Synthesis and comprehensive characterizations of new cis-RuL(2)X(2) (X = Cl, CN, and NCS) sensitizers for nanocrystalline TiO(2) solar cell using Bis-phosphonated bipyridine ligands (L)

The preparation and the properties of several ruthenium complexes of the general formula cis-RuL(2)X(2) with L = 2,2'-bipyridine-4,4'-bisphosphonic acid, L' = 2,2'-bipyridine-5,5'-bisphosphonic acid, and X = Cl, CN, or NCS are reported. The synthesis of these complexes relies on the preparation of the key intermediates cis-Ru(bipyridinebis(diethyl ester phosphonate))Cl(2). The ground-state second pK(a) values of the thiocyanato complexes were determined and are 6.0 and 6.1 for cis-RuL(2)(NCS)(2) and for cis-RuL'(2)(NCS)(2), respectively. For these species, (13)C NMR and IR demonstrate that the thiocyanato ligands are bound to Ru via the N atom. The new complexes exhibit a blue-shifted electronic absorption spectrum with respect to the analogous complexes containing carboxylic acid groups. Density functional theory molecular orbital calculations show that the LUMO of the bipyridine phosphonated ligands is at higher energy than the corresponding dicarboxylate complexes and that the thiocyanato ligands are not simple spectator ligands, whose role is to enrich electron density on the ruthenium, but are also involved in transitions from PiRu-NCS to Pibpy that extend the absorbance of the dye in the low energy part of the absorption spectrum. The photoaction spectra recorded in a sandwich regenerative photovoltaic cell indicate that the cyano and thiocyanato complexes containing the bipyridine substituted in 4,4' positions exhibit a 90-95% photoconversion efficiency on the MLCT band, whereas those containing the bipyridine substituted in 5,5' positions display lower efficiency (60-65%). The most efficient complex in the series is cis-RuL(2)(NCS)(2); however, its overall efficiency is about 30% lower than the analogue cis-Ru(H(2)dcb)(2)(NCS)(2) (H(2)dcb = 2,2'-bipyridine-4,4'-dicarboxylic acid) due to a lower absorbance in the red part of the visible spectrum.     

Syntheses, characterization, and catalytic ability in alkane oxygenation of chloro(dimethyl sulfoxide)ruthenium(II) complexes with tris(2-pyridylmethyl)amine and its derivatives

New ruthenium(II) complexes having a tetradentate ligand such as tris(2-pyridylmethyl)amine (TPA), tris[2-(5-methoxycarbonyl)pyridylmethyl]amine [5-(MeOCO)3-TPA], tris(2-quinolylmethyl)amine (TQA), or bis(2-pyridylmethyl)glycinate (BPG) have been prepared. The reaction of the ligand with [RuCl2(Me2SO)4] resulted in a mixture of trans and cis isomers of the chloro(dimethyl sulfoxide-kappaS)ruthenium(II) complexes containing a TPA or a BPG, whereas a trans(Cl,N(amino)) isomer was selectively obtained for 5-(MeOCO)3-TPA and TQA. The trans and cis isomers of the [RuCl(TPA)(Me2SO)]+ complex were easily separated by fractional recrystallization. The molecular structures of trans- and cis(Cl,N(amino))-[RuCl(TPA)(Me2SO)]+ complexes and the trans(Cl,N(amino))-[RuCl{5-(MeOCO)3-TPA}(Me2SO)]+ complex have been determined by X-ray structural analyses. The reaction of TPA with [RuCl2(PhCN)4] gave a single isomer of the chloro(benzonitrile)ruthenium(II) complex, whereas the bis(benzonitrile)ruthenium(II) complex was obtained with BPG. The cis(Cl,N(amino))-[RuCl(TPA)(Me2SO)]+ complex is thermodynamically much less stable than the trans isomer and isomerizes in dimethyl sulfoxide at 65-100 degrees C. Oxygenation of alkanes catalyzed by these ruthenium(II) complexes has been examined. The chloro(dimethyl sulfoxide-kappaS)ruthenium(II) complexes with TPA and its derivatives using m-chloroperbenzoic acid as a cooxidant showed high catalytic ability. Adamantane was efficiently and selectively oxidized to give 1-adamantanol up to 88%. The chloro(dimethyl sulfoxide-kappaS)ruthenium(II) complex with 5-(MeOCO)3-TPA was found to be the most active catalyst among the complexes examined.     

