Electrochemiluminescence of Tris(2,2′‐bipyridine)ruthenium with Various Co‐reactants under Ultrasound Irradiation

Electrochemiluminescence (ECL) of tris(2,2′‐bipyridine)ruthenium, Ru(bpy)₃²⁺ in the presence of various co‐reactants, such as tripropylamine (TPA), oxalate ion (C₂O₄^2?), ascorbic acid (H₂A) and dehydroascorbic acid (DHA), were investigated under ultrasound irradiation. In sono‐ECL experiments, an indium‐thin‐oxide (ITO) was used as working electrode, and a titanium tipped sonic horn probe (diameter 2 mm) which operated at a frequency of 20 kHz was set in the front of the ITO electrode. Under the ultrasound irradiation, ECL signals were found to be significantly enhanced when TPA and C₂O₄^2? were used as co‐reactants, only slightly enhanced in Ru(bpy)₃²⁺/DHA system, but total quenched in Ru(bpy)₃²⁺/H₂A system. The difference of Ru(bpy)₃²⁺ ECL behaviors for various co‐reactant could to be due to the different kinetics of catalytic reactions associated in ECL schemes. ECL quenching effect observed in Ru(bpy)₃²⁺/H₂A system was suggested to be due to electron transfer (ET) route between the excited state *Ru(bpy)₃²⁺ and ascorbate anion HA^? diffused from the bulk solution, where the diffusional HA^? species served as electron donor. The effect becomes more pronounced upon sonication because the effective collision frequency between *Ru(bpy)₃²⁺ and HA^? would be significantly increased by the enhanced mass transport effect of ultrasound.     

Synthesis and photophysical properties of novel amphiphilic ruthenium (II) complexes containing 4,4′‐dialkylaminomethyl‐2,2′‐bipyridyl ligands

The synthesis of a number of new 2,2′‐bipyridine ligands functionalized with bulky amino side groups is reported. Three homoleptic polypyridyl ruthenium (II) complexes, [Ru(L)₃]²⁺ 2(PF₆^?), where L is 4,4′‐dioctylaminomethyl‐2,2′‐bipyridine (Ru4a), 4,4′‐didodecylaminomethyl‐2,2′‐bipyridine (Ru4b) and 4,4′‐dioctadodecylaminomethyl‐2,2′‐bipyridine (Ru4c), have been synthesized. These compounds were characterized and their photophysical properties examined. The electronic spectra of three complexes show pyridyl π → π* transitions in the UV region and metal‐to‐ligand charge transfer bands in the visible region. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis,spectral characterization and anticancer studies of three novel ruthenium(III) 2,2′‐bipyridine complexes

A series of three new ruthenium(III) bipyridine complexes, [RuCl₃(bipy)L] (L = C₆H₅CHO (Ru1), 4‐CH₃OC₆H₄CHO (Ru2) and 4‐NO₂C₆H₄CHO (Ru3); bipy = 2,2′‐bipyridine), have been synthesized and characterized using microanalysis, magnetic, spectroscopic (IR, UV–visible, electron spin resonance) and cyclic voltammetric techniques. All the ruthenium(III) complexes were found to be stable, paramagnetic and octahedrally coordinated. Electron spin resonance spectra showed an axial symmetry and indicated a tetragonal distortion for the octahedral complexes. All complexes were tested for their cytotoxicities against Ehrlich ascites carcinoma (EAC), superoxide dismutase‐like activities and cytoprotective effects of normal human red blood cells against photo‐irradiation. All the compounds were found to be cytotoxic with half maximal inhibitory concentration (IC₅₀) against EAC at concentrations of 70, 90 and 76 µg for Ru1, Ru2 and Ru3, respectively. Moreover, mean levels of DNA and RNA were significantly elevated in liver tissues of tumorized animals and significantly reduced after treatment of tumorized mice with the complexes. Copyright © 2015 John Wiley & Sons, Ltd.     

trans‐(Cl)‐[Ru(5,5′‐diamide‐2,2′‐bipyridine)(CO)2Cl2]: Synthesis,Structure, and Photocatalytic CO2 Reduction Activity

