Redox-responsive molecular switches based on azoterpyridine-bridged Ru/Os complexes

Three new terpyridine-based dinuclear complexes, [(tpy)Ru(azotpy)Ru(tpy)]4+ (tpy = 2,2':6',2'-terpyridine, azotpy = bis[2,6-bis(2-pyridyl)-4-pyridyl]diazene), [(tpy)Os(azotpy)Os(tpy)]4+, and [(tpy)Ru(azotpy)Os(tpy)]4+ were prepared and their electrochemical and photophysical properties investigated. The bridging ligand, azotpy, in these complexes is reduced at less negative potentials than the unsubstituted tpy ligand. These complexes exhibit absorption bands due to the metal-to-ligand charge-transfer transitions both to the unsubstituted tpy ligand and the bridging azotpy ligand, the latter absorption being observed at the lower energy side of the former. These observations are consistent with the lower lying pi* level of the azotpy ligand than that of the tpy ligand. These complexes are nonluminescent, since the excited electron is trapped in this lower lying pi* level of the azotpy ligand in the excited state. Reduction of this bridging ligand by constant potential electrolysis renders the shape of absorption spectra for these complexes nearly identical to those of the parent complexes, [M(tpy)2]2+ (M = Ru, Os). In this reduced state, the homodinuclear Os complex becomes luminescent at room temperature, whereas the homodinuclear Ru complex becomes luminescent at 77 K, thus establishing their photoswitching behavior. The reduced heterodinuclear complex exhibits luminescence from the Os center, which is sensitized by the Ru center in the same molecule as evidenced by the excitation spectra. Thus, the intramolecular energy transfer can be switched on and off by the redox reaction of the bridging component.     

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.     

Ruthenium(II) complexes with improved photophysical properties based on planar 4'-(2-pyrimidinyl)-2,2':6',2' '-terpyridine ligands

A series of new tridentate polypyridine ligands, made of terpyridine chelating subunits connected to various substituted 2-pyrimidinyl groups, and their homoleptic and heteroleptic Ru(II) complexes have been prepared and characterized. The new metal complexes have general formulas [(R-pm-tpy)Ru(tpy)]2+ and [Ru(tpy-pm-R)2]2+ (tpy = 2,2':6',2' '-terpyridine; R-pm-tpy = 4'-(2-pyrimidinyl)-2,2':6',2' '-terpyridine with R = H, methyl, phenyl, perfluorophenyl, chloride, and cyanide). Two of the new metal complexes have also been characterized by X-ray analysis. In all the R-pm-tpy ligands, the pyrimidinyl and terpyridyl groups are coplanar, allowing an extended delocalization of acceptor orbital of the metal-to-ligand charge-transfer (MLCT) excited state. The absorption spectra, redox behavior, and luminescence properties of the new Ru(II) complexes have been investigated. In particular, the photophysical properties of these species are significantly better compared to those of [Ru(tpy)2]2+ and well comparable with those of the best emitters of Ru(II) polypyridine family containing tridentate ligands. Reasons for the improved photophysical properties lie at the same time in an enhanced MLCT-MC (MC = metal centered) energy gap and in a reduced difference between the minima of the excited and ground states potential energy surfaces. The enhanced MLCT-MC energy gap leads to diminished efficiency of the thermally activated pathway for the radiationless process, whereas the similarity in ground and excited-state geometries causes reduced Franck Condon factors for the direct radiationless decay from the MLCT state to the ground state of the new complexes in comparison with [Ru(tpy)2]2+ and similar species.     

Oligo(U-terpyridines) and their ruthenium(II) complexes: synthesis and structural properties

A highly efficient domino reaction starting from tetrahydroquinolinone and a series of bisiminium salts provides the corresponding bis(U-terpyridines). These ligands have been treated with [(tpy)RuCl3] to afford novel dinuclear complexes [(tpy)Ru(L)Ru(tpy)]4+. The protocol is also applied for the synthesis of a star-shaped tris(U-terpyridine) and the trinuclear complex [{(tpy)Ru}3(L)]6+. In view of potential applications in the fields of metallopolymers and molecular devices, the electronic spectra, as well as the electrochemical potentials of all the complexes have been obtained. According to these data, no significant intermetal interaction has been observed for the ruthenium complexes presented here.     

