Improved deep-red phosphorescence in cyclometalated iridium complexes via ancillary ligand modification

In this work, we describe bis-cyclometalated iridium complexes with efficient deep-red luminescence. Two different cyclometalating ((CN)-N-boolean AND) ligands-1-phenylisoquinoline (piq) and 2-(2-pyridyl)benzothiophene (btp)-are used with five strong pi-donating ancillary ligands ((LX)-X-boolean AND) to furnish a suite of nine new complexes with the general formula Ir((CN)-N-boolean AND)(2)((LX)-X-boolean AND). Improvements in deep-red photoluminescence quantum yields were accomplished by the incorporation of sterically encumbering substituents onto the ancillary ligand, which can enhance the radiative rate constant (k(r)) and/or reduce the non-radiative rate constant (k(nr)). Five of the complexes were characterized by X-ray crystallography, and all of them were investigated by in-depth spectroscopic and electrochemical measurements.