Bipyridine Ruthenium Complex Research Articles

New ruthenium(II) bipyridine complex bearing 2-aminophenylbenzimidazole: Synthesis, spectral characterization and optical properties

Abstract The new bipyridine-based ruthenium(II) complex [Ru(bpy)2(Hapbim)]2+ (bpy being 2,2′-bipyridine, and Hapbim is 2-aminophenylbenzimidazole) was synthesized and characterized. On the basis of elemental analysis, spectroscopic techniques (FTIR, 1H NMR, UV-Visible), magnetic, conductivity and thermal analysis measurements, it was found that the Hapbim ligand coordinates to Ru(II) kernel in a neutral bidentate fashion through cyclic azomethine N of benzimidazole moiety along with the terminal nitrogen of the amino group forming six-membered chelate ring. Thin films of the Ru(II)-complex were prepared using thermal evaporation technique. The thin film structure was characterized using FTIR and X-Ray diffraction techniques. FTIR analysis revealed that the complex is chemically stable under both thermal evaporation and thermal annealing. The optical properties were studied by spectrophotometric measurements. The optical constants of the complex were calculated and it is found to have 1.5 eV band gap. Also, the effect of thermal annealing on the optical properties of the complex is studied. Annealing of the complex thin films increased the values of the dispersion parameters and decreased the value of the band gap.

Poly(NIPAAm-co-Ru(bpy) 3 2+ ) hydrogels crosslinked by double-bond end-capped Pluronic F127: preparation, properties and coupling with the BZ reaction

Topological network design is an effective way to obtain new functionalities and regulate the properties of stimuli responsive hydrogels. In this work, poly(NIPAAm-co-Ru(bpy) 3 2+ ) hydrogels (NIPAAm: N-isopropylacrylamide, Ru(bpy) 3 2+ : Ruthenium bipyridine complex monomer) crosslinked by amphiphilic triblock copolymers were designed and constructed by a photo-induced gelation method, utilizing double-bond end-capped Pluronic F127 (F127DA) as the crosslinking agent, NIPAAm and Ru(bpy) 3 2+ as the monomers, α-ketoglutaric acid as the photoinitiator and H2O as the solvent. The resulting F127DA crosslinked hydrogels exhibit unique swelling behaviors, mechanical properties, fluorescent behaviors and thermosensitive properties and can be coupled with the BZ reaction. The present example may enrich the family of metal-containing polymer materials and provide clues to develop other functional hydrogels by designing topologically crosslinked network.

Design and synthesis of ruthenium bipyridine catalyst: An approach towards low-cost hydroxylation of arenes and heteroarenes

Two new ruthenium bipyridine complexes were designed and synthesized for intermolecular Csp2-H hydroxylation. An environmentally begin and inexpensive oxidant was employed as an oxygen source thereby enhancing its applicability and resulting in the remarkable increase of yield. In the catalytic process a ruthenium (IV) cationic complex is formed which enables the regioselective CO bonds formation and also proves to be tolerant to a broad substrate scope. Activation of CH bonds adjacent to removable and non-removable directing groups have been explored efficiently.

Initiation of the Electrochemical Reduction of CO2 by a Singly Reduced Ruthenium(II) Bipyridine Complex.

The one-electron reduction of [CpRu(bpy)NCCH3]PF6 (Cp = cyclopentadienyl; bpy = 2,2'-bipyridine), abbreviated as [Ru-S]+, where S = CH3CN, in CO2-saturated acetonitrile initiates a cascade of rapid electrochemical and chemical steps (ECEC) at an electrode potential of ca. 100 mV positive of the first reduction of the ruthenium complex. The overall two-electron process leads to the generation of a CO-bound ruthenium complex, [Ru-CO]+, and carbonate, as independently confirmed by NMR spectroscopy. Simulations of the cyclic voltammograms using DigiElch together with density functional theory based calculations reveal that the singly reduced ruthenium complex [Ru-S]0 binds CO2 at a rate of ca. 105 M-1 s-1 at almost zero driving force. Subsequent to CO2 binding, all of the steps leading up to deoxygenation are highly exergonic and rapid. A model of the potential energy profile of the CO2 approach to the Ru center in the singly reduced manifold reveals a direct correlation between the reactivity toward CO2 and the nucleophilicity at the metal center influenced by different ligand environments. Through the binding of CO2 after the first reduction, overpotentials associated with consecutive electrochemical reductions are avoided. This work therefore provides an important design principle for engineering transition-metal complexes to activate CO2 under low driving forces.

