Reversible Reduction Processes Research Articles

Ultrafast Near‐Infrared Luminescence from Cyclometalated Iridium(III) Complexes with Indirubin as Ancillary Ligand

AbstractBeing a constitutional isomer of the indigo dye, indirubin has been known as a purple colourant for a long time. On the other hand, its structural and photophysical properties as ligand in metal complexes are virtually unexplored. Herein, for the first time, we utilized indirubin as ancillary chelator to develop two new heteroleptic iridium(III) complexes equipped with two 2‐phenylpyridine units as archetypical cyclometalating ligands. These new complexes display fully reversible oxidation and reduction processes, and show a panchromatic absorption extending up to 900 nm in acetonitrile solution at 298 K. Moreover, an unexpected broad and unstructured emission band is detected for both complexes in the near‐infrared region, peaking at approx. 1100 nm and having a lifetime of approx. 60 ps; such an emission is attributed to a ligand‐centred triplet excited state (3LC) located on the indirubin ligand itself, as proved by DFT calculations. These findings may pave the way for further exploration of the indirubin dye as a ligand for different types of metal centres to create efficient near‐infrared triplet emitters without the need for difficult synthetic procedures.

Corrosion Behavior of X80 Steel in a Simulated Soil Solution Under Square-Wave Current Interference

The buried pipeline is disturbed by the dynamic direct current (DC) stray current with the subway as the main leakage source, which has the safety risk of accelerating corrosion, resulting in pipeline failure, which not only causes economic losses but also threatens personal safety. Therefore, it is necessary to study the corrosion behavior of pipeline steel under dynamic DC interference. The corrosion behavior of X80 steel under dynamic DC interference were studied by a mass loss test, alternating current impedance, circuit simulation, x-ray diffraction, and a Pourbaix diagram. Combined with the corrosion efficiency and Pourbaix diagram of the Fe-H2O system, the reversible process and reduction process mechanism in the Faraday process are proposed. The reason why the corrosion efficiency slows down in the process of non-Faraday is analyzed by the electric double-layer model of equivalent circuit calculation. In addition, based on the above corrosion process, the corresponding conceptual model of the corrosion mechanism is proposed. The experimental results show that with the asymmetry of positive and negative half-cycle interference duration and the increase of current density, the corrosion efficiency, and current corrosion efficiency of X80 steel decrease, and local corrosion intensifies. The length of the negative half-cycle interference affects the capacitive charge-discharge effect at the metal/solution interface and the reduction reaction process of corrosion products, resulting in corrosion slowing down and corrosion efficiency reduction. This is also an important reason for the reduction of corrosion mass loss observed in the experiment compared with steady-state DC.

Shift of the reduction potential of nickel(II) Schiff base complexes in the presence of redox innocent metal ions.

With the objective of gaining insight into the modulation of the reduction potential of the Ni(II/I) couple, we have synthesized two mononuclear nickel(II) complexes, NiLen (H2Len = N,N'-bis(3-methoxysalicylidene)-1,2-diamino-2-methylpropane) and NiLpn (H2Lpn = N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane) of two N2O4 donor ligands and recorded their cyclic voltammograms. Both the nickel complexes show reversible reduction processes for the Ni(II/I) couple in acetonitrile solution but the reduction potential of NiLpn (E1/2 = -1.883 V) is 188 mV more positive than that of NiLen (E1/2 = -2.071 V). In the presence of redox inactive metal ions (Li+, Na+, K+, Mg2+, Ca2+ and Ba2+), the reduction potentials are shifted by 49-331 mV and 99-435 mV towards positive values compared to NiLen and NiLpn, respectively. The shift increases with the decrease of the pKa of the respective aqua-complexes of the metal ion but is poorly co-linear; however, better linearity is found when the shift of the mono- and bi-positive metal ion aqua complexes is plotted separately. Spectrophotometric titrations of these two nickel complexes with the guest metal ions in acetonitrile showed a well-anchored isosbestic point in all cases, confirming the adduct formation of NiLen and NiLpn with the metal ions. Structural analysis of single crystals, [(NiLen)Li(H2O)2]·ClO4 (1), [(NiLpn)Li(H2O)]·ClO4 (2), [(NiLpn)2Na]·BF4 (3) and [(NiLpn)2Ba(H2O)(ClO4)]·ClO4 (4), also corroborates the heterometallic adduct formation. The orbital energies of the optimised heterometallic adducts from which electron transfers originated were calculated in order to explain the observed reduction process. A strong linear connection between the calculated orbital energies and the experimental E1/2 values was observed. According to MEP and 2D vector field plots, the largest shift for divalent metal ions is most likely caused by the local electric field that they impose in addition to Lewis acidity.

