Symmetric “Double Spiro” Wide Energy Gap Hosts for Blue Phosphorescent OLED Devices

Wide energy gap materials dispiro[fluorene-9,9′-anthracene-10′,9″-fluorene] (SAS) and dispiro[xanthene-9,9′-anthracene-10′,9″-xanthene] (XAX) containing double spiro–carbons, are introduced as hosts for blue phosphorescent organic light-emitting diodes (PHOLEDs). Both SAS and XAX are free of heteroatomic exocyclic bonds, which are implicated in limiting the stability of blue PHOLEDs. The materials are synthesized in gram-scale quantities through short and efficient paths. They have large energy gaps (≥5.0 eV) between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and correspondingly have high triplet energies in solid state (E_T ≈ 3.0 eV). Analysis of devices using SAS and XAX as host materials with the blue phosphorescent dopant fac-tris(N,N-di-p-tolyl-pyrizinoimidazol-2-yl)iridium(III) (Ir(tpz)₃), shows that charges are transported and trapped by the dopant, which subsequently forms excitons directly on the phosphor. As a result, luminescence quenching pathways are suppressed which leads to blue phosphorescent devices with high (≈18%) external quantum efficiency. Thus, SAS and XAX serve as promising host materials, with high triplet energies suitable for blue PHOLEDs.