Transition Metal Ion Complexes Research Articles

Photoswitchable transition metal complexes with azobenzene-functionalized imine-based ligands: structural and kinetic analysis.

We report on the characterization of two imine type ligands containing photoresponsive azobenzene units as side groups and their transition metal ions complexes. The ligands, both free and in their complexes undergo trans- > cis photoisomerization after irradiation with UV light, but binding of metal ions reduces both the photoisomerisation reaction rates and cis isomer concentrations in the photostationary states. The greatest diminution in the photoisomerisation rate was observed for the complex containing Cd(ii), the heaviest among the various transition metal ions tested in this study.

Strategies toward Long-Life Light-Emitting Electrochemical Cells.

This Minireview examines the operational lifetime of light-emitting electrochemical cells (LECs). Under continuous operation, both polymer-based LECs (PLECs) and ionic transition-metal complex (iTMC)-based LECs (iTMC-LECs) now exhibit a luminance half-life exceeding 1000 h. This improved performance was accomplished with several effective strategies aimed at optimizing the operating scheme, the material composition, and the device architecture. These strategies are presented in detail with PLECs as an example. iTMC-LECs are also highlighted owing to their excellent stress stability with regards to both luminance and operating voltage. The survey of literature data points to clear trends, as well as some unexpected results in LECs stressed for an extended period. Major challenges still exist, but long-lasting LECs are possible when the proven strategies are combined with innovative materials and device design.

The Effect of the Dielectric Constant and Ion Mobility in Light-Emitting Electrochemical Cells.

Light-emitting electrochemical cells (LEECs) are a promising low-cost option for display and solid-state lighting. In these devices, the interplay of mobile ions, electrons, and holes makes for rich physics that can be leveraged for high performance. One example of this interplay is in the formation and radiative decay of excitons-bound electron and hole pairs. Considerations from exciton binding and Langevin recombination suggest that a low dielectric constant (ϵ) would enhance emission. However, emission is also enhanced by the product of the bulk hole and electron concentrations, which in LEECs are enhanced by the motion of small mobile ions yielding high dielectric constants. These competing effects make it difficult to predict whether active layers with low or high dielectric constants will optimize device performance. Here, the effect of varying the dielectric constant on the performance of LEEC devices from ionic transition-metal complexes was studied by systematically exchanging the negative counterions paired with an iridium complex emitter. Electrochemical impedance spectroscopy, constant voltage and constant current device studies, and drift-diffusion simulations were performed. The results clarify the competing effects of Langevin bimolecular recombination and ion-assisted injection processes occurring in LEECs.

Investigation of macromolecular metallocomplexes of rare earth and transition metal ions with side chains of polymethacrylic acid regularly grafted to polyimide backbone in aqueous and aqueous-salt solutions by luminescence methods

Using luminescent methods, interactions of rare earth metal ions (Tb3+, Eu3+, Sm3+, Gd3+) with side chains of ionized polymethacrylic acid (PMAA) regularly grafted to a polyimide (PI) backbone are studied in aqueous and aqueous-salt solutions. It is shown that the interaction of ions with carboxylate anionic groups leads to a sharp decrease in the intramolecular mobility of grafted PMAA side chains at the ratio [metal]/[СОО−] > 0.12. It is established that the luminescence duration of Tb3+ ions decreases from 790 to 660 μs when the degree of polymerization of side PMAA chains decreases from 200 to 36. By means of the methodology based on the ability of transition metal ions to quench luminescence, equilibrium stability constants of macromolecular complexes of transition metal ions (Ag+, Cu2+, Ni2+) with luminescent-labeled PI-grafted and free PMAA chains in aqueous and aqueous-salt solutions are determined. It is shown that the complex stability is essentially affected by the nature and valence of a metal and the ionic strength of solution. Grafting of PMAA chains to a PI backbone causes no significant effect on their ability to bind Ag+ and Cu2+ ions, but reduces considerably the ability of binding with Ni2+ ions. An explanation of this effect is suggested.

Supramolecularly Caged Green-Emitting Ionic Ir(III)-Based Complex with Fluorinated C^N Ligands and Its Application in Light-Emitting Electrochemical Cells.

