Singlet Fission Involves an Interplay between Energetic Driving Force and Electronic Coupling in Perylenediimide Films
Singlet Fission Involves an Interplay between Energetic Driving Force and Electronic Coupling in Perylenediimide Films
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DOI：
10.1021/jacs.7b11888
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发表时间：
2018-01-17
影响因子：
15
通讯作者：
Roberts, Sean T.
中科院分区：
文献类型：
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作者：
Le, Aaron K.;Bender, Jon A.;Roberts, Sean T.
由于单线态裂变能够抵消光收集系统中的热化损失，因此单线态裂变已成为一个研究热点。在单线态裂变过程中，有机半导体中的高能自旋单线态将其能量分裂成相邻发色团上的两个低能量自旋三重态激发。虽然对单线态裂变机制的关键见解最近已经获得，但开发光稳定化合物进行定量单线态裂变仍然是一个关键的挑战。在本报告中，我们探索了通过单线态裂变在苝酰亚胺薄膜中产生三重态激子的方法。苝酰亚胺是一类由于其光稳定性而被用作工业染料和颜料的化合物。由于单线态裂变需要相邻分子之间的电子转移，它的速率和产率敏感地依赖于它们之间的电子转移。当地的安排。通过在亚胺的位置添加不同的官能团，我们控制了过二亚胺在固态中的堆积方式。我们发现，在相邻的苝酰亚胺之间诱导类似3埃的长轴位移，在存在类似190 meV的激活势垒的情况下，最大三态产率为178%，裂变速率为245 ps。这些发现与Marcus理论对单重态裂变的最佳过二酰亚胺几何形状的预测不一致，但与Redfield理论的计算一致，该理论允许单重态裂变通过电荷转移介导的超交换机制发生。不幸的是，单线态裂变产生的三重态被发现会在几十纳秒内衰变。我们的研究结果强调，单重态裂变材料必须设计成不仅能产生三重态激子，而且还能促进它们的提取。
Due to its ability to offset thermalization losses in photoharvesting systems, singlet fission has become a topic of research interest. During singlet fission, a high energy spin-singlet state in an organic semiconductor divides its energy to form two lower energy spin-triplet excitations on neighboring chromophores. While key insights into mechanisms leadin to singlet fission have been gained recently, developing photostable compounds that undergo quantitative singlet fission remains a key challenge. In this report, we explore triplet exciton production via singlet fission in films of perylenediimides, a class of compounds with a long history of use as industrial dyes and pigments due to their photostability. As singlet fission necessitates electron transfer between neighboring molecules, its-rate and yield depend sensitively on their. local arrangement. By adding different functional groups at their imide positions, we control how perylenediimides pack in the solid state. We find inducing a long axis displacement of similar to 3 angstrom between neighboring perylenediimides gives a maximal triplet production yield of 178% with a fission rate of similar to 245 ps despite the presence of an activation barrier of similar to 190 meV. These findings disagree with Marcus theory predictions for the optimal perylenediimide geometry for singlet fission, but do agree with Redfield theory calculations that allow singlet fission to occur via a charge transfer-mediated superexchange mechanism. Unfortunately, triplets produced by singlet fission are found to decay over tens of nanoseconds. Our results highlight that singlet fission materials must be designed to not only produce triplet excitons but to also facilitate their extraction.