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

Abstract

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.