Synthesis, characterization and electrochemical studies of mixed ligand complexes of ruthenium(ii) with DNA

Two mixed ligand complexes of ruthenium(ii) [Ru(bzimpy)(bpy)(OH(2))](2+) (1) and [Ru(bzimpy)(phen)(OH(2))](2+) (2) have been synthesized and characterized by FAB mass, (1)H NMR, cyclic voltammetry and spectroelectrochemical measurements. Controlled potential electrolysis of these complexes results in the conversion of ruthenium(ii) to ruthenium(iii) at 0.6 V and ruthenium(iii) to ruthenium(iv) at 0.8 V vs. SCE. The binding constant of these complexes with DNA has been determined electrochemically and found to be (3.58 +/- 0.25) x 10(4) and (2.87+/- 0.2) x 10(4) M(-1). Viscosity measurements suggest that these complexes bind with DNA through intercalation. Such intercalative binding to DNA has been found to induce chirality to the two complexes. Electrochemically generated ruthenium(iv) species of these complexes have been found to bring about oxidative cleavage in DNA.     

手性钌配合物的合成、抗肿瘤活性及其与血清蛋白的相互作用

合成了手性钌配合物Δ, Λ-[Ru(bpy)₂(pyip)]²⁺, 通过元素分析、核磁共振、质谱和CD光谱对配合物进行了表征. 采用MTT法评价了3种异构体对多种肿瘤细胞株的体外抗肿瘤活性以及对正常细胞的毒性. 结果表明, Δ-[Ru(bpy)₂(pyip)]²⁺的抗肿瘤活性明显优于其异构体, 对A375, SW480, MCF-7和A549的半数抑制浓度低于顺铂. 通过荧光光谱法研究了在生理pH条件下, 手性钌配合物与牛血清白蛋白(BSA)之间的结合作用以及荧光猝灭机制. 依据Scatchard方程测定了结合常数和结合位点数, 根据热力学方程讨论了两者间的主要作用力类型. 结果表明, 钌配合物对牛血清白蛋白的荧光猝灭机制为静态猝灭. Δ-1, 1和Λ-1与牛血清白蛋白的结合常数分别为1.16×10⁵, 5.12×10⁴和3.64×10⁴, 结合位点数均为1, 主要作用力类型是静电作用. 钌配合物在体内能够被血清蛋白存储转运且结合时对蛋白构象无影响.     

Combined ruthenium(II) and lipase catalysis for efficient dynamic kinetic resolution of secondary alcohols. Insight into the racemization mechanism

Pentaphenylcyclopentadienyl ruthenium complexes (3) are excellent catalysts for the racemization of secondary alcohols at ambient temperature. The combination of this process with enzymatic resolution of the alcohols results in a highly efficient synthesis of enantiomerically pure acetates at room temperature with short reaction times for most substrates. This new reaction was applied to a wide range of functionalized alcohols including heteroaromatic alcohols, and for many of the latter, enantiopure acetates were efficiently prepared for the first time via dynamic kinetic resolution (DKR). Different substituted cyclopentadienyl ruthenium complexes were prepared and studied as catalysts for racemization of alcohols. Pentaaryl-substituted cyclopentadienyl complexes were found to be highly efficient catalysts for the racemization. Substitution of one of the aryl groups by an alkyl group considerably slows down the racemization process. A study of the racemization of (S)-1-phenylethanol catalyzed by ruthenium hydride eta(5)-Ph(5)CpRu(CO)(2)H (8) indicates that the racemization takes place within the coordination sphere of the ruthenium catalyst. This conclusion was supported by the lack of ketone exchange in the racemization of (S)-1-phenylethanol performed in the presence of p-tolyl methyl ketone (1 equiv), which gave <1% of 1-(p-tolyl)ethanol. The structures of ruthenium chloride and iodide complexes 3a and 3c and of ruthenium hydride complex 8 were confirmed by X-ray analysis.     

