Rational Design of Mono- and Bi-Nuclear Cyclometalated Ir(III) Complexes Containing Di-Pyridylamine Motifs: Synthesis, Structure, and Luminescent Properties

Abstract

Heteroleptic cyclometalated iridium (III) complexes (1–3) containing di-pyridylamine motifs were prepared in a stepwise fashion. The presence of the di-pyridylamine ligands tunes their electronic and optical properties, generating blue phosphorescent emitters at room temperature. Herein we describe the synthesis of the mononuclear iridium complexes [Ir(ppy)2(DPA)][OTf] (1), (ppy = phenylpyridine; DPA = Dipyridylamine) and [Ir(ppy)2(DPA-PhI)][OTf] (2), (DPA-PhI = Dipyridylamino-phenyliodide). Moreover, the dinuclear iridium complex [Ir(ppy)2(L)Ir(ppy)2][OTf]2 (3) containing a rigid angular ligand “L = 3,5-bis[4-(2,2′-dipyridylamino)phenylacetylenyl]toluene” and displaying two di-pyridylamino groups was also prepared. For comparison purposes, the related dinuclear rhodium complex [Rh (ppy)2(L)Rh(ppy)2][OTf]2 (4) was also synthesized. The x-ray molecular structure of complex 2 was reported and confirmed the formation of the target molecule. The rhodium complex 4 was found to be emissive only at low temperature; in contrast, all iridium complexes 1–3 were found to be phosphorescent in solution at 77 K and room temperature, displaying blue emissions in the range of 478–481 nm.

Luminescent Complexes of Platinum, Iridium, and Coinage Metals Containing N-Heterocyclic Carbene Ligands: Design, Structural Diversity, and Photophysical Properties

“…Octahedral cyclometalated Ir­(III) complexes possess a range of important properties such as rigid configurational stability, high emissive quantum yield (φ), microsecond-regime phosphorescence lifetime (τ), and high electrochemical stability. ,− Moreover, they act as high efficiency emitters in OLED devices. ,− This field of study has attracted much attention and continues to be highly investigated; thus, we intend to present the most recent work in this area. As mentioned previously, the presence of NHCs, which act as strong σ-donor ligands, can serve as a tool to push the metal-centered d–d transitions to higher energy in order to make them thermally inaccessible. ,− …”