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 2019-10, Vol.18 (10), p.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: Article
Language:English
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.
ISSN:1476-1122
1476-4660
DOI:10.1038/s41563-019-0465-6