Efficient electroluminescent hybridized local and charge-transfer host materials with small singlet-triplet splitting to enhance exciton utilization efficiency: Excited state transition configuration

Abstract

A series of efficient electroluminescent materials with dual carrier transport properties shows enhanced singlet exciton utilization (ηs) due to small singlet-triplet splitting (ΔEST). The strong orbital-coupling transitions of N-(4-(1-(1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-4,5-diphenyl-1H-imidazol-2-yl)naphthalen-4-yl)phenyl)-N-phenyl benzenamine (DDPB) exhibit deep blue emission at 435 nm (CIEy, 0.07) with an external quantum efficiency of 2.01%. The electroluminescent efficiencies of 2-(1-(9H-carbazol-9-yl)naphthalen-4-yl)-1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-1H-phenanthro[9,10-d]imidazole (CDDPI) (L-3992 cd m-2; ηex-3.01%; ηc-2.56 cd A-1; ηp-2.12 lm W-1) are higher than those of the N-(4-(1-(1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-H-phenanthro[9,10-d]imidazole-2-yl)naphthalen-4-yl)phenyl)-N-phenylbenzenamine (DBDPA) based device (L-3015 cd m-2; ηex-2.85%; ηc-2.01 cd A-1; ηp-1.92 lm W-1). The blue emissive materials CDDPI and DBDPA are used as a host to construct green and red phosphorescent OLEDs: the green device based on CDDPI:Ir(ppy)3 exhibits higher efficiencies (L-8812 cd m-2; ηex-19.0%; ηc-27.5 cd A-1; ηp-33.0 lm W-1) at 2.7 V and the red device based on CDDPI:Ir(MQ)2(acac) exhibits a maximum luminance of 39661 cd m-2 with excellent EL efficiencies [ηex-19.2%; ηc-27.9 cd A-1; ηp-29.2 lm W-1; CIE (0.64, 0.34)] compared with those of the DBDPA:Ir(MQ)2(acac) based device [L-37 621 cd m-2; ηex-18.5%; ηc-25.2 cd A-1; ηp-25.8 lm W-1; CIE (0.64, 0.34)].