Highly efficient blue thermally activated delayed fluorescence emitters based on symmetrical and rigid oxygen-bridged boron acceptors

Materials that exhibit thermally activated delayed fluorescence are promising for the realization of efficient organic light-emitting diodes. However, finding suitable deep-blue thermally activated delayed fluorescence materials is still challenging. Here, we report two highly efficient deep-blue thermally activated delayed fluorescence emitters, TDBA-Ac and TDBA-DI, containing oxygen-bridged, symmetric and rigid boron acceptor moieties. Both emitters have been designed to have high photoluminescence quantum yield and narrow-band blue emission. TDBA-Ac and TDBA-DI exhibited deep-blue emission and a small singlet-triplet energy gap of 0.06 eV and 0.11 eV, respectively, in toluene. The 20wt%-doped films of TDBA-Ac and TDBA-DI in DBFPO host exhibited high photoluminescence quantum yields of 93% and 99%, respectively. The fabricated TDBA-DI device showed an extremely high external quantum efficiency of 38.15 +/- 0.42% in the blue region with low roll-off characteristics of 25.2% at high luminance of up to 5,000 cd m(-2). The TDBA-Ac-doped device exhibited a high external quantum efficiency of 21.50 +/- 0.22% with deep-blue colour coordinates of (0.15, 0.06).