Preparation and multicolor electrochromic performance of a WO3/tris(2,2'-bipyridine)ruthenium(II)/polymer hybrid film

A tungsten trioxide (WO(3))/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)](2+); bpy=2,2'-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) hybrid film was prepared by electrodeposition from a colloidal triad solution containing peroxotungstic acid (PTA), [Ru(bpy)(3)](2+), and PSS. A binary solution of [Ru(bpy)(3)](2+) and PTA (30 vol % ethanol in water) gradually gave an orange precipitate, possibly caused by the electrostatic interaction between the cationic [Ru(bpy)(3)](2+) and the anionic PTA. The addition of PSS to the binary PTA/[Ru(bpy)(3)](2+) solution remarkably suppressed this precipitation and caused a stable, colloidal triad solution to form. The spectrophotometric measurements and lifetime analyses of the photoluminescence from the excited [Ru(bpy)(3)](2+) ion in the colloidal triad solution suggested that the [Ru(bpy)(3)](2+) ion is partially shielded from electrostatic interaction with anionic PTA by the anionic PSS polymer chain. The formation of the colloidal triad made the ternary [Ru(bpy)(3)](2+)/PTA/PSS solution much more redox active. Consequently, the rate of electrodeposition of WO(3) from PTA increased appreciably by the formation of the colloidal triad, and fast electrodeposition is required for the unique preparation of this hybrid film. The absorption spectrum of the [Ru(bpy)(3)](2+) ion in the film was close to its spectrum in water, but the photoexcited state of the [Ru(bpy)(3)](2+) ion was found to be quenched completely by the presence of WO(3) in the hybrid film. The cyclic voltammogram (CV) of the hybrid film suggested that the [Ru(bpy)(3)](2+) ion performs as it is adsorbed onto WO(3) during the electrochemical oxidation. An ohmic contact between the [Ru(bpy)(3)](2+) ion and the WO(3) surface could allow the electrochemical reaction of adsorbed [Ru(bpy)(3)](2+). The composition of the hybrid film, analyzed by electron probe microanalysis (EPMA), suggested that the positive charge of the [Ru(bpy)(3)](2+) ion could be neutralized by partially reduced WO(3)(-) ions, in addition to Cl(-) and PSS units, based on the charge balance in the film. The electrostatic interaction between the WO(3)(-) ion and the [Ru(bpy)(3)](2+) ion might be responsible for forming the electron transfer channel that causes the complete quenching of the photoexcited [Ru(bpy)(3)](2+) ion, as well as the formation of the ohmic contact between the [Ru(bpy)(3)](2+) ion and WO(3). A multicolor electrochromic performance of the WO(3)/[Ru(bpy)(3)](2+)/PSS hybrid film was observed, in which transmittances at 459 and 800 nm could be changed, either individually or at once, by the selection of a potential switch. Fast responses, of within a few seconds, to these potential switches were exhibited by the electrochromic hybrid film.     

Ruthenium(II)-polyazine light absorbers bridged to reactive cis-dichlororhodium(III) centers in a bimetallic molecular architecture

Bimetallic complexes of the form [(bpy)(2)Ru(BL)RhCl(2)(phen)](PF(6))(3), where bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and BL = 2,3-bis(2-pyridyl)pyrazine (dpp) or 2,2'-bipyrimidine (bpm), were synthesized, characterized, and compared to the [{(bpy)(2)Ru(BL)}(2)RhCl(2)](PF(6))(5) trimetallic analogues. The new complexes were synthesized via the building block method, exploiting the known coordination chemistry of Rh(III) polyazine complexes. In contrast to [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) and [{(bpy)(2)Ru(bpm)}(2)RhCl(2)](PF(6))(5), [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) have a single visible light absorber subunit coupled to the cis-Rh(III)Cl(2) moiety, an unexplored molecular architecture. The electrochemistry of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) showed a reversible oxidation at 1.61 V (vs Ag/AgCl) (Ru(III/II)), quasi-reversible reductions at -0.39 V, -0.74, and -0.98 V. The first two reductive couples corresponded to two electrons, consistent with Rh reduction. The electrochemistry of [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) exhibited a reversible oxidation at 1.76 V (Ru(III/II)). A reversible reduction at -0.14 V (bpm(0/-)), and quasi-reversible reductions at -0.77 and -0.91 V each corresponded to a one electron process, bpm(0/-), Rh(III/II), and Rh(II/I). The dpp bridged bimetallic and trimetallic display Ru(dpi)-->dpp(pi*) metal-to-ligand charge transfer (MLCT) transitions at 509 nm (14,700 M(-1) cm(-1)) and 518 nm (26,100 M(-1) cm(-1)), respectively. The bpm bridged bimetallic and trimetallic display Ru(dpi)-->bpm(pi*) charge transfer (CT) transitions at 581 nm (4,000 M(-1) cm(-1)) and 594 nm (9,900 M(-1) cm(-1)), respectively. The heteronuclear complexes [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) had (3)MLCT emissions that are Ru(dpi)-->dpp(pi*) CT in nature but were red-shifted and lower intensity than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4). The lifetimes of the (3)MLCT state of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) at room temperature (30 ns) was shorter than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4), consistent with favorable electron transfer to Rh(III) to generate a metal-to-metal charge-transfer ((3)MMCT) state. The reported synthetic methods provide means to a new molecular architecture coupling a single Ru light absorber to the Rh(III) center while retaining the interesting cis-Rh(III)Cl(2) moiety.     