6-(2-Quinolinyl)-2,2′-bipyridine ruthenium complexes for near-infrared sensitization in dye-sensitized solar cells

Abstract In an effort to obtain a dye-sensitized solar cell (DSC) with a broader absorption band, four ruthenium (Ru) complexes based on 6-(2-quinolinyl)-2,2′-bipyridine ligands with a large π-conjugated system were synthesized. We investigated the relationship between the conversion efficiency of DSC and the structure of quinoline-based Ru complex as well as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) potentials. As compared with black dye, all of these complexes showed red-shifted absorption edges. The results of electrochemical analyses and theoretical calculations indicated that the shift of the absorption bands comes from the electron-withdrawing or electron-delocalization effect of the quinoline ring of the ligands. In addition, the number and position of carboxyl groups significantly affected the distribution of HOMO and LUMO thereby shifting their potentials. Comparison of the performance of the DSCs using different complexes revealed that the electron injection efficiency was also significantly affected by the position of the carboxyl groups. In this study, the Ru complex with the ligand composed of both 4-carboxypyridine and 4-carboxyquinoline efficiently sensitized near-IR photons as well as visible photons.

Electrochemiluminescence of a Vinyl‐Functionalized Ruthenium Complex and Its Monolayer Formed through the Photoinduced Thiol‐Ene Click Reaction

AbstractVinyl‐functionalized bipyridine ruthenium complex, bis(2,2′‐bipyridine)(4,4′‐di(4‐vinylphenyl)‐2,2′‐bipyridine)ruthenium(II) hexaflurophosphate [Ru(bpy)2(dvbpy)](PF6)2, was synthesized and the electrochemiluminescence (ECL) generated in the presence of co‐reactant, namely tri‐n‐propylamine (TPrA), was investigated by using an ECL spooling technique. This complex was then covalently attached to the indium tin oxide electrode surface through photoinduced thiol‐ene click chemistry to prepare a solid‐state ECL sensor. The covalently immobilized [Ru(bpy)2(dvbpy)]2+ monolayer film exhibited excellent stability toward ECL generation. The analytical sensitivity of the solid‐state ECL sensor was evaluated through the detection of TPrA in the aqueous solution. A low limit of detection (LOD) of 0.25 μM and a wide linear range (ca. 10−7–10−4 M) were obtained, indicating its potential usefulness in chemical and biochemical analysis.

Ruthenium(II) bipyridine complexes: from synthesis and crystal structures to electrochemical and cytotoxicity investigation

Complexes 1–4, [Ru(L)(bpy)2]PF6, where bpy = 2,2′-bipyridine; HL = 3-methylpyridine-2-carboxylic acid (HL1), 6-methylpyridine-2-carboxylic acid (HL2), 5-bromopyridine-2-carboxylic acid (HL3) and 6-bromopyridine-2-carboxylic acid (HL4), were synthesized and characterized. The electrochemical character of the complexes was investigated by cyclic voltammetry revealing two reversible reduction waves in the negative range of potentials, most likely due to a reduction of the bipyridine moiety. Cytotoxicity studies by MTT assay for 72 h of drug action revealed that 2–4 exhibited moderate activity in cervical human tumor cells (HeLa). Complex 2 exhibited low activity in colon cancer LS-174 cells (180 ± 10), while all complexes were devoid of activity in lung cancer A549 and non-tumor MRC-5 cells, up to 200 μM. Combinational studies of the most active complex 2, with pharmacological modulators of cell redox status, L-buthionine-sulfoximine (L-BSO) or N-acetyl-L-cysteine (NAC), showed that when L-BSO potentiated, 2 induced a sub-G1 peak of the cell cycle in the HeLa cell line. UV–vis and cyclic voltammetry were performed in order to investigate the binding mode of 2 to DNA and suggested intercalation for the complex–DNA interaction.

Covalent Functionalization of Organic Nanoparticles Using Aryl Diazonium Chemistry and Their Solvent-Dependent Self-Assembly.

