Asymmetric [Ir(C₁N₁)(C₂N2)(LX)]-tris-heteroleptic iridium(iii) complexes enable deep blue phosphorescent emission

Three novel blue iridium(iii) complexes, namely Ir(medfppy)(2)(fptz) (Ir-mm), Ir(dfbpy)(medfppy)(fptz) (Ir-dm), and Ir(medfppy)(dfbpy)(fptz) (Ir-md), were prepared and characterized by adopting a new [Ir(C-1<^>N-1)(C-2<^>N-2)(LX)]-tris-heteroleptic Ir(iii) configuration, where C-1<^>N-1 and C-2<^>N-2 denote two different main ligands and LX denotes a third ancillary ligand. These three complexes exhibited exclusively blue emission peaks from 446 to 454 nm, with high photoluminescence quantum yields (PLQYs) of up to 48% and short decay lifetimes ranging from 0.42 to 2.63 mu s in degassed CH2Cl2 solutions. Density function theory (DFT) calculations showed that the resultant asymmetric isomers, Ir-dm and Ir-md, possessed quite different frontier molecular orbitals when the ligand medfppy in the symmetric complex Ir-mm was replaced by the stronger electron-withdrawing ligand dfbpy. Time-dependent DFT (TD-DFT) calculations suggested that the lowest triplet excited states of the isomers were dominated by the hole-particle transitions and the contributions of ligand-centered transitions (LC) were all higher than 78% for the three complexes. Phosphorescent blue OLEDs based on these complexes exhibited the maximum external quantum efficiencies (EQE(max)) of up to 10.2% with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.24). This study presents the creative application of tris-heteroleptic configuration to blue iridium complexes for efficient OLEDs.