Manipulating the Excited States of Cyclometalated Iridium Complexes with β-Ketoiminate and β-Diketiminate Ligands

A series of cyclometalated iridium complexes with beta-ketoiminate and beta-diketiminate ligands are described. Two different cyclometalating (C boolean AND N) ligands2-phenylpridine (ppy) and 2-phenylbenzothiazole (bt)are used in concert with three different ancillary (LX) ligandsa phenyl-substituted beta-ketoiminate (acNac(Me)), a phenyl-substituted beta-diketiminate (NacNac(Me)), and a fluorinated version of the beta-diketiminate (NacNac(CF3))-to furnish a suite of six complexes. The complexes are prepared by metathesis reactions of chloro-bridged dimers [Ir(C boolean AND N)(2)(mu-Cl)](2) with potassium or lithium salts of the ancillary LX ligand. Four of the complexes are characterized by X-ray crystallography, and all six were subjected to in-depth optical and electrochemical interrogation. Cyclic voltammetry shows both reduction and oxidation waves, with the latter strongly dependent on the identity of the LX ligand. The complexes are all luminescent, with the nature of the emissive excited state and the quantum yield (Phi) dependent on the identity of both the C boolean AND N and LX ligands. Whereas the complexes Ir(ppy)(2)(NacNac(Me)) and Ir(ppy)(2)(acNac(Me)) are weakly luminescent (Phi approximate to 0.01), the complexes Ir(bt)(2)(NacNac(Me)) and Ir(bt)(2)(acNac(Me)) are strongly luminescent, with the latters quantum efficiency (Phi = 0.82) among the highest ever observed for cyclometalated iridium complexes. Fluorination of the NacNac ligand gives rise to completely disparate emission behavior suggestive of a NacNac-centered emissive state. The results described here, in comparison with previous groups studies on acetylacetonate (acac) analogues, suggest that the weaker-field NacNac and acNac ligands raise the energy of the metal-centered HOMO, with energy of the HOMO increasing in the order NacNac(CF3) < acNac(Me) < NacNac(Me).