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A novel type of energy donor-acceptor system on a clay surface has been prepared. The energy transfer between an energy-donating cationic pyrene derivative (An-Py2+) and an energy-accepting tris(bipyridine)ruthenium complex (Ru2+) on the clay surface was investigated using absorption, emission, and lifetime measurements. An obvious energy transfer was observed, and one Ru2+ molecule quenched the emission from five molecules of An-Py2+ with an emission quenching efficiency of 85% on the clay surface. This suggests that the light energies absorbed by five of the An-Py2+ molecules were accumulated in the one Ru2+ molecule. Near-quantitative emission quenching was observed for stoichiometric amounts of An-Py2+ and Ru2+. The apparent quenching rate constant is approximately 1017 L mol-1 s-1, and thus the quenching rate constant is 107-108 times higher than the diffusion rate constant in a homogeneous solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Luminescence quenching of the excited 3MLCT by molecular oxygen. • Photosensitized generation of singlet oxygen by heteroleptic ruthenium (II) complexes. • Energy transfer versus charge transfer in the quenching process. • Effect of the partial charge transfer on the efficiency of singlet oxygen production. The photophysical properties of some synthesized heteroleptic polypyridyl ruthenium(II) complexes of the form [Ru(bpy) 2 L](PF 6) 2 where L = 2,2′-bipyridine, 4,4′-dimethoxy-2,2′-bipyridine, 1,10-phenanthroline, 4,4′-dimethyl-2,2′-bipyridine, 4,7-diphenyl-1,10-phenanthroline and 3,4,7,8-tetramethyl-1,10-phenanthroline, are investigated in acetonitrile. The excited state lifetime of the metal to ligand charge transfer (3MLCT) states of these complex ions are found to be ligand dependent and were found to be in the range 0.56 μs to 1.5 μs. Oxygen quenching of the excited states rate constants, k q , were found to be in the range 1.50–2.24 × 109 M−1s−1. Singlet oxygen quantum yield values, Φ Δ , are found to vary from 0.40 to 0.60 and the efficiency, f Δ T , with which excited singlet oxygen, O 2 (1Δ g), is thereby produced was found to be in the range 0.55–0.85. Treatment of the data with charge transfer and non-charge transfer pathways using Schmidt's model shows that partial charge transfer parameter was in the range of 0.18 to 0.58. It has also been found that f Δ T decreases and oxygen quenching rate constants, k q , increases as p CT increases. [ABSTRACT FROM AUTHOR]

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru( tBu3tpy)(bpy)(NCCH3)]2+ ( tBu3tpy=4,4′,4′′-tri- tert-butyl-2,2′:6′,2′′-terpyridine; bpy=2,2′-bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO2 to CO. The methyl group enables CO2 binding already at the one-electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO2 reduction catalysts. [ABSTRACT FROM AUTHOR]

A series of new RuII complexes has been synthesised, with different azo ligands as additional chromophore. The dyes are all intensely colored due to MLCT and ILCT transitions in the visible region. The photophysical study of the dyes, carried out by UV/Vis absorption and emission spectroscopy, showed unusual features such as intense solvatochromism and solvent-dependent extinction coefficients. The energies of these excited states have been tuned by changing the electron density across the series of azo ligands, and this results in different contributions from each charge transfer process for the different complexes and consequently, different emission behavior. The detailed behaviour of these dyes was further studied and interpreted through electrochemical, structural and computational techniques. The dyes do not work well as sensitisers for DSSCs and this is investigated by emission spectroscopy on TiO2 and ZrO2 films, suggesting poor charge injection to TiO2. [ABSTRACT FROM AUTHOR]

A new tetrapyridine ligand, 5,5′-(3-pyridyl)-2,2′-bipyridine (2) was prepared from 5,5′-dibromo-2,2′-bipyridine (1) via Pd(0)-mediated Suzuki coupling. The reaction was performed either directly upon the free ligand, or upon its Ru(II) complex. The structures of [Ru(1)3](PF6)2and [Ru(2)3](PF6)2were studied in solution by NMR, and in the solid state by single crystal X-ray diffraction. Solution NMR data suggests distorted structures, consistent with the observed slow reactivity of the ligands towards Ru(II) ions, and their reluctance to coordinate to Fe(II) ions. However, solid-state X-ray data indicated little distortion from ideal geometries, suggesting the effect may be more electronic than steric in nature. [ABSTRACT FROM AUTHOR]

