TDBA–Ac is a multiple-resonance thermally activated delayed fluorescence (MR-TADF) deep-blue emitter featuring a small singlet–triplet energy gap (ΔEST) of 0.06 eV and a short delayed fluorescence lifetime (τd) of 900 ns. TDBA–Ac has a rigid oxygen-bridged cyclized triarylboron-based core unit, 2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (TDBA) and an electron-donating 9,9-dimethyl-9,10-dihydroacridine moiety attached to the TDBA core. TDBA is known as a good acceptor for its suitable triplet energy level, good electron transport ability, and rigid planar geometrical configuration enabling low energy loss of excitons and excellent color purity because of its narrow full-width at half-maximum (FWHM) emission.
20 wt.%-doped film of TDBA–Ac in DBFPO host shows high photoluminescence quantum yield (PLQY) of 93%. TADF-OLED device based on TDBA–Ac dopant exhibits a high external quantum efficiency of 21.50% with deep-blue colour coordinates of (0.15, 0.06).