Bis(diphenyltriazine) as a new acceptor of efficient thermally activated delayed fluorescent emitters

Two isomeric thermally activated delayed fluorescent (TADF) emitters, 9,9'-(2,5-bis(4,6-diphenyl-1,3,5-triazin-2-yl)-1,4-phenylene)bis(9H-carbazole) (p2Cz2Trz) and 9,9'-(4,6-bis(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9H-carbazole) (m2Cz2Trz), were synthesized using bis(diphenyltriazine) as a new strong acceptor of the TADF emitters. The m2Cz2Trz showed smaller singlet-triplet energy gap (0.09 eV) and higher photoluminescence quantum yield (0.95) than p2Cz2Trz. As a result, the TADF devices fabricated using the m2Cz2Trz emitter exhibited high external quantum efficiency of 18.5% and small efficiency roll-off, suggesting the potential of bis(diphenyltriazine) as a new acceptor.