To design high efficient red-emitting iridium complexes by variation of ancillary ligand: Emissive rule and quantum yield.

The scarcity of high efficient red-emitting phosphorescent emitters, especially for deeply red emitter, has become the major road stone to block the further development of organic light-emitting diodes. Most of studies have been devoted to developing new Ir(III) complexes by variation of primary ligands. The ancillary ligand has attracted less attention. Four Ir(III) complexes, (DPQ) 2 Ir(pic) ( 1 ), (DPQ) 2 Ir(tmd) ( 2 ), (DPQ) 2 Ir(ozl) ( 3 ), and (DPQ) 2 Ir(iml) ( 4 ) with different ancillary ligands are explored from both emissive rule and quantum yields, where DPQ is 2,4-diphenylquinoline with a CF 3 group at meta position of the phenyl ring, pic is picolinate, tmd is 2,2,6,6-tetramethylheptane-3,5-diketonate, ozl is 2-(4,5-dihydrooxazol-2-yl)phenol, and iml is 2-(1-ethyl-4,5-dihydro-1 H -imidazol-2-yl)phenol. Radiative rate constant for phosphorescence ( k r ) is calculated by quadratic response time-dependent density functional theory (QR-TDDFT). The transition dipole moment, spin-orbit coupling matrix element, and singlet-triplet splitting energy related with the k r are also analyzed to further uncover the crucial factors to affect the k r . While the nonradiative rate constant for phosphorescence ( k nr ) is qualitatively estimated from both temperature-independent nonradiative rate constant ( k ′ nr ) and temperature-dependent nonradiative rate constant ( k nr (T)) viewpoints. The emissive wavelength of new designed Ir(III) complex 4 locates in the deeply red region. Moreover, it has the larger quantum yield because of both larger k r and smaller k nr . The variation of ancillary ligand is also an advisable choice to develop red-emitting Ir(III) complex with ideal quantum efficiency. [ABSTRACT FROM AUTHOR]