Covalent anchoring of a racemization catalyst to CALB-beads: towards dual immobilization of DKR catalysts

The preparation of a heterogeneous bifunctional catalytic system, combining the catalytic properties of an organometallic catalyst (racemization) with those of an enzyme (enantioselective acylation) is described. A novel ruthenium phosphonate inhibitor was synthesized and covalently anchored to a lipase immobilized on a solid support (CALB, Novozym® 435). The immobilized bifunctional catalytic system showed activity in both racemization of (S)-1-phenylethanol and selective acylation of 1-phenylethanol.     

Chemistry of 2-(arylazo)phenolate complexes of ruthenium. Synthesis,structure and reactivities

A group of six ruthenium(III) complexes of type [Ru(acac)(L)₂]where acac=acetylacetonate anion and L=2-(arylazo)-4-methylphenolate anion or 1-(phenylazo)-2-naphtholate anion have been synthesized and characterized Structural characterization of a representative complex where L=1-(phenylazo)-2-naphtholate anionshows that the azophenolate ligands are coordinated as NO-donor ligands forming six-membered chelate rings The complexes are paramagnetic (low-spin d⁵S=1/2) and show rhombic ESR spectra in 1:1 dichloromethane–toluene solution at 77 K In carbon tetrachloride solution these complexes show intense LMCT transitions in the visible region together with weak ligand-field transitions in the near-IR region All the complexes display two cyclic voltammetric responses a ruthenium(III)–ruthenium(IV) oxidation in the range of 083 to 103 V vs SCE and a ruthenium(III)–ruthenium(II) reduction in the range of −024 to −052 V vs SCE Formal potentials of both the couples correlate linearly with the Hammett constant of the para substituent in the arylazo fragment of the 2-(arylazo)-4-methylphenolate ligand The ruthenimn(IV) and ruthenium(II) congeners of the [Ru^III(acac)(L)₂] complexes have been generated by chemical or electrochemical methods and they have been characterized by electronic spectroscopy and cyclic voltammetry.     

Organosoluble zirconium phosphonate nanocomposites and their supported chiral ruthenium catalysts: the first example of homogenization of inorganic-supported catalyst in asymmetric hydrogenation

In this article, we report the synthesis, structure, morphologies, and asymmetric catalytic properties of a series of novel organosoluble zirconium phosphonate nanocomposites and their supported chiral ruthenium catalysts, which have a good organosolubility (0.1-0.5 g mL(-1)) in various solvents and mesoporous, filiform, and layered structures. Due to the organosoluble properties in various organic solvents, the first homogenization of zirconium phosphonate-supported catalyst was realized in the field of catalysis. In the asymmetric hydrogenation of substituted α-ketoesters, enantioselectivities (74.3-84.7% ee) and isolated yields (86.7-93.6%) were higher than the corresponding homogeneous Ru(p-cymene)(S-BINAP)Cl(2) due to the confinement effect caused by the remaining mesopores in the backbone of the zirconium phosphonate. After completing the reaction, the supported catalyst can be readily recovered in quantitative yield by adding cyclohexane and centrifugation, and reused for five consecutive runs without significant loss in catalytic activity.     

Luminescent ruthenium(II) bipyridyl-phosphonic acid complexes: pH dependent photophysical behavior and quenching with divalent metal ions

