o-Carboranyl–Phosphine as a New Class of Strong-Field Ancillary Ligand in Cyclometalated Iridium(III) Complexes: Toward Blue Phosphorescence

Abstract

Heteroleptic tris-cyclometalated Ir(III) complexes supported by the o-carboranyl–phosphine ligand (CBP), (C∧N)2Ir(CBP) (C∧N = ppy (1), dfppy (2)), have been synthesized and characterized. The PL spectra of 1 and 2 displayed substantially blue shifted phosphorescence relative to the corresponding Ir(C∧N)3 complexes. Electrochemical and theoretical studies showed that the CBP ligand functioned as a strong-field ancillary ligand, and the greater HOMO stabilization in comparison to that of the LUMO by the CBP ligand was responsible for the increase in band gap, leading to a large blue shift in phosphorescence.