Effect of substituent groups of porphyrins on the electroluminescent properties of porphyrin‐doped OLED devices

Six tetraphenylporphyrins (TRPPH₂) with different horizontal substituents R (R = H, CH₃, OH, F, Cl, Br) were synthesized, and the organic light‐emitting diode (OLED) devices with a general configuration of ITO/TPD/Alq₃:2%TRPPH₂/Alq₃/Al were prepared. The substituted TRPPH₂ was used as the host dopant, 4,4‐bis‐(m‐tolyphenylamino)biphenyl (TPD) was used as a hole‐transporting material, and aluminum tris(8‐quinolinolato) (Alq₃) was used as an electron‐transporting material. The electroluminescent (EL) properties of these devices were studied to understand the light emitting properties of the substituted TRPPH₂. Previous studies have found that the color emitted by the devices was dependent on the TRPPH₂ dye concentration. The electronic effect of the horizontal substituents R of TRPPH₂ influenced the turn‐on voltage, brightness, and power efficiency of the devices. Also, the electroluminescence performance of the porphyrin‐doped OLED devices depended on the effectual overlaps between the emission of electron‐transporting material and the absorption of the dopants. This means that it is possible to evaluate the electroluminescence performance of the porphyrin‐doped OLED devices based on the emission of electron‐transporting material and the absorption of the dopants. Copyright © 2009 John Wiley & Sons, Ltd.