A simple method for covalent functionalization of Fréchet-type dendron nanoparticles (FDNs) using tris-bipyridylruthenium(II) is described. Covalent functionalization is achieved by chemically reducing the diazo derivative of a ruthenium(II)bipyridine complex in the presence of FDNs wherein the radical species generated gets covalently linked to the nanoparticle surface. Simplicity, rapidity, and robustness are the advantages offered by the present approach. The nanoparticles, post functionalization, were characterized using transmission electron microscopy, thermogravimetric analysis, and infrared, energy-dispersive X-ray, UV-visible, and nuclear magnetic resonance spectroscopic techniques. Depending on the solvent, the ruthenium complex-linked FDN displays a range of morphologies, including nanoparticles, fiber-networks, and nanocapsules. In the nanocapsules and fiber-networks observed in organic solvents, the ruthenium complex is confined within the interior domain of the aggregate, whereas in the nanoparticles observed in water, it is present on the periphery. The formation of predictable morphologies in different solvents plays a key role in using such self-assembled structures for various applications such as sensing, catalysis, and light harvesting. Characterization of these nanoaggregates using different spectroscopic and microscopic techniques is also described.

Chromium complex has a long luminescent glow

Ruthenium bipyridine and related precious-metal complexes are popular because they exhibit long-lived, redox-active excited states that are useful for making solar cells and light-emitting devices and as sensitizers for photocatalytic organic reactions. Researchers would like to replace the precious metals with more abundant first-row transition metals, such as iron, but they have been waylaid so far because the excited-state luminescence lifetimes are too short. A key to modulating the properties of the complexes to extend the lifetime is designing ligands that better stabilize the metal ions. To that end, Laura A. Büldt, Oliver S. Wenger, and their coworkers at the University of Basel have designed a bulky chelating diisocyanide terphenyl ligand that dramatically improves chromium(0)’s excited-state lifetime, surpassing that of the best iron(II) complexes by two orders of magnitude (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.6b11803). The researchers say the electronic effects of their ligand and the cage structure it

Ruthenium(II) bipyridine complexes incorporating (NN′S) azoimine ancillary ligands. Synthesis, spectroscopy, solid state structure and DFT calculations

Abstract Four ruthenium complexes of N’NS donor thiomethyl-azoimine ligands (L) of the general type trans -[Ru II (bipy)(L)(Cl) 2 ]( C1 – C4 ) (L = XC 6 H 4 N NC(COMe) NC 6 H 4 (2-SMe), X = H (L1), C1 ; CH 3 (L2), C2 ; Br (L3), C3 ; NO 2 (L4), C4 ) have been synthesized by the reaction of ruthenium trichloride trihydrate with the corresponding L ligands and bipyridine (bipy) in refluxing ethanol. The molecular structure of trans -[Ru(bpy)(L3)(Cl) 2 ]( C3 ) in the solid state is reported. The thiomethyl-azoimine ligands (L) bind as NN′ bidentate ligands with no direct Ru–S interaction. Furthermore, the complexes have been characterized by spectroscopic data (IR, UV/Vis and 1 H NMR) and cyclic voltammetry. The electrochemical parameters ( E L ( L )) of the azoimine ligands (L1–L4) are reported. The electronic excitations of a representative complex ( C3 ) are interpreted by DFT and TDDFT calculations.

Simultaneous electrochemical detection of Cd(II), Pb(II), As(III) and Hg(II) ions using ruthenium(II)-textured graphene oxide nanocomposite

Simultaneous determination of Cd(II), Pb(II), As(III) and Hg(II) metal ions was carried out based on the synergistic effect of graphene oxide (GO) textured with redox active ruthenium(II) bipyridine complex ([Ru(bpy)3]2+). [Ru(bpy)3]2+-GO nanocomposite on the modified gold (Au) electrode acts as an electrocatalyst and favours the sensitive and selective detection of metal ions. Also, it exhibited an enhanced electron transfer rate with a low solution resistance examined by cyclic voltammetry and impedance analysis. The inherent electrochemical and electrocatalytic behaviours of [Ru(bpy)3]2+-GO on gold electrode were demonstrated for simultaneous detection of heavy metal ions in water matrix. The proposed sensor exhibited a higher sensitivity towards Cd(II), Pb(II), As(III) and Hg(II) metal ions with a lowest detection limit of 2.8, 1.41, 2.3 and 1.6nM respectively. The observed detection limits were less than the World Health Organization standards and hence the developed sensor can be deployed for detecting heavy metal ions in water bodies. Simultaneous electrochemical detection of heavy metal ions in river and tap water was carried out using the developed sensor and the observed results were validated with atomic absorption spectroscopy.