A novel heteroditopic terpyridine-pincer ligand as building block for mono- and heterometallic Pd(II) and Ru(II) complexes

A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)2-3,5}-2,2':6',2' '-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)2, and [Ru(TPBr)2](PF6)2, synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)2 (7) and [Ru(TPPdCl)2](PF6)2 (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)2](PF6)2 (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono- and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (1)MLCT (Ru --> tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)2]2+ indicates stabilization of the luminescent 3MLCT state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)2, are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)2} chromophoric unit and the (non)metalated NCN-pincer moiety.     

Diorganoruthenium complexes incorporating noninnocent [C(6)H(2)(CH(2)ER(2))(2)-3,5](2)(2-) (E = N, P) bis-pincer bridging ligands: synthesis, spectroelectrochemistry, and DFT studies

The dinuclear complex [(tpy)RuII(PCP-PCP)RuII(tpy)]Cl2 (bridging PCP-PCP = 3,3',5,5'-tetrakis(diphenylphosphinomethyl)biphenyl, [C6H2(CH2PPh2)2-3,5]22-) was prepared via a transcyclometalation reaction of the bis-pincer ligand [PC(H)P-PC(H)P] and the Ru(II) precursor [Ru(NCN)(tpy)]Cl (NCN = [C6H3(CH2NMe2)2-2,6]-) followed by a reaction with 2,2':6',2' '-terpyridine (tpy). Electrochemical and spectroscopic properties of [(tpy)RuII(PCP-PCP)RuII(tpy)]Cl2 are compared with those of the closely related [(tpy)RuII(NCN-NCN)RuII(tpy)](PF6)2 (NCN-NCN = [C6H2(CH2NMe2)2-3,5]22-) obtained by two-electron reduction of [(tpy)RuIII(NCN-NCN)RuIII(tpy)](PF6)4. The molecular structure of the latter complex has been determined by single-crystal X-ray structure determination. One-electron reduction of [(tpy)RuIII(NCN-NCN)RuIII(tpy)](PF6)4 and one-electron oxidation of [(tpy)RuII(PCP-PCP)RuII(tpy)]Cl2 yielded the mixed-valence species [(tpy)RuIII(NCN-NCN)RuII(tpy)]3+ and [(tpy)RuIII(PCP-PCP)RuII(tpy)]3+, respectively. The comproportionation equilibrium constants Kc (900 and 748 for [(tpy)RuIII(NCN-NCN)RuIII(tpy)]4+ and [(tpy)RuII(PCP-PCP)RuII(tpy)]2+, respectively) determined from cyclic voltammetric data reveal comparable stability of the [RuIII-RuII] state of both complexes. Spectroelectrochemical measurements and near-infrared (NIR) spectroscopy were employed to further characterize the different redox states with special focus on the mixed-valence species and their NIR bands. Analysis of these bands in the framework of Hush theory indicates that the mixed-valence complexes [(tpy)RuIII(PCP-PCP)RuII(tpy)]3+ and [(tpy)RuIII(NCN-NCN)RuII(tpy)]3+ belong to strongly coupled borderline Class II/Class III and intrinsically coupled Class III systems, respectively. Preliminary DFT calculations suggest that extensive delocalization of the spin density over the metal centers and the bridging ligand exists. TD-DFT calculations then suggested a substantial MLCT character of the NIR electronic transitions. The results obtained in this study point to a decreased metal-metal electronic interaction accommodated by the double-cyclometalated bis-pincer bridge when strong sigma-donor NMe2 groups are replaced by weak sigma-donor, pi-acceptor PPh2 groups.     

Building Block Approach to the Construction of Long-Lived Osmium(II) and Ruthenium(II) Multimetallic Complexes Incorporating the Tridentate Bridging Ligand 2,3,5,6-Tetrakis(2-pyridyl)pyrazine