A series of trans‐(Cl)‐[Ru(L)(CO)₂Cl₂]‐type complexes, in which the ligands L are 2,2′‐bipyridyl derivatives with amide groups at the 5,5′‐positions, are synthesized. The C‐connected amide group bound to the bipyridyl ligand through the carbonyl carbon atom is twisted with respect to the bipyridyl plane, whereas the N‐connected amide group is in the plane. DFT calculations reveal that the twisted structure of the C‐connected amide group raises the level of the LUMO, which results in a negative shift of the first reduction potential (E_p) of the ruthenium complex. The catalytic abilities for CO₂ reduction are evaluated in photoreactions (λ>400 nm) with the ruthenium complexes (the catalyst), [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine; the photosensitizer), and 1‐benzyl‐1,4‐dihydronicotinamide (the electron donor) in CO₂‐saturated N,N‐dimethylacetamide/water. The logarithm of the turnover frequency increases by shifting E_p a negative value until it reaches the reduction potential of the photosensitizer.     

Distance Dependence of Bidirectional Concerted Proton–Electron Transfer in Phenol‐Ru(2,2′‐bipyridine)32+ Dyads

Proton‐coupled electron transfer (PCET) was investigated in three covalent donor–bridge–acceptor molecules with different bridge lengths. Upon photoexcitation of their Ru(bpy)₃²⁺ (bpy=2,2′‐bipyridine) photosensitizer in acetonitrile, intramolecular long‐range electron transfer from a phenolic unit to Ru(bpy)₃²⁺ occurs in concert with release of the phenolic proton to pyrrolidine base. The kinetics of this bidirectional concerted proton–electron transfer (CPET) reaction were studied as a function of phenol–Ru(bpy)₃²⁺ distance by increasing the number of bridging p‐xylene units. A distance decay constant (β) of 0.67±0.23 Å^?1 was determined. The distance dependence of the rates for CPET is thus not significantly steeper than that for ordinary (i.e., not proton coupled) electron transfer across the same bridges, despite the concerted motion of oppositely charged particles into different directions. Long‐range bidirectional CPET is an important reaction in many proteins and plays a key role in photosynthesis; our results are relevant in the context of photoinduced separation of protons and electrons as a means of light‐to‐chemical energy conversion. This is the first determination of β for a bidirectional CPET reaction.     

Electrogenerated Chemiluminescence Sensor Based on Tris(2,2′‐bipyridine)ruthenium(II)‐Immobilized Natural Clay and Ionic Liquid

A novel electrogenerated chemiluminescence (ECL) sensor based on natural clay and ionic liquid was fabricated. Tris(2,2′‐bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) was immobilized on natural clay surface through simple adsorption. An ECL sensor was prepared by mixing Ru(bpy)₃²⁺‐incorporated clay, graphite powder and an ionic liquid (1‐butyl‐3‐methylimidazolium hexafluorophosphate) as the binder. The electrochemical behavior and ECL of the immobilized Ru(bpy)₃²⁺ was investigated. It was observed that the ECL of immobilized Ru(bpy)₃²⁺ was activated by the ionic liquid. The proposed ECL sensor showed high sensitivity to tri‐n‐propylamine (TPrA) and the detection limit was found to be 20 pM. In addition, the ECL sensor displayed good stability for TPrA detection and long‐term storage stability.     

Bis(4,4′‐dimethyl‐2,2′‐bipyridine) ruthenium (II) Complexes Containing 2‐Arylimidazo‐ [4,5‐f] [1,10] phenanthroline: Syntheses,Characterization and Third‐order Nonlinear Optical Properties

Four novel mononuclear ruthenium(II) complexes [Ru(dmb)₂L]²⁺ [dmb = 4,4′‐dimethyl‐2,2′‐bipyridine, L = imidazo‐[4,5‐f][1,10]phenanthroline (IP), 2‐phenylimidazo‐[4,5‐f][1,10]phenanthroline (PIP), 2‐(4′‐hydroxyphenyl)imidazo‐[4,5‐f] [1,10] phenanthroline (HOP), 2‐(4′‐dimethylaminophenyl) imidazo‐[4, 5‐f] [1,10] phenanthroline (DMNP)] were synthesized and characterized by ES‐MS, ¹H NMR, UV‐vis and electrochemistry. The nonlinear optical properties of the ruthenium(II) complexes were investigated by Z‐scan techniques with 12 ns laser pulse at 540 nm, and all of them exhibit both nonlinear optical (NLO) absorption and self‐defocusing effect. The corresponding effective NLO susceptibility |x³| of the complexes is in the range of 2.68 × 10^?12‐4.57 × 10^?12 esu.     

