Iridium(III) complexes based on 5-nitro-2-(2′,4′-difluorophenyl)pyridyl: Syntheses, structures and photoluminescence properties

•Ir(III) complexes containing 5-nitro-2-(2′,4′-difluorophenyl)pyridyl are presented.•Crystal structures of two new Ir(III) complexes are determined.•These Ir(III) complexes emit red-orange phosphorescence.•HOMO–LUMO Eg of these complexes are influenced by the substituents of ligand.

A series of cyclometalated Ir(III) complexes [Ir(dFNppy)2(PPh3)L] (PPh3 = triphenylphosphine, L = Cl−, 1; NCS−, 2; NCO−, 3; N3−, 4) in which 5-nitro-2-(2′,4′-difluorophenyl)pyridyl (dFNppy) is used as the main ligand are synthesized and characterized. The crystal structures of 3 and 4 are determined by X-ray diffraction analyses. Photoluminescence spectra of 1–4 in CH2Cl2 solutions at room temperature show the maximum emission wavelengths (λmax) in the range from 586 to 627 nm, corresponding to red-orange luminescence. HOMO–LUMO energy levels of 1–4 are estimated by cyclic voltammetry measurements. Compared with corresponding 2-phenylpyridyl (ppy)-containing Ir(III) complexes having same ancillary ligands, 1–4 have obviously smaller HOMO–LUMO energy gaps (Eg). Simultaneously, 1–4 show relatively bigger Eg compared with 2-phenyl-5-nitropyridyl (5-NO2-ppy)-containing Ir(III) complexes possessing same ancillary ligands. Methods of Eg adjustment are also discussed.

Graphical AbstractCyclometalated Ir(III) complexes containing 5-nitro-2-(2′,4′-difluorophenyl)pyridyl (dFNppy) are presented. Compared with corresponding ppy-containing Ir(III) complexes with same ancillary ligands, these complexes have obviously smaller Eg. Simultaneously, these complexes show relatively bigger Eg compared with 5-NO2-ppy-containing Ir(III) complexes with same ancillary ligands. The influence of nitro group on Eg is much greater than that of fluorine atoms in these complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide