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Impurity Conundrum of Organic Room Temperature Afterglow

submitted on 24.09.2019 and posted on 27.09.2019 by Chengjian Chen, Zhenguo Chi, Kok Chan Chong, Andrei S. Batsanov, Zhan Yang, Zhu Mao, Zhiyong Yang, Bin Liu

Commercial carbazole has been widely used to synthesize organic functional materials that entwine with the recent breakthroughs in thermally activated delayed fluorescence, organic luminescent radicals and organic laser diodes. Recently, the strategy of stabilizing triplet excited states in carbazole derivatives ignited the booming development of organic room temperature afterglow (RTA). The unusual RTA of carbazole and its derivatives was elaborated by crystal quality and packing. However, impurity hypotheses in organic RTA have been under debate for nearly a century. Here we show that an isomer of carbazole, accompanying the commercial sources with less than 0.5%, is the key to activating RTA for many carbazole derivatives. As compared to commercial carbazole, the fluorescence of lab-synthesized carbazole is blue-shifted by 54 nm and the well-known RTA disappears. The same phenomenon is also observed for a series of carbazole derivatives. Interestingly, even 0.01% isomer doping could yield the reported RTA. Our results demonstrate that the isomer doping in carbazole derivatives is responsible for their RTA. The impurity effect has also been confirmed for dibenzothiophene based RTA. We anticipate that isomer doping effect is applicable to many organic semiconductors derived from commercial carbazole, which will drive the review of organic functional materials in optoelectronics.


Singapore NRF Competitive Research Program (R279-000-483-281)

NRF Investigatorship (R279-000-444-281)

National University of Singapore (R279-000-482-133)


Email Address of Submitting Author


National University of Singapore



ORCID For Submitting Author


Declaration of Conflict of Interest

The authors declare no conflict of interest.

Version Notes

Original version