Electrogenerated chemiluminescence of Pb(II)-bromide complexes

The electrochemistry and electrogenerated chemiluminescence (ECL) of Pb₄Br₁₁ ³⁻ in acetonitrile solution is reported. Pb₄Br₁₁ ³⁻ is formed in situ by the reaction of lead(II) and bromide ions with ECL generated upon sweep to positive potentials using tri-n-propylamine (TPrA) as an oxidative-reductive coreactant. An ECL efficiency (φ_ecl) of 0.0079 was obtained compared to Ir(ppy)₃ (ppy=2-phenylpyridine; φ_ecl=1). The ECL intensity peaks at a potential corresponding to oxidation of TPrA and Pb₄Br₁₁ ³⁻ indicating that emission is from the lead-bromide cluster.     

Synthesis, crystallography and photoluminescence of a new pyrazolonato iridium complex

By using 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone (pmip) as the ancillary ligand, the cyclometalated complex: bis-(2-phenylpyridine)-(pmip)-iridium [(ppy)₂Ir(pmip)] was synthesized. Its crystal structure, absorption and emission were compared with those of its analogue, the frequently used electrophosphorescent material (ppy)₂Ir(dbm) [bis-(2-phenylpyridine)-(dibenzoylmethane) iridium]. For (ppy)₂Ir(pmip) in dichloromethane, the emission is highly structured and the intensity is 5 times higher than that of (ppy)₂Ir(dbm). It is a result of the higher triplet energy level of pmip relative to that of dbm. In solid state, green emission of (ppy)₂Ir(pmip) peaked at 550 nm was observed with a quantum efficiency 0.31% in contrast to the emission at 626 nm with a quantum efficiency of 0.76% for (ppy)₂Ir(dbm). The bathochromical shift and higher efficiency in crystallized (ppy)₂Ir(dbm) was explained by the stronger π-π intermolecular interactions which is unique to in solid state (ppy)₂Ir(dbm) crystals.     

Electrogenerated chemiluminescence of tris(2‐phenylpyridine)iridium(III) in water,acetonitrile and trifluorethanol

The spectroscopic, electrochemical and coreactant electrogenerated chemiluminescence (ECL) properties of Ir(ppy)3 (where ppy = 2‐phenylpyridine) have been obtained in aqueous buffered (KH2PO4), 50 : 50 (v/v) acetonitrile–aqueous buffered (MeCN–KH2PO4) and 30% trifluoroethanol (TFE) solutions. Tri‐n‐propylamine was used as the oxidative‐reductive ECL coreactant. The photoluminescence (PL) efficiency (ϕem) of Ir(ppy)3 in TFE (ϕem ≈ 0.029) was slightly higher than in 50 : 50 MeCN–KH2PO4 (ϕem ≈ 0.0021) and water (ϕem ≈ 0.00016) compared to a Ru(bpy)32+ standard solution in water (Φem ≈ 0.042). PL and ECL emission spectra were nearly identical in all three solvents, with dual emission maxima at 510 and 530 nm. The similarity between the ECL and PL spectra indicate that the same excited state is probably formed in both experiments. ECL efficiencies (ϕecl) in 30% TFE solution (ϕecl = 0.0098) were higher than aqueous solution (ϕecl = 0.00092) system yet lower than a 50% MeCN–KH2PO4 solution (ϕecl = 0.0091). Copyright © 2014 John Wiley & Sons, Ltd.     

Tuning electronic structure and photophysical properties of [Ir(ppy)2(py)2]+ by substituents binding in pyridyl ligand: a computational study

Iridium (III) 2-phenylpyridine (ppy) complexes with two suitable monodentate L ligands [Ir(ppy)(2)(L)(2)](+) (ppy = 2-phenylpyridine, py = pyridine, L = 4-pyCN 1, 4-pyCHO 2, 4-pyCl 3, py 4, 4-pyNH(2) 5) were studied by density functional theory (DFT) and time-dependent DFT methods. The influences of ligands L on the electronic structure and photophysical properties were investigated in detail. The compositions and energy levels of the lowest unoccupied molecular orbital (LUMO) are changed more significantly than those of the highest occupied molecular (HOMO) by tuning L ligands. With the electronegativity decrease of L ligands 4-pyCN > 4-pyCHO > 4-pyCl > py > 4-pyNH(2), the LUMO distributing changes from py to ppy, and the absorptions have an obvious red shift. The calculated results showed that the transition character of the absorption and emission can be changed by adjusting the electronegativity of the L ligands. In addition, no solvent effect was observed in the absorptions and emissions.     

[Ir(acac)(η-C8H14)2]: A precursor in the synthesis of cyclometalated iridium(III) complexes

A new convenient synthesis and the crystallographic characterization of [Ir(acac)(coe)₂] (2, acac = acetylacetonato; coe = cis-cyclooctene) are described. The title compound crystallized from THF/ethanol in two modifications (monoclinic P2₁/c, 2a, and triclinic , 2b). Complex 2 represents an efficient starting material in the synthesis of mononuclear iridium(III) complexes containing cyclometalated 2-phenylpyridinato ligands using oxidative addition reactions of the corresponding ligands towards 2. Thus [Ir(acac)(ppy)₂] (3, ppy = 2-phenylpyridinato) and [Ir(ppy)₃] (4) (mer, 4a; fac, 4b) were prepared in excellent yields and short reaction times in a kind of one-pot procedure starting from [{Ir(μ-Cl)(coe)₂}₂] (1). Furthermore a convenient synthesis of [{Ir(μ-Cl)(ppy)₂}₂] (5) from 1 and Hppy is described.     

Electrochemiluminescence of dipicolinic acid (DPA) and (bpy)(2)Ru(DPA)(+) (bpy = 2,2'-bipyridine).

The spectroscopic and electrochemiluminescence (ECL) properties of dipicolinic acid (DPA), (bpy)(2)Ru(2+) (bpy = 2,2'-bipyridine) and the species formed when DPA and (bpy)(2)Ru(2+) [abbreviated to (bpy)(2)Ru(DPA)(+)] are allowed to react are reported. The UV-Vis absorption maxima for (bpy)(2)Ru(2+) and (bpy)(2)Ru(DPA)(+) are 493 and 475 nm, respectively, indicating the in situ formation of a complex between DPA and (bpy)(2)Ru(2+). DPA, (bpy)(2)Ru(2+) and (bpy)(2)Ru(DPA)(+) display ECL upon oxidation in the presence of the oxidative-reductive co-reactant tri-n-propylamine (TPrA). The ECL of (bpy)(2)Ru(DPA)(+) is at least two-fold higher than either of the parent species. An ECL spectrum of (bpy)(2)Ru(DPA)(+) displays a peak maximum 40 nm red-shifted from the photoluminescence peak maximum, suggesting that the excited state formed electrochemically is different from that formed spectroscopically.     

Efficient synthesis of the cyclometalated complex fac-[Rh(ppy)3] (ppy = 2-phenylpyridinato)

A new convenient high-yield synthesis of the tris-cyclometalated complexes fac-[Rh(ppy)₃] (4; ppy = 2-phenylpyridinato) was developed. Complex 4 was prepared in a kind of one-pot synthesis starting from in situ prepared [Rh(acac)(coe)₂] (2) which was heated in refluxing 2-phenylpyridine for a short time. After purification by filtration over alumina, compound 4 was obtained in yields of 65%. Also [Rh(acac)(ppy)₂] (3) was prepared in a similar manner by oxidative addition of Hppy in refluxing toluene in high yields. In contrast to previous findings with the analogous iridium compounds, there was not any hint at the formation of the isomer mer-[Rh(ppy)₃] using similar reaction conditions as applied for iridium. Furthermore the compound [{Rh(μ-Cl)(ppy)₂}₂] (5) was prepared from [{Rh(μ-Cl)(coe)₂}₂] (1) and Hppy in refluxing toluene in nearly quantitative yield.     

Optically active molecule-based magnets: enantioselective self-assembling, optical, and magnetic properties.