The synthesis, redox behavior, and photophysical properties of a series of Ru(II) bipyridyl complexes having diimine ligands with phosphonate and phosphonic acid substituents are presented. The phosphonate-containing ligands examined include diethyl 4-(2,2'-bipyrid-4-yl)benzylphosphonate (bpbzp), diethyl 4-(2,2'-bipyrid-4-yl)-phenylphosphonate (bppp), and 4,4'-(diethyl phosphonato)-2,2'-bipyridine (bpdp), and the [(bpy)2Ru(L)](PF6)2 complexes of both the diethyl phosphonate and the phosphonic acid were prepared. The Ru(III/II) potentials are more positive for the phosphonate complexes than for the phosphonic acids, and the first reduction is localized on the phosphonate-containing ligand for the bppp and bpdp complexes. The first reduction of the phosphonic acid complexes is at more negative potentials and cannot be distinguished from bpy reduction. For the bppp and bpdp complexes luminescence arises from a Ru(d pi)-->bpy-phosphonate (pi*) MLCT state; the phosphonic acid complexes luminescence at higher energies from a MLCT state not clearly isolated on one ligand. Iron(III) and copper(II) complex with and very efficiently quench the luminescence of all the phosphonic acid complexes in nonaqueous solvents. The quenching mechanism is discussed on the basis of luminescence decay and picosecond transient absorption measurements.     

IR and EXAFS spectroscopic studies of glyphosate protonation and copper(II) complexes of glyphosate in aqueous solution

The varying degrees of protonation of N-(phosphonomethyl)glycine (PMG, glyphosate) were investigated with infrared (IR) spectroscopy and ab initio frequency calculations. The zwitterionic nature of PMG in solution was confirmed, and intramolecular hydrogen bonding was identified. Successive protonation of the PMG molecule follows the order amine, phosphonate, carboxylate. Intramolecular hydrogen bonding is indicated to exist at all stages of protonation: between both RCO(2-) and RNH(2)(+) and RPO(3)(2-) and RNH(2+) in HL(2)(-) (where L represents the ligand PMG); between RCO(2)(-) and RNH(2)(+) in H(2)L(-); predominantly between RPO(3)(2-) and RNH(2)(+) in H(3)L. There are strong indications that the zwitterion is intact throughout the pH range investigated. Results from IR and extended X-ray absorption fine structure (EXAFS) spectroscopies provide new evidence for structures of N-(phosphonomethyl)glycinecopper(II) complexes. The structures of 1:1 complexes, CuL(-) and CuHL, are essentially the same, differing only in protonation of the phosphonate group. Copper(II) lies at the center of a Jahn-Teller distorted octahedron with all three donor groups (amine, carboxylate, phosphonate) of PMG chelating with copper(II) to form two five-membered chelate rings oriented in the equatorial plane. EXAFS indicates that oxygen (most likely a water molecule) is a fourth ligand, which would thus occupy the fourth corner in the equatorial plane of the elongated octahedron. CuL(2)(4-) most probably forms an isomeric mixture in solution, and there are indications that this mixture is dominated by complexes where two PMG ligands are bound to copper(II) via equatorial and axial positions, with both phosphonate and carboxylate donor groups responsible for chelation at axial positions.     

Development of a method for the preparation of ruthenium indenylidene-ether olefin metathesis catalysts

The reactions between several derivatives of 1-(3,5-dimethoxyphenyl)-prop-2-yn-1-ol and different ruthenium starting materials [i.e., RuCl?(PPh?)? and RuCl?(p-cymene)(L), where L is tricyclohexylphosphine di-t-butylmethylphosphine, dicyclohexylphenylphosphine, triisobutylphosphine, triisopropylphosphine, or tri-n-propylphosphine] are described. Several of these reactions allow for the easy, in-situ and atom-economic preparation of olefin metathesis catalysts. Organic precursor 1-(3,5-dimethoxyphenyl)-1-phenyl-prop-2-yn-1-ol led to the formation of active ruthenium indenylidene-ether complexes, while 1-(3,5-dimethoxyphenyl)-prop-2-yn-1-ol and 1-(3,5-dimethoxyphenyl)-1-methyl-prop-2-yn-1-ol did not. It was also found that a bulky and strong σ-donor phosphine ligand was required to impart good catalytic activity to the new ruthenium complexes.     

