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.     

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.     

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.     

Characterization of low energy charge transfer transitions in (terpyridine)(bipyridine)ruthenium(II) complexes and their cyanide-bridged bi- and tri-metallic analogues

The lowest energy metal-to-ligand charge transfer (MLCT) absorption bands found in ambient solutions of a series of [Ru(tpy)(bpy)X](m+) complexes (tpy = 2,2':3',2'-terpyridine; bpy = 2,2'-bipyridine; and X = a monodentate ancillary ligand) feature one or two partly resolved weak absorptions (bands I and/or II) on the low energy side of their absorption envelopes. Similar features are found for the related cyanide-bridged bi- and trimetallic complexes. However, the weak absorption band I of [(bpy)(2)Ru{CNRu(tpy)(bpy)}(2)](4+) is missing in its [(bpy)(2)Ru{NCRu(tpy)(bpy)}(2)](4+) linkage isomer demonstrating that this feature arises from a Ru(II)/tpy MLCT absorption. The energies of the MLCT band I components of the [Ru(tpy)(bpy)X](m+) complexes are proportional to the differences between the potentials for the first oxidation and the first reduction waves of the complexes. Time-dependent density functional theory (TD-DFT) computational modeling indicates that these band I components correspond to the highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition, with the HOMO being largely ruthenium-centered and the LUMO largely tpy-centered. The most intense contribution to a lowest energy MLCT absorption envelope (band III) of these complexes corresponds to the convolution of several orbitally different components, and its absorption maximum has an energy that is about 5000 cm(-1) higher than that of band I. The multimetallic complexes that contain Ru(II) centers linked by cyanide have mixed valence excited states in which more than 10% of electronic density is delocalized between the nearest neighbor ruthenium centers, and the corresponding stabilization energy contributions in the excited states are indistinguishable from those of the corresponding ground states. Single crystal X-ray structures and computational modeling indicate that the Ru-(C≡N)-Ru linkage is quite flexible and that there is not an appreciable variation in electronic structure or energy among the conformational isomers.     

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.     

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.     

2,2':6',2'-terpyridine substituted in the 4'-position by the solubilizing and sterically demanding tert-butyl group: a surprisingly new ligand

We describe the synthesis and characterization of 4'-tert-butyl-2,2':6',2'-terpyridine (4'-(t)Butpy, 1), a convergent tpy ligand that exhibits both a sterically demanding and solubilizing 4'-substituent. In the solid state, molecules of 1 pack with alternating tpy and tert-butyl domains, and the bulky alkyl substituents prevent the molecules from engaging in the face-to-face π-interactions which are typical of simple tpy ligands. Instead, the predominant packing forces involve CH···N hydrogen bonds and weak CH···π contacts. The syntheses of the homoleptic complexes [M(1)(2)][PF(6)](2) (M = Fe, Co, Zn and Ru) and the heteroleptic [Ru(tpy)(1)][PF(6)](2) are described. The complexes have been fully characterized in solution, including the (1)H NMR spectroscopic characterization of the paramagnetic [Co(1)(2)][PF(6)](2). Cyclic voltammetric data are consistent with the tert-butyl substituent being slightly electron releasing. The single crystal structures of [Zn(1)(2)][PF(6)](2) and [Ru(1)(2)][PF(6)](2) have been determined; the compounds are essentially isomorphous. The packing of the cations is such that the tert-butyl substituents are accommodated in pockets between the tpy domains of adjacent cations, and as a consequence, the {M(tpy)(2)}-embrace that is a ubiquitous feature of many related structures is not observed.     

From ruthenium(II) to iridium(III): 15 years of triads based on bis-terpyridine complexes

In order to mimic the photosynthetic reaction centre and better understand photoinduced electron transfer processes, a family of compounds has been studied for the past 15 years. These are transition metal complexes, M(tpy)(2) where tpy is a 2,2':6',2" terpyridine based ligand, bearing on one side a donor group and on the other side an acceptor group. The resulting triad molecules or their two-component reference compounds (donor-M(tpy)(2) and M(tpy)(2-acceptor) can contain Ru, Os, Rh or Ir as the metal centre and both visible-light non absorbing groups and porphyrins as donor and acceptor groups. This tutorial review will briefly present the different systems studied and the reasons that led to the preparation of new systems with improved performances.     