A Bifunctional Electrocatalyst Containing Tris(2,2′‐bipyridine) Ruthenium(II) and 12‐Molybdophosphate Bulk‐Modified Carbon Paste Electrode

The electroactive composite containing tris(2,2′‐bipyridine) ruthenium(II) and 12‐molybdophosphate (RuPMo₁₂) was synthesized and first used as a bifunctional electrocatalyst to fabricate a chemically bulk‐modified carbon paste electrode (RuPMo₁₂‐CPE) by direct mixing. The electrochemical behavior of the RuPMo₁₂‐CPE was studied by cyclic voltammetry. The RuPMo₁₂‐CPE presents good electrocatalytic activity not only toward the reduction of hydrogen peroxide and bromate, which is attributed to the function of molybdophosphate, but also toward the oxidation of arsenite, which is primarily attributed to the function of tris(2,2′‐bipyridine) ruthenium(II). The remarkable advantage of the RuPMo₁₂‐CPE is its good stability owing to the insolubility of RuPMo₁₂ and reproducibility of surface renewal.     

Design and spectroscopic study of new ruthenium(II) complexes containing ligands derived from terpyridine and dipyrido[3,2‐a:2′,3′‐c]phenazine: {Ru(4′‐Rph‐tpy) [dppz(COOH)]Cl}PF6 with R = NO2, Br,Cl

A series of polypyridine ruthenium complexes of the general formula {Ru(Rph‐tpy)[dppz(COOH)]Cl} PF₆ with R = Br ( 1 ), Cl ( 2 ), NO₂ ( 3 ) where Rph‐tpy is 4′‐(4‐Rphenyl‐2,2′:6′,2″‐terpyridine and dppz(COOH) is dipyrido[3,2‐a:2′,3′‐c]phenazine‐2‐carboxylic acid were prepared and characterized. These complexes display intense metal‐to‐ligand charge‐transfer (MLCT) bands centered about 500 nm. The effect of pH on the absorption spectra of these complexes consisting of protonatable ligands has been investigated in water solution by spectrophotometric titration. The electrochemistry shows oxidation potentials for the Ru(II)–Ru(III) couple at +0.881 ( 1 ), +0.907 ( 2 ) and +0.447 V ( 3 ), respectively. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and characterization of tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers via RAFT polymerization

A new bipyridine‐functionalized dithioester was synthesized and further used as a RAFT agent in RAFT polymerization of styrene and N‐isopropylacrylamide. Kinetics analysis indicates that it is an efficient chain transfer agent for RAFT polymerization of the two monomers which produce polystyrene and poly(N‐isopropylacrylamide) polymers with predetermined molecular weights and low polydispersities in addition to the end functionality of bipyridine. The bipyridine end‐functionalized polymers were further used as macroligands for the preparation of star‐shaped metallopolymers. Hydrophobic polystyrene macroligand combined with hydrophiphilic poly(N‐isopropylacrylamide) was complexed with ruthenium ions to produce amphiphilic ruthenium‐cored star‐shaped metallopolymers. The structures of these synthesized metallopolymers were further elucidated by UV–vis, fluorescence, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC) as well as NMR techniques. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4225–4239, 2007     

Self‐assembly of amphiphilic tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers

Amphiphilic tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers consisting of one polystyrene block and two poly(N‐isopropylacrylamide) blocks were prepared by the “arm‐first” method in which RAFT polymerization and nonconvalent ligand–metal complexation were employed. The prepared amphiphilic star‐shaped metallopolymers are able to form micelles in water. The size and distribution of the micelles were studied by dynamic light scattering and transmission electron microscopy techniques. Preliminary studies indicate that the polymer concentration and the hydrophilic poly(N‐isopropylacrylamide) block length can affect the morphologies of the formed metal‐interfaced core–shell micelles in water. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4204–4210, 2007     

Synthesis of ruthenium complexes with carbonyl and polypyridyl ligands derived from dipyrido[3,2‐a:2′,3′‐c]phenazine: application to the water gas shift reaction

The preparation and spectroscopic properties of new dipyrido[3,2‐a:2′,3′‐c]phenazine ruthenium complexes are described. The complexes show high catalytic activity in the water gas shift reaction in a basic medium under mild conditions (P_CO = 0.9 atm at 100 °C). Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of 2‐aminomethylpiperidine ruthenium(II) phosphine complexes and their applications in transfer hydrogenation of aryl ketones

