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

Abstract

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)2Ir(pic) (1), (DPQ)2Ir(tmd) (2), (DPQ)2Ir(ozl) (3), and (DPQ)2Ir(iml) (4) with different ancillary ligands are explored from both emissive rule and quantum yields, where DPQ is 2,4-diphenylquinoline with a CF3 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-1H-imidazol-2-yl)phenol. Radiative rate constant for phosphorescence (kr) 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 kr are also analyzed to further uncover the crucial factors to affect the kr. While the nonradiative rate constant for phosphorescence (knr) is qualitatively estimated from both temperature-independent nonradiative rate constant (k′nr) and temperature-dependent nonradiative rate constant (knr(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 kr and smaller knr. The variation of ancillary ligand is also an advisable choice to develop red-emitting Ir(III) complex with ideal quantum efficiency.