Deep blue diboron embedded multi-resonance thermally activated delayed fluorescence emitters for narrowband organic light emitting diodes

We report three deep blue multiple resonant TADF emitters, m-ν-DABNA, 4F-ν-DABNA, and 4F-m-ν-DABNA by incorporating methyl groups and fluorine atoms in diboron based ν-DABNA core. The introduction of methyl groups at para positions to the boron atoms and fluorine atoms at ortho positions to the nitrogen atoms resulted in bandgap enhancement by electron donating and electron withdawing effects. All three emitters exhibit pure blue emissions with high photoluminescence quantum yield around ∼ 90%, small ΔEST (≤0.07 eV) values, and fast reverse intersystem crossing rate (kRISC). Fabricated OLEDs with these emitters show excellent external quantum efficiency over 33%. Among three materials, 4F-ν-DABNA and 4F-m-ν-DABNA exhibit the CIE y coordinate of 0.08 and 0.06, respectively. Our current material design approach guides a path for the development of deep blue TADF emitters for highly efficient narrowband OLEDs.