Duan Hong-Guang, Jha Ajay, Li Xin, Tiwari Vandana, Ye Hanyang, Nayak Pabitra K, Zhu Xiao-Lei, Li Zheng, Martinez Todd J, Thorwart Michael, Miller R J Dwayne
Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany.
I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, 20355 Hamburg, Germany.
Sci Adv. 2020 Sep 18;6(38). doi: 10.1126/sciadv.abb0052. Print 2020 Sep.
Singlet fission is a spin-allowed exciton multiplication process in organic semiconductors that converts one spin-singlet exciton to two triplet excitons. It offers the potential to enhance solar energy conversion by circumventing the Shockley-Queisser limit on efficiency. We study the primary steps of singlet fission in a pentacene film by using a combination of TG and 2D electronic spectroscopy complemented by quantum chemical and nonadiabatic dynamics calculations. We show that the coherent vibrational dynamics induces the ultrafast transition from the singlet excited electronic state to the triplet-pair state via a degeneracy of potential energy surfaces, i.e., a multidimensional conical intersection. Significant vibronic coupling of the electronic wave packet to a few key intermolecular rocking modes in the low-frequency region connect the excited singlet and triplet-pair states. Along with high-frequency local vibrations acting as tuning modes, they open a new channel for the ultrafast exciton transfer through the resulting conical intersection.
单线态裂变是有机半导体中一种自旋允许的激子倍增过程，它将一个自旋单线态激子转化为两个三线态激子。通过规避肖克利-奎塞尔效率极限，它为提高太阳能转换效率提供了潜力。我们结合瞬态光栅（TG）和二维电子光谱，并辅以量子化学和非绝热动力学计算，研究了并五苯薄膜中单线态裂变的初级步骤。我们表明，相干振动动力学通过势能面简并，即多维锥形交叉，诱导了从单线态激发电子态到三线态对态的超快跃迁。电子波包与低频区域的一些关键分子间摇摆模式的显著振动电子耦合连接了激发单线态和三线态对态。与作为调谐模式的高频局部振动一起，它们通过产生的锥形交叉开辟了一条超快激子转移的新通道。