Comparison of Physical and Photophysical Properties of Monometallic and Bimetallic Ruthenium(II) Complexes Containing Structurally Altered Diimine Ligands

The physical and photophysical properties of a series of monometallic, [Ru(bpy)(2)(dmb)](2+), [Ru(bpy)(2)(BPY)](2+), [Ru(bpy)(Obpy)](2+) and [Ru(bpy)(2)(Obpy)](2+), and bimetallic, [{Ru(bpy)(2)}(2)(BPY)](4+) and [{Ru(bpy)(2)}(2)(Obpy)](4+), complexes are examined, where bpy is 2,2'-bipyridine, dmb is 4,4'-dimethyl-2,2'-bipyridine, BPY is 1,2-bis(4-methyl-2,2'-bipyridin-4'-yl)ethane, and Obpy is 1,2-bis(2,2'-bipyridin-6-yl)ethane. The complexes display metal-to-ligand charge transfer transitions in the 450 nm region, intraligand pi --> pi transitions at energies greater than 300 nm, a reversible oxidation of the ruthenium(II) center in the 1.25-1.40 V vs SSCE region, a series of three reductions associated with each coordinated ligand commencing at -1.3 V and ending at approximately -1.9 V, and emission from a (3)MLCT state having energy maxima between 598 and 610 nm. The Ru(III)/Ru(II) oxidation of the two bimetallic complexes is a single, two one-electron process. Relative to [Ru(bpy)(2)(BPY)](2+), the Ru(III)/Ru(II) potential for [Ru(bpy)(2)(Obpy)](2+) increases from 1.24 to 1.35 V, the room temperature emission lifetime decreases from 740 to 3 ns, and the emission quantum yield decreases from 0.078 to 0.000 23. Similarly, relative to [{Ru(bpy)(2)}(2)(BPY)](4+), the Ru(III)/Ru(II) potential for [{Ru(bpy)(2)}(2)(Obpy)](4+) increases from 1.28 to 1.32 V, the room temperature emission lifetime decreases from 770 to 3 ns, and the room temperature emission quantum yield decreases from 0.079 to 0.000 26. Emission lifetimes measured in 4:1 ethanol:methanol were temperature dependent over 90-360 K. In the fluid environment, emission lifetimes display a biexponential energy dependence ranging from 100 to 241 cm(-)(1) for the first energy of activation and 2300-4300 cm(-)(1) for the second one. The smaller energy is attributed to changes in the local matrix of the chromophores and the larger energy of activation to population of a higher energy dd state. Explanations for the variations in physical properties are based on molecular mechanics calculations which reveal that the Ru-N bond distance increases from 2.05 ? (from Ru(II) to bpy and BPY) to 2.08 ? (from Ru(II) to Obpy) and that the metal-to-metal distance increases from approximately 7.5 ? for [{Ru(bpy)(2)}(2)(Obpy)](4+) to approximately 14 ? for [{Ru(bpy)(2)}(2)(BPY)](4+).     

Sensitization and stabilization of TiO(2) photoanodes with electropolymerized overlayer films of ruthenium and zinc polypyridyl complexes: a stable aqueous photoelectrochemical cell

