Andrew J Tilley 2 , Christopher Grieco 3 , Geoffrey E Purdum 4 , Evgeny E Ostroumov 1 , Devin B Granger 5 , Daniel G Oblinsky 1 , Jacob C Dean 1 , Grayson S Doucette 3 , John B Asbury 3 , Yueh-Lin Loo 4, 6 , Dwight S Seferos 2, 7 , John E Anthony 5 , Gregory D Scholes 1
Chemical Science ( IF 7.6 ) Pub Date : 2018-06-01 00:00:00 , DOI: 10.1039/c8sc00293b Ryan D Pensack 1 , Andrew J Tilley 2 , Christopher Grieco 3 , Geoffrey E Purdum 4 , Evgeny E Ostroumov 1 , Devin B Granger 5 , Daniel G Oblinsky 1 , Jacob C Dean 1 , Grayson S Doucette 3 , John B Asbury 3 , Yueh-Lin Loo 4, 6 , Dwight S Seferos 2, 7 , John E Anthony 5 , Gregory D Scholes 1
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Singlet fission is a process that splits collective excitations, or excitons, into two with unity efficiency. This exciton splitting process, unique to molecular photophysics, has the potential to considerably improve the efficiency of optoelectronic devices through more efficient light harvesting. While the first step of singlet fission has been characterized in great detail, subsequent steps critical to achieving overall highly-efficient singlet-to-triplet conversion are only just beginning to become well understood. One of the most elementary suggestions, which has yet to be tested, is that an appropriately balanced coupling is necessary to ensure overall highly efficient singlet fission; that is, the coupling needs to be strong enough so that the first step is fast and efficient, yet weak enough to ensure the independent behavior of the resultant triplets. In this work, we show how high overall singlet-to-triplet conversion efficiencies can be achieved in singlet fission by ensuring that the triplets comprising the triplet pair behave as independently as possible. We show that side chain sterics govern local packing in amorphous pentacene derivative nanoparticles, and that this in turn controls both the rate at which triplet pairs form and the rate at which they decay. We show how compact side chains and stronger couplings promote a triplet pair that effectively couples to the ground state, whereas bulkier side chains promote a triplet pair that appears more like two independent and long-lived triplet excitations. Our results show that the triplet pair is not emissive, that its decay is best viewed as internal conversion rather than triplet–triplet annihilation, and perhaps most critically that, in contrast to a number of recent suggestions, the triplets comprising the initially formed triplet pair cannot be considered independently. This work represents a significant step toward better understanding intermediates in singlet fission, and how molecular packing and couplings govern overall triplet yields.
中文翻译：
实现分子间耦合的正确平衡以实现高效单线态裂变†
单线态裂变是一种将集体激发或激子以单位效率分裂成两部分的过程。这种激子分裂过程是分子光物理学所独有的，有可能通过更有效的光收集来显着提高光电器件的效率。虽然单线态裂变的第一步已经得到了非常详细的描述，但对于实现整体高效单线态到三线态转换至关重要的后续步骤才刚刚开始被充分理解。最基本的建议之一（尚未经过测试）是，需要适当平衡的耦合来确保整体高效的单线态裂变；也就是说，耦合需要足够强，以便第一步快速有效，但又足够弱，以确保所得三元组的独立行为。在这项工作中，我们展示了通过确保组成三重态对的三重态尽可能独立地表现，在单重态裂变中可以实现多高的整体单重态到三重态转换效率。我们表明，侧链空间控制着无定形并五苯衍生物纳米粒子的局部堆积，这反过来又控制着三重态对形成的速率和它们衰变的速率。我们展示了紧凑的侧链和更强的耦合如何促进有效耦合到基态的三重态对，而较大的侧链促进看起来更像两个独立且长寿命的三重态激发的三重态对。我们的结果表明，三重态对不是发射性的，其衰变最好被视为内部转换而不是三重态-三重态湮灭，也许最关键的是，与最近的一些建议相反，构成最初形成的三重态对的三重态不能独立考虑。这项工作代表了朝着更好地理解单线态裂变中间体以及分子堆积和耦合如何控制总三线态产率迈出的重要一步。
更新日期：2018-06-01
中文翻译：
实现分子间耦合的正确平衡以实现高效单线态裂变†
单线态裂变是一种将集体激发或激子以单位效率分裂成两部分的过程。这种激子分裂过程是分子光物理学所独有的，有可能通过更有效的光收集来显着提高光电器件的效率。虽然单线态裂变的第一步已经得到了非常详细的描述，但对于实现整体高效单线态到三线态转换至关重要的后续步骤才刚刚开始被充分理解。最基本的建议之一（尚未经过测试）是，需要适当平衡的耦合来确保整体高效的单线态裂变；也就是说，耦合需要足够强，以便第一步快速有效，但又足够弱，以确保所得三元组的独立行为。在这项工作中，我们展示了通过确保组成三重态对的三重态尽可能独立地表现，在单重态裂变中可以实现多高的整体单重态到三重态转换效率。我们表明，侧链空间控制着无定形并五苯衍生物纳米粒子的局部堆积，这反过来又控制着三重态对形成的速率和它们衰变的速率。我们展示了紧凑的侧链和更强的耦合如何促进有效耦合到基态的三重态对，而较大的侧链促进看起来更像两个独立且长寿命的三重态激发的三重态对。我们的结果表明，三重态对不是发射性的，其衰变最好被视为内部转换而不是三重态-三重态湮灭，也许最关键的是，与最近的一些建议相反，构成最初形成的三重态对的三重态不能独立考虑。这项工作代表了朝着更好地理解单线态裂变中间体以及分子堆积和耦合如何控制总三线态产率迈出的重要一步。
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