Tuning the Photophysical Properties of Homoleptic Tris-Cyclometalated Ir(III) Complexes by Facile Modification of the Imidazo-Phenanthridine and Their Application to Phosphorescent Organic Light-Emitting Diodes.

ABSTRACT: To explore the excited-state electronic structure of the blue-emitting Ir(dmp)₃ dopant material (dmp = 3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridine), which is notable for durable blue phosphorescent organic light-emitting diode (PhOLED), a series of homoleptic dmp-based Ir(III) complexes (DMP-R, tris[3-(2,6-dimethylphenyl)-7-R-imidazo[1,2-f]phenanthridin-12-yl-κC ¹²,κN ¹]iridium, R = H, CH₃, F, and CF₃) were prepared by introducing an electron-donating group (EDG; -CH₃) or an electron-withdrawing group (EWG; -F and -CF₃) at the 7-position of the imidazo-phenanthridine ligand. The photophysical analysis demonstrated that the alteration from EDG to EWGs led to redshifted structureless emission profiles, which were correlated with variations in the ³MLCT/³ILCT ratio in the T₁ excited state. From electrochemical studies and density functional theory calculations, it turned out that the excited-state nature of the dmp-based Ir(III) complexes was significantly affected by the inductive effect of the 7-substituent of the cyclometalating dmp ligand. As a result of the lowest unoccupied molecular orbital energy stabilization by the EWGs that suppressed the non-radiative pathway from the emissive triplet excited state to the ³ d-d state, the F- and CF₃-modified Ir(dmp)₃ complexes (DMP-F and DMP-CF ₃ ) showed quantum yields of 27-30% in the solution state, which were at least 4- or 5-fold higher than those shown by DMP-H and DMP-CH ₃ . A PhOLED device based on DMP-CF ₃ [CIE chromaticity (0.17, 0.39)], which demonstrated a distinct ³MLCT characteristic, exhibited better electroluminescent efficiencies with an external quantum efficiency of 13.5% than that based on DMP-CH ₃ .

SUBMITTER: Kim SY 

PROVIDER: S-EPMC9134233 | biostudies-literature | 2022 May

REPOSITORIES: biostudies-literature