Synthesis of High-Triplet-Energy Host Polymer for Blue and White Electrophosphorescent Light-Emitting Diodes

A high-triplet-energy host polymer consisting of 9-(4-(bis(9-(2-ethylhexyl)-9H-carbazol-3-yl)methyl)phenyl)-9H-carbazole and tetraphenylsilane units was designed and synthesized. The triplet energy (2.67 eV) is one of the highest values reported for conjugated polymer hosts. Suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of -5.61 and -2.24 eV, respectively, were also observed. Blue phosphorescent polymers were obtained by introducing bis[2-(4,6-difluorophenyl)pyridinato-N,C-2']iridium(III) picolinate (FIrpic) into the host polymer while white phosphorescent polymers were synthesized by introducing red emissive bis[2-phenylquinoline-N,C-2']iridium(III) picolinate ((Phq)(2)Irpic) into the blue phosphorescent one. Polymer light-emitting devices with the configuration ITO/PEDOT:PSS/PVK/EML/TSPO1/LiF/Al [ITO, indium tin oxide; PEDOT, poly(3,4-ethylenedioxythiophene); PSS, poly(styrenesulfonic acid); PVK, poly(N-vinylcarbazole); EML, the emitting layer was composed of polymer or polymer and 1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7) in a doping ratio of 2:1); TSPO1, diphenylphosphine oxide-4-(triphenylsilyl)pheny] were subsequently fabricated. Efficient energy transfer from the host polymer to the blue and red iridium(III) complexes was observed owing to the high triplet energy of the host. One of the fabricated blue phosphorescent devices had a maximum luminous efficiency of 3.57 cd/A.