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., (E)-2-(2-4-(1-2,3-dihydrobenzo­[b]­[1,4]­dioxin-5-yl)-4,5-diphenyl-H-imidazole-2-yl)-[1,1-biphenyl]-4-yl)­vinyl-1-yl­(naphthalene-1-yl)-1H-phenanthro­[9,10-d]­imidazole (DDIBNPPI) and (E)-4-(2-(2-(-4′-1­(2,3-dihyderobenzo­[b]­[1,4]­dioxin-5-yl)-4,5-diphenyl-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)­vinyl)-1H-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 ηc (current efficiency) of 4.91/4.10 cd/A, ηp (power efficiency) of 4.56/3.84 lm/W, and ηex (external quantum efficiency) of 5.11/5.96%. The ηs (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)2(acac) exhibit maximum L of 69889/26319 cd/m2, ηex of 19.6/16.6%, ηc of 34.6/35.6 cd/A, and ηp of 35.8/36.6 lm/W. The device with DDIBPPIN:Ir­(ppy)3/DDIPNPPI:Ir­(ppy)3 exhibits green emission [Commission Internationale de l’Eclairage (0.30,0.60)/(0.30,0.60)] with maximum L of 69906/69482 cd/m2, ηex of 17.9/17.0%, ηc of 59.8/58.6 cd/A, and ηp of 63.6/61.3 lm/W. The white device using DDIBPPI:Ir­(ppy)3 (with 0.4% dopant concentration) exhibits maximum L of 22152 cd/m2, ηex of 15.8%, ηc of 31.4 cd/A, and ηp of 36.1 lm/W.