Selective syntheses of homoleptic Ir(III) complexes bearing di-CF₃-functionalized benzoimidazol-2-ylidenes for generation of blue phosphorescence

Abstract

Homoleptic Ir(III) based carbene complexes are known to be the most promising emitters of future blue OLED devices. To provide the proof-of-concept, we designed a series of functional di-CF3-functionalized benzo[d]imidazol-3-ium pro-chelates, which could afford single product emitters after proper modification. For benzoimidazol-2-ylidene with an N-methyl substituent, selective formation of the product can be achieved by introduction of t-butylphenyl for the phenyl group, as shown by shifting the product from mixed m-Ir(dfp)(3) and f-Ir(dfp)(3) to the single isomer f-Ir(dfpb)(3). Alternatively, for di-N-aryl substituted carbene chelates, the steric encumbrance imposed between the ortho-CF3 group and the adjacent N-aryl substituent redirects the cyclometalation to the other N-aryl substituent, leading to the formation of one single product, e.g., f-Ir(tBpp)(3) and f-Ir(ptBp)(3). Moreover, the doped OLED based on f-Ir(tBpp)(3) delivered true-blue emission centered at 457 nm and a maximum EQE of 15.6%. Furthermore, upon addition of terminal emitters nu-DABNA and t-DABNA, the respective hyper-OLEDs exhibited narrowband blue emission with a maximum EQE of 18.9% at 474 nm and 18.1% at 462 nm, respectively. These highlighted the potential of these Ir(III) emitters in the fabrication of blue OLEDs.