In this short communication we describe the synthesis and the optical and magnetic properties of optically active three dimensional (3D) bimetallic [Cr-Mn] networks [[Delta Cr(III) Delta Mn(II)(ox)(3)][Delta Ru(II)(bpy)(3)]ClO(4)](n)1 - Delta, [[Lambda Cr(III)Lambda Mn(II)(ox)(3)][Lambda Ru(II) (bpy)(3)]ClO(4)](n) 1 - Lambda and [[Delta Cr(III)Delta Mn(II)(ox)(3)][Delta Ru(II)(bpy)(2)p p y]](n) 2 - Delta,[[Lambda Cr(III)Lambda Mn(II)(ox)(3)][Lambda Ru(II)(bpy)(2)ppy]](n) 2 - Lambda (ox = oxalate, bpy = bipyridine, ppy = phenyl-pyridine).     

Color tuning of iridium complexes - Part I: Substituted phenylisoquinoline-based iridium complexes as the triplet emitter

A series of new iridium complexes with isoquinoline derivative ligands were synthesized for application in organic light-emitting diodes (OLEDs). It is demonstrated that varying the substituents at the 2′- or 4′-positions of the isoquinoline ligand makes the color tuning possible. Because of the steric effect, the 6′-substituted complexes: bis[1-(6′-methyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6b1), bis[1-(6′-trifluoromethyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6b2), and bis[1-(6′-methoxy)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6b3) show red-shift effect with respect to the 4′-substituted complexes: bis[1-(4′-methyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6a1), bis[1-(4′-trifluoromethyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6a2), and bis[1-(4′-methoxy)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6a3). All of these complexes are suitable for the red phosphorescent materials in OLEDs.     

Iridium(III) Luminescent Probe for Detection of the Malarial Protein Biomarker Histidine Rich Protein-II

This work outlines the synthesis of a non-emissive, cyclometalated Ir(III) complex, Ir(ppy)₂(H₂O)₂⁺ (Ir1), which elicits a rapid, long-lived phosphorescent signal when coordinated to a histidine-containing protein immobilized on the surface of a magnetic particle. Synthesis of Ir1, in high yields,is complete O/N and involves splitting of the parent cyclometalated Ir(III) chloro-bridged dimer into two equivalents of the solvated complex.To confirm specificity, several amino acids were probed for coordination activity when added to the synthesized probe, and only histidine elicited a signal response. Using BNT-II, a branched peptide mimic of the malarial biomarker Histidine Rich Protein II (pfHRP-II), the iridium probe was validated as a tool for HRP-II detection. Quenching effects were noted in the BNT-II/Ir1 titration when compared to L-Histidine/Ir1, but these were attributed to steric hindrance and triplet state quenching. Biolayer interferometry was used to determine real-time kinetics of interaction of Ir1 with BNT-II. Once the system was optimized, the limit of detection of rcHRP-II using the probe was found to be 12.8 nM in solution. When this protein was immobilized on the surface of a 50 µm magnetic agarose particle, the limit of detection was 14.5 nM. The robust signal response of this inorganic probe, as well as its flexibility of use in solution or immobilized on a surface, can lend itself toward a variety of applications, from diagnostic use to imaging.     

In-situ produced ascorbic acid as coreactant for an ultrasensitive solid-state tris(2,2'-bipyridyl) ruthenium(II) electrochemiluminescence aptasensor

Herein, an ultrasensitive solid-state tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy)(3)(2+)) electrochemiluminescence (ECL) aptasensor using in-situ produced ascorbic acid as coreactant was successfully constructed for detection of thrombin. Firstly, the composite of Ru(bpy)(3)(2+) and platinum nanoparticles (Ru-PtNPs) were immobilized onto Nafion coated glass carbon electrode, followed by successive adsorption of streptavidin-alkaine phosphatase conjugate (SA-ALP) and biotinylated anti-thrombin aptamer to successfully construct an ECL aptasensor for thrombin determination. In our design, Pt nanoparticles in Ru(bpy)(3)(2+)-Nafion film successfully inhibited the migration of Ru(bpy)(3)(2+) into the electrochemically hydrophobic region of Nafion and facilitated the electron transfer between Ru(bpy)(3)(2+) and electrode surface. Furthermore, ALP on the electrode surface could catalyze hydrolysis of ascorbic acid 2-phosphate to in-situ produce ascorbic acid, which co-reacted with Ru(bpy)(3)(2+) to obtain quite fast, stable and greatly amplified ECL signal. The experimental results indicated that the aptasensor exhibited good response for thrombin with excellent sensitivity, selectivity and stability. A linear range of 1 × 10(-15)-1 × 10(-8) M with an ultralow detection limit of 0.33 fM (S/N=3) was obtained. Thus, this procedure has great promise for detection of thrombin present at ultra-trace levels during early stage of diseases.     

