Two isomeric N-heterocyclic carbene Ir(III) complexes, f-Ir-(dbtmi)3 and m-Ir-(dbtmi)3 (dbtmi = N-dibenzothiophenyl-N-methylimidazole), were isolated and systematic investigation of their photophysical and electrochemical properties was carried out. The origin of the phosphorescence emissions differs depending on the configurations of the two isomers. Both isomers, f-Ir-(dbtmi)3 and m-Ir-(dbtmi)3, showed efficient emission in dichloromethane solution with quantum yields of 57% and 48%, respectively, due to unusual properties of the N-heterocyclic carbene (NHC) ligand; – that is, the complexes possess a strong metal–ligand bond that destabilizes the nonradiative metal centred ligand-field states. Depending on their configurations, the two isomers showed slightly different excited states. Even though both isomers possess a largely 3LC characteristic mixed with the 3MLCT characteristic in their excited states, m-Ir-(dbtmi)3 showed a higher 3MLCT characteristic as evidenced by the solvent polarity dependence emission spectra and emission lifetime. DFT calculations clearly support this different photophysical property. Finally, both isomeric complexes were used as dopant materials for the blue PHOLED device. The m-Ir-(dbtmi)3 based device showed relatively high efficiencies with an external quantum efficiency (EQE) of up to 17.1% relative to the analogue m-Ir-(dbfmi)3 (dbfmi = N-dibenzofuranyl-N-methylimidazole). Most importantly, a deep-blue CIE chromaticity diagram (0.14, 0.19) was obtained when m-Ir-(dbtmi)3 is used as a dopant.

Photophysical Studies of Isomeric N-Heterocyclic Carbene Ir(III) Complexes and Their Applications to Deep-Blue Phosphorescent Organic Light-Emitting Diodes (OLEDs)

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.