Ruthenium(II) bipyridine complexes with pendant anthracenyl and naphthyl moieties: A strategy for a ROS generator with DNA binding selectivity

Abstract Coordination compounds that combine selective DNA binding with reactive oxygen species (ROS) generation production have been sought as tools for cell biology studies and cancer therapy. In this respect, the contribution of this work lies on the use of anthracenyl ( Ru-Anth ) and naphthalyl-pedant ( Ru-Naph ) ruthenium(II) bipyridine complexes, which were synthesized and fully characterized by spectroscopic and electrochemical techniques. Both complexes presented efficient 1 O 2 photogeneration, with anthracenyl-pendant showing higher quantum yields as well as OH production. The DNA photocleavage showed to be dependent on the energy of the exciting radiations thus indicating that the photocleavage process mostly involves the 1 O 2 species. In comparison to Ru-Naph , the higher efficiency of the Ru-Anth complex toward the DNA cleavage was assigned to the presence of the anthracenyl moiety that provides an efficient channel to generate 1 O 2 . These findings have validated the use of conjugated organic ligands with metal complexes as a strategy to bring together binding and photooxidative properties.

Chemical two-photon fluorescence.

We describe a method based on a caged fluorescent molecule that can act as a chemical two-photon probe. It is composed of an organic fluorophore and a ruthenium-bipyridine complex that acts as a photoremovable quencher. For the fluorophore to be emissive, two independent photons must act on the molecule: the first photon frees the fluorescent ligand from the Ru complex and the second photon excites the fluorescence. In this two-photon regime, the emission is not proportional to the excitation intensity but rather to its second power, as in traditional two-photon systems based on ultrashort pulsed high-power lasers. This quadratic relationship implies a much higher spatial precision on the z-axis when the probe is used in a microscopy technique. The chemical nature of the two-photon excitation mechanism allows the use of inexpensive low-power lasers.

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.

Synthesis of conjugated polymers bearing pendant bipyridine ruthenium complexes

Abstract Conjugated polymers bearing pendant bipyridine groups, PM1PT-x , were synthesized in high yield from a carefully designed dibromocarbazole monomer M1 using a Suzuki coupling reaction with a phenothiazine diborate monomer. PM1PT-x , where x is the mole percentage of M1 in the total feed of dibromo-monomers and varied to levels of 25%, 50%, 75% and 100%, was reacted with a ruthenium complex to yield conjugated polymers bearing pendant bipyridine ruthenium complexes, PM1PT-x-Ru . The introduction of ruthenium complexes extended the absorption of PM1PT-x-Ru to the visible light region. Furthermore, these polymers demonstrated sufficient stability and suitable energy levels to potentially be highly efficient photoactive materials for polymeric solar cells.

A ruthenium(II) bipyridine complex containing a 4,5-diazafluorene moiety: Synthesis, characterization and its applications in transfer hydrogenation of ketones and dye sensitized solar cells

Abstract The ruthenium(II) complex [Ru(bpy)2L](PF6)2, where bpy is 2,2′-bipyridine and L is 1,5-dihydro-2-H-cyclopenta[1,2-b:5,4-b′]dipyridine-2-one, was synthesized from the reaction of cis-Ru(bpy)2Cl2·2H2O with L, and isolated as the hexafluorophosphate salt. The structure of L was unequivocally elucidated by single-crystal X-ray diffraction analysis. The new ruthenium(II) complex was thoroughly characterized by 1H and 13C NMR spectroscopy, along with FTIR, UV–Vis and LC MS/MS Triple Quadrupole Mass spectroscopy and elemental analysis. The catalytic activity of [Ru(bpy)2L](PF6)2 was tested in the transfer hydrogenation of various ketones in 2-propanol as both the solvent and hydrogen donor. The usage of [Ru(bpy)2L](PF6)2 for the formation of a dye sensitized solar cell is also presented.

