Amidate Iridium(III) Bis(2-pyridyl)phenyl Complexes: Application Examples of Amidate Ancillary Ligands in Iridium(III)-Cyclometalated Complexes

The syntheses, structures, and photophysical properties of a series of iridium(III) bis(2-pyridyl)-phenyl complexes, (ppy)(2)Ir(LX) (LX = amide ligands), are described. The complex (ppy)(2)Ir(N-phenylmethacrylamide) (5), bearing an acrylamidate ligand, has been further employed for polymerization to generate the metal-containing homopolymer poly((ppy)(2)Ir(N-phenylmethacrylamide)) (6). In addition, the complexes (ppy)(2)Ir(acetylaniline) (2) and (ppy)(2)Ir(N-phenylbenzamide) (3) have been structurally characterized by X-ray crystallography. It was found that the amidate ligand binds to the Ir center in an imine/alkoxide mode via a four-membered, nearly planar ring (N-Ir-O-C); the limited delocalization is supported by the lengthened C-O bond compared to the C-N bond length in the amidate backbone and no strong absorption around 1650 cm(-1) in the infrared spectra. The photophysical and electrochemical properties of these complexes were then studied. The maximum emission wavelengths ranging from 510 to 548 nm as well as the Delta E-p values varying from 2.55 to 2.77 V can be attributed to the different effects of ancillary amide ligands tolerating different electronic characters. The HOMO and LUMO energy levels and compositions of the iridium complexes were investigated by DFT calculations. The amidate ancillary ligands affect the absorption and emission energies of these complexes by tuning the HOMO energies.