Synthesis and redox properties of cyclometallated iridium (III) complexes modified with arylamino groups

Abstract

We present herein the synthesis, structure, redox and electronic absorption studies of a series of cyclometalated iridium-triarylamine complexes 1−7. For complexes 1-4 where the amine nitrogen is in the meta position to the Ir–CC^N bond, the electronic nature of the triarylamine units is varied by using different substituents (H, Me, OMe and Cl). In order to study the relationship between the connection mode and the intramolecular electron coupling properties, the amine nitrogen is placed in the para position with respect to the Ir–CC^N bond in complexes 5 and 6. And it should be noted that all of these complexes exhibit two well-defined redox processes (N/N•+ and IrIII/IV) within the available potential window at appreciably low potentials. The neutral, one-electron-oxidized states of complexes 3 and 6 were investigated by cyclic voltammetry (CV) and square-wave voltammetry (SWV), UV-vis-NIR spectroelectrochemistry and theoretical calculations. Experimental results show that the above mentioned four different substituents does not have a significant effect on the potential splitting ΔE between the two anodic redox waves of complexes 1-4. But, the ΔE of complex 6 is larger than that of complex 3, indicating that the electron coupling of arylamine and iridium units in the para position (6) is stronger than that in the meta position (3), which is also verified by in-situ absorption spectroelectrochemistry. It is worth noting that the directions of intramolecular charge-transfer in complexes 1 and 5 is reversed due to the different arylamine groups attachment sites (either meta or para to the Ir–CC^N bond).