Overlayer thin films of vinylbipyridine (vbpy)-containing Ru and Zn complexes have been formed on top of ruthenium dye complexes adsorbed to TiO(2) by reductive electropolymerization. The goal was to create an efficient, water-stable photoelectrode or electrodes. An adsorbed-[Ru(vbpy)(2)(dcb)](PF(6))(2)/poly-[Ru(vbpy)(3)](PF(6))(2) surface composite displays excellent stability toward dissolution in water, but the added overlayer film greatly decreases incident photon-to-current conversion efficiencies (IPCE) in propylene carbonate with I(3)(-)/I(-) as the carrier couple. An ads-[Ru(vbpy)(2)(dcb)](PF(6))(2)/poly-[Zn(vbpy)(3)](PF(6))(2) composite displays no loss in IPCE compared to ads-[Ru(vbpy)(2)(dcb)](PF(6))(2) but is susceptible to film breakdown in the presence of water by solvolysis and loss of the cross-linking Zn(2+) ions. Success was attained with an ads-[Ru(vbpy)(2)(dcb)](PF(6))(2)/poly-[Ru(vbpy)(2)(dppe)](PF(6))(2) composite. In this case the electropolymerized layer is transparent in the visible. The composite electrode is stable in water, the IPCE in propylene carbonate with I(3)(-)/I(-) is comparable to the adsorbed complex, and a significant IPCE is observed in water with the quinone/hydroquinone carrier couple. The assembly [(bpy)(2)(CN)Ru(CN)Ru(vbpy)(2)(NC)Ru(CN)(bpy)(2)](PF(6))(2) ([Ru(CN)Ru(NC)Ru](PF(6))(2)) adsorbs spontaneously on TiO(2), and electropolymerization of thin layers of the assembly to give ads-[Ru(CN)Ru(NC)Ru](PF(6))(2)/poly-[Ru(CN)Ru(NC)Ru](PF(6))(2) enhances IPCE and has no deleterious effect on the IPCE/Ru.     

Self assembled composites of luminescent Ru(II) metallopolymers and the Dawson polyoxometalate α-[Mo18O54(SO4)2]4-

The interaction of two luminescent metallopolymers; [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP)co-poly(7)](+), where bpy is 2,2'-bipyridyl, PVP is polyvinylpyridine, and (CAIP)co-poly(7) is poly(styrene(6)-co-p-(aminomethyl)styrene) amide linked to 2-(4-carboxyphenyl)imidazo[4,5-f] [1,10]phenanthroline, with the Dawson polyoxomolybdate α-[Mo(18)O(54)(SO(4))(2)](4-) is described. Both metallopolymers undergo electrostatic association with the polyoxometalate. From both electronic and luminescence spectroscopy the thermodynamic products were determined to be {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) and {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+), i.e. in both instances, the number of ruthenium centres in the cluster exceeds the number required for charge neutralization of the molybdate centre. Association quenches the luminescence of the metallopolymer although, consistent with the excess of Ru(ii) present in the associated composites, emission is not completely extinguished even when a large excess of [Mo(18)O(54)(SO(4))(2)](4-) is present. The observed emission lifetime was not affected by [Mo(18)O(54)(SO(4))(2)](4-) therefore quenching was deemed static. The luminescent intensity data was found to fit best to a (sphere of action) Perrin model from which the radii of the quenching were calculated as 4.6 ? and 5.8 ? for [Ru(bpy)(2)(PVP)(10)](2+) and [Ru(bpy)(2)(CAIP co-poly)(7)](+) respectively. Both UV/Vis and resonance Raman data indicate the presence of a new optical transition centered around 490 nm for the composite, {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). This indicates strong electronic interaction between the metal centres in the former composite, which despite good thermodynamic analogy, is not observed for {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+). These results are consistent with photoelectrochemical studies of layer by layer assemblies of these films which indicate that the ruthenium centre sensitizes polyoxometalate photo-oxidation of benzyl alcohol in {[Ru(bpy)(2)(PVP)(10)](4.5)[Mo(18)O(54)(SO(4))(2)]}(5+) but not in {[Ru(bpy)(2)(CAIP)co-poly(7)](5)[Mo(18)O(54)(SO(4))(2)]}(+).     

Electronic and photophysical properties of adducts of [Ru(bpy)3]2+ and Dawson-type sulfite polyoxomolybdates α/β-[Mo18O54(SO3)2]4-

The spectroscopic and photophysical properties of [Ru(bpy)(3)](2)[[Mo(18)O(54)(SO(3))(2)], where bpy is 2,2'-bipyridyl and [Mo(18)O(54)(SO(3))(2)](4-) is either the α or β-sulfite containing polyoxomolybdate isomer, have been measured and compared with those for the well known but structurally distinct sulfate analogue, α-[Mo(18)O(54)(SO(4))(2)](4-). Electronic difference spectroscopy revealed the presence of new spectral features around 480 nm, although they are weak in comparison with the [Ru(bpy)(3)](2)[Mo(18)O(54)(SO(4))(2)] analogue. Surprisingly, Stern-Volmer plots of [Ru(bpy)(3)](2+) luminescence quenching by the polyoxometallate revealed the presence of both static and dynamic quenching for both α and β-[Mo(18)O(54)(SO(3))(2)](4-). The association constant inferred for the ion cluster [Ru(bpy)(3)](2)α-[Mo(18)O(54)(SO(4))(2)] is K = 5.9 ± 0.56 × 10(6) and that for [Ru(bpy)(3)](2)β-[Mo(18)O(54)(SO(4))(2)] is K = 1.0 ± 0.09 × 10(7). Unlike the sulfate polyoxometalates, both sulfite polyoxometalate-ruthenium adducts are non-luminescent. Despite the strong electrostatic association in the adducts resonance Raman and photoelectrochemical studies suggests that unlike the sulfato polyoxometalate analogue there is no sensitization of the polyoxometalate photochemistry by the ruthenium centre for the sulfite anions. In addition, the adducts exhibit photochemical lability in acetonitrile, attributable to decomposition of the ruthenium complex, which has not been observed for other [Ru(bpy)(3)](2+) -polyoxometalate adducts. These observations suggest that less electronic communication exists between the [Ru(bpy)(3)](2+) and the sulfite polyoxoanions relative to their sulfate polyoxoanion counterparts, despite their structural and electronic analogy. The main distinction between sulfate and sulfite polyoxometalates lies in their reversible reduction potentials, which are more positive by approximately 100 mV for the sulfite anions. This suggests that the capacity for [Ru(bpy)(3)](2+) or analogues to sensitize photoreduction in the adducts of polyoxometalates requires very sensitive redox tuning.     

