Spin–orbit coupling analyses of phosphorescence: the effects of cyclometalated ligand replacement in fac-Ir(ppy)3with various bpy ligands on blue phosphorescence

Multi-configuration self-consistent field (MCSCF) calculations followed by second-order configuration interaction (SOCI) and spin–orbit coupling (SOC) calculations were performed using one of the effective core potentials and its associated basis set, the Stevens–Basch–Krauss–Jasien–Cundari (SBKJC) basis set referred to here as SBKJC+p, in order to examine the effects of replacement of a methine group in each phenylpyridine (ppy) ligand of the facial (fac) isomer of tris(2-phenylpyridinato)iridium(III)[fac-Ir(ppy)3] by a nitrogen atom for the purpose of obtaining deep blue phosphorescence. Only replacements of the methine group at the 3′ or 5′ site of each ppy ligand by nitrogen atoms were calculated to induce a spectral shift to the blue region. These results can be explained by the strong electronegativity of nitrogen atoms and by the magnitude of the electron density at the 2′ carbon atom of the ppy or bipyridine (bpy) ligands. Subsequently, the substituent effects in the fac isomer of tris(bipyridinato)iridium(III)[fac-Ir(bpy)3] were investigated and found to be similar to those in fac-Ir(ppy)3 as reported in our previous study (RSC Adv., 2015, 5, 35760–35772). Based on systematic calculations and theoretical consideration, the most effective modification for deep blue phosphorescence should be the introduction of a nitrogen atom into the 3′ or/and 5′ site of benzene rings of the ppy ligands in fac-Ir(ppy)3 together with the combination of the substituents X = F, NR2, or OR (R = alkyl group) and Y = CN or NO2.