Synthesis, crystal structure and photoluminescent property of an iridium complex with coumarin derivative ligand

Novel iridium complex containing coumarin derivative as a cyclometalated ligand (L) and picolinate (pic) as the ancillary ligand, Ir(III)bis(3-(pyridin-2-yl)coumarinato N,C⁴)(picolinate) [Ir(L)₂(pic)], was synthesized and characterized. It was demonstrated that the iridium (III) ion in Ir(L)₂(pic) is hexacoordinated by two C atoms and two N atoms from 3-(pyridin-2-yl)coumarin ligands and one N atom and one O atom from picolinate ligand, displaying a distorted octahedral coordination geometry. The Ir(L)₂(pic) has very strong absorption and intensive emission at 532 nm. These results show the promising future of that Ir(L)₂(pic) in fabrication organic light-emitting diodes.     

Synthesis and characterization of phosphorescent iridium complexes containing trifluoromethyl-substituted phenyl pyridine based ligands

Several iridium complexes containing trifluoromethyl-substituted phenyl pyridine based ligands have been synthesized and characterized to try to investigate the effect of trifluoromethyl group and its position on physical properties. The complexes have the general structure of (C-N)₂Ir(LX), where the C-N are 2-phenylpyridine (ppy), 2-(3,5-bis-trifluoromethylphenyl)pyridine (fmppy), 2-(3,5-bis-trifluoromethylphenyl)-4-methylpyridine (fmpmpy), 2-(3,5-bis-trifluoromethylphenyl)-5-trifluoromethylpyridine (tfmppy) and the LX are 2-picolinic acid (pic) and acetylacetonate (acac). The (tfmppy)₂Ir(pic) was characterized using X-ray crystallography. The absorption, emission, and thermostability of the complexes were systematically investigated. Introduction of CF₃ substituents into 2-phenylpyridine in (ppy)₂Ir(pic) lead to some decrease in the sublimation temperature, which is more suitable to devices fabrication. The experimental results revealed that the emissive colors of these complexes could be finely tuned by suitable incorporation of trifluoromethyl substituents on the 2-phenylpyridine ligand, obtaining bright green-blue emission λ_max values from 471 to 489 nm in CH₂Cl₂ solution at room temperature, with high solution quantum efficiencies ranging from 0.37 to 1.89 relative to Ir(ppy)₃.     

Strain in organometallics II: controlling the properties of tetra-coordinated iridium complexes using diastereomers of a bis(tropp) ligand system

