Extreme Tuning of Redox and Optical Properties of Cationic Cyclometalated Iridium(III) Isocyanide Complexes
We report seven heteroleptic cationic iridium(III) complexes with cyclometalating N-arylazoles and alkyl/aryl isocyanides, [((CN)-N-boolean AND)(2)Ir(CNR)(2)](CF3SO3), and characterize two of them by crystal structure analysis. The complexes are air- and moisture-stable white solids that have electronic transitions at very high energy with absorption onset at 320-380 nm. The complexes are difficult to reduce and oxidize; they exhibit irreversible electrochemical processes with peak potentials (against ferrocene) at -2.74 to -2.37 V (reduction) and 0.99-1.56 V (oxidation) and have a large redox gap of 3.49-4.26 V. The reduction potential of the complex is determined by the azole heterocycle (pyrazole or indazole) and by the isocyanide (tert-butyl or 2,6-dimethylphenyl) and the oxidation potential by the Ir-aryl fragment [aryl = 2',4'-R-2-phenyl (R = H/F), 9',9'-dihexy1-2'-fluorenyl]. Three of the complexes exhibit phosphorescence in argon-saturated dichloromethane and acetonitrile solutions at room temperature with 0-0 transitions at 473-478 nm (green color; the emission spectra are solvent-independent), quantum yields of 3-25%, and long excited-state lifetimes of 62-350 mu s. All of the complexes are phosphorescent at 77 K with 0-0 transitions at 387-474 nm (blue to green color). The extremely long calculated radiative lifetimes, 0.5-3.5 ms, confirm that the complexes emit from a cyclometalating-ligand-centered excited state.