Wirelike dinuclear ruthenium complexes connected by bis(ethynyl)oligothiophene

Preparation and characterization of a series of rodlike binuclear ruthenium polyynediyl complexes capped with redox-active organometallic fragments [(bph)(PPh3)2Ru]+ (bph=N-(benzoyl)-N'-(picolinylidene)-hydrazine) or [(Phtpy)(PPh3)2Ru]2+ (Phtpy=4'-phenyl-2,2':6',2' '-terpyridine) have been carried out. The length of the molecular rods is extended by successive insertion of 2,5-thiophene or 1,4-phenylene spacers in the bridging ligands. Oxidation of thiophene-containing Ru2II,II complexes induces isolation of stable Ru2II,III or Ru2III,III species. Electrochemical and UV-vis-NIR spectral studies demonstrate that the polyynediyl bridges with 2,5-thiophene units are more favorable for metal-metal charge transfer compared with those containing the same number of 1,4-phenylene units. Successive increase of thiophene spacers in mixed-valence complexes {RuII}-CC(C4H2S)mCC-{RuIII} (m=1, 2, 3) induced a smooth transition from almost electronic delocalization (m=1) to localization (m=3). For binuclear ruthenium complexes with intramolecular electron transfer transmitted across nine Ru-C and C-C bonds, electronic conveying capability follows {Ru}-CC(CC)2CC-{Ru}>{Ru}-CC(C4H2S)CC-{Ru}>{Ru}-CC(C6H4)CC-{Ru}>{Ru}-CC(CH=CH)2CC-{Ru}. It is revealed that molecular wires capped with electron-rich (bph)(PPh3)2Ru endgroups are much more favorable for electronic communication than the corresponding electron-deficient (Phtpy)(PPh3)2Ru-containing counterparts. The intermetallic electronic communication is fine-tuned by modification of both the bridging spacers and the ancillary ligands.     

Photoinduced Electron and Energy Transfer in Rigidly Bridged Ru(II)-Rh(III) Binuclear Complexes

A series of binuclear Ru(II)-Rh(III) complexes of general formula (ttpy)Ru-tpy-(ph)(n)-tpy-Rh(ttpy)(5+) (n = 0-2) have been synthesized, where ttpy = 4'-p-tolyl-2,2':6,2"-terpyridine and tpy-(ph)(n)-tpy represents a bridging ligand where two 2,2':6',2"-terpyridine units are either directly linked together (n = 0) or connected through one (n = 1) or two (n = 2) phenyl spacers in the 4'-position. This series of complexes is characterized by (i) rigid bridge structures and (ii) variable metal-metal distances (11 ? for n = 0, 15.5 ? for n = 1, 20 ? for n = 2). The photophysics of these binuclear complexes has been investigated in 4:1 methanol/ethanol at 77 K (rigid glass) and 150 K (fluid solution) and compared with that of mononuclear [Ru(ttpy)(2)(2+) and Rh(ttpy)(2)(3+)] or binuclear [(ttpy)Ru-tpy-tpy-Ru(ttpy)(4+)] model compounds. At 77 K, no quenching of the Ru(II)-based excited state is observed, whereas energy transfer from excited Rh(III) to Ru(II) is observed for all complexes. At 150 K, energy transfer from excited Rh(III) to Ru(II) is again observed for all complexes, while quenching of excited Ru(II) by electron transfer to Rh(III) is observed, but only in the complex with n = 0. The reasons for the observed behavior can be qualitatively understood in terms of standard electron and energy transfer theory. The different behavior between n = 0 and n = 1, 2 can be rationalized in terms of better electronic factors and smaller reorganizational energies for the former species. The freezing of electron transfer quenching but not of energy transfer, in rigid glasses reflects the different reorganizational energies involved in the two processes. Unusual results arising from multiphotonic and conformational effects have also been observed with these systems.     