Cobalt and nickel homobinuclear metallomacrocycles based on the redox-active bis-semiquinonato ligands as potential functional absorbing materials

Recently obtained bis-o-quinone with resorcinol as a bridge was utilized for synthesis of cobalt and nickel homobinuclear complexes. Two bis-o-semiquinonato metal fragments are situated co-facially to each other forming metallomacrocycle. Metals in both fragments bond diethyl ether solvate molecules externally as well as internally in the cell. At 100 K one of two metal atoms in the macrocycle is five-coordinated whereas the other one is six-coordinated due to internal solvent molecule. Heating to room temperature results in disordering of internal solvent molecule in two positions: coordinated to different nickel atoms. Variable temperature magnetic measurements indicate both complexes to be bis-o-semiquinonato anion-radical adducts of high spin metals with magnetic interactions inside of bis-o-semiquinonato units. Sign and energy of interactions depend on the coordination number of metal. Exchange interactions between units are weak. UV–Vis absorption spectrum is determined by ligands centered bands. CV indicates reversible reduction processes involving redox active dioxolene ligands.

Electroanalytical characterization of chloroquinoline substituted redox-active phthalocyanines

In the first part of this study, the synthesis and characterization of organosoluble 5-chloroquinolin-8-yloxy substituted iron(II) (2) and oxo-titanium (IV) phthalocyanines (3) are reported for the first time. These compounds have been characterized by elemental analysis, Fourier transform infrared, electronic spectroscopy, and mass spectra. Electrochemical behaviors of metal-free and cobalt phthalocyanines and further new types of iron and oxo-titanium phthalocyanines were investigated using electroanalytical methods, such as cyclic (CV) and square wave voltammetry (SWV). According to the electrochemical results, phthalocyanines by and large showed one-electron metal- and/or ligand-based reversible or quasi-reversible reduction and oxidation processes.
 All in all, this study's results inevitably create a useful way to use them in possible future studies, which will particularly attempt to use the compound investigated in potential areas of use.

Biologically inspired 3Fe4S cluster as structural mimics of FeMoco M‐cluster

AbstractA 3Fe4S cluster related to M‐cluster of Mo‐nitrogenase is reported. [K(THF)5][Fe3(μ‐bdt)2(μ‐PPh2)(CO)5] (1) is synthesized from photo‐assisted structural rearrangement of [K(THF)2][(μ,κ2‐bdt)Fe2(μ‐PPh2)(CO)5] under visible light irradiation. The molecular structure of 1 consists of a Fe3 core bearing one dithiolate bridge and the second dithiolate group capping onto the metallic plane. The structural motif of 1 is analogous to that of Mo‐participated 3Fe4S unit in M‐cluster of Mo‐nitrogenase, with the similar Fe‐Fe and Fe‐S bond distances. Upon protonation in 193 K, a Fe‐hydride species (1H) is generated and characterized to possess the bridging hydride group (δ = −12.57 ppm) by 1H‐NMR spectroscopy and DFT calculation. In CH3CN solution, complex 1 exhibits a reversible reduction and oxidation process at = −1.94 V and = −0.18 V, respectively, at 273 K. The reduction behavior of 1 in CH2Cl2 solution at 243 K displays a slight modification in the presence of trifluoroacetic acid, revealing a moderate anodic potential shift (~50 mV). The current amplitude of the reduction wave is linearly increased with the increasement of acid added, indicative of the catalytic event.

