Syntheses, structures and properties of cyclometalated iridium(III) complexes based on 2-phenyl-5-nitropyridyl and different strong-field ancillary ligands

The reactions of [Ir(5-NO2-ppy)(2)(PPh3)Cl] (5-NO2-ppy = 2-phenyl-5-nitropyridyl, PPh3 = triphenylphosphine, 1) with pseudohalides, replacing the weak pi donor Cl with strong sigma donors and pi acceptors, lead to three new iridium(III) cyclometalated complexes [Ir(5-NO2-ppy)(2)(PPh3)(L)] (L = NCO , 2; NCS , 3; N-3 , 4) based on 2-phenylpyridyl (ppy) derivative, PPh3 and different pseudohalogen strong-field ancillary ligands. 2-4 are unambiguously characterized and their crystal structures are also determined by X-ray crystallography. The HOMO-LUMO electronic energy gaps of 1-4 estimated from the cyclic voltammetry measurements are comparable with those calculated from the UV-Vis absorption spectra, which are both in the order of 3 > 1 > 2 > 4. Furthermore, the electrochemical and photophysical properties of 1-4 show that the introduction of the electron-withdrawing nitro group to the pyridyl ring of the ppy backbone narrows the HOMO-LUMO electronic energy gaps, compared with those of corresponding ppy-containing iridium(III) complexes. (C) 2013 Elsevier B.V. All rights reserved.