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.     

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).     

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 and study of Ru,Rh,Ru triads: modulation of orbital energies in a supramolecular architecture

Supramolecular trimetallic complexes [((tpy)RuCl(BL))(2)RhCl(2)](3+) where tpy = 2,2':6',2' '-terpyridine and BL = dpp or bpm [dpp = 2,3-bis(2-pyridyl)pyrazine and bpm = 2,2'-bipyrimidine] have been synthesized and characterized. The mixed-metal complexes couple a reactive rhodium(III) center to two ruthenium(II) light absorbers to form a light absorber-electron collector-light absorber triad. The variation of the bridging (dpp and bpm) and terminal (tpy in lieu of bpy) ligands has some profound effects on the properties of these complexes, and they are remarkably different from the previously reported [((bpy)(2)Ru(bpm))(2)RhCl(2)](5+) system. The electrochemical data for both title trimetallics consist of overlapping Ru(III/II) couples for both terminal metals at 1.12 V versus the Ag/AgCl reference electrode. Cathodically an irreversible Rh(III/I) reduction followed by bridging ligand reductions is seen. This is indicative of highest occupied molecular orbitals (HOMO) localized on the terminal ruthenium metal centers and a lowest unoccupied molecular orbital (LUMO) residing on the rhodium. This rhodium-based LUMO is in contrast to the bpy analogue [((bpy)(2)Ru(bpm))(2)RhCl(2)](5+), which has a bpm(pi) localized LUMO. This orbital inversion by terminal ligand variation illustrates the similar energy of these Rh(dsigma) and bpm(pi) orbitals within this structural motif. Both title trimetallics possess broad, low-energy Ru --> BL charge transfer absorbances at 540 nm (dpp) and 656 nm (bpm). A comparison of the spectroscopic, electrochemical, and spectroelectrochemical properties of these trimetallic complexes is presented.     

Electronic and magnetic communication in mixed-valent and homovalent ruthenium complexes containing phenylcyanamide type bridging ligands

Four new phenylcyanamido-bridge dinuclear ruthenium complexes [{Ru(tpy)(thd)}2(mu-L)] with tpy = 2,2':6',2' '-terpyridine, thd = 2,2,6,6-tetramethyl-3,5-heptanedione and L = dcbp = 4,4'-dicyanamidobiphenyl; bcpa = bis(4-cyanamidophenyl)acetylene; bcpda = bis(4-cyanamidophenyl)diacetylene; bcpea = 9,10,-bis(4-cyanamidophenylethynyl)anthracene have been prepared and fully characterized. The mixed valent Ru(II)Ru(III) and homovalent paramagnetic Ru(III)Ru(III) forms of all the complexes were electrochemically generated and studied by UV-vis-NIR and EPR spectroscopy. Electronic communication was quantified by the electronic coupling parameter V(ab) extracted from intervalence measurements in the near IR area, and magnetic communication was quantified in terms of the exchange coupling constant J, accessible from the intensity of the EPR signal when varying the temperature. Exponential decays for both electronic and magnetic coupling versus intermetallic distance were obtained and discussed.     

Ligands and complexes with supramolecular aromatic-aromatic interactions: iron(II) and ruthenium(II) complexes of 2,2':6',2'-terpyridines with pendant naphthalene groups

The synthesis and characterisation of five new ligands (L), each containing a terpy binding domain and bearing a pendant naphthalene group in the 4'-position are described; homoleptic complexes, [ML2][PF6]4 (M = Fe, Ru) have been studied and structural data for four complexes are reported.     