Di- and tetranuclear ruthenium(II) and/or osmium(II) complexes of polypyridyl ligands bridged by a fully conjugated aromatic spacer: synthesis,characterization, and electrochemical and photophysical studies

A series of mono-, di-, and tetranuclear homo/heterometallic complexes of Ru(II) and Os(II) based on the bridging ligand dppz(11-11')dppz (where dppz = dipyrido[3,2-a:2',3'-c]phenazine) (BL) have been synthesized and characterized. This bridging ligand is a long rigid rod with only one rotational degree of freedom and provides complete conjugation between the chromophores. The complexes synthesized are of general formula [(bpy)(2)Ru-BL](2+), [(phen)(2)/(bpy)(2)M-BL-M(bpy)(2)/(phen)(2)](4+) (M = Ru(II) and Os(II)), [(bpy)(2)Ru-BL-Os(bpy)(2)](4+), and [((bpy)(2)Ru-BL)(3)M](8+). Detailed (1)H NMR studies of these complexes revealed that each chiral center does not influence its neighbor because of the long distance between the metal centers and the superimposed resonances of the diastereoisomers, which allowed the unambiguous assignment of the signals, particularly for homonuclear complexes. Concentration-dependent (1)H NMR studies show molecular aggregation of the mono- and dinuclear complexes in solution by pi-pi stacking. Electrospray mass spectrometry data are consistent with dimerization of mono- and dinuclear complexes in solution. Electrochemical studies show oxidations of Ru(II) and Os(II) in the potential ranges +1.38 to +1.40 and +0.92 to +1.01 V, respectively. The bridging ligand exhibits two one-electron reductions, and it appears that the added electrons are localized on the phenazene moieties of the spacer. All of these complexes show strong metal-to-ligand charge-transfer (MLCT) absorption and (3)MLCT luminescence at room temperature. Quantum yields have been calculated, and the emission lifetimes of all complexes have been measured by laser flash photolysis experiments. The luminescence intensity and lifetime data suggest that the emission due to the Ru center of the heteronuclear complexes is strongly quenched (>90%) compared to that of the corresponding model complexes. This quenching is attributed to intramolecular energy transfer from the Ru(II) center to the Os(II) center (k = (3-5) x 10(7) s(-1)) across the bridging ligand.     

Outer sphere perturbation of delocalized mixed-valence complexes

The complexes [[Ru(ttp)(bpy)](2)(micro-adpc)][PF(6)](2) and [[Ru(ttp)(bpy)](2)(micro-dicyd)][PF(6)](2), where ttp is 4-toluene-2,2':6',2' '-terpyridine, bpy is 2,2'-bipyridine, adpc(2)(-) is azodi(phenylcyanamide), and dicyd(2)(-) is 1,4-dicyanamidebenzene, were prepared and characterized by IR and NIR, vis spectroelectrochemistry, and cyclic voltammetry. The crystal structure of the complex, [[Ru(ttp)(bpy)](2)(micro-adpc)][PF(6)](2).6DMF, revealed a planar bridging adpc(2)(-) ligand with the cyanamide groups adopting an anti configuration. IR and comproportionation data are consistent with delocalized mixed-valence complexes, and a spectroscopic analysis assuming C(2)(h) microsymmetry leads to a prediction of multiple MMCT transitions with the lowest energy transition equal to the resonance exchange integral for the mixing of ruthenium donor and acceptor orbitals with a bridging ligand orbital (the preferred superexchange pathway). The solvent dependence of the MMCT band energy that is seen for [[Ru(ttp)(bpy)](2)(micro-adpc)](3+) is due to a ground state weakening of metal-metal coupling because of solvent donor interactions with the acceptor azo group of the bridging ligand.     