Charge delocalization of 1,4-benzenedicyclometalated ruthenium: a comparison between tris-bidentate and bis-tridentate complexes

A dimetallic biscyclometalated ruthenium complex, [(bpy)(2)Ru(dpb)Ru(bpy)(2)](2+) (bpy = 2,2'-bipyridine; dpb = 1,4-di-2-pyridylbenzene), with a tris-bidentate coordination mode has been prepared. The electronic properties of this complex were studied by electrochemical and spectroscopic analysis and DFT/TDDFT calculations on both rac and meso isomers. Complex [(bpy)(2)Ru(dpb)Ru(bpy)(2)](2+) has a similar 1,4-benzenedicyclometalated ruthenium (Ru-phenyl-Ru) structural component with a previously reported bis-tridentate complex, [(tpy)Ru(tpb)Ru(tpy)](2+) (tpy = 2,2';6',2″-terpyridine; tpb = 1,2,4,5-tetra-2-pyridylbenzene). The charge delocalizations of these complexes across the Ru-phenyl-Ru array were investigated and compared by studying the corresponding one-electron-oxidized species, generated by chemical oxidation or electrochemical electrolysis, with DFT/TDDFT calculations and spectroscopic and EPR analysis. These studies indicate that both [(bpy)(2)Ru(dpb)Ru(bpy)(2)](3+) and [(tpy)Ru(tpb)Ru(tpy)](3+) are fully delocalized systems. However, the coordination mode of the metal component plays an important role in influencing their electronic properties.     

Changing the role of 2,2'-bipyridine from secondary ligand to protagonist in [Ru(bpy)2(N-N)]2+ complexes: low-energy, red emission from a ruthenium(II)-to-2,2'-bipyridine 3MLCT state

Two new bidentate ligands (1 and 2) with bicyclic guanidine moieties were synthesized and attached to a Ru(II)(bpy)(2) core (bpy = 2,2'-bipyridine) to afford complexes 3 and 4, which were characterized by spectroscopic and electrochemical methods. Complex 4 was further characterized by X-ray crystallography. In cyclic voltammetric studies, both complexes show a Ru(II/III) couple, which is 500 mV less positive than the Ru(II/III) couple of Ru(bpy)(3)(2+). The (1)MLCT and (3)MLCT states of 3 (560 nm/745 nm) and 4 (550 nm/740 nm) are significantly red-shifted with respect to Ru(bpy)(3)(2+) (440 nm/620 nm). Compounds 3 and 4 exhibit emission from a Ru(II)-to-bpy (3)MLCT state, which is rarely the emitting state at λ > 700 nm in [Ru(bpy)(2)(N-N)](2+) complexes.     

Photophysical and novel charge-transfer properties of adducts between [RuII(bpy)3]2+ and [S2Mo18O62]4-

The photophysical properties of acetonitrile solutions of [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) are described. We discuss evidence for ion cluster formation in solution and the observation that despite the strong donor ability of the excited state of [Ru(bpy)(3)](2+) and its inherent photolability, adducts with [S(2)Mo(18)O(62)](4-) were photostable. Photophysical studies suggest that the quenching of the [Ru(bpy)(3)](2+) excited state by [S(2)Mo(18)O(62)](4-) occurs via a static mechanism and that binding is largely electrostatic in nature. Evidence is provided from difference spectroscopy and luminescence excitation spectroscopy for good electronic communication between [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) with the presence of a novel, luminescent, inter-ion charge-transfer transition. The identity of the transition is confirmed by resonance Raman spectroscopy.     

