Deep-blue light–emitting cationic iridium(III) complexes featuring diamine ancillary ligands: Experimental and theoretical investigations.

[Display omitted] • Increasing the nitrogen content of the cyclometallated ligands lower the energy of the highest occupied molecular orbital, which was achieved by introducing 2,4′-bpy moieties. • Decreasing the electron donating ability of the ancillary ligand raise the energy of the lowest unoccupied molecular orbital, which was achieved by introducing diamine ligands. • Combining both approaches produced unexpected deep-blue emission at wavelengths shorter than 400 nm, which, to the best of the author's knowledge, has never been reported. Deep-blue emitters based on combining two approaches are reported here. In the first approach, the nitrogen content of the cyclometallated ligand is increased using 2,4′-bpy ligands, leading to a low highest occupied molecular orbital energy. In the second approach, 2,2′-bpy is replaced with a lower electron donating ligand, leading to a high lowest unoccupied molecular orbital (LUMO) energy. Thus, three new ionic transition metal complexes of [Ir(2,4′-bpy) 2 (NN)]PF 6 [where NN is 2,2′-bpy (1), o -phenylenediamine (2), and 4-methoxy- o -phenylenediamine (3)] were synthesized, and their electronic and photophysical features were studied. In solution, [Ir(2,4′-bpy) 2 bpy]PF 6 emits blue light centered at 396 nm, which is blue-shifted compared to [Ir(ppy) 2 bpy]PF 6. The low electron donation of the diamine ancillary ligands introduces the contribution of the cyclometallated ligand to the LUMO, changing the nature of the emission and leading to different photophysical features. Density functional theory calculations indicate the long bond distances of Ir–Ns at the diamine ligands, suggesting weak metal–ligand interactions and low quantum yields. 1 1 DFT Density functional theory, ECP Effective core potential, FMO Frontier molecular orbitals, HOMO Highest occupied molecular orbital, LEEC Light-emitting electrochemical cells, LUMO Lowest unoccupied molecular orbital, NMR Nuclear magnetic resonance, OLED Organic light-emitting diodes, SCF Self-consistent-field, ILCT Interligand charge transfer, LLCT Ligand to ligand charge transfer, PLQY Photoluminescence quantum yield. [ABSTRACT FROM AUTHOR]