Lee Tia S, Lin YunHui L, Kim Hwon, Pensack Ryan D, Rand Barry P, Scholes Gregory D
Department of Chemistry , Princeton University , Princeton , New Jersey 08544 , United States.
Department of Electrical Engineering , Princeton University , Princeton , New Jersey 08544 , United States.
J Phys Chem Lett. 2018 Jul 19;9(14):4087-4095. doi: 10.1021/acs.jpclett.8b01834. Epub 2018 Jul 9.
Singlet fission is a spin-allowed process of exciton multiplication that has the potential to enhance the efficiency of photovoltaic devices. The majority of studies to date have emphasized understanding the first step of singlet fission, where the correlated triplet pair is produced. Here, we examine separation of correlated triplet pairs. We conducted temperature-dependent transient absorption on 6,3-bis(tri isopropylsilylethynyl)pentacene (TIPS-Pn) films, where singlet fission is exothermic. We evaluated time constants to show that their temperature dependence is inconsistent with an exclusively thermally activated process. Instead, we found that the trends can be modeled by a triplet-triplet energy transfer. The fitted reorganization energy and electronic coupling agree closely with values calculated using density matrix renormalization group quantum-chemical theory. We conclude that dissociation of the correlated triplet pair to separated (but spin-entangled) triplet excitons in TIPS-Pn occurs by triplet-triplet energy transfer with a hopping time constant of approximately 3.5 ps at room temperature.
单线态裂变是一种激子倍增的自旋允许过程，有潜力提高光电器件的效率。迄今为止，大多数研究都着重于理解单线态裂变的第一步，即产生关联三重态对的过程。在此，我们研究关联三重态对的分离。我们对6,3-双（三异丙基甲硅烷基乙炔基）并五苯（TIPS-Pn）薄膜进行了温度依赖的瞬态吸收实验，该薄膜中的单线态裂变是放热过程。我们评估了时间常数，结果表明它们的温度依赖性与单纯的热激活过程不一致。相反，我们发现这些趋势可以用三重态-三重态能量转移来建模。拟合得到的重组能和电子耦合与使用密度矩阵重整化群量子化学理论计算的值非常吻合。我们得出结论，在TIPS-Pn中，关联三重态对解离为分离的（但自旋纠缠的）三重态激子是通过三重态-三重态能量转移发生的，在室温下其跳跃时间常数约为3.5皮秒。