Ruthenium(II) 2,2'-Bipyridyl tetrakis acetonitrile undergoes selective axial photocleavage

The complex [Ru(bpy)(AN)4]2+ (bpy = 2,2'-bipyridyl, AN = acetonitrile) has a Ru(II) --> pi(*)(bpy) MLCT band at 388 nm. Upon irradiation on this absorption band, the compound undergoes total regioselective photocleavage yielding complexes fac-[Ru(bpy)(AN)(3)(H(2)O)](2+) and trans-[Ru(bpy)(AN)(2)(H(2)O)(2)](2+) in two consecutive steps with quantum yields of 0.43 and 0.09, respectively. This behavior is a consequence of the stronger sigma-donor ability of the bpy nitrogens that determines the orbital ordering and therefore the nature of the lowest lying 3d-d state responsible for the photochemistry. The two-step photoreaction, which can be followed by UV-vis and NMR spectra, provides a quantitative path to the preparation of trans-polypyridine species with potentially interesting photochemical properties.     

Sensitization of photo-reduction of the polyoxometalate anions [S(2)M(18)O(62)](4-) (M = Mo, W) in the visible spectral region by the [Ru(bpy)(3)](2+) cation

Voltammetric, photo-physical and photo-electrochemical properties of the Dawson polyoxometalate anions alpha-[S(2)M(18)O(62)](4-) (M = Mo, W) are presented, both in the presence and absence of a series of [Ru(II)L(n)](+/2+) cations [L(n) = (bpy)(3), (bpy)(2)(Im)(2), (bpy)(2)(dpq), (bpy)(2)(box) and (biq)(2)(box)]. Electrochemical processes for both the anion and Ru(II/III) couples were detected in solutions of the salts [Ru(II)L(n)](2)[S(2)M(18)O(62)] in dimethylformamide (0.1 M Bu(4)NPF(6)) by both cyclic and hydrodynamic voltammetries. Responses were also detected when the solid salts were adhered to the surface of a glassy carbon electrode in contact with an electrolyte in which they are insoluble (CH(3)CN; 0.1M Bu(4)NPF(6)). Photolysis experiments were performed on solutions of the salts [R(4)N](4)[S(2)M(18)O(62)] (R = n-butyl or n-hexyl) and [Ru(II)L(n)](2)[S(2)M(18)O(62)] at 355 and 420 nm in dimethylformamide and acetonitrile in the presence and absence of benzyl alcohol (10% v/v). When associated with [Ru(bpy)(3)](2+), the molybdate anion exhibited a large increase in the quantum yield for photo-reduction at 420 nm. The quantum yield for the tungstate analogue was lower but the experiments again provided clear evidence for sensitization of the photo-reduction reaction in the visible spectral region. The origin of this sensitization is ascribed to the new optical transition observed around 480 nm in static ion clusters {[Ru(bpy)(3)][S(2)M(18)O(62)]}(2-) and {[Ru(bpy)(3)](2)[S(2)M(18)O(62)]} present in solution. Measurable photocurrents resulted from irradiation of solutions of the anions with white light in the presence of the electron donor dimethylformamide. Evidence is also presented for possible quencher-fluorophore interactions in the presence of certain [Ru(II)L(n)](+) cations.     

Eilatin complexes of ruthenium and osmium. synthesis, electrochemical behavior, and near-IR luminescence

The synthesis and characterization of new Ru(II) and Os(II) complexes of the ligand eilatin (1) are described. The new complexes [Ru(bpy)(eil)(2)](2+) (2), [Ru(eil)(3)](2+) (3), and [Os(eil)(3)](2+) (4) (bpy = 2,2'-bipyridine; eil = eilatin) were synthesized and characterized by NMR, fast atom bombardment mass spectrometry, and elemental analysis. In the series of complexes [Ru(bpy)(x)(eil)(y)()](2+) (x + y = 3), the effect of sequential substitution of eil for bpy on the electrochemical and photophysical properties was examined. The absorption spectra of the complexes exhibit several bpy- and eil-associated pi-pi and metal-to-ligand charge-transfer (MLCT) transitions in the visible region (400-600 nm), whose energy and relative intensity depend on the number of ligands bound to the metal center (x and y). On going from [Ru(bpy)(2)(eil)](2+) (5) to 2 to 3, the d(pi)(Ru) --> pi(eil) MLCT transition undergoes a red shift from 583 to 591 to 599 nm, respectively. Electrochemical measurements performed in dimethyl sulfoxide reveal several ligand-based reduction processes, where each eil ligand can accept up to two electrons at potentials that are significantly anodically shifted (by ca. 1 V) with respect to the bpy ligands. The complexes exhibit near-IR emission (900-1100 nm) of typical (3)MLCT character, both at room temperature and at 77 K. Along the series 5, 2, and 3, upon substitution of eil for bpy, the emission maxima undergo a blue shift and the quantum yields and lifetimes increase. The radiative and nonradiative processes that contribute to deactivation of the excited level are discussed in detail.     