TiO2纳米颗粒对钌(II)三联吡啶配合物光损伤小牛胸腺DNA能力的影响

由于极短的激发态寿命, 钌(II)三联吡啶配合物对脱氧核糖核酸(DNA)的光损伤能力低下. 设计合成了三个钌(II)三联吡啶配合物[Ru(ttp)(tpy)]^2＋ (1), [Ru(ttp-COOH)(tpy)]^2＋ (2)和[Ru(ttp-COOH)(tpy-pyr)]^2＋ (3), 其中tpy为2,2':6',2"-三联吡啶, ttp为4′-(4-甲苯基)-2,2':6',2"-三联吡啶, ttp-COOH为4′-(4-羧基苯基)-2,2':6',2"-三联吡啶, tpy-pyr为4'-(1-芘基)-2,2':6',2"-三联吡啶. 比较了TiO₂纳米颗粒对它们光损伤小牛胸腺DNA的影响. 发现TiO₂纳米颗粒在空气和氩气条件下均可显著提高配合物3光损伤DNA的能力. TiO₂纳米颗粒和配合物3间的光诱导电子转移作用及其该作用生成的钌(III)物种可能是促进配合物3对DNA光损伤的主要原因.     

Fully delocalized (ethynyl)(vinyl)phenylene bridged triruthenium complexes in up to five different oxidation states

Triruthenium [(dppe)(2)Ru{-C≡C-1,4-C(6)H(2)-2,5-R(2)-CH═CH-RuCl(CO)(P(i)Pr(3))(2)}(2)](n+) (4a, R = H; 4b, R = OMe) containing unsymmetrical (ethynyl)(vinyl)phenylene bridging ligands and displaying five well-separated redox states (n = 0-4) are compared to their bis(alkynyl)ruthenium precursors (dppe)(2)Ru{-C≡C-1,4-C(6)H(2)-2,5-R(2)-C≡CR'} (2a,b: R' = TMS; 3a,b: R' = H) and their symmetrically substituted bimetallic congeners, complexes {Cl(dppe)(2)Ru}(2){μ-C≡C-1,4-C(6)H(2)-2,5-R(2)-C≡C} (A(a), R = H; A(b), R = OMe) and {RuCl(CO)(P(i)Pr(3))(2)}(2){μ-CH═CH-1,4-C(6)H(2)-2,5-R(2)-CH═CH} (V(a), R = H; V(b), R = OMe) as well as the mixed (ethynyl)(vinyl)phenylene bridged [Cl(dppe)(2)Ru-C≡C-1,4-C(6)H(4)-CH═CH-RuCl(CO)(P(i)Pr(3))(2)] (M(a)). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV-vis-NIR-IR spectroelectrochemistry. These studies show that the first oxidation mainly involves the central bis(alkynyl) ruthenium moiety with only limited effects on the appended vinyl ruthenium moieties. The second to fourth oxidations (n = 2, 3, 4) involve the entire carbon-rich conjugated path of the molecule with an increased charge uniformly distributed between the two arms of the molecules, including the terminal vinyl ruthenium sites. In order to assess the charge distribution, we judiciously use (13)CO labeled analogues to distinguish stretching vibrations due to the acetylide triple bonds and the intense and charge-sensitive Ru(CO) IR probe in different oxidation states. The comparison between complex pairs 4a,b(n+) (n = 0-3), A(a,b)(n+) and V(a,b)(n+) (n = 0-2) serves to elucidate the effect of the methoxy donor substituents on the redox and spectroscopic properties of these systems in their various oxidation states and on the metal/ligand contributions to their frontier orbitals.     

Photoinduced energy- and electron-transfer processes in dinuclear Ru(II)-Os(II), Ru(II)-Os(III), and Ru(III)-Os(II) trisbipyridine complexes containing a shape-persistent macrocyclic spacer.

