New Class of Hole-Blocking Amorphous Molecular Materials and Their Application in Blue-Violet-Emitting Fluorescent and Green-Emitting Phosphorescent Organic Electroluminescent Devices

A new class of hole-blocking amorphous molecular materials for use in organic electroluminescent (EL) devices have been developed, which include 1,3,5-tri(4-biphenylyl)benzene, 1,3,5-tris(4-fluorobiphenyl-4‘-yl)benzene (F-TBB), 1,3,5-tris(9,9-dimethylfluoren-2-yl)benzene, and 1,3,5-tris[4-(9,9-dimethylfluoren-2-yl)phenyl]benzene. They readily form stable amorphous glasses with well-defined glass-transition temperatures and are characterized by relatively high oxidation potentials and large HOMO−LUMO energy gaps. The use of these materials as hole blockers enabled blue-violet emission from several emitting amorphous molecular materials with hole-transporting properties in organic EL devices. A multilayer organic EL device using N, N -bis(9,9-dimethylfluoren-2-yl)aniline (F 2 PA) as a blue-violet emitter, F-TBB as a hole blocker, and 4,4‘,4‘ ‘-tris[3-methylphenyl(phenyl)amino]triphenylamine and tris(8-quinolinolato)aluminum as hole and electron transporters, respectively, exhibited blue-violet emission peaking at 405 nm with a high external quantum efficiency of 1.95%. This device also enabled the doping of a phosphorescent iridium complex, tris(2-phenylpyridine)iridium (Ir(ppy) 3 ), tuning the emission color from blue violet to green by excitation energy transfer from F 2 PA to Ir(ppy) 3 .