University of Colorado Boulder, Department of Chemistry, Boulder, Colorado 80309, United States.
National Renewable Energy Laboratory, Golden, Colorado 80401, United States.
J Phys Chem Lett. 2023 Mar 9;14(9):2387-2394. doi: 10.1021/acs.jpclett.2c03665. Epub 2023 Feb 27.
Singlet fission proceeds through a manifold of triplet-pair states that are exceedingly difficult to distinguish spectroscopically. Here, we introduce a new implementation of photoinduced-absorption-detected magnetic resonance (PADMR) and use it to understand the excited-state absorption spectrum of a tri-2-pentylsilylethynyl pentadithiophene (TSPS-PDT) film. These experiments allow us to directly correlate magnetic transitions driven by RF with electronic transitions in the visible and near-infrared spectrum with high sensitivity. We find that the new near-infrared excited-state transitions that arise in thin films of TSPS-PDT are correlated with the magnetic transitions of T, not TT. Thus, we assign these features to the excited-state absorption of TT, which is depleted when T states are driven to a spin configuration that forbids subsequent fusion. These results clarify the disputed origin of triplet-associated near-infrared absorption features in singlet-fission materials and demonstrate an incisive general purpose tool for studying the evolution of high-spin excited states.
单重态裂变通过一系列难以在光谱上区分的三重态对态进行。在这里，我们引入了一种新的光诱导吸收检测磁共振（PADMR）的实现方法，并使用它来理解三-2-戊基硅基乙炔基五噻吩（TSPS-PDT）薄膜的激发态吸收光谱。这些实验使我们能够直接将由 RF 驱动的磁跃迁与可见光和近红外光谱中的电子跃迁相关联，具有高灵敏度。我们发现，在 TSPS-PDT 薄膜中出现的新的近红外激发态跃迁与 T 的磁跃迁相关，而不是 TT。因此，我们将这些特征分配给 TT 的激发态吸收，当 T 态被驱动到一种禁止随后融合的自旋构型时，TT 就会被耗尽。这些结果澄清了在单重态裂变材料中与三重态相关的近红外吸收特征的争议起源，并展示了一种用于研究高自旋激发态演化的锐利的通用工具。