The PF6- salt of the dinuclear [(bpy)2Ru(1)Os(bpy)2]4+ complex, where 1 is a phenylacetylene macrocycle which incorporates two 2,2'-bipyridine (bpy) chelating units in opposite sites of its shape-persistent structure, was prepared. In acetonitrile solution, the Ru- and Os-based units display their characteristic absorption spectra and electrochemical properties as in the parent homodinuclear compounds. The luminescence spectrum, however, shows that the emission band of the Ru(II) unit is almost completely quenched with concomitant sensitization of the emission of the Os(II) unit. Electronic energy transfer from the Ru(II) to the Os(II) unit takes place by two distinct processes (k(en) = 2.0x10(8) and 2.2x10(7) s(-1) at 298 K). Oxidation of the Os(II) unit of [(bpy)2Ru(1)Os(bpy)2]4+ by Ce(IV) or nitric acid leads quantitatively to the [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ complex which exhibits a bpy-to-Os(III) charge-transfer band at 720 nm (epsilon(max) = 250 M(-1) cm(-1)). Light excitation of the Ru(II) unit of [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ is followed by electron transfer from the Ru(II) to the Os(III) unit (k(el,f) = 1.6x10(8) and 2.7x10(7) s(-1)), resulting in the transient formation of the [(bpy)2Ru(III)(1)Os(II)(bpy)2]5+ complex. The latter species relaxes to the [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ one by back electron transfer (k(el,b) = 9.1x10(7) and 1.2x10(7) s(-1)). The biexponential decays of the [(bpy)2*Ru(II)(1)Os(II)(bpy)2]4+, [(bpy)2*Ru(II)(1)Os(III)(bpy)2]5+, and [(bpy)2Ru(III)(1)Os(II)(bpy)2]5+ species are related to the presence of two conformers, as expected because of the steric hindrance between hydrogen atoms of the pyridine and phenyl rings. Comparison of the results obtained with those previously reported for other Ru-Os polypyridine complexes shows that the macrocyclic ligand 1 is a relatively poor conducting bridge.     

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.     

DNA mismatch detection by resonance energy transfer between ruthenium(II) and osmium(II) tris(2,2'-bipyridyl) chromophores

Octahedral tris-chelate complexes [M(II)(bpy)(3)](2+) (M = Ru or Os, bpy = 2,2'-bipyridyl), covalently attached to the 3'- and 5'-phosphates of two oligonucleotides, are juxtaposed when hybridized contiguously to a fully complementary DNA target. Visible metal-to-ligand charge-transfer (MLCT) excitation of the [Ru(II)(bpy)(3)](2+) unit leads to resonance energy transfer to the MLCT state of the [Os(II)(bpy)(3)](2+) moiety, with the energy transfer efficiency depending on the degree of hybridization. The extent of attenuation of the intense red luminescence from the Ru(II) chromophore hence allows highly sensitive structural probing of the assembly and constitutes a novel approach to DNA sensing which is capable of detecting mutations.     

Switchable antenna: a star-shaped ruthenium/osmium tetranuclear complex with azobis(bipyridine) bridging ligands

A star-shaped Ru/Os tetranuclear complex, in which a central Os unit is linked to three peripheral Ru units by 4,4'-azobis(2,2'-bipyridine) (azobpy) bridging ligands, was prepared to examine the unique photodynamics regulated by its redox state. The Ru/Os tetranuclear complex exhibits Ru-based luminescence at 77 K, whereas the three-electron reduction (one for each azobpy) of the Ru/Os complex results in luminescence from the Os unit. The photoexcited state of the Ru/Os complex rapidly decays into low energy metal-to-ligand charge-transfer states, in which the excited electron is localized in the azobpy ligand in the form of azobpy(.-). Upon the one-electron reduction of the azobpy ligands, the above-mentioned low-energy states become unavailable to the photoexcited complex. As a result, an energy transfer from the Ru-based excited state to the Os-based excited state becomes possible. Ultrafast transient absorption measurements revealed that the energy transfer process consists of two steps; intramolecular electron transfer from the terminal bipyridine ligand (bpy(.-)) to form azobpy(2-) followed by a metal-to-metal electron transfer. Thus, the Ru/Os tetranuclear complex collects light energy into the central Os unit depending on the redox state of the bridging ligands, qualifying as a switchable antenna.     

