Exploration of the Structural and Photophysical Characteristics of Mono- and Binuclear Ir(III) Cyclometalated Complexes for Optoelectronic Applications

Rational design of efficient photosensitizers based on cyclometalated iridium(III) complexes with 2-arylbenzimidazole and aromatic 1,3-diketone ligands

A judicious selection of substituents in cyclometalating 2-arylbenzimidazoles and an ancillary aromatic 1,3-diketone enabled the creation of heteroleptic iridium(III) complexes demonstrating strong light absorption up to 500 nm (ε ≈ 10 000-12 000 M-1 cm-1). The complexes, which were studied by various spectroscopic techniques, single-crystal X-ray diffraction and cyclic voltammetry, displayed tunable absorption maxima depending on the nature of substituents and their positions. The experimental study was corroborated by quantum chemical calculations, which showed an increased contribution of intraligand charge transfer transitions to the visible light absorption in the case of complexes containing electron-withdrawing substituents in the ligands. Despite being of high intensity, some of these transitions are responsible for the formation of the excited states located at large distances from the 'anchoring' fragment incorporated in the ancillary ligand. In turn, incorporation of electron-donating substituents at the para-position to the Ir-C bonds increases the number of excited states located on the ancillary ligand. The destabilization of the HOMO, which is caused by the increase in the electron-donating ability of the substituents in the metalated rings, translated into negative shifts of the Ir4+/Ir3+ redox potential, affecting, in some cases, the degree of electrochemical reversibility of the complexes. Several complexes having strong light-harvesting characteristics and undergoing reversible oxidation in the appropriate potential range were used for coating the TiO2 photoanodes, which reached an efficiency of 2.15% upon irradiation with the standard AM 1.5 spectrum.

Highly Active Single-Atom Nanozymes with High-Loading Iridium for Sensitive Detection of Pesticides

Single-atom nanozymes (SAzymes) are novel mimic-enzyme materials with atomically doped active sites. They play a pivotal role in the field of nanozymes because of their excellent catalytic activities, high utilization efficiency of the metal atoms, and simple model of active sites. Herein, the peroxidase (POD)-like SAzymes with high-loading iridium (Ir) (5.31%) on graphene oxide (GO) nanosheets [Ir(III)/GO] were prepared through a coordination reaction between the Ir(III) complex and the oxygen-containing groups in GO. The preparation strategy avoids nitrogen doping and pyrolysis procedures which are the usually used strategies to improve the GO-based enzyme mimic activity. Ascribed to the highly active Ir atoms, Ir(III)/GO SAzymes demonstrate outstanding POD-like activity without the oxidase-like activity. In advantage of the excellent POD-like activity, a simple and sensitive colorimetric pesticide detection platform is established. The developed sensing platform offers an excellent "switch-on" pirimicarb (PIB) detection in the linear range of 10-300 nM with a limit of detection (LOD) of 2.81 nM. Moreover, the detection platform was fabricated into a portable test kit, which is composed of a test swab and sample processing tube. In the aid of a color-reading APP, the test kit can detect PIB with the LOD of 3.31 nM. It is astonishing to get this excellent detection sensitivity just using the simple colorimetric strategy. This work not only provides a novel strategy to synthesize Ir-based SAzymes but also exhibits the super capability of Ir(III)/GO in the biosensing field.

Luminescent 2-phenylbenzothiazole cyclometalated PtII and IrIII complexes with chelating P^O ligands

