Intramolecular singlet fission (SF) in multichromophore systems is of high interest for photovoltaic application. As an attractive candidate for SF-based devices, enabling efficient SF in covalent oligomers of perylene diimide (PDI) still remains challenging. In this work, inter-PDI SF with τ_SF = ∼150 ps and ∼150% triplet yield in a covalent tetramer COTh-FPDI was facilitated by employing a saddle-shaped cyclooctatetrathiophene (COTh) core and fused linking with PDIs. In comparison, ultrafast symmetry-breaking charge separation (τ_CS = ∼100 fs) was observed for the tetramer COTh-αPDI with flexible linking. Taking advantage of rigid linking and minimized excited-state structural relaxation, unique inter-PDI geometry in COTh-FPDI can be fully defined by the topological characteristic of COTh, which plays a key role for inter-PDI electronic coupling required by SF. Our work provides a new strategy for enabling intramolecular SF by predefining interchromophore geometry by a rigid structure, which might be inspired for future designing of multichromophore SF systems.

中文翻译：

---

使用马鞍形连接子在苝二亚胺四聚体中实现超快分子内单线态裂变


多发色团系统中的分子内单线态裂变 （SF） 在光伏应用中具有很高的意义。作为基于 SF 的器件的有吸引力的候选产品，在苝二酰亚胺 （PDI） 的共价低聚物中实现高效的 SF 仍然具有挑战性。在这项工作中，通过采用马鞍形环八噻吩 （COTh） 核心并与 PDI 熔融连接，促进了共价四聚体 COTh-FPDI 中 τ_SF = ∼150 ps 和 ∼150% 三重态产率的 inter-PDI SF。相比之下，对于具有柔性连接的四聚体 COTh-αPDI，观察到超快对称性断裂电荷分离 （τ_CS = ∼100 fs）。利用刚性连接和最小化的激发态结构弛豫，COTh-FPDI 中独特的 PDI 间几何结构可以完全由 COTh 的拓扑特性定义，这对于 SF 所需的 PDI 间电子耦合起着关键作用。我们的工作提供了一种通过刚性结构预定义色间几何形状来实现分子内 SF 的新策略，这可能会为未来多色团 SF 系统的设计提供灵感。