Electrochemical probing of ground state electronic interactions in polynuclear complexes of a new heteroditopic ligand

The synthesis and electronic properties of dinuclear ([(bipy)2Ru(I)M(terpy)][PF6]4(bipy = 2,2'-bipyridine, terpy = 2,2':6',2'-terpyridine; M = Ru, Os)) and trinuclear ([[(bipy)2Ru(I)]2M][PF6]6 M = Ru, Os, Fe, Co) complexes bridged by 4'-(2,2'-bipyridin-4-yl)-2,2':6',2'-terpyridine (I) have been investigated and are compared with those of mononuclear model complexes. The electrochemical analysis using cyclic voltammetry and differential pulse voltammetry reveals that there are no interactions in the ground state between adjacent metal centres. However, there is strong electronic communication between the 2,2'-bipyridine and 2,2':6',2'-terpyridine components of the bridging ligand. This conclusion is supported by a step-by-step reduction of the dinuclear and trinuclear complexes and the assignment of each electrochemical process to localised ligand sites within the didentate and terdentate domains. The investigation of the electronic absorption and emission spectra reveals an energy transfer in the excited state from the terminating bipy-bound metal centres to the central terpy-bound metal centre. This indicates that the bridge is able to facilitate energy transfer in the excited state between the metal centres despite the lack of interactions in the ground state.     

Metal-directed synthesis and photophysical studies of trinuclear v-shaped and pentanuclear x-shaped ruthenium and osmium metallorods and metallostars based upon 4'-(3,5-dihydroxyphenyl)-2,2':6',2''-terpyridine divergent units

A new series of V-shaped trinuclear metallorods and X-shaped pentanuclear metallostars has been prepared by the reaction of metal complexes bearing pendant phenolic functionalities with complexes containing electrophilic ligands. Specifically, {M(tpy)2} motifs (M=Ru or Os; tpy=2,2':6',2'-terpyridine) bearing one or two pendant 3,5-dihydroxyphenyl substituents at the 4-position of the central ring of the tpy have been reacted with the complexes [Ru(tpy)(Xtpy)]2+ (X=Cl or Br) to form new ether-linked species. The energy transfer from ruthenium to osmium in these complexes has been investigated in detail and the efficiency of transfer shown to be highly temperature dependent; the energy transfer is highly efficient at low temperature, whereas at room temperature nonradiative and nontransfer deactivation of the excited {Ru(tpy)2}* domains is most significant.     

Synthesis, structural characterization, and photophysical, electrochemical, intercomponent energy-transfer, and anion-sensing studies of imidazole 4,5-bis(benzimidazole)-bridged Os(II)Os(II) and Ru(II)Os(II) bipyridine complexes

Homo- and heterobimetallic complexes of composition [(bpy)(2)M(II)(H(2)Imbzim)M'(II)(bpy)(2)](ClO(4))(3)·nH(2)O, where M(II) = M'(II) = Os (1), M(II) = Ru and M'(II) = Os (2), H(3)Imbzim = 4,5-bis(benzimidazole-2-yl)imidazole, and bpy = 2,2'-bipyridine, have been synthesized and characterized using standard analytical and spectroscopic techniques. Both of the complexes crystallized in monoclinic form with the space group P2(1)/m for 1 and P2(1)/n for 2. The absorption spectra, redox behavior, and luminescence properties of the complexes have been thoroughly investigated. The complexes display very intense, ligand-centered absorption bands in the UV region and moderately intense metal-to-ligand charge-transfer (MLCT) bands in the visible region. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations. The strong fluorescence of free H(3)Imbzim is completely quenched in the metal complexes by energy transfer to the metal-based units, which exhibit their characteristic MLCT phosphorescence. The luminescence data of the heterometallic complex 2 show that electronic energy transfer takes place from the ruthenium center to the osmium-based component. The anion binding properties of the complexes have been studied in solutions using absorption, emission, and (1)H NMR spectral measurements. The metalloreceptors act as sensors for F(-) and AcO(-) ions. Sensing studies indicate the presence of two successive anion-induced deprotonation steps, leading to the formation of [(bpy)(2)M(HImbzim)M'(bpy)(2)](2+) and [(bpy)(2)M(Imbzim)M'(bpy)(2)](+) species. Double deprotonation is also observed in the presence of hydroxide. The binding affinities of different anions toward the receptors have been evaluated. Cyclic voltammetry measurements carried out in acetonitrile have provided evidence in favor of anion-dependent electrochemical responses of the bimetallic metalloreceptors with F(-) and AcO(-) ions.     