Two classes of synthetically useful bimetallic complexes of the form [(tpy)M(tpp)RuCl(3)](PF(6)) and [(tpy)M(tpp)Ru(tpp)](PF(6))(4) have been prepared and their spectroscopic and electrochemical properties investigated (tpy = 2,2':6',2"-terpyridine, tpp = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, and M = Ru(II) or Os(II)). Synthetic methods have been developed for the stepwise construction of tpp-bridged systems using a building block approach. In all four complexes, the tpp that serves as the bridging ligand is the site of localization of the lowest unoccupied molecular orbital (LUMO). The nature of the HOMO (highest occupied molecular orbital) varies depending upon the components present. In the systems of the type [(tpy)M(tpp)RuCl(3)](PF(6)), the ruthenium metal coordinated to tpp and three chlorides is the easiest to oxidize and is the site of localization of the HOMO. In contrast, for the [(tpy)M(tpp)Ru(tpp)](PF(6))(4) systems, the HOMO is based on the metal, M, that is varied, either Ru or Os. This gives rise to systems which possess a lowest lying excited state that is always a metal-to-ligand charge transfer state involving tpp but can be tuned to involve Os or Ru metal centers in a variety of coordination environments. The synthetic variation of the components within this framework has allowed for understanding the spectroscopic and electrochemical properties. Bimetallic systems incorporating this tpp ligand have long-lived excited states at room temperature (lifetimes of ca. 100 ns). The bimetallic system [(tpy)Ru(tpp)Ru(tpp)](PF(6))(4) has a longer excited state lifetime than the monometallic system from which it was constructed, [(tpy)Ru(tpp)](PF(6))(2). Details of the spectroscopic and electrochemical studies are reported herein.     

Synthesis, luminescence, and electrochemical studies of tris(homoleptic) ruthenium(II) and osmium(II) complexes of 6'-tolyl-2,2':4',2'-terpyridine

The synthesis and photophysical and electrochemical properties of tris(homoleptic) complexes [Ru(tpbpy)3](PF6)2 (1) and [Os(tpbpy)3](PF6)2 (2) (tpbpy = 6'-tolyl-2,2':4',2' '-terpyridine) are reported. The ligand tpbpy is formed as the side product during the synthesis of 4'-tolyl-2,2':6',2' '-terpyridine (ttpy) and characterized by single-crystal X-ray diffraction: monoclinic, P21/c. The tridentate tpbpy coordinates as a bidentate ligand. The complexes 1 and 2 exhibit two intense absorption bands in the UV region (200-350 nm) assignable to the ligand-centered (1LC) pi-pi* transitions. The ruthenium(II) complex exhibits a broad absorption band at 470 nm while the osmium(II) complex exhibits an intense absorption band at 485 nm and a weak band at 659 nm assignable to the MLCT (dpi-pi*) transitions. A red shifting of the dpi-pi* MLCT transition is observed on going from the Ru(II) to the Os(II) complex as expected from the high-lying dpi Os orbitals. These complexes exhibit ligand-sensitized emission at 732 and 736 nm, respectively, upon light excitation onto their MLCT band through excitation of higher energy LC bands at room temperature. The MLCT transitions and the emission maxima of 1 and 2 are substantially red-shifted compared to that of [Ru(bpy)3](PF6)2 and [Os(bpy)3](PF6)2. The emission of both the complexes in the presence of acid is completely quenched indicating that the emission is not due to the protonation of the coordinated ligands. Our results indicate the occurrence of intramolecular energy transfer from the ligand to the metal center. Both the complexes undergo quasi-reversible metal-centered oxidation, and the E1/2 values for the M(II)/M(III) redox couples (0.94 and 0.50 V versus Ag/Ag+ for 1 and 2, respectively) are cathodically shifted with respect to that of [Ru(bpy)3](PF6)2 and [Os(bpy)3](PF6)2 (E1/2 = 1.28 and 1.09 V versus Ag/Ag+, respectively). The tris(homoleptic) Ru(II) and Os(II) complexes 1 and 2 could be used to construct polynuclear complexes by using the modular synthetic approach in coordination compounds by exploiting the coordinating ability of the pyridine substituent. Furthermore, these complexes offer the possibility of studying the influence of electron-withdrawing and electron-donating substituents on the photophysical properties of Ru(II) and Os(II) polypyridine complexes.     

Direct measurement of excited-state intervalence transfer in [(tpy)Ru(III)(tppz(*-))Ru(II)(tpy)](4+) by time-resolved near-infrared spectroscopy

Extension of time-resolved infrared (TRIR) measurements into the near-infrared region has allowed the first direct measurement of a mixed-valence band in the metal-to-ligand charge transfer (MLCT) excited state of a symmetrical ligand-bridged complex. Visible laser flash excitation of [(tpy)Ru(tppz)Ru(tpy)]4+ (tppz is 2,3,5,6-tetrakis(2-pyridyl)pyrazine; tpy is 2,2':6',6' '-terpyridine) produces the mixed-valence, MLCT excited state [(tpy)RuIII(tppz*-)RuII(tpy)]4+* with the excited electron localized on the bridging tppz ligand. A mixed-valence band appears at numax = 6300 cm-1 with a bandwidth-at-half- maximum, Deltanu1/2 = 1070 cm-1. In the analogous ground-state complex, [(tpy)Ru(tppz)Ru(tpy)]5+, a mixed-valence band appears at numax = 6550 cm-1 with Deltanu1/2 = 970 cm-1 which allows a comparison to be made of electronic coupling across tppz0 and tppz*- as bridging ligands.     

