Assoc. Prof. Hajime Nakanotani (International Institution for Carbon - Neutral Energy Research/ Center for Organic Photonics and Electronics Research (OPERA), Kyushu University), Mr. Hiroki Noda (Doctoral Course 3d Year), Prof. Chihaya Adachi ( Molecular Photoconversion Devices Division/ OPERA ), Takuya Hosogai Lead Researcher, at Research Institute for Measurement and Analytical Instrumentation ), Prof. Jean-Luc Brédas an Dr. Xian-Kai Chen (Georgia Institute of Technology), their research outcome has been published in Nature Materials (Online).
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.
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Nature Materials - https://www.nature.com/articles/s41563-019-0465-6