Unprecedented Homoleptic Bis-Tridentate Iridium(III) Phosphors: Facile, Scaled-Up Production, and Superior Chemical Stability

Bis-tridentate Ir(III) metal complexes are expected to show great potential in organic light-emitting diode (OLED) applications due to the anticipated, superb chemical and photochemical stability. Unfortunately, their exploitation has long been hampered by lack of adequate methodology and with inferior synthetic yields. This hurdle can be overcome by design of the first homoleptic, bis-tridentate Ir(III) complex [Ir(pzpyph)(pzHpyph)] (1), for which the abbreviation (pzpyph)H (or pzHpyph) stands for the parent 2-pyrazolyl-6-phenyl pyridine chelate. After that, methylation and double methylation of 1 afford the charge-neutral Ir(III) complex [Ir(pzpyph)(pzMepyph)] (2) and cationic complex [Ir(pzMepyph)2][PF6] (3), while deprotonation of 1 gives formation of anionic [Ir(pzpyph)2][NBu4] (4), all in high yields. These bis-tridentate Ir(III) complexes 2–4 are highly emitted in solution and solid states, while the charge-neutral 2 and corresponding t-butyl substituted derivative [Ir(pzpyBuph)(pzMepyBuph)] (5) exhibit superior photostability versus the tris-bidentate references [Ir(ppy)2(acac)] and [Ir(ppy)3] in toluene under argon, making them ideal OLED emitters. For the track record, phosphor 5 gives very small efficiency roll-off and excellent overall efficiencies of 20.7%, 66.8 cd A−1, and 52.8 lm W−1 at high brightness of 1000 cd m−2. These results are expected to inspire further studies on the bis-tridentate Ir(III) complexes, which are judged to be more stable than their tris-bidentate counterparts from the entropic point of view.