Anisotropic Singlet Fission in Single Crystalline Hexacene

• Published in: iScience Vol. 19; no. C; pp. 1079 - 1089
• Main Authors: Sun, Dezheng, Deng, Gang-Hua, Xu, Bolei, Xu, Enshi, Li, Xia, Wu, Yajing, Qian, Yuqin, Zhong, Yu, Nuckolls, Colin, Harutyunyan, Avetik R., Dai, Hai-Lung, Chen, Gugang, Chen, Hanning, Rao, Yi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 27.09.2019; Elsevier
• Subjects: Quantum Phenomena; Science & Technology - Other Topics; Spectroscopy; Theoretical Photophysics; Spectroscopy; Quantum Phenomena; Theoretical Photophysics
• ISSN: 2589-0042; 2589-0042
• DOI: 10.1016/j.isci.2019.08.053

Singlet fission is known to improve solar energy utilization by circumventing the Shockley-Queisser limit. The two essential steps of singlet fission are the formation of a correlated triplet pair and its subsequent quantum decoherence. However, the mechanisms of the triplet pair formation and decoherence still remain elusive. Here we examined both essential steps in single crystalline hexacene and discovered remarkable anisotropy of the overall singlet fission rate along different crystal axes. Since the triplet pair formation emerges on the same timescale along both crystal axes, the quantum decoherence is likely responsible for the directional anisotropy. The distinct quantum decoherence rates are ascribed to the notable difference on their associated energy loss according to the Redfield quantum dissipation theory. Our hybrid experimental/theoretical framework will not only further our understanding of singlet fission, but also shed light on the systematic design of new materials for the third-generation solar cells. [Display omitted] •Remarkable anisotropy of the overall singlet fission along different crystal axes•The correlated triplet pair emerges on the same timescale along both crystal axes•The quantum decoherence is predominantly driven by electron-phonon coupling•The anisotropic decoherence is due to the directional difference of its energy loss Spectroscopy; Theoretical Photophysics; Quantum Phenomena