New 2-phenyl-5-nitropyridyl containing iridium(III) cyclometalated complexes: syntheses, structures, electrochemistry and photophysical properties

A series of new 2-phenyl-5-nitropyridyl containing iridium(III) cyclometalated complexes ([Ir(5-NO2-ppy)(2)Cl](2) (1, 5-NO2-ppy = 2-phenyl-5-nitropyridyl), Ir(5-NO2-ppy)(2)(PPh3)Cl (2, PPh3=triphenylphosphine), Ir(5-NO2-ppy)(2) (pic) (3, pic= picolinic acid)) have been synthesized and unambiguously characterized. The crystal structures of 2 and 3 have been determined by X-ray diffraction analyses. The HOMO-LUMO energy gaps of 1-3 estimated by the cyclic voltammetry (CV) show values in the order of 2 > 3 > 1. The UV-vis absorption and the solid photoluminescence (PL) spectra of 1-3 have also been measured, exhibiting the changing orders being consistent with that of the HOMO-LUMO energy gaps. Moreover, the UV-vis absorption spectra of 1-3 show obvious red-shifts compared with those of the corresponding 2-phenylpyridyl (ppy) containing Ir(III) complexes ([Ir(ppy)(2)Cl](2,) Ir(ppy)(2)(PPh3)Cl and Ir(ppy)(2)(Pic)) in which no strongly electron-withdrawing nitro groups are introduced to the pyridyl rings of the ppy ligands. Thus, the HOMO-LUMO energy gaps of 1-3 should be narrower than those of [Ir (ppy)(2)Cl](2), Ir(ppy)(2)(PPh3)Cl and Ir(ppy)(2)(pic). (C) 2011 Elsevier B.V. All rights reserved.