Towards an efficient blue emission cationic Ir() complex with azole-type ancillary ligands: a joint theoretical and experimental study

Pyridine-azole moieties have proved to be an attractive building block for multifunctional cationic Ir( iii ) complexes, however, few highly efficient blue materials have been demonstrated and the deep structure-property relationships need to be revealed. Herein, a series of cationic [Ir(dfppz) 2 (N ∧ N)][PF 6 ] complexes ( 1-4 ) based on azole-type ancillary ligands, namely, 1,1′-diphenyl-1 H ,1′ H -[2,2′]biimidazolyl (Phbid), 2-(1-phenyl-1 H -imidazol-2-yl)-pyridine (Bpyim), 2-(1-methyl-1 H -imidazol-2-yl)pyridine (Mpyim), and 2-(1,5-dimethyl-1 H -[1,2,4]triazole-3-yl)pyridine (Mpytz), respectively, have been prepared, and their photophysical, electrochemical and charge transporting properties are investigated. The reported complexes exhibit strong perceived green to blue emission as well as excellent redox reversibility at room temperature. Comprehensive density functional theory calculations are performed to provide insight into the electronic structures of 1-4 and disclose the ancillary ligand effect on the emission behavior in detail. The simple methyl group modification endows the triazole-type ancillary with an exceedingly large π-π* energy gap, resulting in the blue emitting complex 4 , namely [Ir(dfppz) 2 (Mpytz)][PF 6 ] with a peak value at 462 nm. Meanwhile, despite the significant 3 LC character, the high efficiency with a quantum yield of 31.6% of 4 is realized in neat film, which is higher than those of reported cationic Ir( iii ) complexes with similar emissions. Additionally, the calculation results also suggest that complexes 2-4 possess better electron-transporting abilities in comparison to those of 1 . A highly efficient blue emitting cationic Ir( iii ) complex based on 1,2,4-triazole-pyridine ligands modified by a simple methyl moiety is reported.