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

•Three new 2-phenyl-5-nitropyridyl-containing iridium(III) complexes are presented.•Electron-withdrawing nitro groups are introduced to the pyridyl of ppy.•The crystal structures of the complexes are determined.•Electrochemistry and photophysical properties of the complexes are investigated.•These Ir(III) complexes show narrow HOMO–LUMO energy gaps.

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.

Graphical abstractA series of new iridium(III) complexes [Ir(5-NO2-ppy)2(PPh3)(L)] (5-NO2-ppy = 2-phenyl-5-nitropyridyl, PPh3 = triphenylphosphine, L = NCO−; NCS−; N3−) are presented. The introduction of electron-withdrawing groups to the pyridyl rings of the ppy backbones narrows the HOMO–LUMO energy gaps of the complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide