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We demonstrate an organic molecule with an energy gap between its singlet and triplet excited states of almost zero (Eₒₓ0 eV). Such separation was realized through proper combination of an electron-donating indolocarbazole group and a diphenyltriazine electron-accepting moiety. Calculated and measured Eₒₓ were 0. 003 and 0. 02 eV, respectively. A total photoluminescence efficiency of 59%2% with 45%2% from a delayed component and 14%2% from a prompt component was obtained for a doped film. Organic light emitting diodes containing this molecule as an emitting dopant exhibited an unexpectedly high external electroluminescence efficiency of ₄ₐ₄=14%1%.
Sato et al. (Mon,) studied this question.