DNA biosensor based on the electrochemiluminescence of Ru(bpy)3(2+) with DNA-binding intercalators

This paper reports a novel detection method for DNA hybridization based on the electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) with a DNA-binding intercalator as a reductant of Ru(bpy)(3)(3+). Some ECL-inducible intercalators have been screened in this study using electrochemical methods combined with a chemiluminescent technique. The double-stranded DNA intercalated by doxorubicin, daunorubicin, or 4',6-diamidino-2-phenylindole (DAPI) shows a good ECL with Ru(bpy)(3)(2+) at +1.19 V (versus Ag/AgCl), while the non-intercalated single-stranded DNA does not. In order to stabilize the self-assembled DNA molecules during ECL reaction, we constructed the ECL DNA biosensor separating the ECL working electrode with an immobilized DNA probe. A gold electrode array on a plastic plate was assembled with a thru-hole array where oligonucleotide probes were immobilized in the side wall of thru-hole array. The fabricated ECL DNA biosensor was used to detect several pathogens using ECL technique. A good specificity of single point mutations for hepatitis disease was obtained by using the DAPI-intercalated Ru(bpy)(3)(2+) ECL.     

Entrapment of [Ru(bpy)3]2+ in the anionic metal-organic framework: novel photoluminescence behavior exhibiting dual emission at room temperature

[Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) ions were entrapped into the cavities of two-dimensional anionic sheet-like coordination polymeric networks of [M(dca)(3)](-) (dca = dicyanamide; M = Mn(II) and Fe(II)). The prepared compounds, {[Ru(bpy)(3)][Mn(dca)(3)](2)}(n) (1) and {[Ru(bpy)(3)][Fe(dca)(3)](2)}(n) (2), were structurally characterized by X-ray single crystal analysis. The spectroscopic properties of the [Ru(bpy)(3)](2+) ion dramatically changed on its entrapment in [M(dca)(3)](-). The [Ru(bpy)(3)](2+) moiety present in 1 and 2 exhibits novel dual photo-emission at room temperature.     

Mononuclear and dinuclear complexes of dibenzoeilatin: synthesis, structure, and electrochemical and photophysical properties

This work describes a study of Ru(II) and Os(II) polypyridyl complexes of the symmetrical, fused-aromatic bridging ligand dibenzoeilatin (1). The synthesis, purification, and structural characterization by NMR of the mononuclear complexes [Ru(bpy)(2)(dbneil)](2+) (2), [Ru(tmbpy)(2)(dbneil)](2+) (3), and [Os(bpy)(2)(dbneil)](2+) (4), the homodinuclear complexes [[Ru(bpy)(2)](2)[micro-dbneil]](4+) (5), [[Ru(tmbpy)(2)](2)[micro-dbneil]](4+) (6), and [[Os(bpy)(2)](2)[micro-dbneil]](4+) (7), and the heterodinuclear complex [[Ru(bpy)(2)][micro-dbneil][Os(bpy)(2)]](4+) (8) are described, along with the crystal structures of 4, 6, and 7. Absorption spectra of the mononuclear complexes feature a low-lying MLCT band around 600 nm. The coordination of a second metal fragment results in a dramatic red shift of the MLCT band to beyond 700 nm. Cyclic and square wave voltammograms of the mononuclear complexes exhibit one reversible metal-based oxidation, as well as several ligand-based reduction waves. The first two reductions, attributed to reduction of the dibenzoeilatin ligand, are substantially anodically shifted compared to [M(bpy)(3)](2+) (M = Ru, Os), consistent with the low-lying pi orbital of dibenzoeilatin. The dinuclear complexes exhibit two reversible, well-resolved, metal-centered oxidation waves, despite the chemical equivalence of the two metal centers, indicating a significant metal-metal interaction mediated by the conjugated dibenzoeilatin ligand. Luminescence spectra, quantum yield, and lifetime measurements at room temperature in argon-purged acetonitrile have shown that the complexes exhibit (3)MLCT emission, which occurs in the IR-region between 950 and 1300 nm. The heterodinuclear complex 8 exhibits luminescence only from the Ru-based fragment, the intensity of which is less than 1% of that observed in the corresponding homodinuclear complex 5; no emission from the Os-based unit is observed, and an intramolecular quenching constant of k(q) > or = 3 x10(9) s(-)(1) is evaluated. The nature of the quenching process is briefly discussed.     