Electrochemical and in-situ spectroelectrochemical properties of novel (5-(tert-butyl)-2-((3,4-dicyanophenoxy)methyl)phenyl)methanolate substituted mononuclear metal phthalocyanines

This work involves the synthesis and characterization of metallic (Co, Fe, Mn, Ni, Zn) ball-type phthalocyanine precursors by using novel 4,4′-(((4-(tert-butyl)-1,2-phenylene)bis-(methylene))bis(oxy))diphthalonitrile starting compound. The classical oxo-bridge in phthalocyanines was altered with the -OCH2- bridge first time for these ball-type phthalocyanine precursors, and the effects of this change on the chemical, physical and spectral features of phthalocyanine complexes were investigated, in the study. The redox properties of phthalocyanines were researched by electrochemical and in situ spectroelectrochemical measurements on a Pt working electrode in non-aqueous medium. The color changes involved in the redox processes were observed via in situ electrocolorimetric techniques. Electrochemical and UV–Vis spectral measurements exhibited that the compounds had reversible and serial one-electron reduction and oxidation processes. Furthermore, they also had nitrile reduction processes because of opened nitrile groups located at peripheral tails of the phthalocyanine complexes. The plentiful redox conducts of the complexes such as Pc ring based and/or central redox active metal-based reduction and oxidation reactions at low potentials showed that these complexes can be used as functional materials. Because of the apparent spectral and net color changes, the complexes are suitable for utilization in electrochromic devices. Moreover, their rich redox features are a sign of their high electrocatalytic activity for oxygen reduction.

A C 54 B 2 Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

A C ₅₄ B ₂ Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

Recent Developments in the Syntheses of Aluminum Complexes Based on Redox-Active Ligands

Applications of aluminum as a catalyst for organic/inorganic transformation reactions are ideal because of its easy availability, inexpensiveness, and non-toxicity. However, successful implementation of Al(III) complexes as catalysts require an easy reduction-oxidation cycle between Al(III) and Al(I). Nevertheless, molecular complexes of Al(I) are not common, often require special efforts for their synthesis and isolation. Additionally, the Al(I)→Al(III) oxidation reaction is facile whereas the corresponding Al(III)→Al(I) reduction occurs only under highly reducing conditions. This creates a problem in developing Al(I)/Al(III) couple catalytic cycle for practical application. But, for aluminum complexes to be applicable in redox transformations, complexes must readily undergo reversible oxidation and reduction processes. One can envision applying a redox-active ligand where instead of aluminum the ligand would be reversibly oxidized and reduced to perform a certain electron transfer process. So, the development of a large pool of aluminum complexes supported by redox-active ligands is very important. In this review article, we have summarized recent developments on the syntheses of aluminum complexes with some redox-active ligands. This may help in designing new catalysts for future applications.

Cation effect on the electrochemical reduction of polyoxometalates in room temperature ionic liquids

Polyoxometalates (POMs) are compounds that undergo multiple successive one-electron redox transitions, making them convenient model reactants to study ion solvation effects. Room temperature ionic liquids (RTILs) are solvents made entirely of ions, and are expected to have interactions with the highly negatively charged POM reduction products. In this work, 12 RTILs with a range of different anions ([FSI]−=bis(fluorosulfonyl)imide, [TFSI]−=bis(trifluoromethylsulfonyl)imide, [BETI]−=bis(pentafluoroethylsulfonyl)imide, [BF4]−, [PF6]−) and cations (imidazolium, pyrrolidinium, sulfonium, ammonium, phosphonium) were employed as solvents to study the kinetics and thermodynamics of [S2W18O62]4− reduction, to shed light on solvation effects and ion-pairing effects caused by different RTIL structures. Up to six reversible reduction processes (producing highly negatively charged [S2W18O62]10−) were observed. For the RTILs that showed multiple processes, a clear trend in both the thermodynamics (inferred from the reduction peak potentials) and kinetics (inferred from the peak-to-peak separation) was observed, in the order: imidazolium < sulfonium ≈ ammonium < pyrrolidinium < phosphonium, supporting strong interactions of the negatively charged POM reduction products with the cation. Two related POMs, [P2W18O62]6− and [PW12O40]3−, were also studied in the optimum RTIL found for [S2W18O62]4− ([C2mim][FSI]=1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide), revealing fast kinetics and asymmetric peaks for [PW12O40]3−. This work demonstrates the importance of understanding the solvation effects of RTIL ions for highly charged electrogenerated products, allowing tuning of the RTIL structure to achieve the optimum kinetics and thermodynamics for an electrochemical process.

