Studies of the 5‘-Substituted Phenylisoquinoline-Based Iridium Complexes Using Density Functional Theory

To examine the effects of coordination sites and the nature of ligands reported for color-tuning of a
few cyclometalated Ir(III) complexes, a series of 3‘-substituted (F, CH3, OCH3, and CF3) phenylisoquinoline
(piq) ligands were synthesized and successfully used to prepare iridium complexes, including bis[1-(5‘-methyl)phenylisoquinolinato-N,C2‘]iridium(III) (acetylacetonate) (6a1), bis[1-(5‘-trifluoromethyl)phenylisoquinolinato-N,C2‘]iridium(III) (acetylacetonate) (6a2), bis[1-(5‘-methoxy)phenylisoquinolinato-N,C2‘]iridium(III) (acetylacetonate) (6a3), and bis[1-(5‘-fluoro)phenylisoquinolinato-N,C2‘]iridium(III) (acetylacetonate) (6a4). Density functional theory results indicate that two conflicting effects, electronic and
steric, can be applied to account for the substitution-sensitive coordination sites of piq:  the methoxyl- or
fluoro-substituted ligand generates both 2‘-coordinated and 6‘-coordinated isomers. Coordination of
methoxy substitution prefers 6‘-coordination of piq dominated by steric effects, while coordination of
fluoro substitution prefers 2‘-coordination, arising from better back-donation of the iridium center.
Correlations of HOMO−LUMO gaps with electroluminescence (EL) data are discussed. More importantly,
the EL data are well predicted by time-dependent density functional theory calculations.