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Efficient doublet emission from radical materials and devices
Feng Li
State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Qianjin Avenue 2699, Changchun, 130012, P. R. China
(E-mail address: lifeng01@jlu.edu.cn)
A new kind of OLEDs based on radicals, in which the emission comes from a spin doublet rather than from a singlet or triplet exciton was developed. The emission process is spin-allowed in these systems, usefully, the classical triplet-limiting efficiency for OLEDs is circumvented for doublets [1]. After continually optimizing materials and devices [2,3], a D-A type luminescent radical emitter, TTM-3NCz, was used as the emitter of an OLED with a maximum external quantum efficiency of 27 %—the highest reported value for deep-red and infrared LEDs [4].
There is only one family of room-temperature luminescent radicals, triphenylmethyl radicals, so far. We synthesized a new stable room-temperature luminescent radical, (N-carbazolyl)bis(2,4,6-tirchlorophenyl)methyl radical (CzBTM), which is beyond the family of triphenylmethyl radicals. A new family of stable luminescent radicals based on CzBTM is anticipated [5].
[1] Q.M. Peng, A. Obolda, M. Zhang, F. Li, Organic Light-Emitting Diodes Using a Neutral pi Radical as Emitter: The Emission from a Doublet, Angew. Chem.-Int. Edit., 54 (2015) 7091-7095.
[2] Y. Gao, W. Xu, H. Ma, A. Obolda, W. Yan, S. Dong, M. Zhang, F. Li, Novel Luminescent Benzimidazole-Substituent Tris(2,4,6-trichlorophenyl)methyl Radicals: Photophysics, Stability, and Highly Efficient Red-Orange Electroluminescence, Chem. Mat., 29 (2017) 6733-6739.
[3] A. Obolda, X. Ai, M. Zhang, F. Li, Up to 100% Formation Ratio of Doublet Exciton in Deep-Red Organic Light-Emitting Diodes Based on Neutral pi-Radical, ACS applied materials & interfaces, 8 (2016) 35472-35478.
[4] X. Ai, E.W. Evans, S. Dong, A.J. Gillett, H. Guo, Y. Chen, T.J.H. Hele, R.H. Friend, F. Li, Efficient radical-based light-emitting diodes with doublet emission, Nature, 563 (2018) 536-540.
[5] X. Ai, Y. Chen, Y. Feng, F. Li, A Stable Room-Temperature Luminescent Biphenylmethyl Radical, Angew. Chem.-Int. Edit., 57 (2018) 2869-2873.
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