The complex trans,cis‐[RuCl₂(PPh₃)₂(ampi)] (2) was prepared by reaction of RuCl₂(PPh₃)₃ with 2‐aminomethylpiperidine(ampi) (1). [RuCl₂(PPh₂(CH₂)_nPPh₂)(ampi) (n = 3, 4, 5)] (3–5) were synthesized by displacement of two PPh₃ with chelating phosphine ligands. All complexes (2–5) were characterized by ¹ H, ¹³C, ³¹P NMR, IR and UV‐visible spectroscopy and elemental analysis. They were found to be efficient catalysts for transfer hydrogen reactions. Copyright © 2012 John Wiley & Sons, Ltd.     

Tris(2,2′‐bipyridyl)ruthenium(II) Electrogenerated Chemiluminescence Sensor Based on Platinized Carbon Nanotube–Zirconia–Nafion Composite Films

Mesoporous films of platinized carbon nanotube–zirconia–Nafion composite have been used for the immobilization of tris(2,2′‐bipyridyl)ruthenium (II) (Ru(bpy)₃²⁺) on an electrode surface to yield a solid‐state electrogenerated chemiluminescence (ECL) sensor. The composite films of Pt–CNT–zirconia–Nafion exhibit much larger pore diameter (3.55 nm) than that of Nafion (2.82 nm) and thus leading to much larger ECL response for tripropylamine (TPA) because of the fast diffusion of the analyte within the films. Due to the conducting and electrocatalytic features of CNTs and Pt nanoparticles, their incorporation into the zirconia–Nafion composite films resulted in the decreased electron transfer resistance within the films. The present ECL sensor based on the Pt–CNT–zirconia–Nafion gave a linear response (R²=0.999) for TPA concentration from 3.0 nM to 1.0 mM with a remarkable detection limit (S/N=3) of 1.0 nM, which is much lower compared to those obtained with the ECL sensors based on other types of sol‐gel ceramic–Nafion composite films such as silica–Nafion and titania–Nafion.     

Synthesis and characterization of new complexes of the type [Ru(CO)2Cl2 (2‐phenyl‐1,8‐naphthyridine‐kN) (2‐phenyl‐1,8‐naphthyridine‐kN′)]. Preliminary applications in homogeneous catalysis

Novel ruthenium (II) complexes were prepared containing 2‐phenyl‐1,8‐naphthyridine derivatives. The coordination modes of these ligands were modified by addition of coordinating solvents such as water into the ethanolic reaction media. Under these conditions 1,8‐naphthyridine (napy) moieties act as monodentade ligands forming unusual [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] complexes. The reaction was reproducible when different 2‐phenyl‐1,8‐naphthyridine derivatives were used. On the other hand, when dry ethanol was used as the solvent we obtained complexes with napy moieties acting as a chelating ligand. The structures proposed for these complexes were supported by NMR spectra, and the presence of two ligands in the [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] type complexes was confirmed using elemental analysis. All complexes were tested as catalysts in the hydroformylation of styrene showing moderate activity in N,N′‐dimethylformamide. Copyright © 2008 John Wiley & Sons, Ltd.     

Photophysics of ruthenium(II) complexes with 2-(2′-pyridyl) pyrimidine and 2,2′-bipyridine ligands in fluid solution

The photophysics of three complexes of the form Ru(bpy)₃₋(pypm)²⁺ (where bpy2,2′-bipyridine, pypm 2-(2′-pyridyl)pyrimidine and P=1, 2 or 3) was examined in H₂O, propylene carbonate, CH₃CN and 4:1 (v/v) C₂H₅OH---CH₃OH; comparison was made with the well-known photophysical behavior of Ru(bpy)₃²⁺. The lifetimes of the luminescent metal-to-ligand charge transfer (MLCT) excited states were determined as a function of temperature (between −103 and 90 °C, depending on the solvent), from which were extracted the rate constants for radiative and non-radiative decay and ΔE, the energy gap between the MLCT and metal-centered (MC) excited states. The results indicate that ^*Ru(bpy)₂(pypm)²⁺ decays via a higher lying MLCT state, whereas ^*Ru(pypm)₃²⁺ and ^*Ru(pypm)₂(bpy)²⁺ decay predominantly via the MC state.