Synthesis,structure and redox properties of mixed ligand complexes of trivalent ruthenium with deprotonated 2-carbamoylpyridine derivatives and 2,2′-bipyridine

Five mixed ligand complexes of trivalent ruthenium with general formula [Ru(L)(bpy)Cl₂], where L=p-substituted N-phenyl derivatives of 2-carbamoylpyridine and bpy=2,2′-bipyridine, have been synthesised and characterised. X-ray crystal structural characterisation of a representative complex, i.e. where L=2-(N-(4-nitrophenyl)carbamoyl)pyridine, shows that the amide-containing ligand coordinates to the ruthenium(III) centre via the pyridyl nitrogen and the amidato nitrogen, forming a five-membered chelate ring. The complexes are paramagnetic (low spin d⁵, S=1/2) and show a single signal in their EPR spectra in 1:1 dichloromethane–toluene solution at 77 K. In dichloromethane solution, these complexes show intense ligand to metal charge transfer transitions in the visible region. All the complexes display two cyclic voltammetric responses, a ruthenium(III)–ruthenium(IV) oxidation in the range from +0.63 to +0.93 V and a ruthenium(III)–ruthenium(II) reduction in the range from −0.63 to −0.73 V(vs ferrocene–ferrocenium couple). The potentials of both couples for all the complexes are found to be sensitive to the nature of the substituents present on the amide ligands, L.     

Dipolar ruthenium(II) ammine complexes as electron transfer mediators of amperometric glucose sensors

The mediation of dipolar ruthenium(II) ammine complexes containing pyridinium ions [Ru(NH(3))(5)(L(+))](3+)(L(+): pyridinium ions) in glucose oxidation has been investigated by a voltammetric method. These ruthenium(II) complexes had appropriate redox potentials of 0.10-0.18 V vs. Ag/AgCl and high k(s) values of 5.7-17 x 10(6) M(-1) s(-1) which are the second-order rate constants for electron transfer from glucose oxidase in reduced form to [Ru(NH(3))(5)(L(+))](4+). In particular, the k(s) values for [Ru(NH(3))(5)(L(+))](3+) were greater than those of osmium(II)-polypyridine complexes possessing similar redox potentials which are most commonly used. All the dipolar ruthenium(II) complexes used in this study are therefore concluded to be useful for the electron transfer mediators of amperometric glucose sensors.     

Electron donor-acceptor dyads based on ruthenium(II) bipyridine and terpyridine complexes bound to naphthalenediimide

Two series of photosensitizer-electron acceptor complexes have been synthesized and fully characterized: ruthenium(II) tris(bipyridine) ([Ru(II)(bpy)(2)(bpy-X-NDI)], where X = -CH(2)-, tolylene, or phenylene, bpy is 2,2'-bipyridine, and NDI is naphthalenediimide) and ruthenium(II) bis(terpyridine) ([Ru(II)(Y-tpy)(tpy-X-NDI)], where Y = H or tolyl and X = tolylene or phenylene, and tpy = 2,2':6',2' '-terpyridine). The complexes have been studied by cyclic and differential pulse voltammetry and by steady state and time-resolved absorption and emission techniques. Rates for forward and backward electron transfer have been investigated, following photoexcitation of the ruthenium(II) polypyridine moiety. The terpyridine complexes were only marginally affected by the linked diimide unit, and no electron transfer was observed. In the bipyridine complexes we achieved efficient charge separation. For the complexes containing a phenyl link between the ruthenium(II) and diimide moieties, our results suggest a biphasic forward electron-transfer reaction, in which 20% of the charge-separated state was formed via population of the naphthalenediimide triplet state.     

