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

Heteroleptic tris-cyclometalated Ir(III) complexes supported by the o -carboranyl–phosphine ligand ( CBP ), (C ∧ N) 2 Ir( 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.