Computational insights into the photophysical and electroluminescence properties of homoleptic fac-Ir(C^N)3 complexes employing different phenyl-derivative-featuring phenylimidazole-based ligands for promising phosphors in OLEDs.

The electronic structures and photophysical properties of three homoleptic iridium(iii) complexes IrL3 with C^N ligands, including 2a (L = 1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole), 5a (L = 1-(2,6-dimethylphenyl)-2-phenyl-1H-imidazole), and 6a (L = 1-(3,5-diisopropylbiphenyl-4-yl)-2-phenyl-1H-imidazole), are investigated by means of the density functional method. Furthermore, seven new complexes are theoretically designed, including 1a (L = 1,2-diphenyl-1H-imidazole), 3a (L = 1-(2,6-dimethoxyphenyl)-2-phenyl-1H-imidazol), 4a (L = 2-(2-phenyl-1H-imidazol-1-yl)isophthalaldehyde), 1b (L = 2-(biphenyl-3-yl)-1H-imidazole), 2b (L = 2-(2',6'-diisopropylbiphenyl-3-yl)-1H-imidazole), 3b (L = 2-(2',6'-dimethoxybiphenyl-3-yl)-1H-imidazole), and 4b (L = 3'-(1H-imidazol-2-yl)biphenyl-2,6-dicarbaldehyde), to explore the influence of different substituents and different substituted positions on the electronic structures, phosphorescence properties, and organic light-emitting diode (OLED) performance. The HOMO-LUMO energy gap is greatly decreased by introduction of the -CHO group into the phenyl ring (4a and 4b see -sketched structures for all the investigated Ir(iii) complexes). As a result, their absorption and emission spectra present red-shifting leading them to be potential red-emitting phosphors. Other complexes are all blue-emitting materials, indicating that the effect of the substituted position on the emitting color is negligible. However, the addition of the substituent on the para-position of the phenyl ring in the phenylimidazole ligand would increase the quantum yield and electroluminescence (EL) performance compared with that on the imidazole ring.