He Guiying, Parenti Kaia R, Campos Luis M, Sfeir Matthew Y
Department of Physics, Graduate Center, City University of New York, New York, NY, 10016, USA.
Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA.
Adv Mater. 2022 Oct;34(40):e2203974. doi: 10.1002/adma.202203974. Epub 2022 Sep 1.
Singlet fission is commonly defined as the generation of two triplet excitons from a single absorbed photon. However, ambiguities within this definition arise due to the complexity of the various double triplet states that exist in SF chromophores and the corresponding interconversion processes. To clarify this process, singlet fission is frequently depicted as sequential two-step conversion in which a singlet exciton decays into a bound triplet-pair biexciton state that dissociates into two "free" triplet excitons. However, this model discounts the potential for direct harvesting from the coupled biexciton state. Here, it is demonstrated that individual triplet excitons can be extracted directly from a bound triplet pair. It is demonstrated that due to the requirement for geminate triplet-triplet annihilation in intramolecular singlet fission compounds, unique spectral and kinetic signatures can be used to quantify triplet-pair harvesting yields. An internal quantum efficiency for triplet exciton transfer from the triplet pair of >50%, limited only by the solubility of the compounds is achieved. The harvesting process is not dependent on the net multiplicity of the triplet-pair state, suggesting that an explicit, independent dissociation step is not a requirement for using triplet pairs to do chemical or electrical work.
单重态裂变通常被定义为一个被吸收的光子产生两个三重态激子。然而，由于单重态裂变发色团中存在的各种双三重态的复杂性以及相应的相互转换过程，这个定义存在模糊性。为了阐明这个过程，单重态裂变常常被描述为连续的两步转换，其中一个单重态激子衰变成一个束缚的三重态对双激子态，该双激子态再解离成两个“自由”的三重态激子。然而，这个模型忽略了从耦合双激子态直接提取的可能性。在此，证明了单个三重态激子可以直接从束缚的三重态对中提取。证明了由于分子内单重态裂变化合物中对孪生三重态-三重态湮灭的要求，可以使用独特的光谱和动力学特征来量化三重态对提取产率。实现了从三重态对转移三重态激子的内部量子效率大于50%，仅受化合物溶解度的限制。提取过程不依赖于三重态对态的净多重性，这表明使用三重态对进行化学或电功并不需要一个明确的、独立的解离步骤。