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.     

Synthesis and study of the spectroscopic and redox properties of Ru(II),Pt(II) mixed-metal complexes bridged by 2,3,5,6-tetrakis(2-pyridyl)pyrazine

The mixed-metal supramolecular complexes [(tpy)Ru(tppz)PtCl](PF6)3 and [ClPt(tppz)Ru(tppz)PtCl](PF6)4 (tpy = 2,2':6',2'-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) were synthesized and characterized. These complexes contain ruthenium bridged by tppz to platinum centers to form stereochemically defined linear assemblies. X-ray crystallographic determinations of the two complexes confirm the identity of the metal complexes and reveal intermolecular interactions of the Pt sites in the solid state for [(tpy)Ru(tppz)PtCl](PF6)3 with a Pt...Pt distance of 3.3218(5) A. The (1)H NMR spectra show the expected splitting patterns characteristic of stereochemically defined mixed-metal systems and are assigned with the use of (1)H-(1)H COSY and NOESY. Electronic absorption spectroscopy displays intense ligand-based pi --> pi* transitions in the UV and MLCT transitions in the visible. Electrochemically [(tpy)Ru(tppz)PtCl](PF6)3 and [ClPt(tppz)Ru(tppz)PtCl](PF6)4 display reversible Ru (II/III) couples at 1.63 and 1.83 V versus Ag/AgCl, respectively. The complexes display very low potential tppz (0/-) and tppz(-/2-) couples, relative to their monometallic synthons, [(tpy)Ru(tppz)](PF6)2 and [Ru(tppz)2](PF6)2, consistent with the bridging coordination of the tppz ligand. The Ru(dpi) --> tppz(pi*) MLCT transitions are also red-shifted relative to the monometallic synthons occurring in the visible centered at 530 and 538 nm in CH3CN for [(tpy)Ru(tppz)PtCl](PF6)3 and [ClPt(tppz)Ru(tppz)PtCl](PF6)4, respectively. The complex [(tpy)Ru(tppz)PtCl](PF6)3 displays a barely detectable emission from the Ru(dpi) --> tppz(pi*) (3)MLCT in CH 3CN solution at RT. In contrast, [ClPt(tppz)Ru(tppz)PtCl](PF6)4 displays an intense emission from the Ru(dpi) --> tppz(pi*) (3)MLCT state at RT with lambda max(em) = 754 nm and tau = 80 ns.     

Ruthenium(ii) bis(terpyridine) electron transfer complexes with alkynyl-ferrocenyl bridges: synthesis, structures, and electrochemical and spectroscopic studies

Two novel alkynyl-bridged symmetric bis-tridentate ligands 1,2-bis(1'-[4'-(2,2':6',2'-terpyridinyl)]ferrocenyl)ethyne (; tpy-Fc-C[triple bond, length as m-dash]C-Fc-tpy; Fc = ferrocenyl; tpy = terpyridyl) and 1,4-bis(1'-[4'-(2,2':6',2'-terpyridinyl)]ferrocenyl)-1,3-butadiyne (; tpy-Fc-C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C-Fc-tpy) and their Ru(2+) complexes and have been synthesized and characterized by cyclic voltammetry, UV-vis and luminescence spectroscopy, and in the case of by single-crystal X-ray diffraction. Cyclic voltammograms of both compounds, and , display two severely overlapping ferrocene-based oxidative peaks with only one reductive peak. The redox behavior of and is dominated by the Ru(2+)/Ru(3+) redox couple (E(1/2) from 1.33 to 1.34 V), the Fe(2+)/Fe(3+) redox couples (E(1/2) from 0.46 to 0.80 V), and the tpy/tpy(-)/tpy(2-) redox couples (E(1/2) from -1.19 to -1.48 V). The UV-vis spectra of and show absorption bands assigned to the (1)[(d(π)(Fe))(6)] → (1)[(d(π)(Fe))(5)(π*(tpy)(Ru))(1)] MMLCT transition at ～555 nm. Complexes and are luminescent in H(2)O-CH(3)CN (4?:?1, v/v) solution at room temperature, and exhibits the strongest luminescence intensity (λ(max)(em): 710 nm, Φ(em): 2.28 × 10(-4), τ: 358 ns) relative to analogous ferrocene-based bis(terpyridine) Ru(ii) complexes reported so far.     

