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Herein, two orange-red emitters, 3,6-bis(9,9-dimethylacridin-10(9H)-yl)-9H-fluoren-9-one (DMAC-FO) and 3,6-di(10H-SP[acridine-9,9′-fluoren]-10-yl)-9H-fluoren-9-one (SPAC-FO), based on fluorenone have been designed and synthesized. As compared to the widely reported benzophenone acceptor, fluorenone has deeper lowest unoccupied molecular orbital (LUMO) because of its more conjugated skeleton and thus it can red-shift the emission maximum. The molecular simulation exhibits both emitters has separated highest occupied molecular orbitals (HOMOs) (@donors) and LUMOs (@acceptor), indicating they could act as thermally activated delayed fluorescence (TADF) materials which are further confirmed by the transient spectra. Consequently, external quantum efficiencies (EQEs) of 10.0% for DMAC-FO and 14.2% for SPAC-FO are achieved in the organic light-emitting diodes (OLEDs). Image 1 • Two orange-red emitters, DMAC-FO and SPAC-FO, based on fluorenone have been designed and synthesized. • TADF properties were realized in DMAC-FO and SPAC-FO due to the highly twisted structure. • High EQEs of 10.0% for DMAC-FO and 14.2% for SPAC-FO were achieved in OLEDs. [ABSTRACT FROM AUTHOR]

Abstract A new sky-blue thermally activated delayed fluorescent (TADF) emitter TRZ-DCF, has been developed based on 2-(9H-carbazol-9-yl)-7,7-dimethyl-5,7-dihydroindeno[2,1- b ]carbazole (DCF) as donor and 2,4-diphenyl-1,3,5-triazine as acceptor. Due to the fusion of fluorene and carbazole moieties into the single carbazole donor, the multimodified emitter exhibits obvious TADF characteristics with a smaller singlet-triplet splitting (Δ E ST) value of 0.22 eV and relatively high photoluminance quantum yield (PLQY) of 84%. As a result, a maximum external quantum efficiency (EQE) of 18.7%, a current efficiency (CE) of 39.0 cd A−1 and a power efficiency (PE) of 30.5 lm W−1 with a Commission Internationale de L' Eclairage (CIE) coordinates of (0.18, 0.34), significantly surpassing the performance of the reference emitter 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (TRTZ), are achieved in optimal device construction. It is found that the EQE roll-off (20.8%) of TRZ-DCF is acceptable, that the efficiency drops to 14.8% at 1000 cd m−2 in optimal device construction. These results demonstrate the multiple modifications of weak electron-donating carbazole donor is an effective way of constructing high-efficiency blue TADF emitters with small roll-off. Graphical abstract Image 1 Highlights • We present a new sky-blue thermally activated delayed fluorescence emitter combining a novel multimodified carbazole donor moiety with triazine-based unit for efficient organic light-emitting diodes. • The external quantum efficiency (18.7%), singlet-triplet splitting (0.22 eV) and photoluminance quantum yield (84%) as well as the roll-off behavior (20.8%) of the emitter TRZ-DCF have been finely tuned through multiple modification of the reference emitter TRTZ. [ABSTRACT FROM AUTHOR]