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

A series of efficient electroluminescent materials with dual carrier transport properties shows enhanced singlet exciton utilization (η(s)) due to small singlet–triplet splitting (ΔE(ST)). 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); η(ex) – 3.01%; η(c) – 2.56 cd A(−1); η(p) – 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); η(ex) – 2.85%; η(c) – 2.01 cd A(−1); η(p) – 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); η(ex) – 19.0%; η(c) – 27.5 cd A(−1); η(p) – 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 39 661 cd m(−2) with excellent EL efficiencies [η(ex) – 19.2%; η(c) – 27.9 cd A(−1); η(p) – 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); η(ex) – 18.5%; η(c) – 25.2 cd A(−1); η(p) – 25.8 lm W(−1); CIE (0.64, 0.34)].