1,8-Naphthalimide-based hybrids for efficient red thermally activated delayed fluorescence organic light-emitting diodes

Abstract The connection of an electron deficient 1,8-naphthalimide acceptor moiety with a phenoxazine or phenothiazine donor moiety afforded 6-(10H-phenoxazin-10-yl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (PXZ-NAI) and 6-(10H-phenothiazin-10-yl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (PTZ-NAI) as two novel red thermally activated delayed fluorescence (TADF) emitters. The two emitters exhibited distinct TADF characteristics with small energy gaps between the lowest singlet and triplet excited states, which originated from the well-separated highest occupied molecular orbital and lowest unoccupied molecular orbital distributions. The optimized TADF organic light-emitting diodes based on PXZ-NAI and PTZ-NAI offered maximum external quantum efficiencies (EQEs) of 13.0% and 11.4% with maximum power efficiencies of 14.8 and 9.8 lm/W, respectively. Both devices emitted red electroluminescence spectra with peaks at 624 and 632 nm, and Commission Internationale de L'Eclairage coordinates of (0.610, 0.388) and (0.630, 0.368), respectively. These findings demonstrate that the combination of 1,8-naphthalimide with phenoxazine or phenothiazine could be an effective pathway for developing red TADF emitters.