Luminescent bis-tridentate ruthenium(II) and osmium(II) complexes based on terpyridyl-imidazole ligand: synthesis, structural characterization, photophysical, electrochemical, and solvent dependence studies

Homo- and heteroleptic bis-tridentate ruthenium(II) and osmium(II) complexes of compositions [(tpy-PhCH(3))Ru(tpy-HImzPh(3))](ClO(4))(2) (1), [(H(2)pbbzim)Ru(tpy-HImzPh(3))] (ClO(4))(2) (2) and [M(tpy-HImzPh(3))(2)](ClO(4))(2) [M = Ru(II) (3) and Os(II) (4)], where tpy-PhCH(3) = p-methylphenyl terpyridine, H(2)pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine and tpy-HImzPh(3) = 4'-[4-(4,5-diphenyl-1H-imidazol-2-yl)-phenyl]-[2,2':6',2']terpyridine, have been synthesized and characterized by using standard analytical and spectroscopic techniques. These compounds were designed to increase the room temperature excited-state lifetimes of bisterpyridine-type ruthenium(II) and osmium(II) complexes. The X-ray crystal structures of two homoleptic complexes 3 and 4 have been determined and show that both the compounds crystallized in orthorhombic form with space group Fddd. The photophysical and redox properties of the complexes have been thoroughly investigated. All the complexes display moderately strong luminescence at room temperature with lifetimes in the range of 6-35 ns. The complexes are found to undergo one reversible oxidation in the positive potential window (0 to +1.6 V) and one irreversible and two successive quasi-reversible reductions in the negative potential window (0 to -2.0 V). The influence of solvents on the photophysical properties of the complexes has also been investigated in detail.     

A strategy for improving the room-temperature luminescence properties of Ru(II) complexes with tridentate ligands

Several ruthenium(II) complexes with new tridentate polypyridine ligands have been prepared, and their photophysical properties have been studied. The new tridentate ligands are tpy-modified systems (tpy = 2,2':6',2' '-terpyridine) in which aromatic substituents designed to be coplanar with the tpy moiety are introduced, with the aim of enhancing delocalization in the acceptor ligand of the potentially luminescent metal-to-ligand charge-transfer (MLCT) state and increasing the MLCT-MC energy gap (MC = metal-centered excited state). Indeed, the Ru(II) complexes obtained with this new family of tridentate ligands exhibit long-lived luminescence at room temperature (up to 200 ns). The enhanced luminescence properties of these complexes support this design strategy and are superior to those of the model Ru(tpy)22+ compound and compare favorably with those of the best Ru(II) complexes with tridentate ligands reported so far.     

Near-infrared absorbing and emitting Ru(II)-Pt(II) heterodimetallic complexes of dpdpz (dpdpz = 2,3-di(2-pyridyl)-5,6-diphenylpyrazine)

The reaction of 2,3-di(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) with K(2)PtCl(4) in a mixture of acetonitrile and water afforded mono-Pt complex (dpdpz)PtCl(2)4 in good yield, with two lateral pyridine nitrogen atoms binding to the metal center. Two types of Ru(II)-Pt(II) heterodimetallic complexes bridged by dpdpz, namely, [(bpy)(2)Ru(dpdpz)Pt(C≡CC(6)H(4)R)](2+) (7-9, R = H, NMe(2), or Cl, respectively) and [(tpy)Ru(dpdpz)Pt(C≡CPh)] (+) (12), were then designed and prepared, where bpy = 2,2'-bipyridine and tpy = 2,2';6',2'-terpyridine. In both cases, the platinum atom binds to dpdpz with a C(∧)N(∧)N tridentate mode. However, the coordination of the ruthenium atom with dpdpz could either be noncyclometalated (N(∧)N bidentate) or cyclometalated (C(∧)N(∧)N tridentate). The electronic properties of these complexes were subsequently studied and compared by spectroscopic and electrochemical analyses and theoretical calculations. These complexes exhibit substantial absorption in the visible to NIR (near-infrared) region because of mixed MLCT (metal-to-ligand-charge-tranfer) transitions from both the ruthenium and the platinum centers. Complexes 7 and 9 were found to emit NIR light with higher quantum yields than those of the mono-Ru complex [(bpy)(2)Ru(dpdpz)](2+) (5) and bis-Ru complex [(bpy)(2)Ru(dpdpz)Ru(bpy)(2)](4+) (13). However, no emission was detected from complex 8 or 12 at room temperature in acetonitrile.     

