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

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 (522 nm) light emission for Complex 1 with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.56) and blue-green (500 nm) light emission for Complex 2 with the CIE coordinates of (0.24, 0.44). Using Complex 1, a maximum luminance of 1191 cd m(-2) and current efficiency of 1.0 cd A(-1) are obtained while that of Complex 2 are 741 cd m(-2) and 0.88 cd A(-1) respectively. (C) 2013 Elsevier B. V. All rights reserved.