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

A series of cyclometalated Ir(III) complexes [Ir(dFNppy)2(PPh3)L] (PPh3 = triphenylphosphine, L = Cl-, 1; NCS-, 2; NCO-, 3; 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 (kna,c) in the range from 586 to 627 nm, corresponding to red-orange luminescence. HOMO-LUMO energy levels of 1-4 are estimated by cydic voltamrnetry measurements. Compared with corresponding 2-phenylpyridyl (ppy)-containing Ir(III) complexes having same ancillaryligands, 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(I11) complexes possessing same ancillary ligands. Methods of Eg adjustment are also discussed. (C) 2015 Elsevier B.V. All rights reserved.