Imaging Singlet Fission in Pentacene Thin Films using Time- and Angle-Resolved Photoemission

The generation of spin-entangled triplet exciton pairs in organic semiconductors is known to occur during the process of singlet fission, where an optically excited singlet exciton splits into two triplet excitons. Spin coherences resulting from singlet fission can persist on the nanosecond time scale, and thus triplet pairs produced via singlet fission are a promising source of entangled spins for quantum information applications if the triplets can be spatially separated while maintaining spin coherence [1]. Optimization of singlet fission requires a detailed mechanistic understanding of the microscopic dynamics and decoherence mechanisms. This has motivated many studies, for example recent time- and angle-resolved photoemission spectroscopy measurements on bulk pentacene crystals [2]. However, these measurements, and the nature of the critical intermediate correlated triplet pair states, remain highly debated. In this work we present a comprehensive set of tr-ARPES measurements on high-quality crystalline pentacene thin films, resolving the participating orbitals in the intermediate correlated triplet pair states of singlet fission.

[1] Smyser and Eaves, Scientific Reports, 10, 18480 (2020).

[2] Neef, et al., Nature, 616, 275-279 (2023).