Spectroscopic and computational studies of a Ru(II) terpyridine complex: the importance of weak intermolecular forces to photophysical properties

The complex [Ru(tpy)(CO)(2)TFA]+[PF(6)]- (where tpy = 2,2':6',2' '-terpyridine and TFA = CF(3)CO(2)-) (1) has been synthesized and fully characterized spectroscopically. The X-ray structure of the complex has been determined. The photopysical properties of the ruthenium complex and the free ligand tpy have been investigated at room temperature and at 77 K in acetonitrile solution and in the solid state. Their electronic spectra are highly influenced by intermolecular stacking interactions, both in solution and in the solid state. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations have been performed to characterize the electronic structure and the excited states of [Ru(tpy)(CO)(2)TFA]+[PF(6)]- and tpy. TDDFT calculations on three different conformations of free ligand have been performed as well. Absorption and emission spectra of tpy have been studied at different temperatures and concentrations in order to have a better understanding of this ruthenium derivative's properties. The absorption spectrum of 1 is characterized by metal-perturbed ligand-centered (LC) bands in the UV region. No metal-to-ligand charge transfer (MLCT) bands are observed in the visible for the complex. Only at high concentrations (10(-4) M) does a very weak band appear at 470 nm. At 77 K and low concentrations, solutions of 1 exhibit a major 3LC emission band centered at 468 nm (21.4 x 10(-3) cm(-1)). When the concentration of the complex is increased, an unstructured narrow emission at 603 nm (16.6 x 10(-3) cm(-1)), with a lifetime of 10 micros, dominates the emission spectrum in glassy acetonitrile. This emission originates from a pi-pi stacked dimeric (or oligomeric) species. TDDFT calculations performed on a tail-to-tail dimer structure, similar to that seen in the solid state, ascribe the transition to a triplet excited state, where intermolecular metal (d) --> ligand (pi*, polypyridine) charge transfer occurs. A good estimate of the transition energy is also obtained (623 nm, 1.94 eV).     

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

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

Photoisomerization and proton-coupled electron transfer (PCET) promoted water oxidation by mononuclear cyclometalated ruthenium catalysts

Photoisomeric transformations in ruthenium polypyridyl complexes have been rarely reported. Herein we report the geometrical transformation of cyclometalated trans-[Ru(tpy)(PAD)(OH(2))](+) ([1](+)) to the cis-[Ru(tpy)(PAD)(OH(2))](+) ([1a](+)) (tpy = 2,2';6',2"-terpyridine, PAD = 2-(pyrid-2'-yl)acridine) isomer upon irradiation of visible light (λ ≥420 nm). Due to a proton-induced tautomeric equilibrium between the Ru-C bond and Ru═C coordination, the π* energy levels of PADH are lower than those of tpy by 12.61 and 12.24 kcal mol(-1), respectively, in [1](+) and [1a](+). Isomers [1](+) and [1a](+) both act as catalytic oxygen-evolving complexes (OECs) chemically as well as electrochemically.     

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.     

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.     

Turning off phototriggered linkage isomerizations in ruthenium dimethyl sulfoxide complexes

We report on the spectroscopy, electrochemistry, and linkage isomerization in a family of [Ru(tpy)(L2)(dmso)](z)()(+) complexes (tpy is 2,2':6',2' '-terpyridine, dmso is dimethyl sulfoxide, and L2 is a variable ligand: 2,2'-bipyridine (bpy), 2-picolinate (pic), N,N,N',N'-tetramethylethylenediamine (tmen), acetylacetonate (acac), or malonate (mal)). The identity of this bidentate ligand serves to tune the absorption maxima (lambda(max) = 419-502 nm) and the reduction potential (E(1/2) = 1.67 to 0.82 V) of these complexes. Photochemical and electrochemical studies show that S-->O and O-->S linkage isomerization may be triggered through an electron transfer mechanism, resulting in dramatic shifts in both the absorption maxima and the reduction potential (for [Ru(tpy)(pic)(dmso)](+) S-bonded, 421 nm, 1.38 V vs Ag/AgCl; O-bonded, 527 nm, 1.38 V vs Ag/AgCl). Certain of these complexes [Ru(tpy)(acac)(dmso)](+) and [Ru(tpy)(mal)(dmso)] do not undergo isomerization. These results are discussed in the context of electron transfer triggered isomerization.