The tetra-chelating ligands 1,2-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-ethane, bis(tropp^Ph)ethane, and 1,3-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-propane, bis(tropp^Ph)propane, were synthesised. For the binding of transition metals, these ligands offer two olefin moieties and two phosphorus centres and form mixtures of diastereomers with a R,S-configuration at the phosphorus centres (meso), or a R,R(S,S)-configuration (rac), respectively. meso/rac-bis(tropp^Ph)ethane was separated by fractional crystallisation and reacted with [Ir(cod)₂]OTf (cod=cylcooctadiene, OTf⁻=CF₃SO₃ ⁻) to give the penta-coordinated complex-cations meso/rac-[Ir(bis(tropp^Ph)ethane)(cod)]⁺, where the bis(tropp^Ph)ethane serves as tridentate ligand merely. One olefin unit remains non-bonded, however, a slow intra-molecular exchange between this olefin and the coordinated olefin unit was established (meso-[Ir(bis(tropp^Ph)ethane)(cod)]⁺: k<0.5 s⁻¹; rac-[Ir(bis(tropp^Ph)ethane)(cod)]⁺: k≈35 s⁻¹). The ligand meso/rac-bis(tropp^Ph)propane reacts with [Ir(cod)₂]OTf to give the corresponding complexes containing the tetra-coordinated 16-electron complex-cations meso/rac-[Ir(bis(tropp^Ph)propane)]⁺. The diastereomers were separated by fractional crystallisation. The complex rac-[Ir(bis(tropp^Ph)propane)]⁺ is reduced at relatively low potentials (E¹_1/2=−0.95 V, E²_1/2=−1.33 V versus Ag/AgCl) to give the neutral 17-electron complex [Ir(bis(tropp^Ph)propane)]⁰ and the 18-electron anionic iridate [Ir(bis(tropp^Ph)propane)]⁻, respectively. With acetonitrile, [Ir(bis(tropp^Ph)propane)]⁺ reacts to give the penta-coordinated complex rac-[Ir(MeCN)(bis(tropp^Ph)propane)]⁺ (K=45 M⁻¹, k_f=6×10³ M⁻¹ s⁻¹, k_d=1×10² s⁻¹) and with chloride to yield the relatively stable complex rac-[Ir(Cl)(bis(tropp^Ph)propane)] (k_d<0.5 s⁻¹). Compared to the rac-isomer, the meso-[Ir(bis(tropp^Ph)propane)]⁺ shows significantly cathodically shifted reduction potentials (E¹_1/2=−1.25 V, E²_1/2=−1.64 V versus Ag/AgCl), an acetonitrile complex could not be detected, and the chloro-complex, meso-[Ir(Cl)(bis(tropp^Ph)propane)], is much more labile (k_d≈20′000 s⁻¹). meso-[Ir(bis(tropp^Ph)propane)]⁺ reacts with one equivalent H₂ to give the trans-dihydride complex-cation, meso-[Ir(H)₂(bis(tropp^Ph)propane)]⁺, while the rac-isomer, rac-[Ir(bis(tropp^Ph)propane)]+, reacts with two equivalents H₂ to give rac-{Ir(H)₂(OTf)[(tropp^Ph)(H₂tropp^Ph)propane]}, a cis-dihydride complex containing a hydrogenated 10,11-dihydro-5H-dibenzo[a,d]cycloheptene unit, H₂tropp^Ph. The triflate anion in this complex is rather firmly bound and dissociates only slowly (k=29 s⁻¹). All differences between the different stereoisomers are attributed to the fact that the ligand backbone in the meso-isomer, meso-[Ir(bis(tropp^Ph)propane)]⁺, enforces a planar coordination sphere at the metal. On the contrary, already in the tetra-coordinated rac-[Ir(bis(tropp^Ph)propane)]⁺, the metal has a tetrahedrally distorted coordination sphere which does not impede the reduction to the d⁹-Ir(0) and d¹⁰-Ir(−1) complexes and allows more easily a distortion towards a trigonal bipyramidal (tbp) or octahedral structure for penta- or hexa-coordinated complexes, respectively. A comparison of the NMR data for iridium bonded olefins in equatorial or axial positions in tbp structures shows that the latter experience only modest metal-to-ligand back-donation, while the olefins in the equatorial positions have a high degree of metallacyclopropane character.     

Electrogenerated chemiluminescence properties of bisalicylideneethylenediamino (salen) metal complexes

