Theoretical studies on structures and spectroscopic properties of a series of novel mixed-ligand Ir(III) complexes [Ir(Mebib)(ppy)X]

The series of novel mixed-ligand iridium(III) complexes Ir(Mebib)(ppy)X (Mebib = bis(N-methylbenzimidazolyl) benzene and ppy = phenylpyridine; X = Cl, 1; X = -C equivalent to CH, 2; X = CN, 3) have been investigated theoretically to explore their electronic structures and spectroscopic properties. The ground and excited state geometries have been fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agree well with the corresponding experimental results. The HOMO of 1 and 3 are mainly localized on the Ir atom, Mebib, and ppy ligand, but that of 2 has significant X ligand composition. Absorptions and phosphorescences in CH2Cl2 media have been calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest lying absorptions of 1 and 3 at 444 and 416 nm are attributed to a {[d(yz)(Ir) + pi(Mebib) + pi(ppy)]->[pi*(Mebib)]} transition with metal-to-ligand, ligand-to-ligand, and intra-ligand charge transfer (MLCT/LLCT/ILCT) character, whereas that of 2 at 458 nm is related to a {[d(yz)(Ir) + pi(Mebib) + pi(ppy) + pi(C equivalent to CH)]->[pi*(Mebib)]} transition with MLCT/LLCT/ILCT and X ligand-to-ligand charge transfer (XLCT) transition character. The phosphorescence of 1 and 3 at 565 and 543 nm originates from the (3){[d(yz)(Ir) + pi(Mebib) + pi(ppy)] [pi*(Mebib)]} excited state, while that of 2 at 576 nm originates from the (3){[d(yz)(Ir) + pi(Mebib) + pi( ppy) + pi(C equivalent to CH)] [pi*(Mebib)]} excited state. The calculation results show that the absorption and emission transition character can be changed by altering the p electron- withdrawing ability of the X ligand and the phosphorescent color can be tuned by adjusting the X ligand.