Synthesis, structure and reactivity of μ3-SnH capped trinuclear nickel cluster.

Treatment of the trichlorotin-capped trinuclear nickel cluster, [Ni3(dppm)3(μ3-Cl)(μ3-SnCl3)], 1, with 4 eq. NaHB(Et)3 yields a μ3-SnH capped trinuclear nickel cluster, [Ni3(dppm)3(μ3-H)(μ3-SnH)], 2 [dppm = bis(diphenylphosphino)methane]. Single-crystal X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, and computational studies together support that cluster 2 is a divalent tin hydride. Complex 2 displays a wide range of reactivity including oxidative addition of bromoethane across the Sn center. Addition of 1 eq. iodoethane to complex 2 releases H2 (g) and generates an ethyltin-capped nickel cluster with a μ3-iodide, [Ni3(dppm)3(μ3-I)(μ3-Sn(CH2CH3))], 4. Notably, insertion of alkynes into the Sn-H bond of 2 can be achieved via addition of 1 eq. 1-hexyne to generate the 1-hexen-2-yl-tin-capped nickel cluster, [Ni3(dppm)3(μ3H)(μ3-Sn(C6H11))], 5. Addition of H2 (g) to 5 regenerates the starting material, 2, and hexane. The formally 44-electron cluster 2 also displays significant redox chemistry with two reversible one-electron oxidations (E = -1.3 V, -0.8 V vs. Fc0/+) and one-electron reduction process (E = -2.7 V vs. Fc0/+) observed by cyclic voltammetry.

1,2,5]Chalcogenadiazole-fused Dicyanonaphthoquinodiimines: Larger Contribution from Chalcogen Bond than Weak Hydrogen Bond in Determining Crystal Structures

The title electron acceptors are planar molecules undergoing reversible two-stage one-electron reduction processes. In the crystal of selenadiazole derivative (1), tetrameric structure is formed by two kinds of chalcogen bond (ChB), which is further connected by ChB and weak hydrogen bond (WHB). Although sulfur analogue (2) has only weaker ChB, it crystallizes isomorphously to 1 forming ChB-tetramer, thus contribution from ChB is more dominant than WHB in determining the crystal packing, which is different from the corresponding tetracyanoquinodimethane analogues.

Long-Range Order in Supramolecular π Assemblies in Discrete Multidecker Naphthalenediimides.

We report herein the solution and solid-state studies of conformationally flexible multidecker naphthalenediimides (NDIs) in which the chromophoric NDI units intramolecularly assemble into a series of discrete π-stacks. The X-ray crystallography reveals the existence of exclusively all-syn NDIs orientations in lower congeners while all-anti in a higher congener, suggesting short- to long-range π···π interactions throughout the slipped πNDI chromophoric array. The UV/vis and fluorescence spectra evaluate the discrete π-stacks by remarkable optical changes upon cooling in solution. Furthermore, we carried out a systematic electrochemical investigation to gain an insight into redox properties of the long-range π-stacked structures. The higher congener (5NDI) shows a ten-electron reversible reduction process in a small working potential window (∼0.8 V). To our knowledge, this is an unusual observation in an organic molecular system to undergo up to ten-electron reduction. These results pave the way to design multidecker π-stacks in which structural control with specific electronic properties would be engineered.

