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%.