Preparation,crystal structures and properties of half-sandwich ruthenium complexes containing salicylbenzoxazole ligands

Three half-sandwich ruthenium complexes [Ru(p-cymene)LCl] containing salicylbenzoxazole ligands [LH = 2-(5-methyl-benzoxazol-2-yl)-4-methyl-phenol (2a), LH = 2-(5-methyl-benzoxazol-2-yl)-4-chloro-phenol (2b), and LH = 2-(5-methyl-benzoxazol-2-yl)-4-bromo-phenol (2c)] were synthesized and characterized. All half-sandwich ruthenium complexes were fully characterized by ¹H and ¹³C NMR spectra, MS, elemental analyses, and UV–vis as well as cyclic voltammetry (CV). The molecular structures of 2a, 2b, and 2c were confirmed by single-crystal X-ray diffraction. Single-crystal X-ray structures show that the synthesized ruthenium complexes are three-legged piano-stools with a six-membered metallocycle formed by coordination of the bidentate salicylbenzoxazole ligands to the metal centers. Data from CV and UV–vis absorption of the ruthenium complexes indicated that by changing the substituent on the para position of (donating or withdraw group) the salicylbenzoxazole ligands, minor changes in redox and electronic properties of the ruthenium complexes were observed.     

Synthesis and redox properties of trinuclear ruthenium-acetylide complexes with tri(ethynylphenyl)amine bridge

Novel trinuclear ruthenium complexes have been prepared by using tri(4-ethynylphenyl)amine as a bridging ligand. Cyclic voltammetry of the trinuclear ruthenium complexes revealed stepwise quasi-reversible redox behavior of three ruthenium-acetylide species and the central triphenylamine unit, whereas the mononuclear analog showed two sequential quasi-reversible redox waves. The spectroelectrochemical UV-VIS spectral studies suggested that the 1e- oxidized triruthenium species was stable and showed a characteristic absorption at lambda(max) = 505 nm. Chemical oxidation of the triruthenium complex with ferrocenium hexafluorophosphate led to the isolation of the 1e- oxidized complex, the near-IR spectrum of which revealed an intervalence charge transfer band due to the electronic coupling among three ruthenium species. The 1e(-) oxidized triruthenium complexes can be classified as class II mixed-valence compounds.     

Stoichiometric photoisomerization of mononuclear ruthenium(II) monoaquo complexes controlling redox properties and water oxidation catalysis

Although various reactions involved in photoexcited states of polypyridyl ruthenium(II) complexes have been extensively studied, photoisomerization of the complexes is very rare. We report the first illustration of stoichiometric photoisomerization of trans-[Ru(tpy)(pynp)OH(2)](2+) (1a) [tpy = 2,2':6',2'-terpyridine; pynp = 2-(2-pyridyl)-1,8-naphthyridine] to cis-[Ru(tpy)(pynp)OH(2)](2+) (1a') and the isolation of 1a and 1a' for X-ray crystallographic analysis. Polypyridyl ruthenium(II) aquo complexes are attracting much attention related to proton-coupled electron transfer and water oxidation catalysis. We demonstrate that the photoisomerization significantly controls the redox reactions and water oxidation catalyses involving the ruthenium(II) aquo complexes 1a and 1a'.     

Lipase active-site-directed anchoring of organometallics: metallopincer/protein hybrids

The work described herein presents a strategy for the regioselective introduction of organometallic complexes into the active site of the lipase cutinase. Nitrophenol phosphonate esters, well known for their lipase inhibitory activity, are used as anchor functionalities and were found to be ideal tools to develop a single-site-directed immobilization method. A small series of phosphonate esters, covalently attached to ECE "pincer"-type d8-metal complexes through a propyl tether (ECE=[C6H3(CH2E)(2)-2,6]-; E=NR2 or SR), were designed and synthesized. Cutinase was treated with these organometallic phosphonate esters and the new metal-complex/protein hybrids were identified as containing exactly one organometallic unit per protein. The organometallic proteins were purified by membrane dialysis and analyzed by ESI-mass spectrometry. The major advantages of this strategy are: 1) one transition metal can be introduced regioselectively and, hence, the metal environment can potentially be fine-tuned; 2) purification procedures are facile due to the use of pre-synthesized metal complexes; and, most importantly, 3) the covalent attachment of robust organometallic pincer complexes to an enzyme is achieved, which will prevent metal leaching from these hybrids. The approach presented herein can be regarded as a tool in the development of regio- and enantioselective catalyst as well as analytical probes for studying enzyme properties (e.g., structure) and, hence, is a "proof-of-principle design" study in enzyme chemistry.     