Ionic Ir(III) complexes are the most promising emitters in light emitting electrochemical cells (LECs), especially in the high energy emission range for which it is difficult to find emitters with sufficient efficiencies and lifetimes. To overcome this challenge, we introduced the concept of intramolecular π-π stacking of an ancillary ligand (6-phenyl-2,2'-bipyridine, pbpy) in the design of a new green-emitting iridium ionic transition metal complex with a fluoro-substituted cyclometallated ligand, 2-(4-fluorophenyl)pyridinato (4Fppy). [Ir(4Fppy)2(pbpy)][PF6] has been synthesized and characterized and its photophysical and electrochemical properties have been studied. The complex emits green light with maxima at 561 and 556 nm under UV excitation from powder and thin film, respectively, and displays a high photoluminescence quantum yield (PLQY) of 78.5%. [Ir(4Fppy)2(pbpy)][PF6] based LECs driven under pulsed current conditions showed under an average current density of 100 A m-2 (at 50% duty cycle) a maximum luminance of 1443 cd m-2, resulting in 14.4 cd A-1 and 7.4 lm W-1 current and power efficiencies, respectively. A remarkable long device lifetime of 214 h was observed. Reducing the average current density to 18.5 A m-2 (at 75% duty cycle) led to an exceptional device performance of 19.3 cd A-1 and 14.4 lm W1- for current and power efficiencies, an initial maximum luminance of 352 cd m-2 and a lifetime of 617 h.

Vacuum-Deposited versus Spin-Coated Emissive Layers for Fabricating High-Performance Blue-Green-Emitting Diodes.

The electroluminescent characteristics of two sublimable cationic iridium(III) complexes that bear the same coordinated iridium(III) cation but different tetraphenylborate-type negative counterions have been investigated. Blue-green-emitting devices were successfully fabricated from these complexes using various preparation processes, namely, spin-coating and vacuum evaporation deposition. Experiments indicated that devices with vacuum-deposited emissive layers showed superior photoelectric properties relative to devices with spin-coated emissive layers, including a maximum current efficiency of 27.91 cd A-1 , an external quantum efficiency of 10.48 %, a power efficiency of 27.73 lm W-1 and the highest luminance of up to 25.34×103 cd m-2 , whereas the turn-on voltages were quite low. The overall device performance surely ranks among the best of phosphorescent organic light-emitting diodes based on ionic transition-metal complexes.

Probing Coordination Complexes by Carbon Nanotube-Assisted Low-Voltage Paper Spray Ionization Mass Spectrometry.

Fragile transition metal complex ions such as [Cr(H2O)4Cl2]+, difficult to be observed by gas-phase spectroscopy, are detected easily with carbon nanotube (CNT)-assisted low-voltage ambient ionization mass spectrometry. Observation of various substituted ions with D2O and ROH (R = CH3, C2H5, ...) established the versatility of the technique in detecting diverse species. Ligand substitution occurring in solution was captured by the low-voltage technique. The extreme softness of the technique coupled with nanoscale ion sources enabled the creation of such species. Analysis was extended to other halides as well. The intensity of these fragile ions gradually disappeared at voltages beyond 500 V and are completely absent in standard high-voltage ionization. Detection of inorganic complexes further enhances the scope of low-voltage ionization.

Films of Transition Metal Complexes Including Ionic Liquids: Dramatic Effects of Processing Parameters and Substrate on the Film Morphology

Bis(2-phenylpyridine-C,N)(2,2′-bipyridine-N,N′) iridium(III) hexafluorophosphate ([Ir(ppy)2(bpy)][PF6]) is an ionic transition-metal complex (iTMC) of interest for use in light-emitting electrochemical cells (LEECs). Films of [Ir(ppy)2(bpy)][PF6] blended with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]), deposited on different substrates, have been investigated for their morphological features, which are expected to affect the functional properties of the films, e.g., charge carrier transport. In literature, ionic liquids have been included in films of transition-metal complexes (TMCs) to increase the ion mobility and improve the performance of LEECs. A systematic comparison between the morphology of pure [Ir(ppy)2(bpy)][PF6] films and [Ir(ppy)2(bpy)][PF6] films containing [BMIm][PF6] has been carried out on different types of substrate, namely Au-patterned SiO2, indium tin oxide (ITO), and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)-modified ITO. Although [Ir(ppy)2(bpy)][PF6] forms smooth films on SiO2, ITO, and PEDOT:PSS-modified ITO substrates, addition of [BMIm][PF6] caused formation of vertical, discontinuous aggregates, which are expected to be detrimental to charge transport in LEECs with planar architecture.

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English

Electrochromism and electrochemical properties of complexes of transition metal ions with benzimidazole-based ligand

Six complexes of transition metal ions have been synthesized and characterized. Complexes showed optical properties dependent on redox state of both metal ions and ligand molecule and can be used for the construction of multielectrochromic devices.

Bio-inspired metal-coordinate hydrogels with programmable viscoelastic material functions controlled by longwave UV light.

