Quantum-chemical studies of homoleptic iridium(III) complexes in OLEDs: fac versus mer isomers

A series of facial fac-[Ir(5-R-bzq)₃] and meridional mer-[Ir(5-R-bzq)₃] Ir(III) complexes bearing benzo[h]quinoline-based ligands have been studied with the help of density functional theory (DFT) methods. A detailed electronic structure comparison of the two isomers has been addressed to point out the differences in their stability and photophysical properties. An influence of substituent impact on optical and electronic properties of Ir(III) homoleptic complexes was also explored by introducing into the cyclometalated ligands substituents characterized with different electronic properties, e.g., R = H, F, OPh, NMe₂, C₆F₅, and p-C₆H₄-NPh₂. The results herein show that fac and mer isomers exhibit remarkable differences in stability and photophysical properties. The introduction of different functional groups into bzq ligands, despite very similar geometrical structures, significantly affected HOMO and LUMO energy levels and energy gaps of the examined Ir(III) complexes.