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 (C^N) ligands-1-phenylisoquinoline (piq) and 2-(2-pyridyl)benzothiophene (btp)-are used with five strong π-donating ancillary ligands (L^X) to furnish a suite of nine new complexes with the general formula Ir(C^N)2(L^X). 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 (kr) and/or reduce the non-radiative rate constant (knr). Five of the complexes were characterized by X-ray crystallography, and all of them were investigated by in-depth spectroscopic and electrochemical measurements.