Two series of cyclometalated Pt^II and Ir^III complexes with general formulas [Pt(pbt){PPh₂(R)-κP,O}] (2a-2c) and [Ir(pbt)₂{PPh₂(R)-κP,O}] (3a-3c), where Hpbt is 2-phenylbenzothiazol and PPh₂(R) is a diphenylphosphino donor functionalized deprotonated acid (R = o-C₆H₄CO₂a, o-C₆H₄SO₃b, CH₂CH₂CO₂c) are presented. The structures of 1, 2a-2c, 3a and 3b were confirmed by single X-ray diffraction analyses, and the intermolecular interactions in 2a were studied using Hirshfeld surface analysis and non-covalent interaction (NCI) methods on its X-ray structure. Their photophysical properties were investigated by absorption and emission analyses [CH₂Cl₂, solid (298, 77 K) and doped polystyrene (PS) films], supported by TD-DFT calculations on 1, 2a-2c and 3a. The Pt^II complexes exhibit bright phosphorescence in the region 525-542 nm, ascribed to a mixed ³IL/³MLCT excited state with a predominant ³IL contribution. The Ir^III derivatives (3a-3c) show orange photoluminescence (535-584 nm, 298 K), blue shifted at 77 K (527-560 nm), originated from the admixture of ³IL/³MLCT/³LLCT excited states. Interestingly, the photoluminescence quantum yields of the Pt complexes 2a-2c (ϕ = 46.5-66.5%) in PS films are remarkably higher than those of the corresponding iridium complexes (ϕ = 17.3-32%) and the precursor 1 (ϕ = 17%). The calculated ³MC-³IL/³MLCT energy gap for 2a and 3a accounts for the higher quantum yield of the Pt in relation to the Ir complex.

Bis-Tridendate Ir(III) Polymer-Metallocomplexes: Hybrid, Main-Chain Polymer Phosphors for Orange-Red Light Emission

In this work, hybrid polymeric bis-tridentate iridium(III) complexes bearing derivatives of terpyridine (tpy) and 2,6-di(phenyl) pyridine as ligands were successfully synthesized and evaluated as red-light emitters. At first, the synthesis of small molecular bis-tridendate Ir(III) complexes bearing alkoxy-, methyl-, or hydroxy-functionalized terpyridines and a dihydroxyphenyl-pyridine moiety was accomplished. Molecular complexes bearing two polymerizable end-hydroxyl groups and methyl- or alkoxy-decorated terpyridines were copolymerized with difluorodiphenyl-sulphone under high temperature polyetherification conditions. Alternatively, the post-polymerization complexation of the terpyridine-iridium(III) monocomplexes onto the biphenyl-pyridine main chain homopolymer was explored. Both cases afforded solution-processable metallocomplex-polymers possessing the advantages of phosphorescent emitters in addition to high molecular weights and excellent film-forming ability via solution casting. The structural, optical, and electrochemical properties of the monomeric and polymeric heteroleptic iridium complexes were thoroughly investigated. The polymeric metallocomplexes were found to emit in the orange-red region (550-600 nm) with appropriate HOMO and LUMO levels to be used in conjunction with blue-emitting hosts. By varying the metal loading on the polymeric backbone, the emitter's specific emission maxima could be successfully tuned.

Phospho-rescent mono- and diiridium(III) complexes cyclo-metalated by fluorenyl- or phenyl-pyridino ligands with bulky substituents, as prospective OLED dopants

The crystal structures of tris-[9,9-dihexyl-2-(5-meth-oxy-pyridin-2-yl-κN)-9H-fluoren-3-yl-κC 3]iridium pentane monosolvate, [Ir(C31H38NO)3]·C5H12, (I), di-μ2-chlorido-bis-{bis-[2-(5-fluoro-pyridin-2-yl)-9,9-dihexyl-9H-fluoren-3-yl]iridium} pentane 0.3-solvate, [Ir2(C30H35FN)4Cl2]·0.3C5H12, (II), di-μ2-cyanato-bis-{bis-[9,9-dihexyl-2-(5-meth-oxy-pyridin-2-yl)-9H-fluoren-1-yl]iridium} pentane monosolvate, [Ir2(C31H38NO)4(NCO)2(NCO)2]·C5H12, (III), and {μ-N,N'-bis-[3,5-bis-(tri-fluoro-meth-yl)phen-yl]oxamidato}bis(bis{2-[4-(2,4,6-trimethylphenyl)pyridin-2-yl]phenyl-κ2 C 1,N'}iridium)-chloro-benzene-pentane (1/2.3/0.4), [Ir2(C20H19N)4(C18H6F12N2O2)]·2.3C6H5Cl·0.4C5H12, (IV), synthesized in the quest for organic light-emitting devices, were determined. The bis-μ2-chloro and bis-μ2-cyanato complexes have ΔΔ and ΛΛ configurations of the distorted octa-hedral Ir centres in racemic crystals, whereas the oxamido complex has a centrosymmetric (meso) structure with the ΔΛ configuration. The bridging oxamido moiety has a nearly planar anti geometry. All structures show substantial disorder of both host mol-ecules and solvents of crystallization.