Fine color-tuning of Ir(iii) tetrazolato complexes: synthesis, photophysical properties and OLED device fabrication

The preparation of a new series of Ir(iii) tetrazolato complexes with the general formula [Ir(C<^>N)2(N<^>N)]0/+, where the ancillary ligand (N<^>N) is represented in turn by 2-pyridyltetrazolato (PTZ-), 2-pyrazinyltetrazolato (PYZ-) or 2-pyridyl 5-trifluoromethyl tetrazolato (PTZ-CF3-), is described herein. The design of the cyclometalated (C<^>N) ligands, namely 2-phenylisonicotinonitrile (ppyCN) and 2-(2,4-difluorophenyl)isonicotinonitrile (F2ppy-CN), features the well-known ppy- or F2ppy core, with the introduction of one electron-withdrawing cyano (-CN) group at the para position of the pyridyl ring. The photophysical and electrochemical properties of the new Ir(iii) cyclometalated complexes have been investigated and the resulting data suggest how the (C<^>N) ligands significantly rule the luminescence behavior of the new complexes. Further blue or red shifting of the emission profiles of the neutral complexes was observed upon their conversion into cationic species through the regioselective addition of a methyl moiety to the coordinated tetrazolato ring. Lastly, neutral [Ir(F2ppy-CN)2(PTZ)] was used as an emissive phosphor for the fabrication of an OLED-type device.