New dicarboxylic acid bipyridine ligand for ruthenium polypyridyl sensitization of TiO2

An ambidentate dicarboxylic acid bipyridine ligand, (4,5-diazafluoren-9-ylidene) malonic acid (dfm), was synthesized for coordination to Ru(II) and mesoporous nanocrystalline (anatase) TiO(2) thin films. The dfm ligand provides a conjugated pathway from the pyridyl rings to the carbonyl carbons of the carboxylic acid groups. X-ray crystal structures of [Ru(bpy)(2)(dfm)]Cl(2) and the corresponding diethyl ester compound, [Ru(bpy)(2)(defm)](PF(6))(2), were obtained. The compounds displayed intense metal-to-ligand charge transfer (MLCT) absorption bands in the visible region (ε > 11,000 M(-1) cm(-1) for [Ru(bpy)(2)(dfm)](PF(6))(2) in acetonitrile). Significant room temperature photoluminescence, PL, was absent in CH(3)CN but was observed at 77 K in a 4:1 EtOH:MeOH (v:v) glass. Cyclic voltammetry measurements revealed quasi-reversible Ru(III/II) electrochemistry. Ligand reductions were quasi-reversible for the diethyl ester compound [Ru(bpy)(2)(defm)](2+), but were irreversible for [Ru(bpy)(2)(dfm)](2+). Both compounds were anchored to TiO(2) thin films by overnight reactions in CH(3)CN to yield saturation surface coverages of 3 × 10(-8) mol/cm(2). Attenuated total reflection infrared measurements revealed that the [Ru(bpy)(2)(dfm)](2+) compound was present in the deprotonated carboxylate form when anchored to the TiO(2) surface. The MLCT excited states of both compounds injected electrons into TiO(2) with quantum yields of 0.70 in 0.1 M LiClO(4) CH(3)CN. Micro- to milli-second charge recombination yielded ground state products. In regenerative solar cells with 0.5 M LiI/0.05 M I(2) in CH(3)CN, the Ru(bpy)(2)(dfm)/TiO(2) displayed incident photon-to-current efficiencies of 0.7 at the absorption maximum. Under the same conditions, the diethylester compound was found to rapidly desorb from the TiO(2) surface.     

Nitric oxide production by visible light irradiation of aqueous solution of nitrosyl ruthenium complexes

[Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](PF(6))(5) (L is NH(3), py, or 4-acpy) was prepared with good yields in a straightforward way by mixing an equimolar ratio of cis-[Ru(NO(2))(bpy)(2)(NO)](PF(6))(2), sodium azide (NaN(3)), and trans-[RuL(NH(3))(4)(pz)] (PF(6))(2) in acetone. These binuclear compounds display nu(NO) at ca. 1945 cm(-)(1), indicating that the nitrosyl group exhibits a sufficiently high degree of nitrosonium ion (NO(+)). The electronic spectrum of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex in aqueous solution displays the bands in the ultraviolet and visible regions typical of intraligand and metal-to-ligand charge transfers, respectively. Cyclic voltammograms of the binuclear complexes in acetonitrile give evidence of three one-electron redox processes consisting of one oxidation due to the Ru(2+/3+) redox couple and two reductions concerning the nitrosyl ligand. Flash photolysis of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex is capable of releasing nitric oxide (NO) upon irradiation at 355 and 532 nm. NO production was detected and quantified by an amperometric technique with a selective electrode (NOmeter). The irradiation at 532 nm leads to NO release as a consequence of a photoinduced electron transfer. All species exhibit similar photochemical behavior, a feature that makes their study extremely important for their future application in the upgrade of photodynamic therapy in living organisms.     

9-Oxidophenalenone: a noninnocent β-diketonate ligand?

The redox systems [Ru(L)(bpy)(2)](k), [Ru(L)(2)(bpy)](m), and [Ru(L)(3)](n) containing the potentially redox-active ligand 9-oxidophenalenone = L(-) were investigated by spectroelectrochemistry (UV-vis-near-IR and electron paramagnetic resonance) in conjunction with density functional theory (DFT) calculations. Compounds [Ru(L(-))(bpy)(2)]ClO(4) ([1]ClO(4)) and [Ru(L(-))(2)(bpy)]ClO(4) ([2]ClO(4)) were structurally characterized. In addition to establishing electron-transfer processes involving the Ru(II)/Ru(III)/Ru(IV) and bpy(0)/bpy(?-) couples, evidence for the noninnocent behavior of L(-) was obtained from [Ru(IV)(L(?))(L(-))(bpy)](3+), which exhibits strong near-IR absorption due to ligand-to-ligand charge transfer. In contrast, the lability of the electrogenerated anion [Ru(L)(2)(bpy)](-) is attributed to a resonance situation [Ru(II)(L(?2-))(L(-))(bpy)](-)/[Ru(II)(L(-))(2) (bpy(?-))](-), as suggested by DFT calculations.     