Síntesis regioespecífica y estudio electroquímico de dos derivados carboxílicos C60 solubles en agua

We report a new methodology for the synthesis of two highly symmetric equatorial malonate hexaadducts of C60 fullerene. The synthetic methodology is based on a series of protection and deprotection steps that allow the preparation of a fullerene [60] functionalized with six symmetrical positioned malonate addends without using complicated and expensive separation techniques (highperformance liquid chromatography, HPLC) or long reaction times. This methodology allowed us to prepare the carboxylic adducts 6 (equatorial octacarboxylic tetraadduct of C60) and 8 (equatorial dodecacarboxylic hexakisadduct of C60). As far as we now, compound 6 has not yet been reported. We also studied the electronic properties of the main compounds by UV-Vis spectroscopy and cyclic voltammetry (CV). The reported fullerene adducts exhibited several reversible reduction processes whose electron transfers are controlled by diffusion.

Tetrakis-1,2,4,5-(bis(3,5-dimethylphenyl)phosphino)benzene (Me16tpbz): A soluble and spectroscopically simple variant of the 1,2,4,5-tetraphosphinobenzene ligand platform

A preparation of 1,2,4,5-tetrakis(bis(3,5-dimethylphenyl)phosphino)benzene (Me16tpbz) has been devised as a two-step synthesis beginning with bis(3,5-dimethylphenyl)chlorophosphine and 1,2,4,5-tetrafluorobenzene, albeit in low overall yield of 10%. The crystal structure of Me16tpbz reveals slight pushing of the phosphorus atoms above and below the central arene ring, suggesting the effect of slight steric pressure, as compared to the fully planar C6P4 core found in 1,2,4,5-tetrakis(diphenylphosphino)benzene (tpbz). Upon exposure to air, solution samples of Me16tpbz degrade to (3,5-Me2C6H3)2PP(O)(C6H3-3,5-Me2)2, identified by X-ray crystallography, which suggests P–C bond scission is a decomposition pathway. The dinickel compound [(mnt)Ni(Me16tpbz)Ni(mnt)] (mnt(2–) = [(NC)2C2S2]2–) has been structurally characterized by X-ray crystallography and reveals a chair-like conformation defined by a 32.3° angle between the NiP2 planes with respect to the central C6P4 mean plane. Compared to the analogous [(mnt)Ni(tpbz)Ni(mnt)], slightly weaker binding of Me16tpbz to Ni is implied by its modestly longer Ni–P bond lengths. The cyclic voltammogram of [(mnt)Ni(Me16tpbz)Ni(mnt)] in CH2Cl2 shows reversible reductions at ~ −1.01 V and −1.21 V, corresponding to sequential Ni2+ + e– → Ni1+ processes, while in DMF, under conditions where [(mnt)Ni(tpbz)Ni(mnt)] shows multiple, reversible reduction processes, its behavior is irreversible and more complex.

