Organic luminescent molecule with energetically equivalent singlet and triplet excited states for organic light-emitting diodes.

We demonstrate an organic molecule with an energy gap between its singlet and triplet excited states of almost zero (ΔE(ST) ∼ 0 eV). Such separation was realized through proper combination of an electron-donating indolocarbazole group and a diphenyltriazine electron-accepting moiety. Calculated and measured ΔE(ST) 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 η(EQE) = 14% ± 1%.