Electrophosphorescent devices based on cationic iridium complexes: The effect of fluorinating the pendant phenyl ring of the ancillary ligand on the device performances

Light-emitting electrochemical cells (LECs) and organic light-emitting diodes (OLEDs) have been investigated based on three blue-green-emitting cationic iridium complexes (1–3). From complexes 1 to 2 and 3, the pendant phenyl ring on the ancillary ligand is gradually fluorinated. It is found that fluorination of the pendant phenyl ring reduces the electrochemical stability of the complexes, which in turn decreases the efficiency and stability of LECs based on the complexes, despite the fact that fluorination reinforces the intramolecular π–π stacking interactions. Fluorination of the pendant phenyl ring also makes the electroluminescent (EL) spectra of LECs red-shifted due to enhanced intermolecular interactions in films. When the complexes are used as dopants in OLEDs, fluorination of the pendant phenyl ring largely enhances the electron-trapping ability of the complexes in the light-emitting layer. Blue-green OLEDs based on complexes 1, 2 and 3 showed promising performances, with peak current efficiencies of 18.3, 9.0 and 14.7 cd A−1, respectively.