Blue Light-Emitting Electrochemical Cells with Ir(Ⅲ) Complex

Light-emitting electrochemical cells (LECs) are one of promising technology for light emitting devices. LECs have some advantages which are single layer structure with air-stable metal electrodes and to use solution process for the device fabrication. Full color emission which means red, green and blue lights is needed for the light application. Phosphorescent Ir(Ⅲ) complex have potential to emit full color because iridium complex has a wide energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In particular, archetypal cationic Ir(Ⅲ) complex [Ir(ppy)2(bpy)]+, where ppy and bpy stands for 2-phenylpyridine (Hppy) as the cyclometalating ligand and 2,2’-bipyridine (bpy) as the ancillary ligand, respectively. Green, yellow, orange and red emitting cationic Ir(Ⅲ) complexes have been synthesized so far. In contrast, the number of blue emitting cationic Ir(Ⅲ) complexes are limited. Blue light emission is essential for full color emission. Widening energy gap of Ir(Ⅲ) complexes causes blue shift. For example, Fluorine element which is electron-deficient substituents have been attached cyclometalating ligands to stabilize HOMO. However, fluorine substitution degrades the electrochemical and thermal stability of the complex. It is necessary to find a cyclometalating ligand without fluorine substitution for stable blue light emission.1-(2,6-dimethylphenyl)-3-methyl-5-phenyl-1H-1,2,4-triazole (dphtz) was synthesized as a cyclometalating ligand for blue light emitting cationic Ir(Ⅲ) complex. 2-(1Hpyraol-1- yl)pyridine (pzpy) was used as an ancillary ligand. [Ir(dphtz)2(pzpy)](TFSI) was synthesized in a three-step reaction. First, the chloro-bridged iridium dimers, [Ir(dphtz)2Cl]2 was synthesized from IrCl3・nH2O and dphtz. Second, [Ir(dphtz)2(pzpy)]Cl was synthesized from [Ir(dphtz)2Cl]2 and pzpy. Third, LiTFSI was added to [Ir(dphtz)2(pzpy)]Cl. Cl- was replaced by TFSI-, and [Ir(dphtz)2(pzpy)](TFSI) was synthesized[1].Absorption and photoluminescence (PL) spectrum of [Ir(dphtz)2(pzpy)](TFSI) were measured in CH3CN solution to characterize photophysical property. Absorption spectrum indicates that the complex has absorption under 399 nm, resulting that the bandgap is calculated to be 3.11 eV. PL spectrum indicates blue emission with peak wavelength of 466 nm. The peak wavelength is blue-shifted by nearly 98 nm compared with archetypal cationic Ir(Ⅲ) [Ir(ppy)2(bpy)](TFSI) (λ= 564 nm) of our previous work. Cyclic voltammetry in solution was performed to investigate the electrochemical property of the complex. The voltammogram shows that the oxidation potential is 1.40 V and reduction potential is -1.77 V vs. Ag/Ag+. From these two values, the theoretical drive voltage of LECs using the complex can be calculated to be 3.17 V. In addition, the complex exhibits reversible oxidation process and irreversible reduction process in CH3CN. These properties would cause unbalanced electron and hole injection of LECs device.LECs using the complex was fabricated. The device structure consists of ITO/complex:20 wt％ EMIMTFSI:6.25 wt％ PMMA(polymethylmethacrylate) /LiF (0.5 nm)/Ag (75 nm). EL spectrum shows blue light emission with centered 440 nm. However, the blue emission did not keep for a long time. After a minute, the emission color changed gray EL with centered 463 nm. Under a constant driving current of 2.0 mA, the LECs provide a peak brightness of 9.9 cd/m2. This low luminance may be due to unbalanced electron and hole injection. Under a constant driving current of 2.0 mA, the driving voltage shows 3.95 V, whereas after a minute, it exceeds 4.5 V, indicating that [Ir(dphtz)2(pzpy)](TFSI) was degraded, and LECs does not function optimally.In conclusion, the blue light emitting complex in this study shows poor luminance and short lifetime for LECs. In order to get higher luminance and longer lifetime, we will improve the chemical stability of the Ir(Ⅲ) complex and the balance of the electron and hole injection into the emitting layer of LECs.Reference[1] X.Wang et al., Inorg.Chem., 58, 12132 (2019).

Negative electrical tunability of chitosan–graphene oxide nanocomposites

Herein, we report negative anomalous electrical tunability of the nanocomposite chitosan and graphene oxide (CS–GO) films based upon the dependence of dielectric constant and resistivity on DC bias. The origin of such anomalous tunability can be traceable to the reversible transformation of GO to reduced graphene oxide. In this transformation, H+ ions are released from water or GO side groups and those of $${\text{NH}}_{3}^{ + }$$ from CS; both ions participate in the reversible reduction process. Here, the capacitance exhibits negative tunability such that the dielectric constant increases and the resistivity decreases with increasing of DC bias. To probe this new phenomenon, we studied GO concentrations from 0 to 15 wt.% and water contents from 0 to 25 wt.%. Our results suggest that chitosan–GO nanocomposites can be readily prepared for the development of novel devices required in flexible organic electronics.

Cationic Iridium Complexes with 3,4,5-Triphenyl-4H-1,2,4-Triazole Type Cyclometalating Ligands: Synthesis, Characterizations, and Their Use in Light-Emitting Electrochemical Cells.

