Sky-blue emitting bridged diiridium complexes: beneficial effects of intramolecular π-π stacking

In Vitro and In Vivo Antitumor Assay of Mitochondrially Targeted Fluorescent Half-Sandwich Iridium(III) Pyridine Complexes

Half-sandwich iridium(III) complexes show potential value in the anticancer field. However, complexes with favorable luminescence performance are rare, which limits further investigation of the anticancer mechanism. In this paper, 10 triphenylamine-modified fluorescent half-sandwich iridium(III) pyridine complexes {[(η⁵-Cp^x)Ir(L)Cl₂]} (Ir1-Ir10) were prepared and showed potential antiproliferative activity, effectively inhibiting the migration of A549 cells. Ir6, showing the best activity among these complexes, exhibited excellent fluorescence performance (absolute fluorescence quantum yield of 15.17%) in solution. Laser confocal detection showed that Ir6 followed an energy-dependent cellular uptake mechanism, specifically accumulating in mitochondria (Pearson co-localization coefficient of 0.95). A Western blot assay further confirmed the existence of a mitochondrial apoptotic channel. Additionally, Ir6 could arrest the cell cycle at the G₂/M phase, catalyze NADH oxidation, reduce the mitochondrial membrane potential, induce an increase in the level of intracellular reactive oxygen species, and exhibit a mechanism of oxidation. An in vivo antitumor assay confirmed that Ir6 can effectively inhibit tumor growth and is safer than cisplatin.

Tuning the Photophysical Properties of Homoleptic Tris-Cyclometalated Ir(III) Complexes by Facile Modification of the Imidazo-Phenanthridine and Their Application to Phosphorescent Organic Light-Emitting Diodes

To explore the excited-state electronic structure of the blue-emitting Ir(dmp)₃ dopant material (dmp = 3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridine), which is notable for durable blue phosphorescent organic light-emitting diode (PhOLED), a series of homoleptic dmp-based Ir(III) complexes (DMP-R, tris[3-(2,6-dimethylphenyl)-7-R-imidazo[1,2-f]phenanthridin-12-yl-κC ¹²,κN ¹]iridium, R = H, CH₃, F, and CF₃) were prepared by introducing an electron-donating group (EDG; -CH₃) or an electron-withdrawing group (EWG; -F and -CF₃) at the 7-position of the imidazo-phenanthridine ligand. The photophysical analysis demonstrated that the alteration from EDG to EWGs led to redshifted structureless emission profiles, which were correlated with variations in the ³MLCT/³ILCT ratio in the T₁ excited state. From electrochemical studies and density functional theory calculations, it turned out that the excited-state nature of the dmp-based Ir(III) complexes was significantly affected by the inductive effect of the 7-substituent of the cyclometalating dmp ligand. As a result of the lowest unoccupied molecular orbital energy stabilization by the EWGs that suppressed the non-radiative pathway from the emissive triplet excited state to the ³ d-d state, the F- and CF₃-modified Ir(dmp)₃ complexes (DMP-F and DMP-CF ₃ ) showed quantum yields of 27-30% in the solution state, which were at least 4- or 5-fold higher than those shown by DMP-H and DMP-CH ₃ . A PhOLED device based on DMP-CF ₃ [CIE chromaticity (0.17, 0.39)], which demonstrated a distinct ³MLCT characteristic, exhibited better electroluminescent efficiencies with an external quantum efficiency of 13.5% than that based on DMP-CH ₃ .

Bis-Heteroleptic Cationic Iridium(III) Complexes Featuring Cyclometalating 2-Phenylbenzimidazole Ligands: A Combined Experimental and Theoretical Study

In this report, we investigate a new family of cationic iridium(III) complexes featuring the cyclometalating ligand 2-phenylbenzimidazole and ancillary ligand 4,4'-dimethyl-2,2'-bipyridine. Our benchmark complex IrL¹₂ (L¹ = 2-phenylbenzimidazole) displays emission properties similar to those of the archetypical complex 2,2'-dipyridylbis(2',4'-phenylpyridine)iridium(III) in deaerated CH₃CN (Φ = 0.20, λ_em = 584 nm and Φ = 0.14, λ_em = 585 nm, respectively) but exhibits a higher photoluminescence quantum yield in deaerated CH₂Cl₂ (Φ = 0.32, λ_em = 566 nm and Φ = 0.20, λ_em = 595 nm, respectively) and especially a lower nonradiative constant (k_nr = 6.6 × 10⁵ s^-1 vs k_nr = 1.4 × 10⁶ s^-1, respectively). As a primary investigation, we explored the influence of the introduction of electron-donating and electron-withdrawing groups on the benzimidazole moiety and the synergetic effect of the substitution of the cyclometalating phenyl moiety at the para position with the same substituents. The emission energy displays very good correlation with the Hammett constants of the introduced substituents as well as with ΔE_redox values, which allow us to ascribe the phosphorescence of these series to emanate mainly from a mixed metal/ligand to ligand charge transfer triplet excited state (³M/LLCT*). Two complexes (IrL⁵₂ and IrL⁸₂) display a switch of the lowest triplet excited state from ³M/LLCT* to ligand centered (³LC*), from the less polar CH₂Cl₂ to the more polar CH₃CN. The observed results are supported by (TD)-DFT computations considering the vibrational contributions to the electronic transitions. Chromaticity diagrams based on the maximum emission wavelength of the recorded and simulated phosphorescence spectra demonstrate the strong promise of our complexes as emitting materials, together with the very good agreement between experimental and theoretical results.

