Hong Yongseok, Kim Juno, Kim Woojae, Kaufmann Christina, Kim Hyungjun, Würthner Frank, Kim Dongho
Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 03722, Korea.
Universitat Würzburg, Institut für Organische Chemie & Center for Nanosystems Chemistry, Am Hubland, Würzburg 97074, Germany.
J Am Chem Soc. 2020 Apr 29;142(17):7845-7857. doi: 10.1021/jacs.0c00870. Epub 2020 Apr 21.
The singlet fission (SF) process is generally defined as the conversion of one singlet exciton (S) into two triplet excitons (2·T), which has the potential to overcome thermalization losses in the field of photovoltaic devices. Among the applicable compounds for SF-based photovoltaic devices, perylene bisimide (PBI) is one of the best candidates because of its electronic tunability and photostability. However, the strategy for efficient SF in PBIs remains ambiguous because of numerous competing relaxation pathways in PBI-based molecular materials. In this regard, for the first time, we observed the SF mechanism in PBI dimers by controlling the intrinsic factor (exciton coupling) and the external environment (solvent polarity and viscosity). Time-resolved spectroscopic measurements and quantum chemical simulations reveal that efficient SF occurs through the charge-transfer-assisted mechanism, entailing a large structural fluctuation. Our findings not only highlight the SF mechanism in PBI dimers but also suggest the factors responsible for an efficient SF process, which are important considerations in the design of molecular materials for photovoltaic devices.
单线态裂变（SF）过程通常被定义为一个单线态激子（S）转化为两个三线态激子（2·T），这有可能克服光伏器件领域中的热化损失。在适用于基于SF的光伏器件的化合物中，苝二酰亚胺（PBI）因其电子可调性和光稳定性而成为最佳候选物之一。然而，由于基于PBI的分子材料中存在众多相互竞争的弛豫途径，PBI中高效SF的策略仍不明确。在这方面，我们首次通过控制内在因素（激子耦合）和外部环境（溶剂极性和粘度）观察到了PBI二聚体中的SF机制。时间分辨光谱测量和量子化学模拟表明，高效SF通过电荷转移辅助机制发生，这需要较大的结构波动。我们的发现不仅突出了PBI二聚体中的SF机制，还指出了高效SF过程的相关因素，这些因素是光伏器件分子材料设计中的重要考虑因素。
