单线态裂分指光激发产生的一个单线态激子裂分为一对三线态激子的激子倍增过程，利用 该过程有望突破单结太阳能电池效率极限。中间三线态激子对的生成是单线态裂分的关键步骤，基 态构型下，单线态与三线态激子对的电子耦合较小，电子振动自由度可能扮演着重要作用，因而 揭示超快单线态裂分的电子振动波包动力学是理解三线态激子对形成机制的核心问题，也是重要 挑战。本文系统介绍了研究电子振动波包动力学的超快光谱技术，深入讨论了电子振动驱动单线 态裂分中间态形成的机制，并总结了该领域目前面临的关键科学问题和技术挑战。 

Singlet fission refers to an exciton multiplication process in which a photoexcited singlet exciton splits into a pair of triplet excitons. This process holds the potential to break the efficiency limit of single-junction solar cells. The generation of the intermediate triplet exciton pair is a critical step in singlet fission. In the ground-state configuration, the electronic coupling between the singlet and triplet exciton pair is relatively weak, suggesting that vibronic degrees of freedom may play a significant role. Therefore, unraveling the ultrafast vibronic wavepacket dynamics in singlet fission is essential to understanding the formation mechanism of triplet exciton pairs—and remains key challenges. This review systematically introduces ultrafast spectroscopic techniques used for probing vibronic wavepacket dynamics, provides an in-depth discussion on the vibronic coupling mechanism of intermediate state formation in singlet fission, and summarizes the key scientific issues and technical challenges in this field.