New blue (DBA-SAB) and deep-blue (TDBA-SAF) thermally activated delayed fluorescence (TADF) emitters are synthesized for blue-emitting organic-light emitting diodes (OLEDs) by incorporating spiro-biacridine and spiro-acridine fluorene donor units with an oxygen-bridged boron acceptor unit, respectively . The molecules show blue and deep-blue emission because of the deep highest occupied molecular energy levels of the donor units . Besides, both emitters exhibit narrow emission spectra with the full-width at half maximum (FWHM) of less than 65 nm due to the rigid donor and acceptor units . In addition, the long molecular structure along the transition dipole moment direction results in a high horizontal emitting dipole ratio over 80% . By combining the effects, the OLED utilizing DBA-SAB as the emitter exhibits a maximum external quantum efficiency (EQE) of 25.7% and 1931 Commission Internationale de l'éclairage (CIE) coordinates of (0.144 , 0.212). Even a higher efficiency deep blue TADF OLED with a maximum EQE of 28.2% and CIE coordinates of (0.142 , 0.090) is realized using TDBA-SAF as the emitter.