Blue emitting iridium complexes: synthesis, photophysics and phosphorescent devices

Homoleptic Ir(F(n)ppy)(3) and heteroleptic (F(n)ppy)(2)Ir(acac) complexes (n = 3: F(3)ppy = 2-(3',4',6'-trifluorophenyl) pyridine; n = 4: F(4)ppy = 2-(3',4',5',6'-tetrafluorophenyl) pyridine; acac = acetylacetonate) have been synthesized and their spectroscopic properties investigated. The homoleptic complexes exist as two stereoisomers, facial (fac) and meridional (mer), that have been isolated and fully characterized. Their electrochemical and photophysical properties have been studied both in solution and in the solid state and electroluminescent devices have been fabricated. The emissive layers in devices have been obtained mixing the iridium complexes with a PVK [poly(9-vinylcarbazole)] host matrix, in the presence of the electron carrier Bu- PBD [2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole]. The application of a voltage (5.0-6.5 V) between the electrodes of devices leads to electro-generated blue luminescence which has similar energy to the solution emissions. Interestingly, the stability of the devices made with the homoleptic fluorinated iridium complexes strongly depends on the stereochemistry of these phosphors and high (up to 5.5%) external quantum efficiencies for the fac complexes are measured.