Performance improvement of yellow emitting electrochemiluminescence devices: Effects of frequency control and coreactant pathway

In this work, we propose an electrochemiluminescence (ECL) luminophore, 2,2′-bipyridylbis(2-phenylpyridine)iridium(III) hexafluorophosphate ([Ir(ppy)₂(bpy)][PF₆]) (1), emitting yellow-colored light for displaying a variety of ECL colors. The synthesized luminophore 1 is optically and electrochemically analyzed. The ECL electrolytes are very simply composed of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), sandwiched between two transparent electrodes used for the devices. The resulting ECL devices are characterized by a low-voltage operation and quick response independent of frequency. We also suggest an efficient method for improving the ECL brightness by incorporating 2,2′-bipyridylbis[2-(2′,4′-difluorophenyl)pyridine]iridium(III) hexafluorophosphate ([Ir(diFppy)₂(bpy)][PF₆]) (2) as a coreactant. The intensity of the emitted yellow light is doubled, when 60 mol% of 2 is included in the mixed-luminophore system. Additionally, we further enhanced the luminance of yellow light emitting ECL devices by adjusting the frequency of applied AC voltage, leading to ∼3.5 times higher brightness at 500 Hz.