Effective Design Strategy for Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence Emitters Achieving 18% External Quantum Efficiency Pure-Blue OLEDs with Extremely Low Roll-Off

High-color purity organic emitters with a simultaneous combination of aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) characteristics are in great demand due to their excellent comprehensive performances toward efficient organic light-emitting diodes (OLEDs). In this work, two D-π-A-structure emitters, ICz-DPS and ICz-BP, exhibiting AIE and TADF properties were developed, and both the emitters have narrow singlet (S₁)-triplet (T₁) splitting (ΔE_ST) and excellent photoluminescence (PL) quantum yields (Φ_PL), derived from the distorted configurations and weak intra/intermolecular interactions, suppressing exciton annihilation and concentration quenching. Their doped OLEDs based on ICz-BP provide an excellent electroluminescence external quantum efficiency (η_ext) and current efficiency (η_C) of 17.7% and 44.8 cd A^-1, respectively, with an η_ext roll-off of 2.9%. Their nondoped OLEDs based on ICz-DPS afford high efficiencies of 11.7% and 30.1 cd A^-1, with pure-blue emission with Commission Internationale de l'Éclairage (CIE) coordinates of (0.15, 0.08) and a low roll-off of 6.0%. This work also shows a strategy for designing AIE-TADF molecules by rational use of steric hindrance and weak inter/intramolecular interactions to realize high Φ_PL values, fast reverse intersystem crossing process, and reduced nonradiative transition process properties, which may open the way toward highly efficient and small-efficiency roll-off devices.

Inherently dinuclear iridium(III) meso architectures accessed by cyclometalation of calix[4]arene-based bis(aryltriazoles)

Conventional cyclometalation of calix[4]arene bis(aryltriazoles) with iridium(III) chloride hydrate leads to unique meso architectures in which the Ir₂Cl₂ core is cross-bound by two (C^N)₂ ligands, which allows further replacement of the chloride bridges with ancillary ligands while maintaining the dinuclear structures of the complexes having independent or coupled iridium pairs.

Synthesis of N,O-Chelating Hydrazidopalladium Complexes from 1,2-Bis(trifluoroacetyl)hydrazine

N,O-chelating dicarbonylhydrazido-palladium complexes were synthesized by treatment of 1,2-bis(trifluoroacetyl)hydrazine with a mixture of a Pd(0) source, [Pd(dba)2] (DBA = dibenzylideneacetone), and four-electron donors including 1,3-bis(diphenylphosphino)propane (DPPP), N,N,N’,N’-tetramethylethylenediamine (TMEDA), and two equivalents of triphenylphosphine. The same products from DPPP and TMEDA could be obtained alternatively by using Pd(OAc)2 through deprotonation of the diacylhydrazine. The five-membered chelate structure was confirmed by NMR spectra and X-ray crystal structure determination. The X-ray structures indicate that the products are formally considered as Pd(II) complexes with a hydrazido(2–) ligand. In the case of the triphenylphosphine-coordinated complex, a fluxional behavior in dichloromethane-d2 was observed by variable temperature NMR experiments, possibly due to structural changes between the square planar and pseudo-tetrahedral geometries.

Cyclometalated Ir(iii) complexes towards blue-emissive dopant for organic light-emitting diodes: fundamentals of photophysics and designing strategies

The fundamental photophysics of cyclometalated Ir(iii) complexes and surveys design strategies for efficient blue phosphorescent Ir(iii) complexes are summarised.

Luminescent Ir(iii)–Ln(iii) coordination polymers showing slow magnetization relaxation

Two structural types of iridium(iii)–lanthanide(iii) coordination polymers, single-chain Ir2Ln and double-chain Ir4Ln2 (Ln = Gd, Dy, Er, and Yb), have been prepared. SMM behaviour and NIR luminescence were observed for the Ir–Er and Ir–Yb systems.

Dinuclear metal complexes: multifunctional properties and applications

Dinuclear metal complexes have enabled breakthroughs in OLEDs, photocatalytic water splitting and CO₂reduction, DSPEC, chemosensors, biosensors, PDT and smart materials.

Early Metal Di(pyridyl) Pyrrolide Complexes with Second Coordination Sphere Arene-π Interactions: Ligand Binding and Ethylene Polymerization

Early metal complexes supported by hemilabile, monoanionic di(pyridyl) pyrrolide ligands substituted with mesityl and anthracenyl groups were synthesized to probe the possibility of second coordination sphere arene-π interactions with ligands with potential for allosteric control in coordination chemistry, substrate activation, and olefin polymerization. Yttrium alkyl, indolide, and amide complexes were prepared and structurally characterized; close contacts between the anthracenyl substituents and Y-bound ligands are observed in the solid state. Titanium, zirconium, and hafnium tris(dimethylamido) complexes were synthesized, and their ethylene polymerization activity was tested. In the solid state structure of one of the Ti tris(dimethylamido) complexes, coordination of Ti to only one of the pyridine donors is observed pointing to the hemilabile character of the di(pyridyl) pyrrolide ligands.

Highly luminescent 2-phenylpyridine-free diiridium complexes with bulky 1,2-diarylimidazole cyclometalating ligands

While a number of highly emissive dinuclear Ir(iii) complexes have been reported, they have generally been restricted to structures based on 2-phenylpyridine (Hppy) cyclometalates.

Cyclometalated Ir(iii) complexes [Ir(tpy)(bbibH2)Cl][PF6] and [Ir(tpy)(bmbib)Cl][PF6]: intramolecular π⋯π interactions leading to facile synthesis and enhanced luminescence

Complexes [Ir(tpy)(bbibH₂)Cl][PF₆] (1·PF6) and [Ir(tpy)(bmbib)Cl][PF₆] (2·PF6) show facile synthesis and enhanced luminescence due to intramolecular π⋯π interactions.