Multifunctional Crosslinkable Iridium Complexes as Hole Transporting/Electron Blocking and Emitting Materials for Solution-Processed Multilayer Organic Light-Emitting Diodes

Abstract

Here, a new series of crosslinkable heteroleptic iridium (III) complexes for use in solution processed phosphorescent organic light emitting diodes (OLEDs) is reported. These iridium compounds have the general formula of (PPZ-VB)(2)Ir((CN)-N-Lambda), where PPZ-VB is phenylpyrazole (PPZ) vinyl benzyl (VB) ether; and the (CN)-N-Lambda ligands represent a family of four different cyclometallating ligands including 1-phenylpyrazolyl (PPZ) (1), 2-(4,6-difluorophenyl)pyridyl (DFPPY) (2), 2-(p-tolyl)pyridyl (TPY) (3), and 2-phenylquinolyl (PQ) (4). With the incorporation of two crosslinkable VB ether groups, these compounds can be fully crosslinked after heating at 180 degrees C for 30 min. The crosslinked films exhibit excellent solvent resistance and film smoothness which enables fabrication of high-performance multilayer OLEDs by sequential solution processing of multiple layers. Furthermore, the photophysical properties of these compounds can be easily controlled by simply changing the cyclometallating (CN)-N-Lambda ligand in order to tune the triplet energy within the range of 3.0-2.2 eV. This diversity makes these materials not only suitable for use in hole transporting and electron blocking but also as emissive layers of several colors. Therefore, these compounds are applied as effective materials for all-solution processed OLEDs with (PPZ-VB)(2)IrPPZ (1) acting as hole transporting and electron blocking layer and host material, as well as three other compounds, (PPZ-VB)(2)IrDFPPY (2), (PPZ-VB)(2)IrTPY(3), and (PPZ-VB)(2)IrPQ(4), used as crosslinkable phosphorescent emitters.