Multifunctional Phenanthroimidazole Derivatives to Realize High-Performance Deep-Blue and White Organic Light-Emitting Diodes

Deep blue emitters with high quantum yield, good stability, and multi-functionality are still the key technology for white organic light-emitting diodes (WOLEDs). To address this, two multifunctional deep-blue materials 4-{2-[4'-(1,4,5-triphenyl-4,5-dihydro-1H-imidazol-2-yl)-biphenyl-4-yl]-3a,11b-dihydro-phenanthro[9,10-d]imidazol-1-yl}-benzonitrile (CPD) and 4-(2-{4'-[1-(4-tert-butyl-phenyl)-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl]-biphenyl-4-yl}-3a,11b-dihydro-phenanthro[9,10-d] imidazol-1-yl)-benzonitrile (tCPD) based on phenanthroimidazole units are designed, synthesized, and characterized. Both the materials show high quantum yields and good stabilities. The deep-blue fluorescent devices using CPD and tCPD as emitters show maximum external quantum efficiency (EQE) of 5.80% and 4.71% along with Commission Internationale de I'Eclairage (CIE) coordinates of (0.15, 0.07) and (0.15, 0.09), respectively. Two-color based WOLEDs are demonstrated by doping Ir(MDQ)(2)acac into CPD and tCPD with a low doping concentration, both devices show high EQEs of 16.4% and 16.6% and CIEs of (0.49, 0.34) and (0.48, 0.32), respectively. Furthermore, three-color based fluorescence/phosphorescence-WOLEDs (F/P-WOLEDs), with reasonable exciton management, are fabricated to enhance exciton utilization and improve device performance. CPD-based WOLED shows high efficiencies of 49.4 cd A(-1), 53.5 lm W-1, 19.0%, and CIE coordinate of (0.46, 0.46). With the same structure, tCPD-based device also shows high efficiencies of 40.6 cd A(-1), 47.2 lm W-1, 19.4% along with CIE coordinate of (0.43, 0.45). These results are among the best of reported deep-blue OLEDs and F/P-WOLEDs.