The spectroscopy, electrochemistry and electrogenerated chemiluminescence (ECL) of eight bisalicylideneethylenediamino (salen) metal complexes are reported. Two of the complexes contain an unsubstituted salen ligand and either cobalt(II) or nickel(II). The others have 1,2-cyclohexanediamonio-N,N′-bis(3,5-di-t-butylsalicylidene) as the ligand, and chromium(III), aluminum(III), cobalt(II), cobalt(III) or manganese(II) as the metal center. The complexes have lowest energy absorption maxima between 350 and 430 nm. When excited at these wavelengths, the complexes emit between 417 and 594 nm in acetonitrile. Photoluminescence efficiencies (?_em) were between 0.0310 and 23.8 compared to Ru(bpy)₃²⁺ (bpy = 2,2′-bipyridine; ?_em = 1), with the aluminum complexes displaying the most intense photoluminescence. Both reversible and irreversible oxidative electrochemistry is displayed by the metal–salen complexes with oxidation potentials ranging between +0.152 and +1.661 V versus Ag/AgCl. The ECL intensity peaks at a potential corresponding to oxidation of both TPrA and the salen systems, indicating that both are involved in the ECL reaction sequence. ECL efficiencies (?_ecl) were between 0.0018 and 0.0086 when compared to Ru(bpy)₃²⁺ (?_ecl = 1) in acetonitrile (0.05 M tri-n-propylamine (TPrA) as an oxidative–reductive ECL coreactant). Also, qualitative studies using transmission filters suggest that the complexes emit ECL in approximately the same region as their photoluminescence, indicating that the same excited state is formed in both experiments.     

Determination of p‐Aminobenzenesulfonic acid based on the electrochemiluminescence quenching of tris (2,2’‐bipyridine)‐ ruthenium (II)

This study describes the quenching effects of p‐aminobenzenesulfonic acid (p‐ABSA) based on electrochemiluminescence (ECL) of the tris (2,2^’‐bipyridyl)‐ruthenium(II)(Ru(bpy)₃²⁺)/tri‐n‐propylamine (TPrA) system in aqueous solution. Quenching behaviours were observed with a 200‐fold excess of p‐ABSA over Ru(bpy)₃²⁺. In the presence of 0.1 M TPrA, the Stern‐Volmer constant (K_SV) of ECL quenching was as high as 1.39 × 10⁴ M^‐1 for p‐ABSA. The logarithmic plot of inhibited ECL versus concentration of p‐ABSA was linear over the range of 6.0 × 10^‐6 ‐3.0 × 10^‐4 mol/L. The corresponding limit of detection was 1.2 × 10^‐6 mol/L for p‐ABSA (S/N = 3). The mechanism of quenching is believed to involve an energy transfer from the excited‐state luminophore to a dimer of p‐ABSA and the adsorption of free radicals of p‐ABSA at the electrode surface that impeded the oxidation of the Ru(bpy)₃²⁺/TPrA system. Copyright © 2012 John Wiley & Sons, Ltd.     

Binding mode of porphyrins to poly[d(A-T)(2)] and poly[d(G-C)(2)

We examined the binding geometry of Co-meso-tetrakis (N-methyl pyridinium-4-yl)porphyrin, Co-meso-tetrakis (N-n-butyl pyridinium-4-yl)porphyrin and their metal-free ligands to poly[d(A-T)(2)] and poly[d(G-C)(2)] by optical spectroscopic methods including absorption, circular and linear dichroism spectroscopy, and fluorescence energy transfer technique. Signs of an induced CD spectrum in the Soret band depend only on the nature of the DNA sequence; all porphyrins exhibit negative CD when bound to poly[d(G-C)(2)] and positive when bound to poly[d(A-T)(2)]. Close analysis of the linear dichroism result reveals that all porphyrins exhibit outside binding when complexed with poly[d(A-T)(2)], regardless of the existence of a central metal and side chain. However, in the case of poly[d(G-C)(2)], we observed intercalative binding mode for two nonmetalloporphyrins and an outside binding mode for metalloporphyrins. The nature of the outside binding modes of the porphyrins, when complexed with poly[d(A-T)(2)] and poly[d(G-C)(2)], are quite different. We also demonstrate that an energy transfer from the excited nucleo-bases to porphyrins can occur for metalloporphyrins.     

