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 π donor Cl− with strong σ donors and π acceptors, lead to three new iridium(III) cyclometalated complexes [Ir(5-NO2-ppy)2(PPh3)(L)] (L = NCO−, 2; NCS−, 3; N3−, 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.