Self-assembly organometallic squares with terpyridyl metal complexes as bridging ligands

A series of novel heterometallic square complexes with the general molecular formulas [fac-Br(CO)(3)Re[mu-(pyterpy)(2)M]](4)(PF(6))(8) and [(dppf)Pd[mu-(pyterpy)(2)Ru]](4)(PF(6))(8)(OTf(8) (4), where M = Fe (1), Ru (2), or Os (3), pyterpy is 4'-(4' "-pyridyl)-2,2':6',2' '-terpyridine, dppf = 1,1'-bis(diphenylphosphino)ferrocene and OTf is trifluoromethanesulfonate, were prepared by self-assembly between BrRe(CO)(5) or (dppf)Pd(H(2)O)(2)(OTf)(2) and (pyterpy)(2)M(PF(6))(2). The obtained NMR spectra, IR spectra, electrospray ionization mass spectra, and elemental analyses are all consistent with the proposed square structures incorporating terpyridyl metal complexes as bridging ligands. Multiple redox processes were observed in all square complexes. All four complexes display strong visible absorptions in the region 400-600 nm, which are assigned as metal (Fe, Ru, or Os)-to-ligand (pyterpy) charge transfer (MLCT) bands. Square 3 exhibits an additional weak band at 676 nm, which is assigned to an Os-based (3)MLCT band. For each complex, the bands centered between 279 and 377 nm are assigned as pyterpy-based pi-pi bands and the Re-based MLCT band. Square 3 is luminescent in room-temperature solution, while squares 1, 2, and 4 do not have any detectable luminescence under identical experimental conditions.     

Metallocyclodextrins as building blocks in noncovalent assemblies of photoactive units for the study of photoinduced intercomponent processes

Cyclodextrin cups have been employed to build supramolecular systems consisting of metal and organic photoactive/redox-active components; the photoinduced communication between redox-active units assembled in water via noncovalent interactions is established. The functionalization of a beta-cyclodextrin with a terpyridine unit, ttp-beta-CD, is achieved by protection of all but one of the hydroxyl groups by methylation and attachment of the ttp unit on the free primary hydroxyl group. The metalloreceptors [(beta-CD-ttp)Ru(ttp)][PF(6)](2), [(beta-CD-ttp)Ru(tpy)][PF(6)](2), and [Ru(beta-CD-ttp)(2)][PF(6)](2) are synthesized and fully characterized. The [(beta-CD-ttp)Ru(ttp)][PF(6)](2) metalloreceptor exhibits luminescence in water, centered at 640 nm, from the (3)MLCT state with a lifetime of 1.9 ns and a quantum yield of Phi = 4.1 x 10(-)(5). Addition of redox-active quinone guests AQS, AQC, and BQ to an aqueous solution of [(beta-CD-ttp)Ru(ttp)](2+) results in quenching of the luminescence up to 40%, 20%, and 25%, respectively. Measurement of the binding strength indicates that, in saturation conditions, 85% for AQS and 77% for AQC are bound. The luminescence quenching is attributed to an intercomponent electron transfer from the appended ruthenium center to the quinone guest inside the cavity. Control experiments demonstrate no bimolecular quenching at these conditions. A photoactive osmium metalloguest, [Os(biptpy)(tpy)][PF(6)], is designed with a biphenyl hydrophobic tail for insertion in the cyclodextrin cavity. The complex is luminescent at room temperature with an emission band maximum at 730 nm and a lifetime of 116 ns. The osmium(III) species are formed for the study of photoinduced electron transfer upon their assembly with the ruthenium cyclodextrin, [(beta-CD-ttp)Ru(ttp)](2+). Time-resolved spectroscopy studies show a short component of 10 ps, attributed to electron transfer from Ru(II) to Os(III) giving an electron transfer rate 9.5 x 10(9) s(-)(1).     

