Red-light-emitting electrochemical cells based on cationic iridium complexes with phenanthroimidazole-type ancillary ligand

Abstract

Red-emitting cationic iridium complexes, namely, [Ir(ppy)2(Qtpi)]PF6 (Complex 1) and [Ir(piq)2(Qtpi)]PF6 (Complex 2) were synthesized using the ancillary ligand 2-(quinolin-2-yl)-1-(p-tolyl)-1H-phenanthro[9,10-d]imidazole (Qtpi) and 2-phenylpyridine (Hppy) and 1-phenylisoquinoline (Hpiq) as cyclometalating ligands. In acetonitrile solution, Complex 1 emitted orange light, centered at 614 nm, whereas Complex 2 gave rise to orange-red emission centered at 603 and a shoulder peak at 630 nm. Extended π-conjugation on the phenylpyridine ligand in Complex 2 lowered the energy-gap, leading to a red-shift the emission compared to that of Complex 1. A light-emitting electrochemical cell (LEC) fabricated with Complex 1 emitted red light with an emission peak at 618 nm and Commission Internationale de L'Eclairage (CIE) coordinates of (0.59, 0.36), respectively, with corresponding values of 692 nm and (0.56, 0.28) for Complex 2. The LEC based on Complex 1 demonstrated superior performance, with a maximum luminance and current efficiency of 808 cd m−2 and 0.73 cd A−1, respectively.