Control over the viscoelastic mechanical properties of hydrogels intended for use as biomedical materials has long been a goal of soft matter scientists. Recent research has shown that materials made from polymers with reversibly associating transient crosslinks are a promising strategy for controlling viscoelasticity in hydrogels, for example leading to systems with precisely tunable mechanical energy-dissipation. We and others have shown that bio-inspired histidine:transition metal ion complexes allow highly precise and tunable control over the viscoelastic properties of transient network hydrogels. In this paper, we extend the design of these hydrogels such that their viscoelastic properties respond to longwave UV radiation. We show that careful selection of the histidine:transition metal ion crosslink mixtures allows unique control over pre- and post-UV viscoelastic properties. We anticipate that our strategy for controlling stimuli-responsive viscoelastic properties will aid biomedical materials scientists in the development of soft materials with specific stress-relaxing or energy-dissipating properties.

Pt(IV), Pd(II), and Rh(III) complexes induced oxidative stress and cytotoxicity in the HCT-116 colon cancer cell line

The use of transition metal complexes as appropriate analogues to cisplatin and similar anticancer drugs nowadays is of utmost importance. The inertness of Pt(IV), Pd(II), and Rh(III) complexes and the choosing of convenient ligands could offer a possible advantage in comparison to Pt(II) complexes. These advantages could be attributed to the better anticancer activity and fewer possible side effects. In this paper, we have chosen three complexes of different transition metal ions, [(TLtBu)PdIICl]ClO4, [RhIII(LH2tBu)Cl3], and [PtIV(LH2tBu)Cl3]Cl (where TLtBu is 2,6-bis[(1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine and LH2tBu is 2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine), for biological tests. All three complexes exerted strong prooxidative and cytotoxic effects on the human colorectal colon cancer HCT-116 cell line. The Pd(II) complex showed the most significant effect, while the Rh(III) complex showed the least effect.

Green-yellow emitting hybrid light emitting electrochemical cell

Greenish light-emitting electrochemical cells (LECs) reaching a lifetime of 271 hours at luminance of 1500 cd m−2 were realized by the introduction of a fluorinated ionic transition metal complex (iTMC) inside the ZnO nanocrystal hybrid-LEC device structure.

Six-Transmembrane Epithelial Antigen of Prostate 1 (STEAP1) Has a Single b Heme and Is Capable of Reducing Metal Ion Complexes and Oxygen.

STEAP1, six-transmembrane epithelial antigen of prostate member 1, is strongly expressed in several types of cancer cells, particularly in prostate cancer, and inhibition of its expression reduces the rate of tumor cell proliferation. However, the physiological function of STEAP1 remains unknown. Here for the first time, we purified a mammalian (rabbit) STEAP1 at a milligram level, permitting its high-quality biochemical and biophysical characterizations. We found that STEAP1 likely assembles as a homotrimer and forms a heterotrimer when co-expressed with STEAP2. Each STEAP1 protomer binds one heme prosthetic group that is mainly low-spin with a pair of histidine axial ligands, with small portions of high-spin and P450-type heme. In its ferrous state, STEAP1 is capable of reducing transition metal ion complexes of Fe3+ and Cu2+. Ferrous STEAP1 also reacts readily with O2 through an outer sphere redox mechanism. Kinetics with all three substrates are biphasic with ∼80 and ∼20% for the fast and slow phases, respectively, in line with its heme heterogeneity. STEAP1 retained a low level of bound FAD during purification, and the binding equilibrium constant, KD, was ∼30 μM. These results highlight STEAP as a novel metal reductase and superoxide synthase and establish a solid basis for further research into understanding how STEAP1 activities may affect cancer progression.

Performance Enhancement by ZnO Nanoparticle Layer in Hybrid Ionic Transition Metal Complex‐Light‐Emitting Electrochemical Cells (iTMC‐LECs)

Light‐emitting electrochemical cells (LECs) are solution processable solid‐state light sources comprising in their simplest architecture an ionic emissive layer in between of two electrodes. Although LECs possess several advantages that make them promising candidates for future large‐area low‐cost lighting technologies, their device wall‐plug efficacies remain so far moderate on the order of a few lumens per watt. One of the reasons therefore is considered to be the charge imbalance within the device. Here, a hybrid LEC device concept is introduced, whereby an additional layer of zinc oxide (ZnO) nanoparticles at the cathode side supports electron injection into the active light‐emitting layer and boosts the performance of the Ir‐based ionic transition metal complex LEC (iTMC‐LEC). The brightness and efficacy of the devices can be increased in average by more than 70% by the implementation of the additional inorganic layer. The time to reach the maximum brightness can be reduced in average by a factor of 7, which is attributed to an improved electron/hole balance in the device due to enhanced electron injection into the active iTMC layer.

