Synthesis and characterization of cationic iridium complexes for the fabrication of green and yellow light-emitting devices

Abstract

Green- and yellow-emitting cationic iridium complexes, [Ir(dfppy)2(pybi)]PF6 (Complex 1) and [Ir(ppz)2(pybi)]PF6 (Complex 2), were synthesized using 2-(2,4-difluorophenyl)pyridine (Hdfppy) and 1-phenylpyrazole (Hppz) as the cyclometalating ligands and 2-(2-pyridyl)benzimidazole (pybi) as the ancillary ligand. In order to gain insight into the photophysical and electrochemical behavior, density functional theory (DFT) calculations were simulated on the above complexes, which showed consistency in energy gaps obtained from both experimental and theoretical results. Light-emitting electrochemical cells (LECs) based on Complex 1 were obtained by solution-processed fabrication, and they showed green (523 nm) electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.58); on the other hand, the LEC utilizing Complex 2 showed yellow electroluminescence with CIE coordinates of (0.41, 0.56). The highest luminance of 1492 cd m−2 and current density of 83.13 mA cm−2 were achieved for the LEC utilizing Complex 2, owing to the more balanced carrier injection and recombination as compared to those for Complex 1. The negative role of the free – NH group in the electroluminescent properties of LECs is confirmed by comparing the current results with those previously reported for N-alkylated benzimidazole moieties.