A new class of functionalized terpyridyl ligands as building blocks for photosensitized supramolecular architectures. Synthesis, structural, and electronic characterizations

A new class of triarylpyridinio-derivatized [4'-(p-phenyl)(n)]terpyridyl ligands, R(1)(2)R(2)TP(+)-(p)(n)tpy, was designed as a novel category of electron-acceptor (A)-substituted proto-photosensitizing molecules. The first elements of this versatile family of ligands (i.e., n = 0, 1 and R(1) = R(2) = H), H(3)TP(+)-tpy and H(3)TP(+)-ptpy, were synthesized as well as their Ru(II) and Os(II) complexes to form the related acceptor-functionalized M(tpy)(2)(2+) and M(ptpy)(2)(2+) photosensitizer components denoted P0 and P1, respectively. Within the P1 series of compounds, an electron-donor (D)-substituted ligand, Me(2)N-ptpy, was also involved and associated with H(3)TP(+)-ptpy, giving rise to various combinations (up to 10 polyad systems). The two resulting series of nanometer-scale rigid rod-like photosensitized supramolecular architectures are of potential interest for long-range photoinduced electron transfer purposes. The main structural features of such supermolecules were determined by comparing the results obtained from (i) single-crystal X-ray analysis of the two free ligands together with that of the P0A/Ru and P1A(2)/Ru complexes and (ii) a detailed solution (1)H NMR study of the P0 series and, more specifically, of the P0A/Ru dyad (ROESY experiment). It is shown that the pseudoperpendicular conformation of the covalently linked A and P subunits found in the solid state is persistent in fluid medium; i.e., A is not conjugated with P (P0 and P1). The first insights regarding the consequences upon intercomponent couplings of combined substituent effects and conjugation (case of D-based polyads)-or absence of conjugation-are discussed in the light of ground-state electronic properties of the compounds.     

Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers

The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2'-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.     

Structural systematics for o-C(6)H(4)XY ligands with X,Y= O,NH, and S donor atoms. o-iminoquinone and o-iminothioquinone complexes of ruthenium and osmium

The structural features of quinone ligands are diagnostic of charge. The o-benzoquinone, radical semiquinonate, and catecholate electronic forms have C-O bond lengths and a pattern of ring C-C bond lengths that point to a specific mode of coordination. This correlation between ligand charge and structure has been extended to iminoquinone and iminothioquinone ligands, giving a charge-localized view of electronic structure for complexes of redox-active metal ions. The radical semiquinonate form of these ligands has been found to be a surprisingly common mode of coordination; however, the paramagnetic character of the radical ligand is often obscured in complexes containing paramagnetic metal ions. In this report, diamagnetic iminosemiquinonate (isq) and iminothiosemiquinonate (itsq) complexes of ls-d(5) Ru(III) with related complexes of osmium are reported. With osmium, the Os(IV)-amidophenolate (ap) redox isomer is formed. Electrochemical and spectral properties are described for Ru(PPh(3))(2)(isq)Cl(2), Ru(PPh(3))(2)(itsq)Cl(2), Os(PPh(3))(2)(ap)Br(2), Os(PPh(3))(2)(atp)Br(2), and Os(PPh(3))(2)(ap)H(2). Crystallographic characterization of Ru(PPh(3))(2)(isq)Cl(2), Ru(PPh(3))(2)(itsq)Cl(2), and Os(PPh(3))(2)(ap)H(2) was used to assign charge distributions.     

Mixed-metal supramolecular complexes coupling phosphine-containing Ru(II) light absorbers to a reactive Pt(II) through polyazine bridging ligands