Synthesis and crystal structures of transition metal ion complexes of di(2-thienyl)imide

Di(2-thienyl)imide, 1, has been shown to chemically polymerize, and, if metal complexes of 1 could be synthesized, the polymer could have potential applications as an ion sensor and environmental remediation agent. As a first step towards this goal, di(2-thienyl)imide is shown to form complexes with Mn (II), Co (II), and Zn (II) perchlorates. The complexes of Mn2+ and Co2+ are isostructural with two di(2-thienyl)imide ligands in equatorial positions and two perchlorate ions axial. The Zn2+ complex has two water molecules in the axial positions and the thiophene rings in the two equatorial ligands are tilted in the same direction from the median plane due to intra- and intermolecular contacts. The crystal structures and infrared spectra, as well as an improved synthesis and polymerization of di(2-thienyl)imide, are reported and discussed.

Bovine Serum Albumin Metal Complexes for Mimic of SOD

Superoxide anion radical (O\(_{2}^{\bullet -}\)) is a noxious reactive oxygen species (ROS). Transition metal ion complexes have been generally used as antioxidants to eliminate ROS. In this work, a neoteric water-soluble biopolymer metal complex (BSA-M) was prepared by conjugating the soluble biopolymer bovine serum albumin (BSA) with three transition metal ions (M, M =Cu, Co, Mn). The binding mode and ratio of metal ions bound to albumin were investigated. The BSA-M complexes were characterized by UV-Vis, circular dichroism (CD) spectra and polyacrylamide gel electrophoresis (PAGE). BSA served as polymer scaffold and the metal complex functioned as the catalytic active center. The results demonstrated that the structure of BSA remained unchanged when the binding ratio of transition metal ion complex to BSA was 5:1. Furthermore, the scavenging superoxide anion free radical (O\(_{2}^{\bullet -}\)) activity of biopolymer-metal complexes were determined by nitroblue tetrazolium light reduction assay method. The antioxidant capacity of BSA-M has markedly increased. The conjugated BSA-M (M=Cu, Mn) showed preeminent scavenging activity for O\(_{2}^{\bullet -}\), and the EC50 value of the BSA-Cu was 0.038 ±0.0013 μ mol⋅L −1, which is comparable to EC50 value (0.041±0.001 μ mol⋅L −1) of the natural superoxide dismutase (SOD), the analog quantity reached 107%. As a consequence, it can be considered as a bio-functional mimic of enzyme SOD and has a promising application prospect in antioxidant drug field. A simple biopolymer metal complex (BSA-M) was formed via BSA binding with transition metal ions, in which BSA served as scaffold and the metal ions as the catalytic active centers. BSA-Cu showed remarkable capacity for scavenging of O2⦁−.

Cationic iridium(III) complexes with different-sized negative counter-ions for solution-processed deep-blue-emitting diodes

A series of blue-emitting cationic iridium(III) complexes featuring the same coordinated iridium(III) cation while different-sized negative counter-ions are reported and investigated. Anionic influence on the physicochemical properties and device performance is studied and explained. Introduction of counter-ions with large steric hindrance, (i) effectively reduces the ionic interaction and molecular aggregation in solid states, improving the photoluminescence efficiency and avoiding the common bathochromic shift; (ii) also restricts anionic drift under the working bias in the optoelectronic devices, achieving solution-processed deep-blue-emitting diodes with a major peak at only 452 nm, among the shortest emission wavelengths of devices based on ionic transition metal complexes.

Quantum Dot/Light-Emitting Electrochemical Cell Hybrid Device and Mechanism of Its Operation

A new type of light-emitting hybrid device based on colloidal quantum dots (QDs) and an ionic transition metal complex (iTMC) light-emitting electrochemical cell (LEC) is introduced. The developed hybrid devices show light emission from both active layers, which are combined in a stacked geometry. Time-resolved photoluminescence experiments indicate that the emission is controlled by direct charge injection into both the iTMC and the QD layer. The turn-on time (time to reach 1 cd/m(2)) at constant voltage operation is significantly reduced from 8 min in the case of the reference LEC down to subsecond in the case of the hybrid device. Furthermore, luminance and efficiency of the hybrid device are enhanced compared to reference LEC directly after device turn-on by a factor of 400 and 650, respectively. We attribute these improvements to an increased electron injection efficiency into the iTMC directly after device turn-on.

Formation and stability of macromolecular complexes of transition-metal ions with copolymers of 2-deoxy-2-methacrylamido-D-glucose and unsaturated carboxylic acids

A method based on the ability of transition-metal ions to quench the fluorescence of labeled polymer molecules is developed to determine the equilibrium stability constants of macromolecular complexes of Ag+, Cu2+, and Ni2+ with the copolymers of 2-deoxy-2-methacrylamido-D-glucose and unsaturated carboxylic acids (methacrylic or acrylic) in aqueous and aqueous–saline media. The stability constants of the complexes strongly depend on the type of transition-metal, the copolymer composition, and the ionic strength of solution, but weakly depend on the type of introduced low-molecular-mass electrolyte and the chemical structure of the carboxyl-containing units.