Efficient deep-blue organic light-emitting diodes: Arylamine-substituted oligofluorenes

Novel deep-blue-light-emitting diphenylamino and triphenylamino end-capped oligofluorenes were synthesized by double palladium-catalyzed Suzuki cross-coupling of dibromo-oligofluorene with the corresponding boronic acid as a key step. These oligofluorenes exhibit deep-blue emission (λ _max^em = 429-432 nm), low and reversible electrochemical oxidation (highest occupied molecular orbital = 5.15-5.20 eV), high fluorescence quantum yield (Φ_FL=0.61-0.93), and good thermal properties (glass-transition temperature, T_g = 99-195°C and decomposition temperature, T_dec > 450°C). Remarkably, saturated deep-blue organic light-emitting diodes, made from these oligofluorenes as dopant emitters, have been achieved with excellent performance and maximum efficiencies up to 2.9 cd A^-1 at 2 mAcm^-2 (external quantum efficiency of 4.1 %) and with Commission Internationale de l'Éclairage (x,y) coordinates of (0.152,0.08), which is very close to the National Television System Committee standard blue.