We have developed new blue-phosphorescent iridium complexes based on 2-phenylpyridine derivatives with pertinent substituents and an ancillary ligand to accomplish selective tuning of the HOMO and LUMO levels toward high energy gap: A polymer light-emitting device doped with the blue phosphor was fabricated to show blue emission.

A series of cyclometalated iridium complexes with a strong electron-donating and bulky diphenylamino group was prepared and the phosphorescence wavelengths were found to be greatly dependent on the substituent positions: some of them afforded high performance electroluminescence (EL) devices.

A series of phosphorescent cyclometalated iridium(III) complexes 4-6 with new ligands of bicyclic phenylvinylpyridines have been synthesized and systematically examined for their photophysical, electrochemical and electroluminescence (EL) properties. All of the bis-and tris-cyclometalated complexes could be characterized by 1 H-NMR, elemental analysis and X-ray crystal structure analysis. The phosphorescence colour of the complexes in solution, the solid state and polymer film is unusually changed depending on the structure of the ligand. EL devices using the complexes exhibited external quantum efficiencies (EQE) of 1.2-8.1% at 100 cd m 22 , and EL colour tuning in the range of 571-635 nm was achieved analogous to PL properties of the phosphors. X-Ray analyses of complexes 4a-c demonstrated that the degree of steric hindrance increases with an increase of the cycloalkane ring size, leading to hypsochromic shifts of emission by the distortion of the phenyl groups. X-Ray analyses also suggested that long iridium-carbon bonds are unfavorable for efficient electroluminescence. In addition, we have found a unique and important aspect for the study of EL devices: the EL devices based on complexes 4c, 6a show moderate EL efficiencies (EQE = 4.0 and 6.1%) although these complexes have no emission in solution at room temperature, indicating that the PL properties of the complexes in solution are not directly related to the EL efficiencies.

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TANAKA*, S.; OGUMA, Y.; TANAKA, Y.; ECHIZEN, H.; MASU, H.; YAMAGUCHI, K.; KISHIKAWA, K.; KOHMOTO, S.; YAMAMOTO, M.; Tetrahedron 64 (2008) 7, 1388-1396; Dep. Appl. Chem. Biotechnol., Fac. Eng., Chiba Univ., Inage, Chiba 263, Japan; Eng.) -Bartels 35-054