Synthesis, structure, and photophysical and electrochemical properties of cyclometallated iridium(III) complexes with phenylated bipyridine ligands

A series of cationic diiminoiridium(III) complexes [Ir(ppyN,C)(2)(L-N,N)](PF(6)) has been prepared [Hppy = 2-phenylpyridine; L = 4,4'-tBu(2)dpbpy (1), 4,4'-Me(2)dpbpy (2), 4,4'Me(2)pbpy (3), 4,4'-Me(2)bpy (4)] and their photophysical and electrochemical properties studied. X-ray diffraction studies of complex 1 reveal a dihedral angle of about 33degrees between the pyridine rings, and that the two phenyl groups are also tilted with respect to the adjacent pyridine rings. All the complexes exhibit moderately intense and long-lived emission. The origin of the emission is tentatively assigned to a triplet metal-to-ligand charge-transfer (3)MLCT [dpi(Ir) --> pi(*)(diimine)] excited state, although the possibility of a triplet sigma-bond-to-ligand charge transfer (3)SBLCT [sigma(Ir-C) --> pi(*)(diimme)] cannot be excluded. The luminescence properties of the complexes are dependent on the substituents on the diimine ligands. Selective N-methylation of the diimine ligands has been achieved and their N,C-coordination to the Ir centre has been attempted. (C) Wiley-VCH Verlag GmbH Co.