Green and blue–green light-emitting electrochemical cells based on cationic iridium complexes with 2-(4-ethyl-2-pyridyl)-1H-imidazole ancillary ligand

Abstract

The ionic iridium complexes, [Ir(ppy)2(EP-Imid)]PF6 (Complex 1) and [Ir(dfppy)2(EP-Imid)]PF6 (Complex 2) are used as the light-emitting material for the fabrication of light-emitting electrochemical cells (LECs). These complexes have been synthesized, employing 2-(4-ethyl-2-pyridyl)-1H-imidazole (EP-Imid) as the ancillary ligand, 2-phenylpyridine (ppy) and 2-(2,4-difluorophenyl)pyridine (dfppy) as the cyclometalated ligands, which were characterized by various spectroscopic, photophysical and electrochemical methods. The photoluminescence (PL) emission spectra in acetonitrile solution show blue–green and blue light emission for Complexes 1 and 2 respectively. However, LECs incorporating these complexes resulted in green (522nm) light emission for Complex 1 with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.33, 0.56) and blue–green (500nm) light emission for Complex 2 with the CIE coordinates of (0.24, 0.44). Using Complex 1, a maximum luminance of 1191cdm−2 and current efficiency of 1.0cd A−1 are obtained while that of Complex 2 are 741cdm−2 and 0.88cd A−1 respectively.