Critical role of intermediate electronic states for spin-flip processes in charge-transfer-type organic molecules with multiple donors and acceptors

Spin-flip in purely organic molecular systems is often described as a forbidden process; however, it is commonly observed and utilized to harvest triplet excitons in a wide variety of organic material-based applications. Although the initial and final electronic states of spin-flip between the lowes...

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Bibliographic Details
Published in:	Nature materials Vol. 18; no. 10; pp. 1084 - 1090
Main Authors:	Noda, Hiroki, Chen, Xian-Kai, Nakanotani, Hajime, Hosokai, Takuya, Miyajima, Momoka, Notsuka, Naoto, Kashima, Yuuki, Brédas, Jean-Luc, Adachi, Chihaya
Format:	Journal Article
Language:	English
Published:	London Nature Publishing Group UK 01-10-2019 Nature Publishing Group Springer Nature - Nature Publishing Group
Subjects:	119/118 140/125 639/301/1019/1020/1091 639/638/440/949 Biomaterials Charge transfer Chemistry and Materials Science Condensed Matter Physics Delayed fluorescence Donors (electronic) Electron spin Electron states Energy Excitation Excited states Excitons First principles MATERIALS SCIENCE Molecular structure Nanotechnology OLED Optical and Electronic Materials Organic chemistry Organic LEDs Photonics Physical properties TADF
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Summary:	Spin-flip in purely organic molecular systems is often described as a forbidden process; however, it is commonly observed and utilized to harvest triplet excitons in a wide variety of organic material-based applications. Although the initial and final electronic states of spin-flip between the lowest singlet and lowest triplet excited state are self-evident, the exact process and the role of intermediate states through which spin-flip occurs are still far from being comprehensively determined. Here, via experimental photo-physical investigations in solution combined with first-principles quantum-mechanical calculations, we show that efficient spin-flip in multiple donor–acceptor charge-transfer-type organic molecular systems involves the critical role of an intermediate triplet excited state that corresponds to a partial molecular structure of the system. Our proposed mechanism unifies the understanding of the intersystem crossing mechanism in a wide variety of charge-transfer-type molecular systems, opening the way to greater control over spin-flip rates. Triplet excited states related to partial molecular structures are shown to mediate spin-flip between lowest singlet and triplet excited states in multiple donor–acceptor charge-transfer-type organic molecules.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 EE0008205; JPMJER1305; JP17J04907; JP18H02047; JP18H03902 USDOE Office of Energy Efficiency and Renewable Energy (EERE) Japan Science and Technology Agency Japan Society for the Promotion of Science KAKENHI
ISSN:	1476-1122 1476-4660
DOI:	10.1038/s41563-019-0465-6