Blue Phosphorescence of Trifluoromethyl- and Trifluoromethoxy-Substituted Cationic Iridium(III) Isocyanide Complexes

We report the first comprehensive comparative synthetic, structural, electrochemical, and spectroscopic study of an extended series of fluorocarbon-modified iridium­(III) complexes. We prepared seven new cationic Ir­(III) complexes with tert-butyl isocyanide and trifluoromethyl- or trifluoromethoxy-substituted cyclometalating 2-phenylpyridines, [(C∧N)2Ir­(CNtBu)2]­(CF3SO3), and characterized five of them by crystal structure analysis. The redox potentials and photophysical properties of Ir­(III) complexes are determined by the type, position, and number of fluorocarbon groups in the cyclometalating ligand. The complexes exhibit pale blue to yellow-green phosphorescence at room temperature with quantum yields and excited-state lifetimes up to 73% and 84 μs in solution (under argon) and 7.5% and 4.3 μs in neat solid (under air). The structured and solvent-independent phosphorescence spectra, with 0–0 emission transition at 445–467 nm, and the long calculated radiative lifetimes, 43–160 μs, indicate that the complexes emit from a cyclometalating-ligand-centered triplet excited state. Bulky fluorocarbon groups prevent intermolecular interaction (aggregation) of the complexes, thereby minimizing red-shift of phosphorescence color in going from solution to neat solid.