Regulation of Singlet and Triplet Excitons in a Single Emission Layer: Efficient Fluorescent/Phosphorescent Hybrid White Organic Light-Emitting Diodes.

Two efficient fluorescent molecules, viz., ()-2-(2-4-(1-2,3-dihydrobenzo[][1,4]dioxin-5-yl)-4,5-diphenyl--imidazole-2-yl)-[1,1-biphenyl]-4-yl)vinyl-1-yl(naphthalene-1-yl)-1-phenanthro[9,10-]imidazole (DDIBNPPI) and ()-4-(2-(2-(-4'-1(2,3-dihyderobenzo[][1,4]dioxin-5-yl)-4,5-diphenyl-1-imidazole-2-yl)-[1,1'-biphenyl]-4-yl)vinyl)-1-phenanthr[9,10-d]imidazole-1-yl)-1-napthronitrile (DDIBPPIN), were designed and synthesized. DDIBNPPI and DDIBPPIN were obtained by rupturing the covalent bond of phenanthrimidazole core to prevent aggregation-induced quenching. In DDIBPPIN, naphthonitrile group was incorporated into azomethine nitrogen of phenanthrimidazole to enhance charge-transfer ability. The DDIBPPIN/CBP:DDIBPPIN-based device shows blue emission with η (current efficiency) of 4.91/4.10 cd/A, η (power efficiency) of 4.56/3.84 lm/W, and η (external quantum efficiency) of 5.11/5.96%. The η (exciton utilization efficiency) values of DDIPNPPI and DDIBPPIN are of 27.0 and 30.3%, respectively. The DDIPNPPI and DDIBPPIN materials employed as a host to fabricate green and red phosphorescent organic light-emitting diodes. The red/white devices (with 0.4% dopant concentration) with DDIBPPIN:Ir(MDQ)(acac) exhibit maximum of 69889/26319 cd/m, η of 19.6/16.6%, η of 34.6/35.6 cd/A, and η of 35.8/36.6 lm/W. The device with DDIBPPIN:Ir(ppy)/DDIPNPPI:Ir(ppy) exhibits green emission [Commission Internationale de l'Eclairage (0.30,0.60)/(0.30,0.60)] with maximum of 69906/69482 cd/m, η of 17.9/17.0%, η of 59.8/58.6 cd/A, and η of 63.6/61.3 lm/W. The white device using DDIBPPI:Ir(ppy) (with 0.4% dopant concentration) exhibits maximum L of 22152 cd/m, η of 15.8%, η of 31.4 cd/A, and η of 36.1 lm/W.