Ideal Design of Platinum (II) Complex with Bulky Blocking Group for Narrow Emission and High Efficiency in Blue Organic Light-Emitting Diodes

Platinum phosphorescent materials are emerging as promising candidates for efficient blue organic light-emitting diodes. Especially, tetradentate ligands with a 5/6/6 configuration have the advantage of having twisted structure to minimize intermolecular interactions. However, the reported platinum complexes in the 5/6/6 configuration still exhibit relatively broad luminescence spectra and low efficiency at high doping concentration due to insufficient intermolecular interaction suppression. It is necessary to introduce the appropriate blocking group at the proper position on the ligand to ensure that intermolecular interactions are inhibited. In this work, we propose an ideal design introducing blocking group for platinum (II) complexes with small changes in efficiency and emission spectra at high doping concentration. The bulky blocking group, 2,6-diisopropylphenyl, introduced at the 3-position of the carbazole is distorted vertically due to steric hindrance, so the energy is still retained. However, the photophysical and device properties were improved by suppression of intermolecular interaction. As a result, Pt-dipCz showed high efficiency of 25.0% with narrow full width at half maximum (FWHM) of 22 nm at 5 wt.% doping concentration. When doping concentration increased to 20 wt.%, high efficiency and narrow FWHM were maintained with small changes of only 4.8% reduction and 2 nm increase, respectively. These values indicate that 2,6-diisopropylphenyl group introduced at carbazole is efficient for suppression of intermolecular interaction.