Polymer based blue electrophosphorescent light emitting devices

A series of bis-orthometalated monocyano Ir(III) complexes, [Ir(ppy)2PX3CN], (X=Oph, Ph and n-bu) were synthesized and the influence of the steric and electronic effects of the phosphine ligand on the photophysical and electrochemical properties of complexes were studied. These cyano phosphine complexes emit light from an admixture of triplet metal-to-ligand charge-transfer (3MLCT) and ligand centered (LC) states in the region of 455-498 nm with a vibronic progression. The trends of the photophysical and electrochemical properties of metal complexes in the series were well understood by the electronic parameter of the phosphine ligands. Polymer light emitting devices were fabricated by doping Ir(ppy)2P(n-bu)3CN in the PVK host and the device performances were investigated. The maximum external quantum efficiency (ηex) was 1.45% for a 10 wt% Ir(ppy)2P(n-bu)3CN doped PVK device. A power efficiency of 0.99 lm/W at 230 cd/m2 and 6 mA/cm2 was obtained. The corresponding chloro complexes of the general formula [Ir(ppy)2PX3Cl] were also synthesized and the optical and device properties were compared with the cyano complexes.