The synthesis of 4,4′-dibenzodifuran-2,2′-bipyridine derivatives as ligands of organic ruthenium dyes for DSSC applications is described. Two new heteroleptic ruthenium complexes have been prepared and compared with commercially available N719 and Z907 dyes, using dip dyeing and flow dyeing methods in large area testing cells prepared for industrial purposes. The newly synthesized dyes revealed higher solar-to-electric energy conversion efficiency ( η ), measured at the AM1.5G conditions, up to 21% compared to N719 and up to 46% compared to Z907 , and external quantum efficiency of 53%. These results can be explained by enhanced light-harvesting of the benzodifuran moiety of the dyes that is related to photocurrent. [ABSTRACT FROM AUTHOR]

A new family of eight ruthenium(II)-cyclopentadienyl bipyridine derivatives, bearing nitrogen, sulfur, phosphorous and carbonyl sigma bonded coligands, has been synthesized. Compounds bearing nitrogen bonded coligands were found to be unstable in aqueous solution, while the others presented appropriate stabilities for the biologic assays and pursued for determination of IC 50 values in ovarian (A2780) and breast (MCF7 and MDAMB231) human cancer cell lines. These studies were also carried out for the [ 5 : HSA] and [ 6 : HSA] adducts (HSA = human serum albumin) and a better performance was found for the first case. Spectroscopic, electrochemical studies by cyclic voltammetry and density functional theory calculations allowed us to get some understanding on the electronic flow directions within the molecules and to find a possible clue concerning the structural features of coligands that can activate bipyridyl ligands toward an increased cytotoxic effect. X-ray structure analysis of compound [Ru(η 5 -C 5 H 5 )(bipy)(PPh 3 )][PF 6 ] ( 7 ; bipy = bipyridine) showed crystallization on C2/c space group with two enantiomers of the [Ru(η 5 -C 5 H 5 )(bipy)(PPh 3 )] + cation complex in the racemic crystal packing. [ABSTRACT FROM AUTHOR]

Self-assembly of 4,4′-bipyridine (bpy) with arene-ruthenium building blocks and 2,2′-bisbenzimidazole (H2BiBzIm) in the presence of AgOTf (OTf = OSO2CF3) afforded tetranuclear cations of the type [Ru4(η6-arene)4(bpy)2(BiBzIm)2]4+(arene = p-iPrC6H4Me1, C6Me62), while similar reactions by use of [(η6-C6Me6)Ru(μ-Cl)Cl]2and excess AgOTf led to isolation of a cationic coordination network {[Ru4(η6-C6Me6)4(bpy)2(BiBzIm)2·Ag2(OTf)4]2+}n(3), which could also be obtained by treatment of [2][OTf]4with AgOTf in methanol. Complex3is constructed byπcoordination of BiBzIm(η2-carcon) with Ag(I). The coordination geometry around the silver(I) ion is pseudo-tetrahedral (taking the C=C group as one ligand). Self-assembly of only two components: [(η6-C6Me6)Ru(μ-Cl)Cl]2reacted with the 3-pyridyl-bian (mPy-bian) linker in the presence of limited AgOTf to give a chloro-bridged metalla-rectangle [Ru4(η6-C6Me6)4(μ-Cl)4(mPy-bian)2Ag]5+(4), which enclosed a silver in the center. The coordination geometry around silver(I) in4is unusual square planar. The molecular structures of1–4were confirmed by X-ray crystallography along with other spectroscopic properties. A 1-D coordination network {[Ru4(η6-C6Me6)4(bpy)2(BiBzIm)2·Ag2(OTf)4]2+}ncontaining silver triflate interaction was synthesizedviaself-assembly of [(C6Me6)RuCl2]2, 4,4′-bipyridine, and 2,2′-bisbenzimidazole in the presence of excess AgOTf or through direct reaction of metalla-rectangle [Ru4(C6Me6)4(bpy)2(BiBzIm)2]4+and AgOTf. [ABSTRACT FROM AUTHOR]

