Evidence for strong mixing between the LC and MLCT excited states in some heteroleptic iridium(III) complexes

J Fluoresc. 2011 Jul;21(4):1585-97. doi: 10.1007/s10895-011-0847-x. Epub 2011 Jan 28.

Abstract

The synthesis, structure and photophysical properties of series of new luminescent cyclometalated Iridium (III) complexes are reported. The cyclometalated ligand used here is 2-aryl imidazole and the auxiliary ligand is acetyl acetone (acac). The crystal structure of the complex (dmdpi)(2)Ir(acac) (5) show that the Iridium(III) ion resides in a distorted octahedral environment. All complexes exhibit bright photoluminescence (PL) at room temperature and (fpdmdmpi)(2)Ir(acac) 4 has a high solution PL quantum efficiency of 0.56. The role played by electron releasing and electron withdrawing substituents of the 2-arylimidazole ligands towards the stability of HOMO and how the substituent influences the luminescent behaviour are discussed. Furthermore those substituents have effect on the contribution to mixing between (3)(π-π*) and (3)(MLCT) for the lowest excited states.