Solvent-Dependent Non-Linear Optical Properties of 5,5′-Disubstituted-2,2′-bipyridine Complexes of Ruthenium(II): A Quantum Chemical Perspective

In this research article, we reported solvent effects on non-linear optical (NLO) properties of 5,5′-disubstituted-2,2′-bipyridine complexes of ruthenium. The polarizability (α) and hyperpolarizability (β) were calculated in the gas phase. Benzene (ϵ (dielectric constant) = 2.3), THF (ϵ = 7.52), dichloromethane (ϵ = 8.93), acetone (ϵ = 21.01), methanol (ϵ = 33.00), and water (ϵ = 80.10) were used by density functional theory. These solvents cover a wide range of polarities. The results of theoretical investigation showed that the non-linear optical properties were significantly increased with the increase in solvent polarity. The results of this study also showed that similarly to structural modifications, polarity of the medium may play a significant role in modulating the NLO properties.

Zinc oxide nanocrystal quenching of emission from electron-rich ruthenium-bipyridine complexes.

A series of heteroleptic bipyridine ruthenium complexes were prepared using known synthetic methods. Each compound incorporated one electron withdrawing 4,4'-dicarboxylic acid-2,2'-bipyridine and two bipyridines each of which had electron donating dialkylamine substituents in the 4 and 4' positions. The electronic absorption spectra exhibited absorptions that moved to lower energy as the donor ability of the amine substituent increased. Density functional calculations established that the HOMO was delocalized over the metal and two pyridine groups located trans to the pyridines of the dicarboxylic acid bipyridine. The LUMO was delocalized over the dicarboxylic acid bipyridine. Cyclic voltammetry of the deprotonated compounds exhibit one quasi-reversible oxidation and three reductions. Coupled with the emission data, the excited state reduction potentials were estimated to range from -0.93 to -1.03 V vs. NHE. Monodispersed 3.2 nm diameter nanocrystals (NCs) of zinc oxide were found to quench partially the excited state of the dyes via a static quenching electron transfer process involving the formation of a dyad of the complex and the NC. The magnitude of the partial quenching of complexed dyes was correlated to the distribution of band gaps for the NCs, which is an inverse function of diameter. Dyes attached to the NCs on the small end of the particle size distribution had electron transfer rates that were uncompetitive with radiative and nonradiative decay mechanisms.

Amphiphilic ruthenium bipyridine complex containing long-chain azopyridine group and the mechanism of electron transfer in Langmuir-Blodgett films

Abstract We synthesized the amphiphilic bis(bipyridine) ruthenium complex [Ru(bipy)2Cl(L)]+ (bipy= 2,2′-bipyridine, L = 4-(4-dodecyloxyphenylazo) pyridine). The long-chain ligand contributed to the self-assembly of the complex at the liquid-air interface, enabling its deposition by the Langmuir-Blodgett technique. The UV-vis, Raman, and specular reflectance FTIR spectroscopies revealed the molecular organization in the LB films: in the free ligand LB film the alkoxyphenylazopyridine species were oriented in parallel to each other and parallel to the normal plane of the substrate, whilst in the ruthenium complex film the alkoxyphenylazopyridine species were oriented in parallel to each other and perpendicular to the normal plane of the substrate. We then prepared multilayer films consisting of layers of ligand L supporting a monolayer of the ruthenium complex and characterized them by electrochemistry. This hybrid film structure led to optimal orientation of the ruthenium centers for electrochemical response. The results indicated that the phenylazo low-lying π-orbital participated in the hopping mechanism that mediated the electron transfer in the LB films with few molecular layers.

Modified bibenzimidazole ligands as spectator ligands in photoactive molecular functional Ru-polypyridine units? Implications from spectroscopy.

The photophysical properties of Ruthenium-bipyridine complexes bearing a bibenzimidazole ligand were investigated. The nitrogens on the bibenzimidazole-ligand were protected, by adding either a phenylene group or a 1,2-ethandiyl group, to remove the photophysical dependence of the complex on the protonation state of the bibenzimidazole ligand. This protection results in the bibenzimidazole ligand contributing to the MLCT transition, which is experimentally evidenced by (resonance) Raman scattering in concert with DFT calculations for a detailed mode assignment in the (resonance) Raman spectra.