Wollscheid Nikolaus, Günther Benjamin, Rao Vaishnavi J, Berger Felix J, Lustres J Luis Pérez, Motzkus Marcus, Zaumseil Jana, Gade Lutz H, Höfener Sebastian, Buckup Tiago
Physikalisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
Centre for Advanced Materials, Universität Heidelberg, Im Neuenheimer Feld 225, D-69120 Heidelberg, Germany.
J Phys Chem A. 2020 Oct 1;124(39):7857-7868. doi: 10.1021/acs.jpca.0c04852. Epub 2020 Sep 22.
Charge carrier multiplication via singlet fission into two triplet states has the potential to increase efficiencies of photovoltaics by one-third due to the reduction of thermalization losses. In the present work, we investigate tetraazaperopyrenes, a class of -heteropolycyles, as suitable singlet fission candidates. Using a combined experimental and theoretical approach, fundamentally different mechanisms for triplet formation in solution and thin film are identified. In solution, an ultrafast intersystem crossing process is observed, which is accelerated for heavier halide substituents not only due to enhanced spin-orbit coupling but also due to the energy tuning between the S and T states. In thin films, a correlated triplet pair is formed coherently upon photoexcitation. Subsequently, an excimer formation is observed, which competes with the electronic decorrelation of the triplet pair. The comparison with peropyrene shows that aza-substitutions within the aromatic core can be a powerful strategy for tuning the energy levels of the states important to singlet fission.
通过单重态裂变产生两个三重态的电荷载流子倍增过程，由于热化损失的减少，有可能将光伏效率提高三分之一。在本工作中，我们研究了一类 - 杂多环化合物四氮杂苝，作为合适的单重态裂变候选物。采用实验和理论相结合的方法，确定了溶液和薄膜中三重态形成的根本不同机制。在溶液中，观察到一个超快的系间窜越过程，对于较重的卤化物取代基，该过程会加速，这不仅是由于自旋 - 轨道耦合增强，还由于单重态和三重态之间的能量调谐。在薄膜中，光激发时会相干地形成一个相关的三重态对。随后，观察到激基缔合物的形成，它与三重态对的电子去相关过程相互竞争。与苝的比较表明，芳环核心内的氮杂取代可以是调节对单重态裂变重要的态的能级的有效策略。