Cationic iridium complexes that show blue-shifted emission and high phosphorescent efficiency have been pursued for their optoelectronic applications. Five cationic iridium complexes with 3,4,5-triphenyl-4H-1,2,4-triazole (tPhTAZ) type cyclometalating ligands (C^N) and 2,2'-bipyridine or 2-(pyridin-2-yl)-1H-benzo[d]imidazole type ancillary ligands (N^N) have been designed and synthesized. Their structures have been confirmed by X-ray crystallography, and their photophysical and electrochemical properties have been comprehensively characterized. In solution and thin films, the complexes afford efficient yellow to blue-green emission. The highest occupied molecular orbitals (HOMOs) of these complexes are delocalized over the C^N ligand and the iridium ion, and compared with the conventional 2-phenylpyridine (Hppy) ligand, the tPhTAZ ligand largely shifts the emission of the complex toward blue by over 40 nm through stabilizing the HOMO. Moreover, the peripheral phenyl rings in tPhTAZ provide steric hindrance to the complexes, which suppresses phosphorescence concentration-quenching of the complexes, leading to high luminescent efficiencies in neat films. Theoretical calculations have shown that the emission of the complexes originates from either the charge-transfer state (Ir/C^N → N^N) or the C^N/N^N-centered 3π-π* state, depending on the local surrounding of the complex. The complexes exhibit good electrochemical stability with reversible oxidation and reduction processes in solution. Solid-state light emitting electrochemical cells (LECs) using the complexes afford yellow to blue-green emission, with peak current efficiencies of up to 34.7 cd A-1 and maximum brightness of up to 256 cd m-2 at 3.0 V, which are among the highest for LECs based on cationic iridium complexes reported so far, indicating the great potential for the use of tPhTAZ-type C^N ligands in construction of cationic iridium complexes for LEC applications.

Redox Control Recombination in Axially Linked “Donor – Aluminum(III) Porphyrin – Fullerene” Reaction Center Models

Aluminum(III) porphyrins (AlPor) are well suited for the construction of axially linked multicomponent donor-acceptor systems. The axial hydroxide reacts with carboxylic acids or alcohols to form covalent ester or ether linkage, respectively. Moreover, they bind Lewis bases such as imidazole or pyridine to form a coordination bond with the Al center. They hold high fluorescence quantum yields with adequate singlet and triplet state lifetimes, as well as rich redox chemistry with two reversible oxidation and reduction processes. They can act as either a photosensitizing electron acceptor or donor with a wide variety of redox and optically active compounds. By exploiting these unique properties, we have designed several donor-AlPor-acceptor systems to mimic the reaction center complex of natural photosynthesis. In these systems, we have studied the electron transfer processes in perpendicular to the porphyrin plane. The optical studies showed that the excitation of AlPor results in a sequential electron transfer between redox-active units to generate long-lived radical pairs. I will discuss some of these systems to show how the recombination dynamics depend on the redox potentials.

Facilitated proton transfer via water autoprotolysis-electron transfer coupled reactions at thick-film modified electrodes

We present the derivation of a general mathematical model for facilitated proton transfer (FPT) reactions across a liquid|liquid (L|L) interface assisted by a protonatable neutral weak base at a thick organic film modified electrode setup. The effect of the explicit consideration of water autoprotolysis is analysed. The model reported in this paper allows us to simulate the system under different experimental conditions, such as initial pH, organic phase to aqueous phase volume ratio and concentration of redox probe and transferring protonated species. This model for the FPT reactions via water autoprotolysis in a system with two polarized interfaces is compared to our previous results calculated for a single polarizable interface [J. Electroanal. Chem. 578 (2005) 159–170]. We simulate a system with a single redox probe with two reversible non-simultaneous reduction processes with the goal of obtaining detailed mechanistic information of the facilitated proton transfer via water autoprotolysis process at thick-film modified electrodes. Our conclusions can be straightforwardly applied in experiments. We focus on a system consisting of 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a redox probe and 2,9-dimethyl-1,10-phenanthroline (2,9-DMP) as a neutral weak base.