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Long-lived Triplet Excitons Formed by Exergonic Intramolecular Singlet Fission of an Adamantane-linked Tetracene Dyad

preprint
submitted on 06.03.2019 and posted on 08.03.2019 by Yasunori Matsui, Shuhei Kawaoka, Hiroki Nagashima, Tatsuo Nakagawa, Naoki Okamura, Takuya Ogaki, Eisuke Ohta, Seiji Akimoto, Shigeyuki Yagi, Yasuhiro Kobori, Hiroshi Ikeda
An adamantane-linked tetracene dyad (Tc–Ad–Tc) undergoes exergonic intramolecular singlet fission (SF), producing longlived (τ = 175 μs) and high-energy (2 x 1.03 eV) multiexcitons. Timeresolved absorption, fluorescence decay, and electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the long-lived triplet species is generated in this system via correlated triplet pair having singlet and quintet characteristics. Time-resolved EPR analysis revealed that conversion of 1(3Tc–Ad–3Tc)* -> 5(3Tc–Ad–3Tc)* requires small conformational dynamics accompanied by molecular motion. Analysis of the geometries of the quintet states shows that formation of the long-lived multiexciton is enabled by precise and close alignment of the tetracene moieties, which leads to their moderate interaction in the singlet excited state, while triplet–triplet annihilation is prevented by quintet generation. The presence of aliphatic linkages, like the rigid adamantane group, might enable effective conservation of intrinsic S1 and T1 levels of the original monomers, and moderate bridge-mediated σ–π interaction leading to exergonic intramolecular SF involving 1Tc*–Ad–Tc -> 1(3Tc–Ad–3Tc)*.

History

Email Address of Submitting Author

matsui@chem.osakafu-u.ac.jp

Institution

Osaka Prefecture University, Kobe University, Unisoku

Country

Japan

ORCID For Submitting Author

0000-0002-7719-0071

Declaration of Conflict of Interest

The authors declare no competing financial interests.

Version Notes

ver March07

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