ARC Centre of Excellence in Exciton Science, School of Chemistry, UNSW Sydney, NSW 2052, Australia.
Department of Chemistry, The University of Adelaide, SA 5005, Australia.
Nat Chem. 2018 Mar;10(3):305-310. doi: 10.1038/nchem.2926. Epub 2018 Jan 22.
Singlet fission is a process whereby two triplet excitons can be produced from one photon, potentially increasing the efficiency of photovoltaic devices. Endothermic singlet fission is desired for a maximum energy-conversion efficiency, and such systems have been considered to form an excimer-like state with multiexcitonic character prior to the appearance of triplets. However, the role of the excimer as an intermediate has, until now, been unclear. Here we show, using 5,12-bis((triisopropylsilyl)ethynyl)tetracene in solution as a prototypical example, that, rather than acting as an intermediate, the excimer serves to trap excited states to the detriment of singlet-fission yield. We clearly demonstrate that singlet fission and its conjugate process, triplet-triplet annihilation, occur at a longer intermolecular distance than an excimer intermediate would impute. These results establish that an endothermic singlet-fission material must be designed to avoid excimer formation, thus allowing singlet fission to reach its full potential in enhancing photovoltaic energy conversion.
单线态裂变是一个过程，其中两个三重态激子可以由一个光子产生，这有可能提高光伏器件的效率。对于最大能量转换效率，需要吸热单线态裂变，并且在三重态出现之前，这样的系统已经被认为形成具有多激子特性的激基复合物态。然而，激基复合物作为中间体的作用，直到现在，还不清楚。在这里，我们使用溶液中的 5,12-双((三异丙基硅基)乙炔基)四并苯作为典型的例子表明，激基复合物不是作为中间体，而是起到了捕获激发态的作用，从而降低了单线态裂变的产率。我们清楚地表明，单线态裂变及其共轭过程，三重态-三重态湮灭，发生在比激基复合物中间体所推测的更长的分子间距离处。这些结果表明，必须设计吸热单线态裂变材料以避免激基复合物形成，从而使单线态裂变在增强光伏能量转换方面发挥其全部潜力。
