Fabrication of efficient light-emitting electrochemical cells utilizing thiazole- and pyridine-based cationic iridium complexes

Abstract

In this paper, we report highly luminescent yellow and orange light-emitting electrochemical cells (LECs) using cationic iridium complexes, i.e., [Ir(ppy)2(mpbi)]PF6 (Complex 1) and [Ir(bpbt)2(mpbi)]PF6 (Complex 2), which contain 2-phenylpyridine (ppy) and 2-(4-bromophenyl)benzothiazole (bpbt) as the cyclometalating ligands, respectively, and 2-(4-methyl-2-pyridyl)-1H-benzimidazole (mpbi) as the ancillary ligand. The emissions of Complex 1 and Complex 2 are yellow and yellowish-green in acetonitrile solution. The geometrical, electronic, and optical properties of the two novel Ir complexes were investigated by density functional theory (DFT) and time-dependent DFT using the B3LYP method. LECs incorporating Complexes 1 and 2 emit yellow (553nm) and orange (600nm) electroluminescence, respectively. Upon the meticulous selection of organic ligands, a significant increase in luminescence was achieved for Complex 1 (3636cd/m2) over that of Complex 2 (2315cd/m2).