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 (Delta E-ST similar to 0 eV). Such separation was realized through proper combination of an electron-donating indolocarbazole group and a diphenyltriazine electron-accepting moiety. Calculated and measured Delta E-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 eta(EQE) = 14% +/- 1%.