Symmetric “Double Spiro” Wide Energy Gap Hosts for Blue Phosphorescent OLED Devices
Jie Ma, Muazzam Idris, Tian Y. Li, Daniel Sylvinson Muthiah Ravinson, Tyler Fleetham, Jongchan Kim, Peter I. Djurovich, Stephen R. Forrest, Mark E. Thompson
Abstract
Abstract 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.