Supramolecular bimetallic Ru(II)/Pt(II) complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) and their synthons [(tpy)Ru(L)(BL)](n)()(+) (where L = Cl(-), CH(3)CN, or PEt(2)Ph; tpy = 2,2':6',2'-terpyridine; and BL = 2,2'-bipyrimidine (bpm) or 2,3-bis(2-pyridyl)pyrazine (dpp)) have been synthesized and studied by cyclic voltammetry, electronic absorption spectroscopy, mass spectral analysis, and (31)P NMR. The mixed-metal bimetallic complexes couple phosphine-containing Ru chromophores to a reactive Pt site. These complexes show how substitution of the monodentate ligand on the [(tpy)RuCl(BL)](+) synthons can tune the properties of these light absorbers (LA) and incorporate a (31)P NMR tag by addition of the PEt(2)Ph ligand. The redox potentials for the Ru(III/II) couples occur at values greater than 1.00 V versus the Ag/AgCl reference electrode and can be tuned to more positive potentials on going from Cl(-) to CH(3)CN or PEt(2)Ph (E(1/2) = 1.01, 1.55, and 1.56 V, respectively, for BL = bpm). The BL(0/-) couple at -1.03 (bpm) and -1.05 V (dpp) for [(tpy)Ru(PEt(2)Ph)(BL)](2+) shifts dramatically to more positive potentials upon the addition of the PtCl(2) moiety to -0.34 (bpm) and -0.50 V (dpp) for the [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) bridged complex. The lowest energy electronic absorption for these complexes is assigned as the Ru(d pi) --> BL(pi*) metal-to-ligand charge transfer (MLCT) transition. These MLCT transitions are tuned to higher energy in the monometallic synthons when Cl(-) is replaced by CH(3)CN or PEt(2)Ph (516, 452, and 450 nm, for BL = bpm, respectively) and to lower energy when Pt(II)Cl(2) is coordinated to the bridging ligand (560 and 506 nm for BL = bpm or dpp). This MLCT state displays a broad emission at room temperature for all the dpp systems with the [(tpy)Ru(PEt(2)Ph)(dpp)PtCl(2)](2+) system exhibiting an emission centered at 750 nm with a lifetime of 56 ns. These supramolecular complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) represent the covalent linkage of TAG-LA-BL-RM assembly (TAG = NMR active tag, RM = Pt(II) reactive metal).     

Conformationally gated photoinduced processes within photosensitizer-acceptor dyads based on osmium(II) complexes with triarylpyridinio-functionalized terpyridyl ligands: insights from experimental study

[(ttpy)Os(tpy-ph-TPH(3)(+))](3+) (2), [(ttpy)Os(tpy-xy-TPH(3)(+))](3+) (3), [(ttpy)Os(tpy-ph-TPH(2)(NO(2))(+))](3+) (4), and [(ttpy)Os(tpy-xy-TPH(2)(NO(2))(+))](3+) (5) are a series of dyads made of an Os(II) bis-tpy complex (tpy = 2,2':6',2"-terpyridine) as the photosensitizer (P) and 2,4,6-triarylpyridinium group (TP(+)) as the electron acceptor (A). These dyads were designed to form charge-separated states (CSS) upon light excitation. Together with analogous Ru(II) complexes (7-10), they have been synthesized and fully characterized. We describe herein how intramolecular photoinduced processes are affected when the electron-accepting strength of A (by nitro-derivatization of TP(+)) and/or the steric hindrance about intercomponent linkage (by replacing a phenyl spacer by a xylyl one) are changed. Electronic absorption and electrochemical behavior revealed that (i) chemical substitution of TP(+) (i.e., TP(+)-NO(2)) has no sizable influence on P-centered electronic features, (ii) reduction processes located on TP(+) depend on the intercomponent tilt angle. Concerning excited-state properties, photophysical investigation evidenced that phosphorescence of P is actually quenched in dyads 4 and 5 only. Ultrafast transient absorption (TA) experiments allowed attributing the quenching in conformationally locked dyad 5 to oxidative electron transfer (ET) from the (3)MLCT level to the TP(+)-NO(2) acceptor (k(el) = 1.1 x 10(9) s(-)(1)). For 4, geometrically unlocked, the (3)MLCT state was shown to first rapidly equilibrate (reversible energy transfer; k(eq) approximately 2 x 10(9) s(-)(1)) with a ligand centered triplet state before undergoing CSS formation. Thus, the pivotal role of conformation in driving excited-state decay pathways is demonstrated. Also, inner P structural planarization as a relaxation mode of the (3)MLCT states has been inferred from TA experiments.