Photoluminescence and Electroluminescence of d6 Metal−Organic Conjugated Oligomers:  Correlation of Photophysics and Device Performance

• Published in: The journal of physical chemistry. B 2003-11, Vol.107 (46), p.12569-12572
• Main Authors: Cunningham, Garry B, Li, Yiting, Liu, Shengxia, Schanze, Kirk S
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp0358228

The photophysical and electroluminescent device properties of a series of d6 transition metal complexes that feature an oligo(aryleneethynylene) (OAE) “ligand” have been investigated. The metals are coordinated η2- to the OAE via a 2,2‘-bipyridine moiety that is in the “core” of the oligomer, and the metals used are η2-Ir(ppy)2 +, η2-Ru(bpy)2 2+, and η2-Os(bpy)2 2+ (Ir-2, Ru-2, and Os-2, respectively, where ppy = 2-phenylpyridine and bpy = 2,2‘-bipyridine). The photoluminescence spectra and excited-state decay parameters for the metal−OAEs indicate that at ambient temperature Ru-2 and Os-2 feature a lowest 3MLCT excited state; however, in Ir-2 the lowest excited state is 3π,π* localized on the OAE. Electroluminescent (EL) devices that contain the metal−OAEs dispersed at 5 wt % in a poly(vinyl carbazole):2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole matrix exhibit electroluminescence at wavelengths that correlate well with the photoluminescence from the complexes in a rigid glass at low temperature. The EL efficiency of the devices varies in the order Ir-2 > Ru-2 ≫ Os-2. Factors that may contribute to the difference in EL efficiencies are discussed.