Abstract: Coordination chemistry of 2,2′-bipyridine bearing an ortho-substituted phenyl group at the 6-position, i.e., 6-(o-X-phenyl)-2,2′-bipyridine (MeO-L: X = OMe; Me2N-L: X = NMe2) with [Ru(ttpy)Cl3] (ttpy = 4′-(4-tolyl)-2,2′;6′,2″-terpyridine) was investigated. The reaction of MeO-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded demethylated, O-coordinated complex [Ru(O-L)(ttpy)]+ (O-L: X = O) as well as the cyclometalated, C-coordinated complex [Ru(MeO-L)(ttpy)]+. On the other hand, reaction of Me2N-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded only N-coordinated complex [Ru(Me2N-L)(ttpy)]2+. The crystal structures, spectroscopic and redox properties were examined supplemented by DFT calculations. The spectroscopic and redox properties of RuN are more or less similar to those of [Ru(ttpy)Cl3]. On the other hand, the properties of RuC and RuO are mutually similar but significantly different from those of RuN. The anionic ligand in RuC and RuO raises the HOMO energy as compared to the neutral ligand in RuN, which is manifested in negatively shifted redox potentials, particularly the oxidation potentials, and thus, the red shift in the visible absorption band. Relevance of these complexes to sensitizers for dye-sensitized solar cells is briefly discussed. [Copyright &y& Elsevier]

Based on the raw material of 4-methylpyridine, a series of bipyridyl derivatives were synthesized. Using bipyridyl derivatives as ligands, dye-sensitizers of Ru (4, 4′-dicarboxylic-2, 2′-bipyridyl)(NCS), Ru (2, 2′-bipyridyl)(4, 4′-dicarboxylic-2, 2′-bipyridyl)(NCS), and Ru (4, 4′-dimethyl-2, 2′-bipyridyl)(4, 4′-dicarboxylic-2, 2′-bipyridyl)(NCS) were prepared. The structures of these compounds were characterized by IR, element analysis, and H NMR, and proved to be the target products. The dye sensitizers' XPS showed that bipyridyl and -NCS coordinate with central metal ruthenium very well. The dye sensitizers' properties were measured by TG, UV-Vis, and Cyclic voltammetry, and it was found that these dye sensitizers have excellent themostability, wide absorption range in the visible region, and match well with the requirements of the dye-sensitized solar cells, which can guarantee the solar cells long-term use. Ru (4, 4′-dicarboxylic-2, 2′-bipyridyl)(NCS) was found to have better thermal stability and larger molar absorption, resulting in better absorption than the other two dye sensitizers. [ABSTRACT FROM AUTHOR]

The ability to confine photoactive catalysts within metal–organicframework (MOF) materials affords the opportunity to expand the functionaldiversity of these materials into solar based applications. Here,the confinement of Ru(II)tris(2,2′-bipyridine) (RuBpy) by aMOF material derived from Zn(II) ions and trimesic acid (hereafter,USF2) is examined. Although the encapsulated RuBpy could not be crystallographicallyresolved within the MOF framework, the photophysical properties ofthe complex are characteristic of confinement including extended tripletmetal-to-ligand (3MLCT) lifetime (τethanol= 614 ns and τUSF2= 1.2 μs at 25 °C)and a slight hypsochromic shift in the steady-state emission spectrumrelative to RuBpy in ethanol. The extended lifetime is attributedto a deactivation of a nonradiative 3dd that is antibondingwith respect to the Ru(II)-bipyridine due to a confined molecularenvironment. These results represent one of the first examples ofRuBpy encapsulation and photophysical characterization within a polyhedralMOF material. [ABSTRACT FROM AUTHOR]

Nucleophilic substitutions involving [Ru(η2-bipy)2(η2-bipy–Cl2)]2+2PF6 − (bipy=2,2′-bipyridine; bipy–Cl2=4,4′-dichloro-2,2′-bipyridine) and NaSH or LiS(p-tol) (p-tol=4-CH3–C6H4), carried out in tetrahydrofuran at 115 °C, lead to [Ru(η2-bipy)2(η2-bipy–(SH)2)]2+2PF6 − or [Ru(η2-bipy)2{η2-bipy–(S(p-tol))2}]2+2PF6 −, respectively. Treatment of [Ru(η2-bipy)2(η2-bipy–Cl2)]2+2PF6 − with NaCN in methanol at 55 °C leads to [Ru(η2-bipy)2{η2-bipy–(OCH3)2}]2+2PF6 −. The complexes [Ru(η2-bipy)2(η2-bipy–X2)]2+2PF6 −, with X=Cl and OCH3, were structurally characterized by single crystal X-ray diffraction. Some spectroscopic features of the products are presented. [Copyright &y& Elsevier]