Anisotropic Singlet Fission in Single Crystalline Hexacene

Dezheng Sun; Gang-Hua Deng; Bolei Xu; Enshi Xu; Xia Li; Yajing Wu; Yuqin Qian; Yu Zhong; Colin Nuckolls; Avetik R Harutyunyan; Hai-Lung Dai; Gugang Chen; Hanning Chen; Yi Rao

doi:10.1016/j.isci.2019.08.053

Anisotropic Singlet Fission in Single Crystalline Hexacene

iScience. 2019 Sep 27:19:1079-1089. doi: 10.1016/j.isci.2019.08.053. Epub 2019 Aug 30.

Authors

Dezheng Sun¹, Gang-Hua Deng², Bolei Xu³, Enshi Xu⁴, Xia Li², Yajing Wu³, Yuqin Qian², Yu Zhong⁵, Colin Nuckolls⁵, Avetik R Harutyunyan⁶, Hai-Lung Dai³, Gugang Chen⁷, Hanning Chen⁸, Yi Rao⁹

Affiliations

¹ Department of Physics, Columbia University, New York, NY 10027, USA.
² Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322, USA.
³ Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
⁴ Department of Chemistry, George Washington University, Washington, DC 20052, USA.
⁵ Department of Chemistry, Columbia University, New York, NY 10027, USA.
⁶ Honda Research Institute USA, Inc., San Jose, CA 95134, USA.
⁷ Honda Research Institute USA, Inc., San Jose, CA 95134, USA. Electronic address: gchen@honda-ri.com.
⁸ Department of Chemistry, George Washington University, Washington, DC 20052, USA. Electronic address: chenhanning@email.gwu.edu.
⁹ Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322, USA. Electronic address: yi.rao@usu.edu.

Abstract

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.

Keywords: Quantum Phenomena; Spectroscopy; Theoretical Photophysics.