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Long Persistent Luminescence Enabled by Dissociation of Triplet Intermediate States in an Organic Guest/Host System

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journal contribution
posted on 23.04.2020, 14:06 by Leixin Xiao, Zhiwei Wang, Chunfeng Zhang, Xiaoyu Xie, Haibo Ma, Qian Peng, Zhongfu An, Xiaoyong Wang, Zhigang Shuai, Min Xiao
Organic guest/host systems with long persistent luminescence benefiting from the formation of a long-lived charge-separated state have recently been demonstrated. However, the photogeneration mechanism of such key charge-separated states remains elusive. Here, we report the identification of intermediate triplet states with mixed local excitation and charge-transfer character that connect the initial photoexcited singlet states and the long-lived charge-separated states. Using time-resolved optical spectroscopy, we observe the intersystem crossing from photoexcited singlet charge-transfer states to triplet intermediate states on a time scale of ∼52 ns. Temperature-dependent measurements reveal that the long-lived triplet intermediate states ensure a relatively high efficiency of diffusion-driven charge separation to form the charge-separated state responsible for LPL emission. The findings in this work provide a rationale for the development of new LPL materials that may also improve our understanding of the mechanism of photon-to-charge conversion in many organic optoelectronic devices.