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.     

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.     

Synthesis and properties of the elusive ruthenium(II) complexes of 4'-cyano-2,2':6',2' '-terpyridine

The heteroleptic and homoleptic ruthenium(II) complexes of 4'-cyano-2,2':6',2' '-terpyridine are synthesized by palladium catalyzed cyanation of the corresponding Ru(II) complexes of 4'-chloro-2,2':6',2' '-terpyridine. The introduction of the strongly electron-withdrawing cyano group into the Ru(tpy)(2)(2+) moiety dramatically changes its photophysical and redox properties as well as prolongs its room temperature excited-state lifetime.     

Synthesis, structural characterization, photophysical, electrochemical, and anion-sensing studies of luminescent homo- and heteroleptic ruthenium(II) and osmium(II) complexes based on terpyridyl-imidazole ligand

A series of hetero- and homoleptic tridentate ruthenium(II) and osmium(II) complexes of compositions [(tpy-PhCH(3))Ru(tpy-HImzphen)](ClO(4))(2) (1), [(H(2)pbbzim)Ru(tpy-HImzphen)](ClO(4))(2) (2), and [M(tpy-HImzphen)(2)](ClO(4))(2) [M = Ru(II) (3) and Os(II) (4)], where tpy-PhCH(3) = 4'-(4-methylphenyl)-2,2':6',2"-terpyridine, H(2)pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine and tpy-HImzphen = 2-(4-[2,2':6',2"]terpyridine-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole, have been synthesized and characterized by using standard analytical and spectroscopic techniques. X-ray crystal structures of three complexes 2, 3, and 4 have been determined. The absorption spectra, redox behavior, and luminescence properties of the complexes have been thoroughly investigated. All of the complexes display moderately strong luminescence at room temperature with lifetimes in the range of 10-55 ns. The effect of solvents on the absorption and emission spectral behavior of the complexes has also been studied in detail. The anion sensing properties of all the complexes have been studied in solution using absorption, emission, and (1)H NMR spectral studies and by cyclic voltammetric (CV) measurements. It has been observed that the complexes 1, 3, and 4 act as sensors for F(-)only, whereas 2 acts as sensor for F(-), AcO(-), and to some extent for H(2)PO(4)(-). It is evident that in the presence of excess of anions deprotonation of the imidazole N-H fragment(s) occurs in all cases, an event which is signaled by the development of vivid colors visible with the naked eye. The receptor-anion binding/equilibrium constants have been evaluated.     

Electronic coupling between two cyclometalated ruthenium centers bridged by 1,3,6,8-tetrakis(1-butyl-1H-1,2,3-triazol-4-yl)pyrene

A new bridging ligand 1,3,6,8-tetrakis(1-butyl-1H-1,2,3-triazol-4-yl)pyrene (ttapyr) was designed and synthesized by "click" chemistry. This ligand was used to construct a linear dimetallic biscyclometalated Ru(II) complex [(tpy)Ru(ttapyr)Ru(tpy)](2+) and a monometallic complex [(tpy)Ru(ttapyr)](+), where tpy is 2,2':6',2″-terpyridine. The electronic properties of these complexes were studied and compared by electrochemical and spectroscopic methods with the aid of DFT calculations. One-electron oxidation of [(tpy)Ru(ttapyr)Ru(tpy)](2+) with cerium ammonium nitrate produced a mixed-valent complex [(tpy)Ru(ttapyr)Ru(tpy)](3+). The intramolecular electronic coupling between individual metal centers was quantified by the intervalence charge transfer transition analysis. Mixed-valent complex [(tpy)Ru(ttapyr)Ru(tpy)](3+) exhibits a metal-centered rhombic EPR signal at 77 K with an average g factor of 2.203.