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

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)]PF6 [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)2bpy]PF6 emits blue light centered at 396 nm, which is blue-shifted compared to [Ir(ppy)2bpy]PF6. 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.