Investigation of the electronic, photosubstitution, redox, and surface properties of new ruthenium(II)-containing amphiphiles

A series of pyridine- and phenol-based ruthenium(II)-containing amphiphiles with bidentate ligands of the following types are reported: [(L(PyI))Ru(II)(bpy)(2)](PF(6))(2) (1), [(L(PyA))Ru(II)(bpy)(2)](PF(6))(2) (2), [(L(PhBuI))Ru(II)(bpy)(2)](PF(6)) (3), and [(L(PhClI))Ru(II)(bpy)(2)](PF(6)) (4). Species 1 and 2 are obtained by treatment of [Ru(bpy)(2)Cl(2)] with the ligands L(PyI) (N-(pyridine-2-ylmethylene)octadecan-1-amine) and L(PyA) (N-(pyridine-2-ylmethyl)octadecan-1-amine). The imine species 3 and 4 are synthesized by reaction of [Ru(bpy)(2)(CF(3)SO(3))(2)] with the amine ligands HL(PhBuA) (2,4-di-tert-butyl-6-((octadecylamino)methyl)phenol), and HL(PhClA) (2,4-dichloro-6-((octadecylamino)methyl)phenol). Compounds 1-4 are characterized by means of electrospray ionization (ESI(+)) mass spectrometry, elemental analyses, as well as electrochemical methods, infrared and UV-visible absorption and emission spectroscopies. The cyclic voltammograms (CVs) of 1-2 are marked by two successive processes around -1.78 and -2.27 V versus Fc(+)/Fc attributed to bipyridine reduction. A further ligand-centered reductive process is seen for 1. The Ru(II)/Ru(III) couple appears at 0.93 V versus Fc(+)/Fc. The phenolato-containing 3 and 4 species present relatively lower reduction potentials and more reversible redox behavior, along with Ru(II/III) and phenolate/phenoxyl oxidations. The interpretation of observed redox behavior is supported by density functional theory (DFT) calculations. Complexes 1-4 are surface-active as characterized by compression isotherms and Brewster angle microscopy. Species 1 and 2 show collapse pressures of about 29-32 mN·m(-1), and are strong candidates for the formation of redox-responsive monolayer films.     

Enhancement of metal-metal coupling at a considerable distance by using 4-pyridinealdazine as a bridging ligand in polynuclear complexes of rhenium and ruthenium

Novel polynuclear complexes of rhenium and ruthenium containing PCA (PCA = 4-pyridinecarboxaldehyde azine or 4-pyridinealdazine or 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) as a bridging ligand have been synthesized as PF(6-) salts and characterized by spectroscopic, electrochemical, and photophysical techniques. The precursor mononuclear complex, of formula [Re(Me(2)bpy)(CO)(3)(PCA)](+) (Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine), does not emit at room temperature in CH(3)CN, and the transient spectrum found by flash photolysis at lambda(exc) = 355 nm can be assigned to a MLCT (metal-to-ligand charge transfer) excited state [(Me(2)bpy)(CO)(3)Re(II)(PCA(-))](+), with lambda(max) = 460 nm and tau < 10 ns. The spectral properties of the related complexes [[Re(Me(2)bpy)(CO)(3)}(2)(PCA)](2+), [Re(CO)(3)(PCA)(2)Cl], and [Re(CO)(3)Cl](3)(PCA)(4) confirm the existence of this low-energy MLCT state. The dinuclear complex, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(II)(NH(3))(5)](3+), presents an intense absorption in the visible spectrum that can be assigned to a MLCT d(pi)(Ru) --> pi(PCA); in CH(3)CN, the value of lambda (max) = 560 nm is intermediate between those determined for [Ru(NH(3))(5)(PCA)](2+) (lambda(max) = 536 nm) and [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](4+) (lambda(max) = 574 nm), indicating a significant decrease in the energy of the pi-orbital of PCA. The mixed-valent species, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(III)(NH(3))(5)](4+), was obtained in CH(3)CN solution, by bromine oxidation or by controlled-potential electrolysis at 0.8 V in a OTTLE cell of the [Re(I),Ru(II)] precursor; the band at lambda(max) = 560 nm disappears completely, and a new band appears at lambda(max) = 483 nm, assignable to a MMCT band (metal-to-metal charge transfer) Re(I) --> Ru(III). By using the Marcus-Hush formalism, both the electronic coupling (H(AB)) and the reorganization energy (lambda) for the metal-to-metal intramolecular electron transfer have been calculated. Despite the considerable distance between both metal centers (approximately 15.0 Angstroms), there is a moderate coupling that, together with the comproportionation constant of the mixed-valent species [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](5+) (K(c) approximately 10(2), in CH(3)CN), puts into evidence an unusual enhancement of the metal-metal coupling in the bridged PCA complexes. This effect can be accounted for by the large extent of "metal-ligand interface", as shown by DFT calculations on free PCA. Moreover, lambda is lower than the driving force -DeltaG degrees for the recombination charge reaction [Re(II),Ru(II)] --> [Re(I),Ru(III)] that follows light excitation of the mixed-valent species. It is then predicted that this reverse reaction falls in the Marcus inverted region, making the heterodinuclear [Re(I),Ru(III)] complex a promising model for controlling the efficiency of charge-separation processes.