Tris-heteroleptic Iridium Complexes Based on Cyclometalated Ligands with Different Cores

Abstract

A series of tris-heteroleptic iridium complexes of the form [Ir(C^N)(C^N)(acac)] combining 2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)pyridine (dFppy), 1-phenylpyrazole (ppz), and 1-(2,4-difluorophenyl)pyrazole (dFppz) as the C^N ligands have been synthesized and fully characterized by NMR, X-ray crystallography, UV-vis absorption and emission spectroscopy, and electrochemical methods. It is shown that "static properties" (e.g., absorption and emission spectra and redox potentials) are primarily dictated by the overall architecture of the complex, while "dynamic properties" (e.g., excited-state lifetime and radiative and nonradiative rate constants) are, in addition, sensitive to the specific positioning of the substituents. As a result, the two complexes [Ir(dFppy)(ppz)(acac)] and [Ir(ppy)(dFppz)(acac)] have the same emission maxima and redox potentials, but their radiative and nonradiative rate constants differ significantly by a factor ∼2. Then acetylacetonate (acac) was replaced by picolinate (pic), and two pairs of diastereoisomers were obtained. As expected, the use of pic as the ancillary ligand results in blue-shifted emission, stabilization of the oxidation potential, and improvement of the photoluminescence quantum yield, and only minor differences in the optoelectronic properties are found between the two diastereoisomers of each pair.

Suzuki–Miyaura Cross-Coupling Reactions for Increasing the Efficiency of Tris-Heteroleptic Iridium(III) Emitters

“…Data of UV/vis spectra of 1.0 × 10 –5 M 2-methyltetrahydrofuran (2-MeTHF) solutions of 2 – 4 , at room temperature, are collected in Table S1. The spectra of the three compounds are very similar, showing bands in three different zones of energy (Figures S5–S7): 220–240, 320–470, and greater than 470 nm, respectively, in agreement with other tris-heteroleptic iridium­(III) emitters. − , The respective transitions were assigned on the basis of the results of time-dependent density functional theory calculations (B3LYP-GD3//SDD­(f)/6-31G**) computed in tetrahydrofuran. Absorptions at the highest-energy region are due to 1 π–π* intraligand transitions.…”

“…However, the preparation in moderated yield of neutral [3b + 3b′ + 3b′′] tris-heteroleptic compounds of iridium­(III) with two different ortho-metalated 2-phenylpyridines and a third ligand, usually acetylacetonate (acac), is certainly a true challenge. This is because the one-pot procedures lead to statistical mixtures of ligand distribution products, which usually afford the target emitter with a maximum yield of about 30%, and the sequential coordination of the different ligands needs several steps and has only a relative success when the three ligands are of very different nature: for instance, cyclometalated phenylpyridine, cyclometalated carbene, and acac . Accordingly, the development of procedures that selectively give these emitters is of great relevance.…”

Monodentate Benzo[d]imidazole‐Based Iridium(III) Complexes and Their Dual Fluorescent and Phosphorescent Emissions

“…Elemental analysis was carried out on an EA1110 analyzer (Fisons Instruments). The dfphpy ligand and [(dfphpy) 2 Ir(μ‐Cl)] 2 were prepared according to literature procedures.…”

Cyclometalated Iridium(III) Complexes Incorporating Aromatic Phosphonate Ligands: Syntheses, Structures, and Tunable Optical Properties

“…Generally, the emissions of cyclometalated iridium­(III) complexes are assigned to the mixed metal to ligand charge transfer (MLCT) and the π–π* transition of ligands. Both the cyclometalating and the ancillary ligands can pose significant influences on the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap and hence tune the electronic and optical properties of the complexes. , Noting that picolinate was frequently utilized as the ancillary ligand to adjust the HOMO–LUMO gap of cyclometalated iridium­(III) complexes, − herein we use two related phosphonate ligands, namely, 2-pyridylphosphonic acid (H 2 L 1 ) and 2-quinolinephosphonic acid (H 2 L 2 ). Four new complexes are obtained successfully with formulae [Ir­(ppy) 2 (HL 1 )]·0.5H 2 O ( 1 ), [Ir­(ppy) 2 (HL 2 )]·0.5H 2 O ( 2 ), [Ir­(dfppy) 2 (HL 1 )] ( 3 ), and [Ir­(dfppy) 2 (HL 2 )]·3.5H 2 O ( 4 ) (ppy = 2-phenylpyridine, dfppy = 2-(2,4-difluorophenyl)­pyridine) (Scheme ), which provide the first examples of mononuclear cyclometalated iridium­(III) complexes incorporating phosphonate ligands.…”