Kinetics and mechanism of the Ir(III)-catalyzed oxidation of xylose and maltose by potassium iodate in aqueous alkaline medium

For the first time, the Ir(III) catalysis of the iodate oxidation of xylose and maltose in aqueous alkaline medium has been investigated. The reactions exhibit first-order kinetics with respect to lower [IO(3)(-)] and [OH(-)] and show zero-order kinetics at their higher concentrations. Unity order at low concentrations of maltose becomes zero order at its higher concentrations, whereas zero-order kinetics with respect to [xylose] was observed throughout its variation. The reaction rate is found to be directly proportional to [Ir(III)] in the oxidation of both reducing sugars. Negligible effect of [Cl(-)] and nil effect of ionic strength (mu) on the rate of oxidation have also been noted. The species, [IrCl(3)(H(2)O)(2)OH](-) was ascertained as the reactive species of Ir(III) chloride for both the redox systems. Various activation parameters have been calculated. Formic acid and arabinonic acid for maltose and formic acid and threonic acid for xylose were identified as the main oxidation products of the reactions. Mechanisms consistent with the observed kinetic data and spectral evidence have been proposed for the oxidation of xylose and maltose.     

Determination of bergenin based on the electrochemiluminescence quenching of tris(2,2′‐bipyridine)‐ruthenium(II)

Quenching effects of bergenin, based on the electrochemiluminescence (ECL) of the tris(2,2′‐bipyridyl)‐ruthenium(II) (Ru(bpy)₃²⁺)/tri‐n‐propylamine (TPrA) system in aqueous solution, is been described. The quenching behavior can be observed with a 100‐fold excess of bergenin over Ru(bpy)₃²⁺. In the presence of 0.1 m TPrA, the Stern–Volmer constant (K_SV) of the ECL quenching is as high as 1.16 × 10⁴ M^?1 for bergenin. The logarithmic plot of the inhibited ECL versus logarithmic plot of the concentration of bergenin was linear over the range 3.0 × 10^?6–1.0 × 10^?4 mol/L. The corresponding limit of detection was 6.0 × 10^?7 mol/L for bergenin (S/N = 3). In the mechanism of quenching it is believed that the competition of the active free radicals between Ru(bpy)₃²⁺/TPrA and bergenin was the key factor for the ECL inhibition of the system. Photoluminescence, cyclic voltammetry, coupled with bulk electrolysis, supports the supposition mechanism of the Ru(bpy)₃²⁺/TPrA–bergenin system. Copyright © 2015 John Wiley & Sons, Ltd.     

The excitation mechanism of btp2Ir(acac) in CBP host

Whether bis(2‐(2′‐benzo[4,5‐α]thienyl)pyridinato‐N,C3′)iridium(acetylacetonate) (btp₂Ir(acac)) emission comes from carrier trapping and/or energy transfer, when doped in the 4,4′‐bis(N‐carbazolyl)biphenyl (CBP) host in organic light‐emitting devices, is not clear; therefore, the btp₂Ir(acac) emission in CBP hosts was studied. In the red‐doped device, both N,N′‐bis(1‐naphthyl)‐N,N′‐diphenyl‐1.1′‐bipheny1–4‐4′‐diamine (NPB) and (1,1′‐biphenyl‐4′‐oxy)bis(8‐hydroxy‐2‐methylquinolinato)‐aluminum (BAlq) emission appeared, which illustrated that CBP excitons cannot be formed at two emissive layer (EML) interfaces in the device. In the co‐doped devices, NPB and BAlq emissions disappear and 1,4‐bis[2‐(3‐N‐ethylcarbazoryl)vinyl]benzene (BCzVB) emission appears, illustrating the formation of CBP excitons at two EML interfaces in these devices. The reason for this difference was analyzed and it was found that holes in the NPB layer could be made directly into the CBP host in the EML interface of the red‐doped device. In contrast, holes were injected into CBP host via the btp₂Ir(acac)/BCzVB dopants in the co‐doped devices, which facilitated hole injection from the NPB layer to the EML, leading to the formation of CBP excitons at two EML interfaces in the co‐doped devices. Therefore, btp₂Ir(acac) emission was caused by carrier trapping in the red‐doped device, while, in the co‐doped devices, it resulted from both carrier trapping and energy transfer from the CBP. Furthermore, it was revealed that the carrier trapping mechanism is less efficient than the energy transfer mechanism for btp₂Ir(acac) excitation in co‐doped devices. In summary, our results clarified the excitation mechanism of btp₂Ir(acac) in the CBP host.