Green to blue-green-emitting cationic iridium complexes with a CF3-substituted phenyl-triazole type cyclometalating ligand: synthesis, characterization and their use for efficient light-emitting electrochemical cells

Record-High Efficiency Blue-Green Cationic Ir(III) Complexes for Light-Emitting Electrochemical Cells with EQE Approaching 40

Light-emitting electrochemical cells (LECs) provide a cost-effective solution for lighting applications and are well-suited for large-area and industrial-scale manufacturing. However, enhancing the efficiency of LECs remains a significant challenge. To address this issue, this study presents a series of blue-green iridium complexes with promising phosphorescent emission properties. Among these, di[1-(2,4-difluorophenyl)-pyrazolyl]-5,5'-difluoro-2,2'-bipyridyl iridium(III) hexafluorophosphate stands out, demonstrating exceptional performance. Following optimizing the device with varying thicknesses, an EQE of 16.8% and a current efficiency of 47.2 cd A-1 were attained. Further enhancements through the integration of a diffusive layer resulted in a 270% increase in efficiency, reaching an EQE of 39.3% and current efficiency of 109.6 cd A-1. This efficient technology demonstrates significant potential and lays the groundwork for future high-performance light-emitting devices.

Iridium(III) Complexes of Bifunctional 2-(2-Pyridyl)imidazole Ligands: Electrochemiluminescent Emitters in Aqueous Media

A series of electrochemiluminescent (ECL) iridium(III) complexes with the general formula [Ir(C∧N)2(pim)]+ (where C∧N = cyclometalating ligands 2-phenylpyridinato (ppy) or 2-(2,4-difluorophenyl)pyridinato (dFppy), and pim = 2-(2-pyridyl)imidazole) have been synthesized. In each case, the 2-(2-pyridyl)imidazole ancillary ligand has been modified to facilitate bioconjugation and ECL label development. All complexes exhibit blue-shifted optical and electro-generated phosphorescence relative to the archetypal complex [Ir(ppy)2(bpy)]+ (bpy = 2,2'-bipyridine). The emission energies for the complexes were unperturbed by functionalization of the imidazole unit of the pim ligand, whereas the emission energy was significantly blue-shifted when the pyridyl group was modified with an electron-donating oxyethanol unit. Cyclic voltammetric studies provide results consistent with fluorine substituents on the cyclometalating ligands, or an oxyethanol substituent on the neutral pim ligand, widening the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of these complexes. Most of the complexes have high photoluminescence quantum yields (ΦPL) in acetonitrile (up to 0.91), and some have higher ECL efficiencies than [Ru(bpy)3]2+ in both acetonitrile (up to 177%) and ProCell buffer (up to 202%). Theoretical studies provide additional insights into the photophysical and electrochemical properties of this series of compounds.

Aqueous emissive cyclometalated iridium photoreductants: synthesis, computational analysis and the photocatalytic reduction of 4-nitrophenol

Herein, we present luminescent mononuclear iridium complexes [1]3+-[4]3+ using NEt3-appended C^N chelating benzimidazole (L1-L4) and semi-flexible phenanthroline-pyrazine-based (phpy) ligands exhibiting photocatalytic reduction of 4-nitrophenol (4-NP) in the presence of NEt3 in an aqueous medium. The formation of [1]3+-[4]3+ was confirmed by HRMS, 1H-1H COSY, and 13C and 19F NMR spectroscopy. The complex [4]3+ is water soluble, whereas the others ([1]3+-[3]3+) are partially soluble. The complexes are luminescent in both CH3CN and H2O media. The DFT study reveals that the HOMO of [1]3+ resides on the C^N chelating benzimidazole and iridium center. However, it moves to the pyrazine-pyridine of the phpy unit in the case of [2]3+-[4]3+. The LUMOs are localized on the phenanthroline unit of phpy for all the complexes. This suggests an important role of the fluorine atom on electron density distribution. Spin density analysis demonstrates that the emission bands of the complexes arise from 3MLLCT states. The complex [4]3+ displays promising photocatalytic activity towards 4-NP photoreduction, whereas complexes [1]3+-[3]3+ exhibit lower reactivity. The mechanistic study suggests that the reaction proceeds through an oxidative quenching pathway, where 4-NP is reduced by accepting an electron from excited [Ir(III)] and gets oxidized to Ir(IV), which comes back to its original Ir(III) state by accepting an electron from the sacrificial electron donor NEt3.

Cationic Ir(III) Complexes with 4-Fluoro-4'-pyrazolyl-(1,1'-biphenyl)-2-carbonitrile as the Cyclometalating Ligand: Synthesis, Characterizations, and Application to Ultrahigh-Efficiency Light-Emitting Electrochemical Cells

Light-emitting electrochemical cells (LECs) promise low-cost, large-area luminescence applications with air-stabilized electrodes and a versatile fabrication that enables the use of solution processes. Nevertheless, the commercialization of LECs is still encountering many obstacles, such as low electroluminescence (EL) efficiencies of the ionic materials. In this paper, we propose five blue to yellow ionic Ir complexes possessing 4-fluoro-4'-pyrazolyl-(1,1'-biphenyl)-2-carbonitrile (ppfn) as a novel cyclometalating ligand and use them in LECs. In particular, the device within di[4-fluoro-4'-pyrazolyl-(1,1'-biphenyl)-2-carbonitrile]-4,4'-di-tert-butyl-2,2'-bipyridyl iridium(III) hexafluorophosphate (DTBP) shows a remarkable photoluminescence quantum yield (PLQY) of 70%, and by adjusting the emissive-layer thickness, the maximal external quantum efficiency (EQE) reaches 22.15% at 532 nm under the thickness of 0.51 μm, showing the state-of-the-art value for the reported blue-green LECs.

Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of "AIEgens" was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic-inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d10 zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016-2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.