Ruthenium-manganese complexes for artificial photosynthesis: factors controlling intramolecular electron transfer and excited-state quenching reactions

Continuing our work toward a system mimicking the electron-transfer steps from manganese to P(680)(+) in photosystem II (PS II), we report a series of ruthenium(II)-manganese(II) complexes that display intramolecular electron transfer from manganese(II) to photooxidized ruthenium(III). The electron-transfer rate constant (k(ET)) values span a large range, 1 x 10(5)-2 x 10(7) s(-1), and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (lambda = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically lambda approximately 1.0 eV). This result indicates that the inner reorganization energy is relatively large and, consequently, that at moderate driving force values manganese complexes are not fast donors. Both the type of manganese ligand and the link between the two metals are shown to be of great importance to the electron-transfer rate. In contrast, we show that the quenching of the excited state of the ruthenium(II) moiety by manganese(II) in this series of complexes mainly depends on the distance between the metals. However, by synthetically modifying the sensitizer so that the lowest metal-to-ligand charge transfer state was localized on the nonbridging ruthenium(II) ligands, we could reduce the quenching rate constant in one complex by a factor of 700 without changing the bridging ligand. Still, the manganese(II)-ruthenium(III) electron-transfer rate constant was not reduced. Consequently, the modification resulted in a complex with very favorable properties.     

Oligothiophene-2-yl-vinyl bridged mono- and binuclear ruthenium(II) tris-bipyridine complexes: Synthesis, photophysics, electrochemistry and electrogenerated chemiluminescence

A series of mono- and binuclear ruthenium(II) tris-bipyridine complexes tethered to oligothienylenevinylenes have been synthesized and characterized by ¹H NMR, ¹³C NMR and TOF-MS spectrometry. Photophysics, electrochemistry and electrogenerated chemiluminescence (ECL) properties of these complexes are investigated. The electronic absorption spectra of the mononuclear ruthenium complexes show a significant red shift both at MLCT (metal-to-ligand charge transfer) and π-π^∗ transitions of oligothienylenevinylenes with increase in the number of thiophenyl-2-yl-vinyl unit. For the binuclear complexes these two absorption bands are overlapped. All the metal complexes have very weak emission compared to that of the reference complex Ru(bpy)²⁺₃. The first reduction potentials of all mononuclear ruthenium complexes are less negative than that of Ru(bpy)²⁺₃, due to the moderate electron-withdrawing effect of oligothienylenevinylenes. For binuclear ruthenium complexes, only one Ru(II/III) oxidation peak (E_1/2 = 0.96 V vs. Ag/Ag⁺) was observed, suggesting a weak interaction between two metal centers. Three successive reduction processes of bipyridine ligands are similar among all ruthenium complexes except for RuTRu, which has a very sharp peak owing to the accumulation of neutral product on the electrode surface. All these ruthenium complexes exhibited different ECL property in CH₃CN solution without any additional reductant or oxidant. For three mononuclear ruthenium complexes, the ECL intensity strengthens with increase in the number of thiophene-2-yl-vinyl unit. However, the ECL efficiency dramatically decreased in the binuclear ruthenium complexes. The ECL efficiencies of all the reported complexes do not exceed that of Ru(bpy)²⁺₃, where the ECL efficiency decreases in the order of RuTRu > Ru3T > Ru2T > RuT > Ru2TRu (RuT,bis-2,2′-bipyridyl-(4-methyl-4′-(2-thienylethenyl)-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru2T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru3T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}}-2,2′-bipyridine) ruthenium dihexafluorophosphate; RuTRu, bis-2,2′-bipyridyl-ruthenium-bis-[2-((E)-4′-methyl-2, 2′-bipyridinyl-4)-ethenyl]-thienyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate; Ru2TRu, bis-2,2′-bipyridyl-ruthenium-(E)-1,2-bis-{2-[2-((E)-4′-methyl-2,2′-bipyridinyl-4)-ethenyl]-thienyl}-ethenyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate).